x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

198 files changed, 31793 insertions, 0 deletions

diff --git a/arch/um/.gitignore b/arch/um/.gitignore
new file mode 100644
index 000000000..d69ea5b56
--- /dev/null
+++ b/arch/um/.gitignore
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0-only
+kernel/config.c
+kernel/config.tmp
+kernel/vmlinux.lds
+kernel/capflags.c
diff --git a/arch/um/Kbuild b/arch/um/Kbuild
new file mode 100644
index 000000000..6cf0c1e59
--- /dev/null
+++ b/arch/um/Kbuild
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+obj-y += kernel/ drivers/ os-Linux/
diff --git a/arch/um/Kconfig b/arch/um/Kconfig
new file mode 100644
index 000000000..d9541d13d
--- /dev/null
+++ b/arch/um/Kconfig
@@ -0,0 +1,306 @@
+# SPDX-License-Identifier: GPL-2.0
+
+menu "UML-specific options"
+
+config UML
+	bool
+	default y
+	select ARCH_DISABLE_KASAN_INLINE if STATIC_LINK
+	select ARCH_NEEDS_DEFER_KASAN if STATIC_LINK
+	select ARCH_WANTS_DYNAMIC_TASK_STRUCT
+	select ARCH_HAS_CACHE_LINE_SIZE
+	select ARCH_HAS_CPU_FINALIZE_INIT
+	select ARCH_HAS_FORTIFY_SOURCE
+	# Clang 20 & 21 miscompute __builtin_object_size() under -fprofile-arcs
+	# on 32-bit, causing spurious compile-time errors in check_copy_size().
+	select ARCH_HAS_GCOV_PROFILE_ALL if !(!64BIT && CLANG_VERSION >= 200000 && CLANG_VERSION < 220100)
+	select ARCH_HAS_KCOV
+	select ARCH_HAS_STRNCPY_FROM_USER
+	select ARCH_HAS_STRNLEN_USER
+	select ARCH_HAS_STRICT_KERNEL_RWX
+	select HAVE_ARCH_AUDITSYSCALL
+	select HAVE_ARCH_KASAN if X86_64
+	select HAVE_ARCH_KASAN_VMALLOC if HAVE_ARCH_KASAN
+	select HAVE_ARCH_SECCOMP_FILTER
+	select HAVE_ASM_MODVERSIONS
+	select HAVE_UID16
+	select HAVE_DEBUG_KMEMLEAK
+	select HAVE_DEBUG_BUGVERBOSE
+	select HAVE_PAGE_SIZE_4KB
+	select NO_DMA if !UML_DMA_EMULATION
+	select OF_EARLY_FLATTREE if OF
+	select GENERIC_IRQ_SHOW
+	select GENERIC_CPU_DEVICES
+	select GENERIC_SMP_IDLE_THREAD
+	select HAVE_GCC_PLUGINS
+	select ARCH_SUPPORTS_LTO_CLANG
+	select ARCH_SUPPORTS_LTO_CLANG_THIN
+	select TRACE_IRQFLAGS_SUPPORT
+	select TTY # Needed for line.c
+	select HAVE_ARCH_VMAP_STACK
+	select HAVE_RUST
+	select ARCH_HAS_UBSAN
+	select HAVE_ARCH_TRACEHOOK
+	select HAVE_SYSCALL_TRACEPOINTS
+	select THREAD_INFO_IN_TASK
+	select SPARSE_IRQ
+	select MMU_GATHER_RCU_TABLE_FREE
+
+config MMU
+	bool
+	default y
+
+config UML_DMA_EMULATION
+	bool
+
+config NO_IOMEM
+	bool "disable IOMEM" if EXPERT
+	depends on !INDIRECT_IOMEM
+	default y
+
+config UML_IOMEM_EMULATION
+	bool
+	select INDIRECT_IOMEM
+	select GENERIC_PCI_IOMAP
+
+config ISA
+	bool
+
+config SBUS
+	bool
+
+config LOCKDEP_SUPPORT
+	bool
+	default y
+
+config STACKTRACE_SUPPORT
+	bool
+	default y
+	select STACKTRACE
+
+config GENERIC_CALIBRATE_DELAY
+	bool
+	default y
+
+config HZ
+	int
+	default 100
+
+config UML_SUBARCH_SUPPORTS_SMP
+	bool
+
+config SMP
+	bool "Symmetric multi-processing support"
+	default n
+	depends on UML_SUBARCH_SUPPORTS_SMP
+	help
+	  This option enables UML SMP support.
+
+	  With this enabled, users can tell UML to start multiple virtual
+	  processors. Each virtual processor is represented as a separate
+	  host thread.
+
+	  In UML, kthreads and normal threads (when running in kernel mode)
+	  can be scheduled and executed simultaneously on different virtual
+	  processors. However, the userspace code of normal threads still
+	  runs within their respective single-threaded stubs.
+
+	  That is, SMP support is available both within the kernel and
+	  across different processes, but remains limited within threads
+	  of the same process in userspace.
+
+config NR_CPUS_RANGE_BEGIN
+	int
+	default 1 if !SMP
+	default 2
+
+config NR_CPUS_RANGE_END
+	int
+	default 1 if !SMP
+	default 64
+
+config NR_CPUS_DEFAULT
+	int
+	default 1 if !SMP
+	default 2
+
+config NR_CPUS
+	int "Maximum number of CPUs" if SMP
+	range NR_CPUS_RANGE_BEGIN NR_CPUS_RANGE_END
+	default NR_CPUS_DEFAULT
+
+source "arch/$(HEADER_ARCH)/um/Kconfig"
+
+config MAY_HAVE_RUNTIME_DEPS
+	bool
+
+config STATIC_LINK
+	bool "Force a static link"
+	depends on !MAY_HAVE_RUNTIME_DEPS
+	help
+	  This option gives you the ability to force a static link of UML.
+	  Normally, UML is linked as a shared binary.  This is inconvenient for
+	  use in a chroot jail.  So, if you intend to run UML inside a chroot,
+	  you probably want to say Y here.
+	  Additionally, this option enables using higher memory spaces (up to
+	  2.75G) for UML.
+
+	  NOTE: This option is incompatible with some networking features which
+	  depend on features that require being dynamically loaded (like NSS).
+
+config LD_SCRIPT_STATIC
+	bool
+	default y
+	depends on STATIC_LINK
+
+config LD_SCRIPT_DYN
+	bool
+	default y
+	depends on !LD_SCRIPT_STATIC
+
+config LD_SCRIPT_DYN_RPATH
+	bool "set rpath in the binary" if EXPERT
+	default y
+	depends on LD_SCRIPT_DYN
+	help
+	  Add /lib (and /lib64 for 64-bit) to the linux binary's rpath
+	  explicitly.
+
+	  You may need to turn this off if compiling for nix systems
+	  that have their libraries in random /nix directories and
+	  might otherwise unexpected use libraries from /lib or /lib64
+	  instead of the desired ones.
+
+config HOSTFS
+	tristate "Host filesystem"
+	help
+	  While the User-Mode Linux port uses its own root file system for
+	  booting and normal file access, this module lets the UML user
+	  access files stored on the host.  It does not require any
+	  network connection between the Host and UML.  An example use of
+	  this might be:
+
+	  mount none /tmp/fromhost -t hostfs -o /tmp/umlshare
+
+	  where /tmp/fromhost is an empty directory inside UML and
+	  /tmp/umlshare is a directory on the host with files the UML user
+	  wishes to access.
+
+	  For more information, see
+	  <http://user-mode-linux.sourceforge.net/hostfs.html>.
+
+	  If you'd like to be able to work with files stored on the host,
+	  say Y or M here; otherwise say N.
+
+config MCONSOLE
+	bool "Management console"
+	depends on PROC_FS
+	default y
+	help
+	  The user mode linux management console is a low-level interface to
+	  the kernel, somewhat like the i386 SysRq interface.  Since there is
+	  a full-blown operating system running under every user mode linux
+	  instance, there is much greater flexibility possible than with the
+	  SysRq mechanism.
+
+	  If you answer 'Y' to this option, to use this feature, you need the
+	  mconsole client (called uml_mconsole) which is present in CVS in
+	  2.4.5-9um and later (path /tools/mconsole), and is also in the
+	  distribution RPM package in 2.4.6 and later.
+
+	  It is safe to say 'Y' here.
+
+config MAGIC_SYSRQ
+	bool "Magic SysRq key"
+	depends on MCONSOLE
+	help
+	  If you say Y here, you will have some control over the system even
+	  if the system crashes for example during kernel debugging (e.g., you
+	  will be able to flush the buffer cache to disk, reboot the system
+	  immediately or dump some status information). A key for each of the
+	  possible requests is provided.
+
+	  This is the feature normally accomplished by pressing a key
+	  while holding SysRq (Alt+PrintScreen).
+
+	  On UML, this is accomplished by sending a "sysrq" command with
+	  mconsole, followed by the letter for the requested command.
+
+	  The keys are documented in <file:Documentation/admin-guide/sysrq.rst>. Don't say Y
+	  unless you really know what this hack does.
+
+config KERNEL_STACK_ORDER
+	int "Kernel stack size order"
+	default 2 if 64BIT
+	range 2 10 if 64BIT
+	default 1 if !64BIT
+	help
+	  This option determines the size of UML kernel stacks.  They will
+	  be 1 << order pages.  The default is OK unless you're running Valgrind
+	  on UML, in which case, set this to 3.
+	  It is possible to reduce the stack to 1 for 64BIT and 0 for 32BIT on
+	  older (pre-2017) CPUs. It is not recommended on newer CPUs due to the
+	  increase in the size of the state which needs to be saved when handling
+	  signals.
+
+config PGTABLE_LEVELS
+	int
+	default 4 if 64BIT
+	default 2 if !64BIT
+
+config UML_TIME_TRAVEL_SUPPORT
+	bool
+	prompt "Support time-travel mode (e.g. for test execution)"
+	# inf-cpu mode is incompatible with the benchmarking
+	depends on !RAID6_PQ_BENCHMARK
+	depends on !SMP
+	help
+	  Enable this option to support time travel inside the UML instance.
+
+	  After enabling this option, two modes are accessible at runtime
+	  (selected by the kernel command line), see the kernel's command-
+	  line help for more details.
+
+	  It is safe to say Y, but you probably don't need this.
+
+config UML_MAX_USERSPACE_ITERATIONS
+	int
+	prompt "Maximum number of unscheduled userspace iterations"
+	default 10000
+	depends on UML_TIME_TRAVEL_SUPPORT
+	help
+	  In UML inf-cpu and ext time-travel mode userspace can run without being
+	  interrupted. This will eventually overwhelm the kernel and create OOM
+	  situations (mainly RCU not running). This setting specifies the number
+	  of kernel/userspace switches (minor/major page fault, signal or syscall)
+	  for the same userspace thread before the sched_clock is advanced by a
+	  jiffie to trigger scheduling.
+
+	  Setting it to zero disables the feature.
+
+config KASAN_SHADOW_OFFSET
+	hex
+	depends on KASAN
+	default 0x100000000000
+	help
+	  This is the offset at which the ~16TB of shadow memory is
+	  mapped and used by KASAN for memory debugging. This can be any
+	  address that has at least KASAN_SHADOW_SIZE (total address space divided
+	  by 8) amount of space so that the KASAN shadow memory does not conflict
+	  with anything. The default is 0x100000000000, which works even if mem is
+	  set to a large value. On low-memory systems, try 0x7fff8000, as it fits
+	  into the immediate of most instructions, improving performance.
+
+endmenu
+
+source "arch/um/drivers/Kconfig"
+
+config ARCH_SUSPEND_POSSIBLE
+	def_bool y
+	depends on !SMP
+
+menu "Power management options"
+
+source "kernel/power/Kconfig"
+
+endmenu
diff --git a/arch/um/Kconfig.debug b/arch/um/Kconfig.debug
new file mode 100644
index 000000000..1dfb2959c
--- /dev/null
+++ b/arch/um/Kconfig.debug
@@ -0,0 +1,38 @@
+# SPDX-License-Identifier: GPL-2.0
+
+config GPROF
+	bool "Enable gprof support"
+	depends on DEBUG_INFO && FRAME_POINTER
+	help
+	  This allows profiling of a User-Mode Linux kernel with the gprof
+	  utility.
+
+	  See <http://user-mode-linux.sourceforge.net/old/gprof.html> for more
+	  details.
+
+	  If you're involved in UML kernel development and want to use gprof,
+	  say Y.  If you're unsure, say N.
+
+config GCOV
+	bool "Enable gcov support"
+	depends on DEBUG_INFO
+	depends on !KCOV
+	depends on !MODULES
+	help
+	  This option allows developers to retrieve coverage data from a UML
+	  session.
+
+	  See <http://user-mode-linux.sourceforge.net/old/gprof.html> for more
+	  details.
+
+	  If you're involved in UML kernel development and want to use gcov,
+	  say Y.  If you're unsure, say N.
+
+config EARLY_PRINTK
+	bool "Early printk"
+	default y
+	help
+	  Write kernel log output directly to stdout.
+
+	  This is useful for kernel debugging when your machine crashes very
+	  early before the console code is initialized.
diff --git a/arch/um/Makefile b/arch/um/Makefile
new file mode 100644
index 000000000..937639edc
--- /dev/null
+++ b/arch/um/Makefile
@@ -0,0 +1,156 @@
+#
+# This file is included by the global makefile so that you can add your own
+# architecture-specific flags and dependencies.
+#
+# Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+# Licensed under the GPL
+#
+
+# select defconfig based on actual architecture
+ifeq ($(SUBARCH),x86)
+  ifeq ($(shell uname -m),x86_64)
+        KBUILD_DEFCONFIG := x86_64_defconfig
+  else
+        KBUILD_DEFCONFIG := i386_defconfig
+  endif
+else
+        KBUILD_DEFCONFIG := $(SUBARCH)_defconfig
+endif
+
+ARCH_DIR := arch/um
+# We require bash because the vmlinux link and loader script cpp use bash
+# features.
+SHELL := bash
+
+MODE_INCLUDE	+= -I$(srctree)/$(ARCH_DIR)/include/shared/skas
+
+HEADER_ARCH 	:= $(SUBARCH)
+
+ifneq ($(filter $(SUBARCH),x86 x86_64 i386),)
+	HEADER_ARCH := x86
+endif
+
+ifdef CONFIG_64BIT
+	KBUILD_CFLAGS += -mcmodel=large
+endif
+
+HOST_DIR := arch/$(HEADER_ARCH)
+
+include $(srctree)/$(ARCH_DIR)/Makefile-skas
+include $(srctree)/$(HOST_DIR)/Makefile.um
+
+core-y += $(HOST_DIR)/um/
+
+SHARED_HEADERS	:= $(ARCH_DIR)/include/shared
+ARCH_INCLUDE	:= -I$(srctree)/$(SHARED_HEADERS)
+ARCH_INCLUDE	+= -I$(srctree)/$(HOST_DIR)/um/shared
+KBUILD_CPPFLAGS += -I$(srctree)/$(HOST_DIR)/um
+
+# -Dstrrchr=kernel_strrchr (as well as the various in6addr symbols) prevents
+#  anything from referencing
+# libc symbols with the same name, which can cause a linker error.
+#
+# -Dlongjmp=kernel_longjmp prevents anything from referencing the libpthread.a
+# embedded copy of longjmp, same thing for setjmp.
+#
+# These apply to USER_CFLAGS too.
+
+KBUILD_CFLAGS += $(CFLAGS) $(CFLAGS-y) -D__arch_um__ \
+	$(ARCH_INCLUDE) $(MODE_INCLUDE)	\
+	-Dlongjmp=kernel_longjmp -Dsetjmp=kernel_setjmp \
+	-Din6addr_loopback=kernel_in6addr_loopback \
+	-Din6addr_any=kernel_in6addr_any -Dstrrchr=kernel_strrchr \
+	-D__close_range=kernel__close_range
+
+KBUILD_RUSTFLAGS += -Crelocation-model=pie
+
+KBUILD_AFLAGS += $(ARCH_INCLUDE)
+
+USER_CFLAGS = $(patsubst $(KERNEL_DEFINES),,$(patsubst -I%,,$(KBUILD_CFLAGS))) \
+		$(ARCH_INCLUDE) $(MODE_INCLUDE) $(filter -I%,$(CFLAGS)) \
+		-D_FILE_OFFSET_BITS=64 -idirafter $(srctree)/include \
+		-idirafter $(objtree)/include -D__KERNEL__ -D__UM_HOST__ \
+		-include $(srctree)/include/linux/compiler-version.h \
+		-include $(srctree)/include/linux/kconfig.h \
+		-idirafter $(ARCH_DIR)/include/generated
+
+#This will adjust *FLAGS accordingly to the platform.
+include $(srctree)/$(ARCH_DIR)/Makefile-os-Linux
+
+KBUILD_CPPFLAGS += -I$(srctree)/$(HOST_DIR)/include \
+		   -I$(srctree)/$(HOST_DIR)/include/uapi \
+		   -I$(objtree)/$(HOST_DIR)/include/generated \
+		   -I$(objtree)/$(HOST_DIR)/include/generated/uapi
+
+# -Derrno=kernel_errno - This turns all kernel references to errno into
+# kernel_errno to separate them from the libc errno.  This allows -fno-common
+# in KBUILD_CFLAGS.  Otherwise, it would cause ld to complain about the two different
+# errnos.
+# These apply to kernelspace only.
+#
+# strip leading and trailing whitespace to make the USER_CFLAGS removal of these
+# defines more robust
+
+KERNEL_DEFINES = $(strip -Derrno=kernel_errno -Dsigprocmask=kernel_sigprocmask \
+			 -Dmktime=kernel_mktime $(ARCH_KERNEL_DEFINES))
+KBUILD_CFLAGS += $(KERNEL_DEFINES)
+
+PHONY += linux
+
+all: linux
+
+linux: vmlinux
+	@echo '  LINK $@'
+	$(Q)ln -f $< $@
+
+define archhelp
+  echo '* linux		- Binary kernel image (./linux) - for backward'
+  echo '		   compatibility only, this creates a hard link to the'
+  echo '		   real kernel binary, the "vmlinux" binary you'
+  echo '		   find in the kernel root.'
+endef
+
+archheaders:
+	$(Q)$(MAKE) -f $(srctree)/Makefile ARCH=$(HEADER_ARCH) asm-generic archheaders
+
+archprepare:
+	$(Q)$(MAKE) $(build)=$(HOST_DIR)/um include/generated/user_constants.h
+
+LINK-$(CONFIG_LD_SCRIPT_STATIC) += -static
+LINK-$(CONFIG_LD_SCRIPT_DYN) += -no-pie
+LINK-$(CONFIG_LD_SCRIPT_DYN_RPATH) += -Wl,-rpath,/lib
+
+CFLAGS_NO_HARDENING := $(call cc-option, -fno-PIC,) $(call cc-option, -fno-pic,) \
+	-fno-stack-protector $(call cc-option, -fno-stack-protector-all)
+
+# Options used by linker script
+export LDS_START      := $(START)
+export LDS_ELF_ARCH   := $(ELF_ARCH)
+export LDS_ELF_FORMAT := $(ELF_FORMAT)
+
+# The wrappers will select whether using "malloc" or the kernel allocator.
+LINK_WRAPS = -Wl,--wrap,malloc -Wl,--wrap,free -Wl,--wrap,calloc
+
+# Avoid binutils 2.39+ warnings by marking the stack non-executable and
+# ignorning warnings for the kallsyms sections.
+LDFLAGS_EXECSTACK = -z noexecstack
+ifeq ($(CONFIG_LD_IS_BFD),y)
+LDFLAGS_EXECSTACK += $(call ld-option,--no-warn-rwx-segments)
+endif
+
+LD_FLAGS_CMDLINE = $(foreach opt,$(KBUILD_LDFLAGS) $(LDFLAGS_EXECSTACK),-Wl,$(opt))
+
+# Used by link-vmlinux.sh which has special support for um link
+export CFLAGS_vmlinux := $(LINK-y) $(LINK_WRAPS) $(LD_FLAGS_CMDLINE) $(CC_FLAGS_LTO)
+
+# When cleaning we don't include .config, so we don't include
+# TT or skas makefiles and don't clean skas_ptregs.h.
+CLEAN_FILES += linux x.i gmon.out
+MRPROPER_FILES += $(HOST_DIR)/include/generated
+
+archclean:
+	@find . \( -name '*.bb' -o -name '*.bbg' -o -name '*.da' \
+		-o -name '*.gcov' \) -type f -print | xargs rm -f
+	$(Q)$(MAKE) -f $(srctree)/Makefile ARCH=$(HEADER_ARCH) clean
+
+export HEADER_ARCH SUBARCH USER_CFLAGS CFLAGS_NO_HARDENING DEV_NULL_PATH
diff --git a/arch/um/Makefile-os-Linux b/arch/um/Makefile-os-Linux
new file mode 100644
index 000000000..2c8a598ec
--- /dev/null
+++ b/arch/um/Makefile-os-Linux
@@ -0,0 +1,9 @@
+# 
+# Copyright (C) 2000 Jeff Dike (jdike@karaya.com)
+# Licensed under the GPL
+#
+
+# To get a definition of F_SETSIG
+USER_CFLAGS += -D_GNU_SOURCE -D_LARGEFILE64_SOURCE
+KBUILD_CFLAGS += -D_LARGEFILE64_SOURCE
+DEV_NULL_PATH = \"/dev/null\"
diff --git a/arch/um/Makefile-skas b/arch/um/Makefile-skas
new file mode 100644
index 000000000..1a27e65bc
--- /dev/null
+++ b/arch/um/Makefile-skas
@@ -0,0 +1,17 @@
+# 
+# Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
+# Licensed under the GPL
+#
+
+export UM_GPROF_OPT += -pg
+
+ifdef CONFIG_CC_IS_CLANG
+export UM_GCOV_OPT += -fprofile-instr-generate -fcoverage-mapping
+else
+export UM_GCOV_OPT += -fprofile-arcs -ftest-coverage
+endif
+
+CFLAGS-$(CONFIG_GCOV) += $(UM_GCOV_OPT)
+CFLAGS-$(CONFIG_GPROF) += $(UM_GPROF_OPT)
+LINK-$(CONFIG_GCOV) += $(UM_GCOV_OPT)
+LINK-$(CONFIG_GPROF) += $(UM_GPROF_OPT)
diff --git a/arch/um/configs/i386_defconfig b/arch/um/configs/i386_defconfig
new file mode 100644
index 000000000..29d9666ec
--- /dev/null
+++ b/arch/um/configs/i386_defconfig
@@ -0,0 +1,64 @@
+# CONFIG_COMPACTION is not set
+CONFIG_BINFMT_MISC=m
+CONFIG_HOSTFS=y
+CONFIG_MAGIC_SYSRQ=y
+CONFIG_KERNEL_STACK_ORDER=1
+CONFIG_SYSVIPC=y
+CONFIG_POSIX_MQUEUE=y
+CONFIG_NO_HZ=y
+CONFIG_HIGH_RES_TIMERS=y
+CONFIG_BSD_PROCESS_ACCT=y
+CONFIG_IKCONFIG=y
+CONFIG_IKCONFIG_PROC=y
+CONFIG_LOG_BUF_SHIFT=14
+CONFIG_CGROUPS=y
+CONFIG_CGROUP_FREEZER=y
+CONFIG_CGROUP_DEVICE=y
+CONFIG_CPUSETS=y
+CONFIG_CGROUP_CPUACCT=y
+CONFIG_CGROUP_SCHED=y
+CONFIG_BLK_CGROUP=y
+# CONFIG_PID_NS is not set
+CONFIG_SYSFS_DEPRECATED=y
+CONFIG_CC_OPTIMIZE_FOR_SIZE=y
+CONFIG_MODULES=y
+CONFIG_MODULE_UNLOAD=y
+# CONFIG_BLK_DEV_BSG is not set
+CONFIG_IOSCHED_BFQ=m
+CONFIG_SSL=y
+CONFIG_NULL_CHAN=y
+CONFIG_PORT_CHAN=y
+CONFIG_PTY_CHAN=y
+CONFIG_TTY_CHAN=y
+CONFIG_XTERM_CHAN=y
+CONFIG_CON_CHAN="pts"
+CONFIG_SSL_CHAN="pts"
+CONFIG_SOUND=m
+CONFIG_UML_SOUND=m
+CONFIG_DEVTMPFS=y
+CONFIG_DEVTMPFS_MOUNT=y
+CONFIG_BLK_DEV_UBD=y
+CONFIG_BLK_DEV_LOOP=m
+CONFIG_BLK_DEV_NBD=m
+CONFIG_DUMMY=m
+CONFIG_TUN=m
+CONFIG_PPP=m
+CONFIG_SLIP=m
+CONFIG_LEGACY_PTY_COUNT=32
+# CONFIG_HW_RANDOM is not set
+CONFIG_UML_RANDOM=y
+CONFIG_NET=y
+CONFIG_PACKET=y
+CONFIG_UNIX=y
+CONFIG_INET=y
+# CONFIG_IPV6 is not set
+CONFIG_EXT4_FS=y
+CONFIG_QUOTA=y
+CONFIG_AUTOFS_FS=m
+CONFIG_ISO9660_FS=m
+CONFIG_JOLIET=y
+CONFIG_PROC_KCORE=y
+CONFIG_TMPFS=y
+CONFIG_NLS=y
+CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
+CONFIG_DEBUG_KERNEL=y
diff --git a/arch/um/configs/x86_64_defconfig b/arch/um/configs/x86_64_defconfig
new file mode 100644
index 000000000..af6ff784e
--- /dev/null
+++ b/arch/um/configs/x86_64_defconfig
@@ -0,0 +1,63 @@
+# CONFIG_COMPACTION is not set
+CONFIG_BINFMT_MISC=m
+CONFIG_HOSTFS=y
+CONFIG_MAGIC_SYSRQ=y
+CONFIG_SYSVIPC=y
+CONFIG_POSIX_MQUEUE=y
+CONFIG_NO_HZ=y
+CONFIG_HIGH_RES_TIMERS=y
+CONFIG_BSD_PROCESS_ACCT=y
+CONFIG_IKCONFIG=y
+CONFIG_IKCONFIG_PROC=y
+CONFIG_LOG_BUF_SHIFT=14
+CONFIG_CGROUPS=y
+CONFIG_CGROUP_FREEZER=y
+CONFIG_CGROUP_DEVICE=y
+CONFIG_CPUSETS=y
+CONFIG_CGROUP_CPUACCT=y
+CONFIG_CGROUP_SCHED=y
+CONFIG_BLK_CGROUP=y
+# CONFIG_PID_NS is not set
+CONFIG_SYSFS_DEPRECATED=y
+CONFIG_CC_OPTIMIZE_FOR_SIZE=y
+CONFIG_MODULES=y
+CONFIG_MODULE_UNLOAD=y
+# CONFIG_BLK_DEV_BSG is not set
+CONFIG_IOSCHED_BFQ=m
+CONFIG_SSL=y
+CONFIG_NULL_CHAN=y
+CONFIG_PORT_CHAN=y
+CONFIG_PTY_CHAN=y
+CONFIG_TTY_CHAN=y
+CONFIG_XTERM_CHAN=y
+CONFIG_CON_CHAN="pts"
+CONFIG_SSL_CHAN="pts"
+CONFIG_SOUND=m
+CONFIG_UML_SOUND=m
+CONFIG_DEVTMPFS=y
+CONFIG_DEVTMPFS_MOUNT=y
+CONFIG_BLK_DEV_UBD=y
+CONFIG_BLK_DEV_LOOP=m
+CONFIG_BLK_DEV_NBD=m
+CONFIG_DUMMY=m
+CONFIG_TUN=m
+CONFIG_PPP=m
+CONFIG_SLIP=m
+CONFIG_LEGACY_PTY_COUNT=32
+# CONFIG_HW_RANDOM is not set
+CONFIG_UML_RANDOM=y
+CONFIG_NET=y
+CONFIG_PACKET=y
+CONFIG_UNIX=y
+CONFIG_INET=y
+# CONFIG_IPV6 is not set
+CONFIG_EXT4_FS=y
+CONFIG_QUOTA=y
+CONFIG_AUTOFS_FS=m
+CONFIG_ISO9660_FS=m
+CONFIG_JOLIET=y
+CONFIG_PROC_KCORE=y
+CONFIG_TMPFS=y
+CONFIG_NLS=y
+CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT=y
+CONFIG_DEBUG_KERNEL=y
diff --git a/arch/um/drivers/Kconfig b/arch/um/drivers/Kconfig
new file mode 100644
index 000000000..6a0354ca0
--- /dev/null
+++ b/arch/um/drivers/Kconfig
@@ -0,0 +1,190 @@
+# SPDX-License-Identifier: GPL-2.0
+
+menu "UML Character Devices"
+
+config STDERR_CONSOLE
+	bool "stderr console"
+	default y
+	help
+	  console driver which dumps all printk messages to stderr.
+
+config SSL
+	bool "Virtual serial line"
+	help
+	  The User-Mode Linux environment allows you to create virtual serial
+	  lines on the UML that are usually made to show up on the host as
+	  ttys or ptys.
+
+	  See <http://user-mode-linux.sourceforge.net/old/input.html> for more
+	  information and command line examples of how to use this facility.
+
+	  Unless you have a specific reason for disabling this, say Y.
+
+config NULL_CHAN
+	bool "null channel support"
+	help
+	  This option enables support for attaching UML consoles and serial
+	  lines to a device similar to /dev/null.  Data written to it disappears
+	  and there is never any data to be read.
+
+config PORT_CHAN
+	bool "port channel support"
+	help
+	  This option enables support for attaching UML consoles and serial
+	  lines to host portals.  They may be accessed with 'telnet <host>
+	  <port number>'.  Any number of consoles and serial lines may be
+	  attached to a single portal, although what UML device you get when
+	  you telnet to that portal will be unpredictable.
+	  It is safe to say 'Y' here.
+
+config PTY_CHAN
+	bool "pty channel support"
+	help
+	  This option enables support for attaching UML consoles and serial
+	  lines to host pseudo-terminals.  Access to both traditional
+	  pseudo-terminals (/dev/pty*) and pts pseudo-terminals are controlled
+	  with this option.  The assignment of UML devices to host devices
+	  will be announced in the kernel message log.
+	  It is safe to say 'Y' here.
+
+config TTY_CHAN
+	bool "tty channel support"
+	help
+	  This option enables support for attaching UML consoles and serial
+	  lines to host terminals.  Access to both virtual consoles
+	  (/dev/tty*) and the slave side of pseudo-terminals (/dev/ttyp* and
+	  /dev/pts/*) are controlled by this option.
+	  It is safe to say 'Y' here.
+
+config XTERM_CHAN
+	bool "xterm channel support"
+	help
+	  This option enables support for attaching UML consoles and serial
+	  lines to xterms.  Each UML device so assigned will be brought up in
+	  its own xterm.
+	  It is safe to say 'Y' here.
+
+config XTERM_CHAN_DEFAULT_EMULATOR
+	string "xterm channel default terminal emulator"
+	depends on XTERM_CHAN
+	default "xterm"
+	help
+	  This option allows changing the default terminal emulator.
+
+config NOCONFIG_CHAN
+	bool
+	default !(XTERM_CHAN && TTY_CHAN && PTY_CHAN && PORT_CHAN && NULL_CHAN)
+
+config CON_ZERO_CHAN
+	string "Default main console channel initialization"
+	default "fd:0,fd:1"
+	help
+	  This is the string describing the channel to which the main console
+	  will be attached by default.  This value can be overridden from the
+	  command line.  The default value is "fd:0,fd:1", which attaches the
+	  main console to stdin and stdout.
+	  It is safe to leave this unchanged.
+
+config CON_CHAN
+	string "Default console channel initialization"
+	default "xterm"
+	help
+	  This is the string describing the channel to which all consoles
+	  except the main console will be attached by default.  This value can
+	  be overridden from the command line.  The default value is "xterm",
+	  which brings them up in xterms.
+	  It is safe to leave this unchanged, although you may wish to change
+	  this if you expect the UML that you build to be run in environments
+	  which don't have X or xterm available.
+
+config SSL_CHAN
+	string "Default serial line channel initialization"
+	default "pty"
+	help
+	  This is the string describing the channel to which the serial lines
+	  will be attached by default.  This value can be overridden from the
+	  command line.  The default value is "pty", which attaches them to
+	  traditional pseudo-terminals.
+	  It is safe to leave this unchanged, although you may wish to change
+	  this if you expect the UML that you build to be run in environments
+	  which don't have a set of /dev/pty* devices.
+
+config UML_SOUND
+	tristate "Sound support"
+	depends on SOUND
+	select SOUND_OSS_CORE
+	help
+	  This option enables UML sound support.  If enabled, it will pull in
+	  the UML hostaudio relay, which acts as a intermediary
+	  between the host's dsp and mixer devices and the UML sound system.
+	  It is safe to say 'Y' here.
+
+endmenu
+
+menu "UML Network Devices"
+	depends on NET
+
+config UML_NET_VECTOR
+	bool "Vector I/O high performance network devices"
+	select MAY_HAVE_RUNTIME_DEPS
+	help
+	  This User-Mode Linux network driver uses multi-message send
+	  and receive functions. The host running the UML guest must have
+	  a linux kernel version above 3.0 and a libc version > 2.13.
+	  This driver provides tap, raw, gre and l2tpv3 network transports.
+
+	  For more information, including explanations of the networking
+	  and sample configurations, see
+	  <file:Documentation/virt/uml/user_mode_linux_howto_v2.rst>.
+
+endmenu
+
+config VIRTIO_UML
+	bool "UML driver for virtio devices"
+	select VIRTIO
+	help
+	  This driver provides support for virtio based paravirtual device
+	  drivers over vhost-user sockets.
+
+config UML_RTC
+	bool "UML RTC driver"
+	depends on RTC_CLASS
+	# there's no use in this if PM_SLEEP isn't enabled ...
+	depends on PM_SLEEP
+	help
+	  When PM_SLEEP is configured, it may be desirable to wake up using
+	  rtcwake, especially in time-travel mode. This driver enables that
+	  by providing a fake RTC clock that causes a wakeup at the right
+	  time.
+
+config UML_PCI
+	bool
+	select FORCE_PCI
+	select IRQ_MSI_LIB
+	select UML_IOMEM_EMULATION
+	select UML_DMA_EMULATION
+	select PCI_MSI
+	select PCI_LOCKLESS_CONFIG
+
+config UML_PCI_OVER_VIRTIO
+	bool "Enable PCI over VIRTIO device simulation"
+	# in theory, just VIRTIO is enough, but that causes recursion
+	depends on VIRTIO_UML
+	select UML_PCI
+
+config UML_PCI_OVER_VIRTIO_DEVICE_ID
+	int "set the virtio device ID for PCI emulation"
+	default -1
+	depends on UML_PCI_OVER_VIRTIO
+	help
+	  There's no official device ID assigned (yet), set the one you
+	  wish to use for experimentation here. The default of -1 is
+	  not valid and will cause the driver to fail at probe.
+
+config UML_PCI_OVER_VFIO
+	bool "Enable VFIO-based PCI passthrough"
+	select UML_PCI
+	help
+	  This driver provides support for VFIO-based PCI passthrough.
+	  Currently, only MSI-X capable devices are supported, and it
+	  is assumed that drivers will use MSI-X.
diff --git a/arch/um/drivers/Makefile b/arch/um/drivers/Makefile
new file mode 100644
index 000000000..36dc57840
--- /dev/null
+++ b/arch/um/drivers/Makefile
@@ -0,0 +1,55 @@
+# SPDX-License-Identifier: GPL-2.0
+# 
+# Copyright (C) 2000, 2002, 2003 Jeff Dike (jdike@karaya.com)
+#
+
+# pcap is broken in 2.5 because kbuild doesn't allow pcap.a to be linked
+# in to pcap.o
+
+vector-objs := vector_kern.o vector_user.o vector_transports.o
+mconsole-objs := mconsole_kern.o mconsole_user.o
+hostaudio-objs := hostaudio_kern.o
+ubd-objs := ubd_kern.o ubd_user.o
+port-objs := port_kern.o port_user.o
+harddog-objs := harddog_kern.o
+harddog-builtin-$(CONFIG_UML_WATCHDOG) := harddog_user.o harddog_user_exp.o
+rtc-objs := rtc_kern.o rtc_user.o
+vfio_uml-objs := vfio_kern.o vfio_user.o
+
+#XXX: The call below does not work because the flags are added before the
+# object name, so nothing from the library gets linked.
+#$(call if_changed,ld)
+
+# When the above is fixed, don't forget to add this too!
+#targets += $(obj)/pcap.o
+
+obj-y := stdio_console.o fd.o chan_kern.o chan_user.o line.o
+obj-$(CONFIG_SSL) += ssl.o
+obj-$(CONFIG_STDERR_CONSOLE) += stderr_console.o
+
+obj-$(CONFIG_UML_NET_VECTOR) += vector.o
+obj-$(CONFIG_MCONSOLE) += mconsole.o
+obj-$(CONFIG_BLK_DEV_UBD) += ubd.o 
+obj-$(CONFIG_UML_SOUND) += hostaudio.o
+obj-$(CONFIG_NULL_CHAN) += null.o 
+obj-$(CONFIG_PORT_CHAN) += port.o
+obj-$(CONFIG_PTY_CHAN) += pty.o
+obj-$(CONFIG_TTY_CHAN) += tty.o 
+obj-$(CONFIG_XTERM_CHAN) += xterm.o xterm_kern.o
+obj-$(CONFIG_UML_WATCHDOG) += harddog.o
+obj-y += $(harddog-builtin-y) $(harddog-builtin-m)
+obj-$(CONFIG_BLK_DEV_COW_COMMON) += cow_user.o
+obj-$(CONFIG_UML_RANDOM) += random.o
+obj-$(CONFIG_VIRTIO_UML) += virtio_uml.o
+obj-$(CONFIG_UML_RTC) += rtc.o
+obj-$(CONFIG_UML_PCI) += virt-pci.o
+obj-$(CONFIG_UML_PCI_OVER_VIRTIO) += virtio_pcidev.o
+obj-$(CONFIG_UML_PCI_OVER_VFIO) += vfio_uml.o
+
+# pcap_user.o must be added explicitly.
+USER_OBJS := fd.o null.o pty.o tty.o xterm.o vector_user.o
+CFLAGS_null.o = -DDEV_NULL=$(DEV_NULL_PATH)
+
+CFLAGS_xterm.o += '-DCONFIG_XTERM_CHAN_DEFAULT_EMULATOR="$(CONFIG_XTERM_CHAN_DEFAULT_EMULATOR)"'
+
+include $(srctree)/arch/um/scripts/Makefile.rules
diff --git a/arch/um/drivers/chan.h b/arch/um/drivers/chan.h
new file mode 100644
index 000000000..5a61db512
--- /dev/null
+++ b/arch/um/drivers/chan.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2000, 2001 Jeff Dike (jdike@karaya.com)
+ */
+
+#ifndef __CHAN_KERN_H__
+#define __CHAN_KERN_H__
+
+#include <linux/tty.h>
+#include <linux/list.h>
+#include <linux/console.h>
+#include "chan_user.h"
+#include "line.h"
+
+struct chan {
+	struct list_head list;
+	struct list_head free_list;
+	struct line *line;
+	char *dev;
+	unsigned int primary:1;
+	unsigned int input:1;
+	unsigned int output:1;
+	unsigned int opened:1;
+	unsigned int enabled:1;
+	int fd_in;
+	int fd_out; /* only different to fd_in if blocking output is needed */
+	const struct chan_ops *ops;
+	void *data;
+};
+
+extern void chan_interrupt(struct line *line, int irq);
+extern int parse_chan_pair(char *str, struct line *line, int device,
+			   const struct chan_opts *opts, char **error_out);
+extern int write_chan(struct chan *chan, const u8 *buf, size_t len,
+			     int write_irq);
+extern int console_write_chan(struct chan *chan, const char *buf, 
+			      int len);
+extern int console_open_chan(struct line *line, struct console *co);
+extern void deactivate_chan(struct chan *chan, int irq);
+extern void chan_enable_winch(struct chan *chan, struct tty_port *port);
+extern int enable_chan(struct line *line);
+extern void close_chan(struct line *line);
+extern int chan_window_size(struct line *line, 
+			     unsigned short *rows_out, 
+			     unsigned short *cols_out);
+extern int chan_config_string(struct line *line, char *str, int size,
+			      char **error_out);
+
+#endif
diff --git a/arch/um/drivers/chan_kern.c b/arch/um/drivers/chan_kern.c
new file mode 100644
index 000000000..db2bb032b
--- /dev/null
+++ b/arch/um/drivers/chan_kern.c
@@ -0,0 +1,610 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
+ */
+
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include "chan.h"
+#include <os.h>
+#include <irq_kern.h>
+
+#ifdef CONFIG_NOCONFIG_CHAN
+static void *not_configged_init(char *str, int device,
+				const struct chan_opts *opts)
+{
+	printk(KERN_ERR "Using a channel type which is configured out of "
+	       "UML\n");
+	return NULL;
+}
+
+static int not_configged_open(int input, int output, int primary, void *data,
+			      char **dev_out)
+{
+	printk(KERN_ERR "Using a channel type which is configured out of "
+	       "UML\n");
+	return -ENODEV;
+}
+
+static void not_configged_close(int fd, void *data)
+{
+	printk(KERN_ERR "Using a channel type which is configured out of "
+	       "UML\n");
+}
+
+static int not_configged_read(int fd, u8 *c_out, void *data)
+{
+	printk(KERN_ERR "Using a channel type which is configured out of "
+	       "UML\n");
+	return -EIO;
+}
+
+static int not_configged_write(int fd, const u8 *buf, size_t len, void *data)
+{
+	printk(KERN_ERR "Using a channel type which is configured out of "
+	       "UML\n");
+	return -EIO;
+}
+
+static int not_configged_console_write(int fd, const char *buf, int len)
+{
+	printk(KERN_ERR "Using a channel type which is configured out of "
+	       "UML\n");
+	return -EIO;
+}
+
+static int not_configged_window_size(int fd, void *data, unsigned short *rows,
+				     unsigned short *cols)
+{
+	printk(KERN_ERR "Using a channel type which is configured out of "
+	       "UML\n");
+	return -ENODEV;
+}
+
+static void not_configged_free(void *data)
+{
+	printk(KERN_ERR "Using a channel type which is configured out of "
+	       "UML\n");
+}
+
+static const struct chan_ops not_configged_ops = {
+	.init		= not_configged_init,
+	.open		= not_configged_open,
+	.close		= not_configged_close,
+	.read		= not_configged_read,
+	.write		= not_configged_write,
+	.console_write	= not_configged_console_write,
+	.window_size	= not_configged_window_size,
+	.free		= not_configged_free,
+	.winch		= 0,
+};
+#endif /* CONFIG_NOCONFIG_CHAN */
+
+static inline bool need_output_blocking(void)
+{
+	return time_travel_mode == TT_MODE_INFCPU ||
+	       time_travel_mode == TT_MODE_EXTERNAL;
+}
+
+static int open_one_chan(struct chan *chan)
+{
+	int fd, err;
+
+	if (chan->opened)
+		return 0;
+
+	if (chan->ops->open == NULL)
+		fd = 0;
+	else fd = (*chan->ops->open)(chan->input, chan->output, chan->primary,
+				     chan->data, &chan->dev);
+	if (fd < 0)
+		return fd;
+
+	err = os_set_fd_block(fd, 0);
+	if (err)
+		goto out_close;
+
+	chan->fd_in = fd;
+	chan->fd_out = fd;
+
+	/*
+	 * In time-travel modes infinite-CPU and external we need to guarantee
+	 * that any writes to the output succeed immdiately from the point of
+	 * the VM. The best way to do this is to put the FD in blocking mode
+	 * and simply wait/retry until everything is written.
+	 * As every write is guaranteed to complete, we also do not need to
+	 * request an IRQ for the output.
+	 *
+	 * Note that input cannot happen in a time synchronized way. We permit
+	 * it, but time passes very quickly if anything waits for a read.
+	 */
+	if (chan->output && need_output_blocking()) {
+		err = os_dup_file(chan->fd_out);
+		if (err < 0)
+			goto out_close;
+
+		chan->fd_out = err;
+
+		err = os_set_fd_block(chan->fd_out, 1);
+		if (err) {
+			os_close_file(chan->fd_out);
+			goto out_close;
+		}
+	}
+
+	chan->opened = 1;
+	return 0;
+
+out_close:
+	(*chan->ops->close)(fd, chan->data);
+	return err;
+}
+
+static int open_chan(struct list_head *chans)
+{
+	struct list_head *ele;
+	struct chan *chan;
+	int ret, err = 0;
+
+	list_for_each(ele, chans) {
+		chan = list_entry(ele, struct chan, list);
+		ret = open_one_chan(chan);
+		if (chan->primary)
+			err = ret;
+	}
+	return err;
+}
+
+void chan_enable_winch(struct chan *chan, struct tty_port *port)
+{
+	if (chan && chan->primary && chan->ops->winch)
+		register_winch(chan->fd_in, port);
+}
+
+static void line_timer_cb(struct work_struct *work)
+{
+	struct line *line = container_of(work, struct line, task.work);
+
+	if (!line->throttled)
+		chan_interrupt(line, line->read_irq);
+}
+
+int enable_chan(struct line *line)
+{
+	struct list_head *ele;
+	struct chan *chan;
+	int err;
+
+	INIT_DELAYED_WORK(&line->task, line_timer_cb);
+
+	list_for_each(ele, &line->chan_list) {
+		chan = list_entry(ele, struct chan, list);
+		err = open_one_chan(chan);
+		if (err) {
+			if (chan->primary)
+				goto out_close;
+
+			continue;
+		}
+
+		if (chan->enabled)
+			continue;
+		err = line_setup_irq(chan->fd_in, chan->input,
+				     chan->output && !need_output_blocking(),
+				     line, chan);
+		if (err)
+			goto out_close;
+
+		chan->enabled = 1;
+	}
+
+	return 0;
+
+ out_close:
+	close_chan(line);
+	return err;
+}
+
+/* Items are added in IRQ context, when free_irq can't be called, and
+ * removed in process context, when it can.
+ * This handles interrupt sources which disappear, and which need to
+ * be permanently disabled.  This is discovered in IRQ context, but
+ * the freeing of the IRQ must be done later.
+ */
+static DEFINE_RAW_SPINLOCK(irqs_to_free_lock);
+static LIST_HEAD(irqs_to_free);
+
+void free_irqs(void)
+{
+	struct chan *chan;
+	LIST_HEAD(list);
+	struct list_head *ele;
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&irqs_to_free_lock, flags);
+	list_splice_init(&irqs_to_free, &list);
+	raw_spin_unlock_irqrestore(&irqs_to_free_lock, flags);
+
+	list_for_each(ele, &list) {
+		chan = list_entry(ele, struct chan, free_list);
+
+		if (chan->input && chan->enabled)
+			um_free_irq(chan->line->read_irq, chan);
+		if (chan->output && chan->enabled &&
+		    !need_output_blocking())
+			um_free_irq(chan->line->write_irq, chan);
+		chan->enabled = 0;
+	}
+}
+
+static void close_one_chan(struct chan *chan, int delay_free_irq)
+{
+	unsigned long flags;
+
+	if (!chan->opened)
+		return;
+
+	if (delay_free_irq) {
+		raw_spin_lock_irqsave(&irqs_to_free_lock, flags);
+		list_add(&chan->free_list, &irqs_to_free);
+		raw_spin_unlock_irqrestore(&irqs_to_free_lock, flags);
+	} else {
+		if (chan->input && chan->enabled)
+			um_free_irq(chan->line->read_irq, chan);
+		if (chan->output && chan->enabled &&
+		    !need_output_blocking())
+			um_free_irq(chan->line->write_irq, chan);
+		chan->enabled = 0;
+	}
+	if (chan->fd_out != chan->fd_in)
+		os_close_file(chan->fd_out);
+	if (chan->ops->close != NULL)
+		(*chan->ops->close)(chan->fd_in, chan->data);
+
+	chan->opened = 0;
+	chan->fd_in = -1;
+	chan->fd_out = -1;
+}
+
+void close_chan(struct line *line)
+{
+	struct chan *chan;
+
+	/* Close in reverse order as open in case more than one of them
+	 * refers to the same device and they save and restore that device's
+	 * state.  Then, the first one opened will have the original state,
+	 * so it must be the last closed.
+	 */
+	list_for_each_entry_reverse(chan, &line->chan_list, list) {
+		close_one_chan(chan, 0);
+	}
+}
+
+void deactivate_chan(struct chan *chan, int irq)
+{
+	if (chan && chan->enabled)
+		deactivate_fd(chan->fd_in, irq);
+}
+
+int write_chan(struct chan *chan, const u8 *buf, size_t len, int write_irq)
+{
+	int n, ret = 0;
+
+	if (len == 0 || !chan || !chan->ops->write)
+		return 0;
+
+	n = chan->ops->write(chan->fd_out, buf, len, chan->data);
+	if (chan->primary) {
+		ret = n;
+	}
+	return ret;
+}
+
+int console_write_chan(struct chan *chan, const char *buf, int len)
+{
+	int n, ret = 0;
+
+	if (!chan || !chan->ops->console_write)
+		return 0;
+
+	n = chan->ops->console_write(chan->fd_out, buf, len);
+	if (chan->primary)
+		ret = n;
+	return ret;
+}
+
+int console_open_chan(struct line *line, struct console *co)
+{
+	int err;
+
+	err = open_chan(&line->chan_list);
+	if (err)
+		return err;
+
+	printk(KERN_INFO "Console initialized on /dev/%s%d\n", co->name,
+	       co->index);
+	return 0;
+}
+
+int chan_window_size(struct line *line, unsigned short *rows_out,
+		      unsigned short *cols_out)
+{
+	struct chan *chan;
+
+	chan = line->chan_in;
+	if (chan && chan->primary) {
+		if (chan->ops->window_size == NULL)
+			return 0;
+		return chan->ops->window_size(chan->fd_in, chan->data,
+					      rows_out, cols_out);
+	}
+	chan = line->chan_out;
+	if (chan && chan->primary) {
+		if (chan->ops->window_size == NULL)
+			return 0;
+		return chan->ops->window_size(chan->fd_in, chan->data,
+					      rows_out, cols_out);
+	}
+	return 0;
+}
+
+static void free_one_chan(struct chan *chan)
+{
+	list_del(&chan->list);
+
+	close_one_chan(chan, 0);
+
+	if (chan->ops->free != NULL)
+		(*chan->ops->free)(chan->data);
+
+	if (chan->primary && chan->output)
+		ignore_sigio_fd(chan->fd_in);
+	kfree(chan);
+}
+
+static void free_chan(struct list_head *chans)
+{
+	struct list_head *ele, *next;
+	struct chan *chan;
+
+	list_for_each_safe(ele, next, chans) {
+		chan = list_entry(ele, struct chan, list);
+		free_one_chan(chan);
+	}
+}
+
+static int one_chan_config_string(struct chan *chan, char *str, int size,
+				  char **error_out)
+{
+	int n = 0;
+
+	if (chan == NULL) {
+		CONFIG_CHUNK(str, size, n, "none", 1);
+		return n;
+	}
+
+	CONFIG_CHUNK(str, size, n, chan->ops->type, 0);
+
+	if (chan->dev == NULL) {
+		CONFIG_CHUNK(str, size, n, "", 1);
+		return n;
+	}
+
+	CONFIG_CHUNK(str, size, n, ":", 0);
+	CONFIG_CHUNK(str, size, n, chan->dev, 0);
+
+	return n;
+}
+
+static int chan_pair_config_string(struct chan *in, struct chan *out,
+				   char *str, int size, char **error_out)
+{
+	int n;
+
+	n = one_chan_config_string(in, str, size, error_out);
+	str += n;
+	size -= n;
+
+	if (in == out) {
+		CONFIG_CHUNK(str, size, n, "", 1);
+		return n;
+	}
+
+	CONFIG_CHUNK(str, size, n, ",", 1);
+	n = one_chan_config_string(out, str, size, error_out);
+	str += n;
+	size -= n;
+	CONFIG_CHUNK(str, size, n, "", 1);
+
+	return n;
+}
+
+int chan_config_string(struct line *line, char *str, int size,
+		       char **error_out)
+{
+	struct chan *in = line->chan_in, *out = line->chan_out;
+
+	if (in && !in->primary)
+		in = NULL;
+	if (out && !out->primary)
+		out = NULL;
+
+	return chan_pair_config_string(in, out, str, size, error_out);
+}
+
+struct chan_type {
+	char *key;
+	const struct chan_ops *ops;
+};
+
+static const struct chan_type chan_table[] = {
+	{ "fd", &fd_ops },
+
+#ifdef CONFIG_NULL_CHAN
+	{ "null", &null_ops },
+#else
+	{ "null", &not_configged_ops },
+#endif
+
+#ifdef CONFIG_PORT_CHAN
+	{ "port", &port_ops },
+#else
+	{ "port", &not_configged_ops },
+#endif
+
+#ifdef CONFIG_PTY_CHAN
+	{ "pty", &pty_ops },
+	{ "pts", &pts_ops },
+#else
+	{ "pty", &not_configged_ops },
+	{ "pts", &not_configged_ops },
+#endif
+
+#ifdef CONFIG_TTY_CHAN
+	{ "tty", &tty_ops },
+#else
+	{ "tty", &not_configged_ops },
+#endif
+
+#ifdef CONFIG_XTERM_CHAN
+	{ "xterm", &xterm_ops },
+#else
+	{ "xterm", &not_configged_ops },
+#endif
+};
+
+static struct chan *parse_chan(struct line *line, char *str, int device,
+			       const struct chan_opts *opts, char **error_out)
+{
+	const struct chan_type *entry;
+	const struct chan_ops *ops;
+	struct chan *chan;
+	void *data;
+	int i;
+
+	ops = NULL;
+	data = NULL;
+	for(i = 0; i < ARRAY_SIZE(chan_table); i++) {
+		entry = &chan_table[i];
+		if (!strncmp(str, entry->key, strlen(entry->key))) {
+			ops = entry->ops;
+			str += strlen(entry->key);
+			break;
+		}
+	}
+	if (ops == NULL) {
+		*error_out = "No match for configured backends";
+		return NULL;
+	}
+
+	data = (*ops->init)(str, device, opts);
+	if (data == NULL) {
+		*error_out = "Configuration failed";
+		return NULL;
+	}
+
+	chan = kmalloc_obj(*chan, GFP_ATOMIC);
+	if (chan == NULL) {
+		*error_out = "Memory allocation failed";
+		return NULL;
+	}
+	*chan = ((struct chan) { .list	 	= LIST_HEAD_INIT(chan->list),
+				 .free_list 	=
+				 	LIST_HEAD_INIT(chan->free_list),
+				 .line		= line,
+				 .primary	= 1,
+				 .input		= 0,
+				 .output 	= 0,
+				 .opened  	= 0,
+				 .enabled  	= 0,
+				 .fd_in		= -1,
+				 .fd_out	= -1,
+				 .ops 		= ops,
+				 .data 		= data });
+	return chan;
+}
+
+int parse_chan_pair(char *str, struct line *line, int device,
+		    const struct chan_opts *opts, char **error_out)
+{
+	struct list_head *chans = &line->chan_list;
+	struct chan *new;
+	char *in, *out;
+
+	if (!list_empty(chans)) {
+		line->chan_in = line->chan_out = NULL;
+		free_chan(chans);
+		INIT_LIST_HEAD(chans);
+	}
+
+	if (!str)
+		return 0;
+
+	out = strchr(str, ',');
+	if (out != NULL) {
+		in = str;
+		*out = '\0';
+		out++;
+		new = parse_chan(line, in, device, opts, error_out);
+		if (new == NULL)
+			return -1;
+
+		new->input = 1;
+		list_add(&new->list, chans);
+		line->chan_in = new;
+
+		new = parse_chan(line, out, device, opts, error_out);
+		if (new == NULL)
+			return -1;
+
+		list_add(&new->list, chans);
+		new->output = 1;
+		line->chan_out = new;
+	}
+	else {
+		new = parse_chan(line, str, device, opts, error_out);
+		if (new == NULL)
+			return -1;
+
+		list_add(&new->list, chans);
+		new->input = 1;
+		new->output = 1;
+		line->chan_in = line->chan_out = new;
+	}
+	return 0;
+}
+
+void chan_interrupt(struct line *line, int irq)
+{
+	struct tty_port *port = &line->port;
+	struct chan *chan = line->chan_in;
+	int err;
+	u8 c;
+
+	if (!chan || !chan->ops->read)
+		goto out;
+
+	do {
+		if (!tty_buffer_request_room(port, 1)) {
+			schedule_delayed_work(&line->task, 1);
+			goto out;
+		}
+		err = chan->ops->read(chan->fd_in, &c, chan->data);
+		if (err > 0)
+			tty_insert_flip_char(port, c, TTY_NORMAL);
+	} while (err > 0);
+
+	if (err == -EIO) {
+		if (chan->primary) {
+			tty_port_tty_hangup(&line->port, false);
+			if (line->chan_out != chan)
+				close_one_chan(line->chan_out, 1);
+		}
+		close_one_chan(chan, 1);
+		if (chan->primary)
+			return;
+	}
+ out:
+	tty_flip_buffer_push(port);
+}
diff --git a/arch/um/drivers/chan_user.c b/arch/um/drivers/chan_user.c
new file mode 100644
index 000000000..35f9beeb1
--- /dev/null
+++ b/arch/um/drivers/chan_user.c
@@ -0,0 +1,323 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
+ */
+
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sched.h>
+#include <signal.h>
+#include <termios.h>
+#include <sys/ioctl.h>
+#include "chan_user.h"
+#include <os.h>
+#include <um_malloc.h>
+
+void generic_close(int fd, void *unused)
+{
+	close(fd);
+}
+
+int generic_read(int fd, __u8 *c_out, void *unused)
+{
+	int n;
+
+	CATCH_EINTR(n = read(fd, c_out, sizeof(*c_out)));
+	if (n > 0)
+		return n;
+	else if (n == 0)
+		return -EIO;
+	else if (errno == EAGAIN)
+		return 0;
+	return -errno;
+}
+
+/* XXX Trivial wrapper around write */
+
+int generic_write(int fd, const __u8 *buf, size_t n, void *unused)
+{
+	int written = 0;
+	int err;
+
+	/* The FD may be in blocking mode, as such, need to retry short writes,
+	 * they may have been interrupted by a signal.
+	 */
+	do {
+		errno = 0;
+		err = write(fd, buf + written, n - written);
+		if (err > 0) {
+			written += err;
+			continue;
+		}
+	} while (err < 0 && errno == EINTR);
+
+	if (written > 0)
+		return written;
+	else if (errno == EAGAIN)
+		return 0;
+	else if (err == 0)
+		return -EIO;
+	return -errno;
+}
+
+int generic_window_size(int fd, void *unused, unsigned short *rows_out,
+			unsigned short *cols_out)
+{
+	struct winsize size;
+	int ret;
+
+	if (ioctl(fd, TIOCGWINSZ, &size) < 0)
+		return -errno;
+
+	ret = ((*rows_out != size.ws_row) || (*cols_out != size.ws_col));
+
+	*rows_out = size.ws_row;
+	*cols_out = size.ws_col;
+
+	return ret;
+}
+
+void generic_free(void *data)
+{
+	kfree(data);
+}
+
+int generic_console_write(int fd, const char *buf, int n)
+{
+	sigset_t old, no_sigio;
+	struct termios save, new;
+	int err;
+
+	if (isatty(fd)) {
+		sigemptyset(&no_sigio);
+		sigaddset(&no_sigio, SIGIO);
+		if (sigprocmask(SIG_BLOCK, &no_sigio, &old))
+			goto error;
+
+		CATCH_EINTR(err = tcgetattr(fd, &save));
+		if (err)
+			goto error;
+		new = save;
+		/*
+		 * The terminal becomes a bit less raw, to handle \n also as
+		 * "Carriage Return", not only as "New Line". Otherwise, the new
+		 * line won't start at the first column.
+		 */
+		new.c_oflag |= OPOST;
+		CATCH_EINTR(err = tcsetattr(fd, TCSAFLUSH, &new));
+		if (err)
+			goto error;
+	}
+	err = generic_write(fd, buf, n, NULL);
+	/*
+	 * Restore raw mode, in any case; we *must* ignore any error apart
+	 * EINTR, except for debug.
+	 */
+	if (isatty(fd)) {
+		CATCH_EINTR(tcsetattr(fd, TCSAFLUSH, &save));
+		sigprocmask(SIG_SETMASK, &old, NULL);
+	}
+
+	return err;
+error:
+	return -errno;
+}
+
+/*
+ * UML SIGWINCH handling
+ *
+ * The point of this is to handle SIGWINCH on consoles which have host
+ * ttys and relay them inside UML to whatever might be running on the
+ * console and cares about the window size (since SIGWINCH notifies
+ * about terminal size changes).
+ *
+ * So, we have a separate thread for each host tty attached to a UML
+ * device (side-issue - I'm annoyed that one thread can't have
+ * multiple controlling ttys for the purpose of handling SIGWINCH, but
+ * I imagine there are other reasons that doesn't make any sense).
+ *
+ * SIGWINCH can't be received synchronously, so you have to set up to
+ * receive it as a signal.  That being the case, if you are going to
+ * wait for it, it is convenient to sit in sigsuspend() and wait for
+ * the signal to bounce you out of it (see below for how we make sure
+ * to exit only on SIGWINCH).
+ */
+
+static void winch_handler(int sig)
+{
+}
+
+struct winch_data {
+	int pty_fd;
+	int pipe_fd;
+};
+
+static __noreturn int winch_thread(void *arg)
+{
+	struct winch_data *data = arg;
+	sigset_t sigs;
+	int pty_fd, pipe_fd;
+	int count;
+	char c = 1;
+
+	os_set_pdeathsig();
+
+	pty_fd = data->pty_fd;
+	pipe_fd = data->pipe_fd;
+	count = write(pipe_fd, &c, sizeof(c));
+	if (count != sizeof(c))
+		os_info("winch_thread : failed to write synchronization byte, err = %d\n",
+			-count);
+
+	/*
+	 * We are not using SIG_IGN on purpose, so don't fix it as I thought to
+	 * do! If using SIG_IGN, the sigsuspend() call below would not stop on
+	 * SIGWINCH.
+	 */
+
+	signal(SIGWINCH, winch_handler);
+	sigfillset(&sigs);
+	/* Block all signals possible. */
+	if (sigprocmask(SIG_SETMASK, &sigs, NULL) < 0) {
+		os_info("winch_thread : sigprocmask failed, errno = %d\n",
+			errno);
+		goto wait_kill;
+	}
+	/* In sigsuspend(), block anything else than SIGWINCH. */
+	sigdelset(&sigs, SIGWINCH);
+
+	if (setsid() < 0) {
+		os_info("winch_thread : setsid failed, errno = %d\n",
+		       errno);
+		goto wait_kill;
+	}
+
+	if (ioctl(pty_fd, TIOCSCTTY, 0) < 0) {
+		os_info("winch_thread : TIOCSCTTY failed on "
+			"fd %d err = %d\n", pty_fd, errno);
+		goto wait_kill;
+	}
+
+	if (tcsetpgrp(pty_fd, os_getpid()) < 0) {
+		os_info("winch_thread : tcsetpgrp failed on fd %d err = %d\n",
+			pty_fd, errno);
+		goto wait_kill;
+	}
+
+	/*
+	 * These are synchronization calls between various UML threads on the
+	 * host - since they are not different kernel threads, we cannot use
+	 * kernel semaphores. We don't use SysV semaphores because they are
+	 * persistent.
+	 */
+	count = read(pipe_fd, &c, sizeof(c));
+	if (count != sizeof(c))
+		os_info("winch_thread : failed to read synchronization byte, err = %d\n",
+			errno);
+
+	while(1) {
+		/*
+		 * This will be interrupted by SIGWINCH only, since
+		 * other signals are blocked.
+		 */
+		sigsuspend(&sigs);
+
+		count = write(pipe_fd, &c, sizeof(c));
+		if (count != sizeof(c))
+			os_info("winch_thread : write failed, err = %d\n",
+				errno);
+	}
+
+wait_kill:
+	c = 2;
+	count = write(pipe_fd, &c, sizeof(c));
+	while (1)
+		pause();
+}
+
+static int winch_tramp(int fd, struct tty_port *port, int *fd_out,
+		       unsigned long *stack_out)
+{
+	struct winch_data data;
+	int fds[2], n, err, pid;
+	char c;
+
+	err = os_pipe(fds, 1, 1);
+	if (err < 0) {
+		printk(UM_KERN_ERR "winch_tramp : os_pipe failed, err = %d\n",
+		       -err);
+		goto out;
+	}
+
+	data = ((struct winch_data) { .pty_fd 		= fd,
+				      .pipe_fd 		= fds[1] } );
+	/*
+	 * CLONE_FILES so this thread doesn't hold open files which are open
+	 * now, but later closed in a different thread.  This is a
+	 * problem with /dev/net/tun, which if held open by this
+	 * thread, prevents the TUN/TAP device from being reused.
+	 */
+	pid = run_helper_thread(winch_thread, &data, CLONE_FILES, stack_out);
+	if (pid < 0) {
+		err = pid;
+		printk(UM_KERN_ERR "fork of winch_thread failed - errno = %d\n",
+		       -err);
+		goto out_close;
+	}
+
+	*fd_out = fds[0];
+	n = read(fds[0], &c, sizeof(c));
+	if (n != sizeof(c)) {
+		printk(UM_KERN_ERR "winch_tramp : failed to read "
+		       "synchronization byte\n");
+		printk(UM_KERN_ERR "read failed, err = %d\n", errno);
+		printk(UM_KERN_ERR "fd %d will not support SIGWINCH\n", fd);
+		err = -EINVAL;
+		goto out_close;
+	}
+
+	err = os_set_fd_block(*fd_out, 0);
+	if (err) {
+		printk(UM_KERN_ERR "winch_tramp: failed to set thread_fd "
+		       "non-blocking.\n");
+		goto out_close;
+	}
+
+	return pid;
+
+ out_close:
+	close(fds[1]);
+	close(fds[0]);
+ out:
+	return err;
+}
+
+void register_winch(int fd, struct tty_port *port)
+{
+	unsigned long stack;
+	int pid, thread, count, thread_fd = -1;
+	char c = 1;
+
+	if (!isatty(fd))
+		return;
+
+	pid = tcgetpgrp(fd);
+	if (is_skas_winch(pid, fd, port)) {
+		register_winch_irq(-1, fd, -1, port, 0);
+		return;
+	}
+
+	if (pid == -1) {
+		thread = winch_tramp(fd, port, &thread_fd, &stack);
+		if (thread < 0)
+			return;
+
+		register_winch_irq(thread_fd, fd, thread, port, stack);
+
+		count = write(thread_fd, &c, sizeof(c));
+		if (count != sizeof(c))
+			printk(UM_KERN_ERR "register_winch : failed to write "
+			       "synchronization byte, err = %d\n", errno);
+	}
+}
diff --git a/arch/um/drivers/chan_user.h b/arch/um/drivers/chan_user.h
new file mode 100644
index 000000000..e158e16fb
--- /dev/null
+++ b/arch/um/drivers/chan_user.h
@@ -0,0 +1,54 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2000, 2001 Jeff Dike (jdike@karaya.com)
+ */
+
+#ifndef __CHAN_USER_H__
+#define __CHAN_USER_H__
+
+#include <init.h>
+#include <linux/types.h>
+
+struct chan_opts {
+	void (*const announce)(char *dev_name, int dev);
+	char *xterm_title;
+	int raw;
+};
+
+struct chan_ops {
+	char *type;
+	void *(*init)(char *, int, const struct chan_opts *);
+	int (*open)(int, int, int, void *, char **);
+	void (*close)(int, void *);
+	int (*read)(int, __u8 *, void *);
+	int (*write)(int, const __u8 *, size_t, void *);
+	int (*console_write)(int, const char *, int);
+	int (*window_size)(int, void *, unsigned short *, unsigned short *);
+	void (*free)(void *);
+	int winch;
+};
+
+extern const struct chan_ops fd_ops, null_ops, port_ops, pts_ops, pty_ops,
+	tty_ops, xterm_ops;
+
+extern void generic_close(int fd, void *unused);
+extern int generic_read(int fd, __u8 *c_out, void *unused);
+extern int generic_write(int fd, const __u8 *buf, size_t n, void *unused);
+extern int generic_console_write(int fd, const char *buf, int n);
+extern int generic_window_size(int fd, void *unused, unsigned short *rows_out,
+			       unsigned short *cols_out);
+extern void generic_free(void *data);
+
+struct tty_port;
+extern void register_winch(int fd,  struct tty_port *port);
+extern void register_winch_irq(int fd, int tty_fd, int pid,
+			       struct tty_port *port, unsigned long stack);
+
+#define __channel_help(fn, prefix) \
+__uml_help(fn, prefix "[0-9]*=<channel description>\n" \
+"    Attach a console or serial line to a host channel.  See\n" \
+"    http://user-mode-linux.sourceforge.net/old/input.html for a complete\n" \
+"    description of this switch.\n\n" \
+);
+
+#endif
diff --git a/arch/um/drivers/cow.h b/arch/um/drivers/cow.h
new file mode 100644
index 000000000..9a67c0170
--- /dev/null
+++ b/arch/um/drivers/cow.h
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __COW_H__
+#define __COW_H__
+
+#include <asm/types.h>
+
+extern int init_cow_file(int fd, char *cow_file, char *backing_file,
+			 int sectorsize, int alignment, int *bitmap_offset_out,
+			 unsigned long *bitmap_len_out, int *data_offset_out);
+
+extern int file_reader(__u64 offset, char *buf, int len, void *arg);
+extern int read_cow_header(int (*reader)(__u64, char *, int, void *),
+			   void *arg, __u32 *version_out,
+			   char **backing_file_out, long long *mtime_out,
+			   unsigned long long *size_out, int *sectorsize_out,
+			   __u32 *align_out, int *bitmap_offset_out);
+
+extern int write_cow_header(char *cow_file, int fd, char *backing_file,
+			    int sectorsize, int alignment,
+			    unsigned long long *size);
+
+extern void cow_sizes(int version, __u64 size, int sectorsize, int align,
+		      int bitmap_offset, unsigned long *bitmap_len_out,
+		      int *data_offset_out);
+
+#endif
diff --git a/arch/um/drivers/cow_sys.h b/arch/um/drivers/cow_sys.h
new file mode 100644
index 000000000..916811ef5
--- /dev/null
+++ b/arch/um/drivers/cow_sys.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __COW_SYS_H__
+#define __COW_SYS_H__
+
+#include <kern_util.h>
+#include <os.h>
+#include <um_malloc.h>
+
+static inline void *cow_malloc(int size)
+{
+	return uml_kmalloc(size, UM_GFP_KERNEL);
+}
+
+static inline void cow_free(void *ptr)
+{
+	kfree(ptr);
+}
+
+#define cow_printf printk
+
+static inline char *cow_strdup(char *str)
+{
+	return uml_strdup(str);
+}
+
+static inline int cow_seek_file(int fd, __u64 offset)
+{
+	return os_seek_file(fd, offset);
+}
+
+static inline int cow_file_size(char *file, unsigned long long *size_out)
+{
+	return os_file_size(file, size_out);
+}
+
+static inline int cow_write_file(int fd, void *buf, int size)
+{
+	return os_write_file(fd, buf, size);
+}
+
+#endif
diff --git a/arch/um/drivers/cow_user.c b/arch/um/drivers/cow_user.c
new file mode 100644
index 000000000..dc1d1bcd8
--- /dev/null
+++ b/arch/um/drivers/cow_user.c
@@ -0,0 +1,450 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
+ */
+
+/*
+ * _XOPEN_SOURCE is needed for pread, but we define _GNU_SOURCE, which defines
+ * that.
+ */
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <arpa/inet.h>
+#include <endian.h>
+#include "cow.h"
+#include "cow_sys.h"
+
+/*
+ * arch/um/Makefile remaps strrchr to kernel_strrchr; call the kernel
+ * name directly to avoid glibc >= 2.43's C23 strrchr macro.
+ */
+char *kernel_strrchr(const char *, int);
+
+#define PATH_LEN_V1 256
+
+/* unsigned time_t works until year 2106 */
+typedef __u32 time32_t;
+
+struct cow_header_v1 {
+	__s32 magic;
+	__s32 version;
+	char backing_file[PATH_LEN_V1];
+	time32_t mtime;
+	__u64 size;
+	__s32 sectorsize;
+} __attribute__((packed));
+
+/*
+ * Define PATH_LEN_V3 as the usual value of MAXPATHLEN, just hard-code it in
+ * case other systems have different values for MAXPATHLEN.
+ *
+ * The same must hold for V2 - we want file format compatibility, not anything
+ * else.
+ */
+#define PATH_LEN_V3 4096
+#define PATH_LEN_V2 PATH_LEN_V3
+
+struct cow_header_v2 {
+	__u32 magic;
+	__u32 version;
+	char backing_file[PATH_LEN_V2];
+	time32_t mtime;
+	__u64 size;
+	__s32 sectorsize;
+} __attribute__((packed));
+
+/*
+ * Changes from V2 -
+ *	PATH_LEN_V3 as described above
+ *	Explicitly specify field bit lengths for systems with different
+ *		lengths for the usual C types.  Not sure whether char or
+ *		time_t should be changed, this can be changed later without
+ *		breaking compatibility
+ *	Add alignment field so that different alignments can be used for the
+ *		bitmap and data
+ * 	Add cow_format field to allow for the possibility of different ways
+ *		of specifying the COW blocks.  For now, the only value is 0,
+ * 		for the traditional COW bitmap.
+ *	Move the backing_file field to the end of the header.  This allows
+ *		for the possibility of expanding it into the padding required
+ *		by the bitmap alignment.
+ * 	The bitmap and data portions of the file will be aligned as specified
+ * 		by the alignment field.  This is to allow COW files to be
+ *		put on devices with restrictions on access alignments, such as
+ *		/dev/raw, with a 512 byte alignment restriction.  This also
+ *		allows the data to be more aligned more strictly than on
+ *		sector boundaries.  This is needed for ubd-mmap, which needs
+ *		the data to be page aligned.
+ *	Fixed (finally!) the rounding bug
+ */
+
+/*
+ * Until Dec2005, __attribute__((packed)) was left out from the below
+ * definition, leading on 64-bit systems to 4 bytes of padding after mtime, to
+ * align size to 8-byte alignment.  This shifted all fields above (no padding
+ * was present on 32-bit, no other padding was added).
+ *
+ * However, this _can be detected_: it means that cow_format (always 0 until
+ * now) is shifted onto the first 4 bytes of backing_file, where it is otherwise
+ * impossible to find 4 zeros. -bb */
+
+struct cow_header_v3 {
+	__u32 magic;
+	__u32 version;
+	__u32 mtime;
+	__u64 size;
+	__u32 sectorsize;
+	__u32 alignment;
+	__u32 cow_format;
+	char backing_file[PATH_LEN_V3];
+} __attribute__((packed));
+
+/* This is the broken layout used by some 64-bit binaries. */
+struct cow_header_v3_broken {
+	__u32 magic;
+	__u32 version;
+	__s64 mtime;
+	__u64 size;
+	__u32 sectorsize;
+	__u32 alignment;
+	__u32 cow_format;
+	char backing_file[PATH_LEN_V3];
+};
+
+/* COW format definitions - for now, we have only the usual COW bitmap */
+#define COW_BITMAP 0
+
+union cow_header {
+	struct cow_header_v1 v1;
+	struct cow_header_v2 v2;
+	struct cow_header_v3 v3;
+	struct cow_header_v3_broken v3_b;
+};
+
+#define COW_MAGIC 0x4f4f4f4d  /* MOOO */
+#define COW_VERSION 3
+
+#define DIV_ROUND(x, len) (((x) + (len) - 1) / (len))
+#define ROUND_UP(x, align) DIV_ROUND(x, align) * (align)
+
+void cow_sizes(int version, __u64 size, int sectorsize, int align,
+	       int bitmap_offset, unsigned long *bitmap_len_out,
+	       int *data_offset_out)
+{
+	if (version < 3) {
+		*bitmap_len_out = (size + sectorsize - 1) / (8 * sectorsize);
+
+		*data_offset_out = bitmap_offset + *bitmap_len_out;
+		*data_offset_out = (*data_offset_out + sectorsize - 1) /
+			sectorsize;
+		*data_offset_out *= sectorsize;
+	}
+	else {
+		*bitmap_len_out = DIV_ROUND(size, sectorsize);
+		*bitmap_len_out = DIV_ROUND(*bitmap_len_out, 8);
+
+		*data_offset_out = bitmap_offset + *bitmap_len_out;
+		*data_offset_out = ROUND_UP(*data_offset_out, align);
+	}
+}
+
+static int absolutize(char *to, int size, char *from)
+{
+	char save_cwd[256], *slash;
+	int remaining;
+
+	if (getcwd(save_cwd, sizeof(save_cwd)) == NULL) {
+		cow_printf("absolutize : unable to get cwd - errno = %d\n",
+			   errno);
+		return -1;
+	}
+	slash = kernel_strrchr(from, '/');
+	if (slash != NULL) {
+		*slash = '\0';
+		if (chdir(from)) {
+			*slash = '/';
+			cow_printf("absolutize : Can't cd to '%s' - "
+				   "errno = %d\n", from, errno);
+			return -1;
+		}
+		*slash = '/';
+		if (getcwd(to, size) == NULL) {
+			cow_printf("absolutize : unable to get cwd of '%s' - "
+			       "errno = %d\n", from, errno);
+			return -1;
+		}
+		remaining = size - strlen(to);
+		if (strlen(slash) + 1 > remaining) {
+			cow_printf("absolutize : unable to fit '%s' into %d "
+			       "chars\n", from, size);
+			return -1;
+		}
+		strcat(to, slash);
+	}
+	else {
+		if (strlen(save_cwd) + 1 + strlen(from) + 1 > size) {
+			cow_printf("absolutize : unable to fit '%s' into %d "
+			       "chars\n", from, size);
+			return -1;
+		}
+		strcpy(to, save_cwd);
+		strcat(to, "/");
+		strcat(to, from);
+	}
+	if (chdir(save_cwd)) {
+		cow_printf("absolutize : Can't cd to '%s' - "
+			   "errno = %d\n", save_cwd, errno);
+		return -1;
+	}
+	return 0;
+}
+
+int write_cow_header(char *cow_file, int fd, char *backing_file,
+		     int sectorsize, int alignment, unsigned long long *size)
+{
+	struct cow_header_v3 *header;
+	long long modtime;
+	int err;
+
+	err = cow_seek_file(fd, 0);
+	if (err < 0) {
+		cow_printf("write_cow_header - lseek failed, err = %d\n", -err);
+		goto out;
+	}
+
+	err = -ENOMEM;
+	header = cow_malloc(sizeof(*header));
+	if (header == NULL) {
+		cow_printf("write_cow_header - failed to allocate COW V3 "
+			   "header\n");
+		goto out;
+	}
+	header->magic = htobe32(COW_MAGIC);
+	header->version = htobe32(COW_VERSION);
+
+	err = -EINVAL;
+	if (strlen(backing_file) > sizeof(header->backing_file) - 1) {
+		/* Below, %zd is for a size_t value */
+		cow_printf("Backing file name \"%s\" is too long - names are "
+			   "limited to %zd characters\n", backing_file,
+			   sizeof(header->backing_file) - 1);
+		goto out_free;
+	}
+
+	if (absolutize(header->backing_file, sizeof(header->backing_file),
+		      backing_file))
+		goto out_free;
+
+	err = os_file_modtime(header->backing_file, &modtime);
+	if (err < 0) {
+		cow_printf("write_cow_header - backing file '%s' mtime "
+			   "request failed, err = %d\n", header->backing_file,
+			   -err);
+		goto out_free;
+	}
+
+	err = cow_file_size(header->backing_file, size);
+	if (err < 0) {
+		cow_printf("write_cow_header - couldn't get size of "
+			   "backing file '%s', err = %d\n",
+			   header->backing_file, -err);
+		goto out_free;
+	}
+
+	header->mtime = htobe32(modtime);
+	header->size = htobe64(*size);
+	header->sectorsize = htobe32(sectorsize);
+	header->alignment = htobe32(alignment);
+	header->cow_format = COW_BITMAP;
+
+	err = cow_write_file(fd, header, sizeof(*header));
+	if (err != sizeof(*header)) {
+		cow_printf("write_cow_header - write of header to "
+			   "new COW file '%s' failed, err = %d\n", cow_file,
+			   -err);
+		goto out_free;
+	}
+	err = 0;
+ out_free:
+	cow_free(header);
+ out:
+	return err;
+}
+
+int file_reader(__u64 offset, char *buf, int len, void *arg)
+{
+	int fd = *((int *) arg);
+
+	return pread(fd, buf, len, offset);
+}
+
+/* XXX Need to sanity-check the values read from the header */
+
+int read_cow_header(int (*reader)(__u64, char *, int, void *), void *arg,
+		    __u32 *version_out, char **backing_file_out,
+		    long long *mtime_out, unsigned long long *size_out,
+		    int *sectorsize_out, __u32 *align_out,
+		    int *bitmap_offset_out)
+{
+	union cow_header *header;
+	char *file;
+	int err, n;
+	unsigned long version, magic;
+
+	header = cow_malloc(sizeof(*header));
+	if (header == NULL) {
+	        cow_printf("read_cow_header - Failed to allocate header\n");
+		return -ENOMEM;
+	}
+	err = -EINVAL;
+	n = (*reader)(0, (char *) header, sizeof(*header), arg);
+	if (n < offsetof(typeof(header->v1), backing_file)) {
+		cow_printf("read_cow_header - short header\n");
+		goto out;
+	}
+
+	magic = header->v1.magic;
+	if (magic == COW_MAGIC)
+		version = header->v1.version;
+	else if (magic == be32toh(COW_MAGIC))
+		version = be32toh(header->v1.version);
+	/* No error printed because the non-COW case comes through here */
+	else goto out;
+
+	*version_out = version;
+
+	if (version == 1) {
+		if (n < sizeof(header->v1)) {
+			cow_printf("read_cow_header - failed to read V1 "
+				   "header\n");
+			goto out;
+		}
+		*mtime_out = header->v1.mtime;
+		*size_out = header->v1.size;
+		*sectorsize_out = header->v1.sectorsize;
+		*bitmap_offset_out = sizeof(header->v1);
+		*align_out = *sectorsize_out;
+		file = header->v1.backing_file;
+	}
+	else if (version == 2) {
+		if (n < sizeof(header->v2)) {
+			cow_printf("read_cow_header - failed to read V2 "
+				   "header\n");
+			goto out;
+		}
+		*mtime_out = be32toh(header->v2.mtime);
+		*size_out = be64toh(header->v2.size);
+		*sectorsize_out = be32toh(header->v2.sectorsize);
+		*bitmap_offset_out = sizeof(header->v2);
+		*align_out = *sectorsize_out;
+		file = header->v2.backing_file;
+	}
+	/* This is very subtle - see above at union cow_header definition */
+	else if (version == 3 && (*((int*)header->v3.backing_file) != 0)) {
+		if (n < sizeof(header->v3)) {
+			cow_printf("read_cow_header - failed to read V3 "
+				   "header\n");
+			goto out;
+		}
+		*mtime_out = be32toh(header->v3.mtime);
+		*size_out = be64toh(header->v3.size);
+		*sectorsize_out = be32toh(header->v3.sectorsize);
+		*align_out = be32toh(header->v3.alignment);
+		if (*align_out == 0) {
+			cow_printf("read_cow_header - invalid COW header, "
+				   "align == 0\n");
+		}
+		*bitmap_offset_out = ROUND_UP(sizeof(header->v3), *align_out);
+		file = header->v3.backing_file;
+	}
+	else if (version == 3) {
+		cow_printf("read_cow_header - broken V3 file with"
+			   " 64-bit layout - recovering content.\n");
+
+		if (n < sizeof(header->v3_b)) {
+			cow_printf("read_cow_header - failed to read V3 "
+				   "header\n");
+			goto out;
+		}
+
+		/*
+		 * this was used until Dec2005 - 64bits are needed to represent
+		 * 2106+. I.e. we can safely do this truncating cast.
+		 *
+		 * Additionally, we must use be32toh() instead of be64toh(), since
+		 * the program used to use the former (tested - I got mtime
+		 * mismatch "0 vs whatever").
+		 *
+		 * Ever heard about bug-to-bug-compatibility ? ;-) */
+		*mtime_out = (time32_t) be32toh(header->v3_b.mtime);
+
+		*size_out = be64toh(header->v3_b.size);
+		*sectorsize_out = be32toh(header->v3_b.sectorsize);
+		*align_out = be32toh(header->v3_b.alignment);
+		if (*align_out == 0) {
+			cow_printf("read_cow_header - invalid COW header, "
+				   "align == 0\n");
+		}
+		*bitmap_offset_out = ROUND_UP(sizeof(header->v3_b), *align_out);
+		file = header->v3_b.backing_file;
+	}
+	else {
+		cow_printf("read_cow_header - invalid COW version\n");
+		goto out;
+	}
+	err = -ENOMEM;
+	*backing_file_out = cow_strdup(file);
+	if (*backing_file_out == NULL) {
+		cow_printf("read_cow_header - failed to allocate backing "
+			   "file\n");
+		goto out;
+	}
+	err = 0;
+ out:
+	cow_free(header);
+	return err;
+}
+
+int init_cow_file(int fd, char *cow_file, char *backing_file, int sectorsize,
+		  int alignment, int *bitmap_offset_out,
+		  unsigned long *bitmap_len_out, int *data_offset_out)
+{
+	unsigned long long size, offset;
+	char zero = 0;
+	int err;
+
+	err = write_cow_header(cow_file, fd, backing_file, sectorsize,
+			       alignment, &size);
+	if (err)
+		goto out;
+
+	*bitmap_offset_out = ROUND_UP(sizeof(struct cow_header_v3), alignment);
+	cow_sizes(COW_VERSION, size, sectorsize, alignment, *bitmap_offset_out,
+		  bitmap_len_out, data_offset_out);
+
+	offset = *data_offset_out + size - sizeof(zero);
+	err = cow_seek_file(fd, offset);
+	if (err < 0) {
+		cow_printf("cow bitmap lseek failed : err = %d\n", -err);
+		goto out;
+	}
+
+	/*
+	 * does not really matter how much we write it is just to set EOF
+	 * this also sets the entire COW bitmap
+	 * to zero without having to allocate it
+	 */
+	err = cow_write_file(fd, &zero, sizeof(zero));
+	if (err != sizeof(zero)) {
+		cow_printf("Write of bitmap to new COW file '%s' failed, "
+			   "err = %d\n", cow_file, -err);
+		if (err >= 0)
+			err = -EINVAL;
+		goto out;
+	}
+
+	return 0;
+ out:
+	return err;
+}
diff --git a/arch/um/drivers/fd.c b/arch/um/drivers/fd.c
new file mode 100644
index 000000000..082d739dc
--- /dev/null
+++ b/arch/um/drivers/fd.c
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <termios.h>
+#include "chan_user.h"
+#include <os.h>
+#include <um_malloc.h>
+
+struct fd_chan {
+	int fd;
+	int raw;
+	struct termios tt;
+	char str[sizeof("1234567890\0")];
+};
+
+static void *fd_init(char *str, int device, const struct chan_opts *opts)
+{
+	struct fd_chan *data;
+	char *end;
+	int n;
+
+	if (*str != ':') {
+		printk(UM_KERN_ERR "fd_init : channel type 'fd' must specify a "
+		       "file descriptor\n");
+		return NULL;
+	}
+	str++;
+	n = strtoul(str, &end, 0);
+	if ((*end != '\0') || (end == str)) {
+		printk(UM_KERN_ERR "fd_init : couldn't parse file descriptor "
+		       "'%s'\n", str);
+		return NULL;
+	}
+
+	data = uml_kmalloc(sizeof(*data), UM_GFP_KERNEL);
+	if (data == NULL)
+		return NULL;
+
+	*data = ((struct fd_chan) { .fd  	= n,
+				    .raw  	= opts->raw });
+	return data;
+}
+
+static int fd_open(int input, int output, int primary, void *d, char **dev_out)
+{
+	struct fd_chan *data = d;
+	int err;
+
+	if (data->raw && isatty(data->fd)) {
+		CATCH_EINTR(err = tcgetattr(data->fd, &data->tt));
+		if (err)
+			return err;
+
+		err = raw(data->fd);
+		if (err)
+			return err;
+	}
+	sprintf(data->str, "%d", data->fd);
+	*dev_out = data->str;
+	return data->fd;
+}
+
+static void fd_close(int fd, void *d)
+{
+	struct fd_chan *data = d;
+	int err;
+
+	if (!data->raw || !isatty(fd))
+		return;
+
+	CATCH_EINTR(err = tcsetattr(fd, TCSAFLUSH, &data->tt));
+	if (err)
+		printk(UM_KERN_ERR "Failed to restore terminal state - "
+		       "errno = %d\n", -err);
+	data->raw = 0;
+}
+
+const struct chan_ops fd_ops = {
+	.type		= "fd",
+	.init		= fd_init,
+	.open		= fd_open,
+	.close		= fd_close,
+	.read		= generic_read,
+	.write		= generic_write,
+	.console_write	= generic_console_write,
+	.window_size	= generic_window_size,
+	.free		= generic_free,
+	.winch		= 1,
+};
diff --git a/arch/um/drivers/harddog.h b/arch/um/drivers/harddog.h
new file mode 100644
index 000000000..6d9ea60e7
--- /dev/null
+++ b/arch/um/drivers/harddog.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef UM_WATCHDOG_H
+#define UM_WATCHDOG_H
+
+int start_watchdog(int *in_fd_ret, int *out_fd_ret, char *sock);
+void stop_watchdog(int in_fd, int out_fd);
+int ping_watchdog(int fd);
+
+#endif /* UM_WATCHDOG_H */
diff --git a/arch/um/drivers/harddog_kern.c b/arch/um/drivers/harddog_kern.c
new file mode 100644
index 000000000..819aabb4e
--- /dev/null
+++ b/arch/um/drivers/harddog_kern.c
@@ -0,0 +1,174 @@
+/* UML hardware watchdog, shamelessly stolen from:
+ *
+ *	SoftDog	0.05:	A Software Watchdog Device
+ *
+ *	(c) Copyright 1996 Alan Cox <alan@redhat.com>, All Rights Reserved.
+ *				http://www.redhat.com
+ *
+ *	This program is free software; you can redistribute it and/or
+ *	modify it under the terms of the GNU General Public License
+ *	as published by the Free Software Foundation; either version
+ *	2 of the License, or (at your option) any later version.
+ *
+ *	Neither Alan Cox nor CymruNet Ltd. admit liability nor provide
+ *	warranty for any of this software. This material is provided
+ *	"AS-IS" and at no charge.
+ *
+ *	(c) Copyright 1995    Alan Cox <alan@lxorguk.ukuu.org.uk>
+ *
+ *	Software only watchdog driver. Unlike its big brother the WDT501P
+ *	driver this won't always recover a failed machine.
+ *
+ *  03/96: Angelo Haritsis <ah@doc.ic.ac.uk> :
+ *	Modularised.
+ *	Added soft_margin; use upon insmod to change the timer delay.
+ *	NB: uses same minor as wdt (WATCHDOG_MINOR); we could use separate
+ *	    minors.
+ *
+ *  19980911 Alan Cox
+ *	Made SMP safe for 2.3.x
+ *
+ *  20011127 Joel Becker (jlbec@evilplan.org>
+ *	Added soft_noboot; Allows testing the softdog trigger without
+ *	requiring a recompile.
+ *	Added WDIOC_GETTIMEOUT and WDIOC_SETTIMOUT.
+ */
+
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/miscdevice.h>
+#include <linux/watchdog.h>
+#include <linux/reboot.h>
+#include <linux/mutex.h>
+#include <linux/init.h>
+#include <linux/spinlock.h>
+#include <linux/uaccess.h>
+#include "mconsole.h"
+#include "harddog.h"
+
+MODULE_DESCRIPTION("UML hardware watchdog");
+MODULE_LICENSE("GPL");
+
+static DEFINE_MUTEX(harddog_mutex);
+static DEFINE_SPINLOCK(lock);
+static int timer_alive;
+static int harddog_in_fd = -1;
+static int harddog_out_fd = -1;
+
+/*
+ *	Allow only one person to hold it open
+ */
+
+static int harddog_open(struct inode *inode, struct file *file)
+{
+	int err = -EBUSY;
+	char *sock = NULL;
+
+	mutex_lock(&harddog_mutex);
+	spin_lock(&lock);
+	if(timer_alive)
+		goto err;
+#ifdef CONFIG_WATCHDOG_NOWAYOUT
+	__module_get(THIS_MODULE);
+#endif
+
+#ifdef CONFIG_MCONSOLE
+	sock = mconsole_notify_socket();
+#endif
+	err = start_watchdog(&harddog_in_fd, &harddog_out_fd, sock);
+	if(err)
+		goto err;
+
+	timer_alive = 1;
+	spin_unlock(&lock);
+	mutex_unlock(&harddog_mutex);
+	return stream_open(inode, file);
+err:
+	spin_unlock(&lock);
+	mutex_unlock(&harddog_mutex);
+	return err;
+}
+
+static int harddog_release(struct inode *inode, struct file *file)
+{
+	/*
+	 *	Shut off the timer.
+	 */
+
+	spin_lock(&lock);
+
+	stop_watchdog(harddog_in_fd, harddog_out_fd);
+	harddog_in_fd = -1;
+	harddog_out_fd = -1;
+
+	timer_alive=0;
+	spin_unlock(&lock);
+
+	return 0;
+}
+
+static ssize_t harddog_write(struct file *file, const char __user *data, size_t len,
+			     loff_t *ppos)
+{
+	/*
+	 *	Refresh the timer.
+	 */
+	if(len)
+		return ping_watchdog(harddog_out_fd);
+	return 0;
+}
+
+static int harddog_ioctl_unlocked(struct file *file,
+				  unsigned int cmd, unsigned long arg)
+{
+	void __user *argp= (void __user *)arg;
+	static struct watchdog_info ident = {
+		WDIOC_SETTIMEOUT,
+		0,
+		"UML Hardware Watchdog"
+	};
+	switch (cmd) {
+		default:
+			return -ENOTTY;
+		case WDIOC_GETSUPPORT:
+			if(copy_to_user(argp, &ident, sizeof(ident)))
+				return -EFAULT;
+			return 0;
+		case WDIOC_GETSTATUS:
+		case WDIOC_GETBOOTSTATUS:
+			return put_user(0,(int __user *)argp);
+		case WDIOC_KEEPALIVE:
+			return ping_watchdog(harddog_out_fd);
+	}
+}
+
+static long harddog_ioctl(struct file *file,
+			  unsigned int cmd, unsigned long arg)
+{
+	long ret;
+
+	mutex_lock(&harddog_mutex);
+	ret = harddog_ioctl_unlocked(file, cmd, arg);
+	mutex_unlock(&harddog_mutex);
+
+	return ret;
+}
+
+static const struct file_operations harddog_fops = {
+	.owner		= THIS_MODULE,
+	.write		= harddog_write,
+	.unlocked_ioctl	= harddog_ioctl,
+	.compat_ioctl	= compat_ptr_ioctl,
+	.open		= harddog_open,
+	.release	= harddog_release,
+};
+
+static struct miscdevice harddog_miscdev = {
+	.minor		= WATCHDOG_MINOR,
+	.name		= "watchdog",
+	.fops		= &harddog_fops,
+};
+module_misc_device(harddog_miscdev);
diff --git a/arch/um/drivers/harddog_user.c b/arch/um/drivers/harddog_user.c
new file mode 100644
index 000000000..9ed893049
--- /dev/null
+++ b/arch/um/drivers/harddog_user.c
@@ -0,0 +1,128 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stdio.h>
+#include <unistd.h>
+#include <errno.h>
+#include <os.h>
+#include "harddog.h"
+
+struct dog_data {
+	int stdin_fd;
+	int stdout_fd;
+	int close_me[2];
+};
+
+static void pre_exec(void *d)
+{
+	struct dog_data *data = d;
+
+	dup2(data->stdin_fd, 0);
+	dup2(data->stdout_fd, 1);
+	dup2(data->stdout_fd, 2);
+	close(data->stdin_fd);
+	close(data->stdout_fd);
+	close(data->close_me[0]);
+	close(data->close_me[1]);
+}
+
+int start_watchdog(int *in_fd_ret, int *out_fd_ret, char *sock)
+{
+	struct dog_data data;
+	int in_fds[2], out_fds[2], pid, n, err;
+	char pid_buf[sizeof("nnnnnnn\0")], c;
+	char *pid_args[] = { "/usr/bin/uml_watchdog", "-pid", pid_buf, NULL };
+	char *mconsole_args[] = { "/usr/bin/uml_watchdog", "-mconsole", NULL,
+				  NULL };
+	char **args = NULL;
+
+	err = os_pipe(in_fds, 1, 0);
+	if (err < 0) {
+		printk("harddog_open - os_pipe failed, err = %d\n", -err);
+		goto out;
+	}
+
+	err = os_pipe(out_fds, 1, 0);
+	if (err < 0) {
+		printk("harddog_open - os_pipe failed, err = %d\n", -err);
+		goto out_close_in;
+	}
+
+	data.stdin_fd = out_fds[0];
+	data.stdout_fd = in_fds[1];
+	data.close_me[0] = out_fds[1];
+	data.close_me[1] = in_fds[0];
+
+	if (sock != NULL) {
+		mconsole_args[2] = sock;
+		args = mconsole_args;
+	}
+	else {
+		/* XXX The os_getpid() is not SMP correct */
+		sprintf(pid_buf, "%d", os_getpid());
+		args = pid_args;
+	}
+
+	pid = run_helper(pre_exec, &data, args);
+
+	close(out_fds[0]);
+	close(in_fds[1]);
+
+	if (pid < 0) {
+		err = -pid;
+		printk("harddog_open - run_helper failed, errno = %d\n", -err);
+		goto out_close_out;
+	}
+
+	n = read(in_fds[0], &c, sizeof(c));
+	if (n == 0) {
+		printk("harddog_open - EOF on watchdog pipe\n");
+		helper_wait(pid);
+		err = -EIO;
+		goto out_close_out;
+	}
+	else if (n < 0) {
+		printk("harddog_open - read of watchdog pipe failed, "
+		       "err = %d\n", errno);
+		helper_wait(pid);
+		err = n;
+		goto out_close_out;
+	}
+	*in_fd_ret = in_fds[0];
+	*out_fd_ret = out_fds[1];
+	return 0;
+
+ out_close_in:
+	close(in_fds[0]);
+	close(in_fds[1]);
+ out_close_out:
+	close(out_fds[0]);
+	close(out_fds[1]);
+ out:
+	return err;
+}
+
+void stop_watchdog(int in_fd, int out_fd)
+{
+	close(in_fd);
+	close(out_fd);
+}
+
+int ping_watchdog(int fd)
+{
+	int n;
+	char c = '\n';
+
+	n = write(fd, &c, sizeof(c));
+	if (n != sizeof(c)) {
+		printk("ping_watchdog - write failed, ret = %d, err = %d\n",
+		       n, errno);
+		if (n < 0)
+			return n;
+		return -EIO;
+	}
+	return 1;
+
+}
diff --git a/arch/um/drivers/harddog_user_exp.c b/arch/um/drivers/harddog_user_exp.c
new file mode 100644
index 000000000..c74d4b815
--- /dev/null
+++ b/arch/um/drivers/harddog_user_exp.c
@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/export.h>
+#include "harddog.h"
+
+#if IS_MODULE(CONFIG_UML_WATCHDOG)
+EXPORT_SYMBOL(start_watchdog);
+EXPORT_SYMBOL(stop_watchdog);
+EXPORT_SYMBOL(ping_watchdog);
+#endif
diff --git a/arch/um/drivers/hostaudio_kern.c b/arch/um/drivers/hostaudio_kern.c
new file mode 100644
index 000000000..7ce98f148
--- /dev/null
+++ b/arch/um/drivers/hostaudio_kern.c
@@ -0,0 +1,353 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 Steve Schmidtke
+ */
+
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/sound.h>
+#include <linux/soundcard.h>
+#include <linux/mutex.h>
+#include <linux/uaccess.h>
+#include <init.h>
+#include <os.h>
+
+struct hostaudio_state {
+	int fd;
+};
+
+struct hostmixer_state {
+	int fd;
+};
+
+#define HOSTAUDIO_DEV_DSP "/dev/sound/dsp"
+#define HOSTAUDIO_DEV_MIXER "/dev/sound/mixer"
+
+/*
+ * Changed either at boot time or module load time.  At boot, this is
+ * single-threaded; at module load, multiple modules would each have
+ * their own copy of these variables.
+ */
+static char *dsp = HOSTAUDIO_DEV_DSP;
+static char *mixer = HOSTAUDIO_DEV_MIXER;
+
+#define DSP_HELP \
+"    This is used to specify the host dsp device to the hostaudio driver.\n" \
+"    The default is \"" HOSTAUDIO_DEV_DSP "\".\n\n"
+
+#define MIXER_HELP \
+"    This is used to specify the host mixer device to the hostaudio driver.\n"\
+"    The default is \"" HOSTAUDIO_DEV_MIXER "\".\n\n"
+
+module_param(dsp, charp, 0644);
+MODULE_PARM_DESC(dsp, DSP_HELP);
+module_param(mixer, charp, 0644);
+MODULE_PARM_DESC(mixer, MIXER_HELP);
+
+#ifndef MODULE
+static int set_dsp(char *name, int *add)
+{
+	*add = 0;
+	dsp = name;
+	return 0;
+}
+
+__uml_setup("dsp=", set_dsp, "dsp=<dsp device>\n" DSP_HELP);
+
+static int set_mixer(char *name, int *add)
+{
+	*add = 0;
+	mixer = name;
+	return 0;
+}
+
+__uml_setup("mixer=", set_mixer, "mixer=<mixer device>\n" MIXER_HELP);
+#endif
+
+static DEFINE_MUTEX(hostaudio_mutex);
+
+/* /dev/dsp file operations */
+
+static ssize_t hostaudio_read(struct file *file, char __user *buffer,
+			      size_t count, loff_t *ppos)
+{
+	struct hostaudio_state *state = file->private_data;
+	void *kbuf;
+	int err;
+
+#ifdef DEBUG
+	printk(KERN_DEBUG "hostaudio: read called, count = %d\n", count);
+#endif
+
+	kbuf = kmalloc(count, GFP_KERNEL);
+	if (kbuf == NULL)
+		return -ENOMEM;
+
+	err = os_read_file(state->fd, kbuf, count);
+	if (err < 0)
+		goto out;
+
+	if (copy_to_user(buffer, kbuf, err))
+		err = -EFAULT;
+
+out:
+	kfree(kbuf);
+	return err;
+}
+
+static ssize_t hostaudio_write(struct file *file, const char __user *buffer,
+			       size_t count, loff_t *ppos)
+{
+	struct hostaudio_state *state = file->private_data;
+	void *kbuf;
+	int err;
+
+#ifdef DEBUG
+	printk(KERN_DEBUG "hostaudio: write called, count = %d\n", count);
+#endif
+
+	kbuf = memdup_user(buffer, count);
+	if (IS_ERR(kbuf))
+		return PTR_ERR(kbuf);
+
+	err = os_write_file(state->fd, kbuf, count);
+	if (err < 0)
+		goto out;
+	*ppos += err;
+
+ out:
+	kfree(kbuf);
+	return err;
+}
+
+static __poll_t hostaudio_poll(struct file *file,
+				struct poll_table_struct *wait)
+{
+#ifdef DEBUG
+	printk(KERN_DEBUG "hostaudio: poll called (unimplemented)\n");
+#endif
+
+	return 0;
+}
+
+static long hostaudio_ioctl(struct file *file,
+			   unsigned int cmd, unsigned long arg)
+{
+	struct hostaudio_state *state = file->private_data;
+	unsigned long data = 0;
+	int err;
+
+#ifdef DEBUG
+	printk(KERN_DEBUG "hostaudio: ioctl called, cmd = %u\n", cmd);
+#endif
+	switch(cmd){
+	case SNDCTL_DSP_SPEED:
+	case SNDCTL_DSP_STEREO:
+	case SNDCTL_DSP_GETBLKSIZE:
+	case SNDCTL_DSP_CHANNELS:
+	case SNDCTL_DSP_SUBDIVIDE:
+	case SNDCTL_DSP_SETFRAGMENT:
+		if (get_user(data, (int __user *) arg))
+			return -EFAULT;
+		break;
+	default:
+		break;
+	}
+
+	err = os_ioctl_generic(state->fd, cmd, (unsigned long) &data);
+
+	switch(cmd){
+	case SNDCTL_DSP_SPEED:
+	case SNDCTL_DSP_STEREO:
+	case SNDCTL_DSP_GETBLKSIZE:
+	case SNDCTL_DSP_CHANNELS:
+	case SNDCTL_DSP_SUBDIVIDE:
+	case SNDCTL_DSP_SETFRAGMENT:
+		if (put_user(data, (int __user *) arg))
+			return -EFAULT;
+		break;
+	default:
+		break;
+	}
+
+	return err;
+}
+
+static int hostaudio_open(struct inode *inode, struct file *file)
+{
+	struct hostaudio_state *state;
+	int r = 0, w = 0;
+	int ret;
+
+#ifdef DEBUG
+	kernel_param_lock(THIS_MODULE);
+	printk(KERN_DEBUG "hostaudio: open called (host: %s)\n", dsp);
+	kernel_param_unlock(THIS_MODULE);
+#endif
+
+	state = kmalloc_obj(struct hostaudio_state);
+	if (state == NULL)
+		return -ENOMEM;
+
+	if (file->f_mode & FMODE_READ)
+		r = 1;
+	if (file->f_mode & FMODE_WRITE)
+		w = 1;
+
+	kernel_param_lock(THIS_MODULE);
+	mutex_lock(&hostaudio_mutex);
+	ret = os_open_file(dsp, of_set_rw(OPENFLAGS(), r, w), 0);
+	mutex_unlock(&hostaudio_mutex);
+	kernel_param_unlock(THIS_MODULE);
+
+	if (ret < 0) {
+		kfree(state);
+		return ret;
+	}
+	state->fd = ret;
+	file->private_data = state;
+	return 0;
+}
+
+static int hostaudio_release(struct inode *inode, struct file *file)
+{
+	struct hostaudio_state *state = file->private_data;
+
+#ifdef DEBUG
+	printk(KERN_DEBUG "hostaudio: release called\n");
+#endif
+	os_close_file(state->fd);
+	kfree(state);
+
+	return 0;
+}
+
+/* /dev/mixer file operations */
+
+static long hostmixer_ioctl_mixdev(struct file *file,
+				  unsigned int cmd, unsigned long arg)
+{
+	struct hostmixer_state *state = file->private_data;
+
+#ifdef DEBUG
+	printk(KERN_DEBUG "hostmixer: ioctl called\n");
+#endif
+
+	return os_ioctl_generic(state->fd, cmd, arg);
+}
+
+static int hostmixer_open_mixdev(struct inode *inode, struct file *file)
+{
+	struct hostmixer_state *state;
+	int r = 0, w = 0;
+	int ret;
+
+#ifdef DEBUG
+	printk(KERN_DEBUG "hostmixer: open called (host: %s)\n", mixer);
+#endif
+
+	state = kmalloc_obj(struct hostmixer_state);
+	if (state == NULL)
+		return -ENOMEM;
+
+	if (file->f_mode & FMODE_READ)
+		r = 1;
+	if (file->f_mode & FMODE_WRITE)
+		w = 1;
+
+	kernel_param_lock(THIS_MODULE);
+	mutex_lock(&hostaudio_mutex);
+	ret = os_open_file(mixer, of_set_rw(OPENFLAGS(), r, w), 0);
+	mutex_unlock(&hostaudio_mutex);
+	kernel_param_unlock(THIS_MODULE);
+
+	if (ret < 0) {
+		kernel_param_lock(THIS_MODULE);
+		printk(KERN_ERR "hostaudio_open_mixdev failed to open '%s', "
+		       "err = %d\n", dsp, -ret);
+		kernel_param_unlock(THIS_MODULE);
+		kfree(state);
+		return ret;
+	}
+
+	file->private_data = state;
+	return 0;
+}
+
+static int hostmixer_release(struct inode *inode, struct file *file)
+{
+	struct hostmixer_state *state = file->private_data;
+
+#ifdef DEBUG
+	printk(KERN_DEBUG "hostmixer: release called\n");
+#endif
+
+	os_close_file(state->fd);
+	kfree(state);
+
+	return 0;
+}
+
+/* kernel module operations */
+
+static const struct file_operations hostaudio_fops = {
+	.owner          = THIS_MODULE,
+	.read           = hostaudio_read,
+	.write          = hostaudio_write,
+	.poll           = hostaudio_poll,
+	.unlocked_ioctl	= hostaudio_ioctl,
+	.compat_ioctl	= compat_ptr_ioctl,
+	.mmap           = NULL,
+	.open           = hostaudio_open,
+	.release        = hostaudio_release,
+};
+
+static const struct file_operations hostmixer_fops = {
+	.owner          = THIS_MODULE,
+	.unlocked_ioctl	= hostmixer_ioctl_mixdev,
+	.open           = hostmixer_open_mixdev,
+	.release        = hostmixer_release,
+};
+
+static struct {
+	int dev_audio;
+	int dev_mixer;
+} module_data;
+
+MODULE_AUTHOR("Steve Schmidtke");
+MODULE_DESCRIPTION("UML Audio Relay");
+MODULE_LICENSE("GPL");
+
+static int __init hostaudio_init_module(void)
+{
+	kernel_param_lock(THIS_MODULE);
+	printk(KERN_INFO "UML Audio Relay (host dsp = %s, host mixer = %s)\n",
+	       dsp, mixer);
+	kernel_param_unlock(THIS_MODULE);
+
+	module_data.dev_audio = register_sound_dsp(&hostaudio_fops, -1);
+	if (module_data.dev_audio < 0) {
+		printk(KERN_ERR "hostaudio: couldn't register DSP device!\n");
+		return -ENODEV;
+	}
+
+	module_data.dev_mixer = register_sound_mixer(&hostmixer_fops, -1);
+	if (module_data.dev_mixer < 0) {
+		printk(KERN_ERR "hostmixer: couldn't register mixer "
+		       "device!\n");
+		unregister_sound_dsp(module_data.dev_audio);
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+static void __exit hostaudio_cleanup_module (void)
+{
+	unregister_sound_mixer(module_data.dev_mixer);
+	unregister_sound_dsp(module_data.dev_audio);
+}
+
+module_init(hostaudio_init_module);
+module_exit(hostaudio_cleanup_module);
diff --git a/arch/um/drivers/line.c b/arch/um/drivers/line.c
new file mode 100644
index 000000000..c851a5928
--- /dev/null
+++ b/arch/um/drivers/line.c
@@ -0,0 +1,771 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/irqreturn.h>
+#include <linux/kd.h>
+#include <linux/sched/signal.h>
+#include <linux/slab.h>
+
+#include "chan.h"
+#include <irq_kern.h>
+#include <irq_user.h>
+#include <kern_util.h>
+#include <os.h>
+
+#define LINE_BUFSIZE 4096
+
+static irqreturn_t line_interrupt(int irq, void *data)
+{
+	struct chan *chan = data;
+	struct line *line = chan->line;
+
+	if (line)
+		chan_interrupt(line, irq);
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * Returns the free space inside the ring buffer of this line.
+ *
+ * Should be called while holding line->lock (this does not modify data).
+ */
+static unsigned int write_room(struct line *line)
+{
+	int n;
+
+	if (line->buffer == NULL)
+		return LINE_BUFSIZE - 1;
+
+	/* This is for the case where the buffer is wrapped! */
+	n = line->head - line->tail;
+
+	if (n <= 0)
+		n += LINE_BUFSIZE; /* The other case */
+	return n - 1;
+}
+
+unsigned int line_write_room(struct tty_struct *tty)
+{
+	struct line *line = tty->driver_data;
+	unsigned long flags;
+	unsigned int room;
+
+	spin_lock_irqsave(&line->lock, flags);
+	room = write_room(line);
+	spin_unlock_irqrestore(&line->lock, flags);
+
+	return room;
+}
+
+unsigned int line_chars_in_buffer(struct tty_struct *tty)
+{
+	struct line *line = tty->driver_data;
+	unsigned long flags;
+	unsigned int ret;
+
+	spin_lock_irqsave(&line->lock, flags);
+	/* write_room subtracts 1 for the needed NULL, so we readd it.*/
+	ret = LINE_BUFSIZE - (write_room(line) + 1);
+	spin_unlock_irqrestore(&line->lock, flags);
+
+	return ret;
+}
+
+/*
+ * This copies the content of buf into the circular buffer associated with
+ * this line.
+ * The return value is the number of characters actually copied, i.e. the ones
+ * for which there was space: this function is not supposed to ever flush out
+ * the circular buffer.
+ *
+ * Must be called while holding line->lock!
+ */
+static int buffer_data(struct line *line, const u8 *buf, size_t len)
+{
+	int end, room;
+
+	if (line->buffer == NULL) {
+		line->buffer = kmalloc(LINE_BUFSIZE, GFP_ATOMIC);
+		if (line->buffer == NULL) {
+			printk(KERN_ERR "buffer_data - atomic allocation "
+			       "failed\n");
+			return 0;
+		}
+		line->head = line->buffer;
+		line->tail = line->buffer;
+	}
+
+	room = write_room(line);
+	len = (len > room) ? room : len;
+
+	end = line->buffer + LINE_BUFSIZE - line->tail;
+
+	if (len < end) {
+		memcpy(line->tail, buf, len);
+		line->tail += len;
+	}
+	else {
+		/* The circular buffer is wrapping */
+		memcpy(line->tail, buf, end);
+		buf += end;
+		memcpy(line->buffer, buf, len - end);
+		line->tail = line->buffer + len - end;
+	}
+
+	return len;
+}
+
+/*
+ * Flushes the ring buffer to the output channels. That is, write_chan is
+ * called, passing it line->head as buffer, and an appropriate count.
+ *
+ * On exit, returns 1 when the buffer is empty,
+ * 0 when the buffer is not empty on exit,
+ * and -errno when an error occurred.
+ *
+ * Must be called while holding line->lock!*/
+static int flush_buffer(struct line *line)
+{
+	int n, count;
+
+	if ((line->buffer == NULL) || (line->head == line->tail))
+		return 1;
+
+	if (line->tail < line->head) {
+		/* line->buffer + LINE_BUFSIZE is the end of the buffer! */
+		count = line->buffer + LINE_BUFSIZE - line->head;
+
+		n = write_chan(line->chan_out, line->head, count,
+			       line->write_irq);
+		if (n < 0)
+			return n;
+		if (n == count) {
+			/*
+			 * We have flushed from ->head to buffer end, now we
+			 * must flush only from the beginning to ->tail.
+			 */
+			line->head = line->buffer;
+		} else {
+			line->head += n;
+			return 0;
+		}
+	}
+
+	count = line->tail - line->head;
+	n = write_chan(line->chan_out, line->head, count,
+		       line->write_irq);
+
+	if (n < 0)
+		return n;
+
+	line->head += n;
+	return line->head == line->tail;
+}
+
+void line_flush_buffer(struct tty_struct *tty)
+{
+	struct line *line = tty->driver_data;
+	unsigned long flags;
+
+	spin_lock_irqsave(&line->lock, flags);
+	flush_buffer(line);
+	spin_unlock_irqrestore(&line->lock, flags);
+}
+
+/*
+ * We map both ->flush_chars and ->put_char (which go in pair) onto
+ * ->flush_buffer and ->write. Hope it's not that bad.
+ */
+void line_flush_chars(struct tty_struct *tty)
+{
+	line_flush_buffer(tty);
+}
+
+ssize_t line_write(struct tty_struct *tty, const u8 *buf, size_t len)
+{
+	struct line *line = tty->driver_data;
+	unsigned long flags;
+	int n, ret = 0;
+
+	spin_lock_irqsave(&line->lock, flags);
+	if (line->head != line->tail)
+		ret = buffer_data(line, buf, len);
+	else {
+		n = write_chan(line->chan_out, buf, len,
+			       line->write_irq);
+		if (n < 0) {
+			ret = n;
+			goto out_up;
+		}
+
+		len -= n;
+		ret += n;
+		if (len > 0)
+			ret += buffer_data(line, buf + n, len);
+	}
+out_up:
+	spin_unlock_irqrestore(&line->lock, flags);
+	return ret;
+}
+
+void line_throttle(struct tty_struct *tty)
+{
+	struct line *line = tty->driver_data;
+
+	deactivate_chan(line->chan_in, line->read_irq);
+	line->throttled = 1;
+}
+
+void line_unthrottle(struct tty_struct *tty)
+{
+	struct line *line = tty->driver_data;
+
+	line->throttled = 0;
+	chan_interrupt(line, line->read_irq);
+}
+
+static irqreturn_t line_write_interrupt(int irq, void *data)
+{
+	struct chan *chan = data;
+	struct line *line = chan->line;
+	int err;
+
+	/*
+	 * Interrupts are disabled here because genirq keep irqs disabled when
+	 * calling the action handler.
+	 */
+
+	spin_lock(&line->lock);
+	err = flush_buffer(line);
+	if (err == 0) {
+		spin_unlock(&line->lock);
+		return IRQ_NONE;
+	} else if ((err < 0) && (err != -EAGAIN)) {
+		line->head = line->buffer;
+		line->tail = line->buffer;
+	}
+	spin_unlock(&line->lock);
+
+	tty_port_tty_wakeup(&line->port);
+
+	return IRQ_HANDLED;
+}
+
+int line_setup_irq(int fd, int input, int output, struct line *line, void *data)
+{
+	const struct line_driver *driver = line->driver;
+	int err;
+
+	if (input) {
+		err = um_request_irq(UM_IRQ_ALLOC, fd, IRQ_READ,
+				     line_interrupt, 0,
+				     driver->read_irq_name, data);
+		if (err < 0)
+			return err;
+
+		line->read_irq = err;
+	}
+
+	if (output) {
+		err = um_request_irq(UM_IRQ_ALLOC, fd, IRQ_WRITE,
+				     line_write_interrupt, 0,
+				     driver->write_irq_name, data);
+		if (err < 0)
+			return err;
+
+		line->write_irq = err;
+	}
+
+	return 0;
+}
+
+static int line_activate(struct tty_port *port, struct tty_struct *tty)
+{
+	int ret;
+	struct line *line = tty->driver_data;
+
+	ret = enable_chan(line);
+	if (ret)
+		return ret;
+
+	if (!line->sigio) {
+		chan_enable_winch(line->chan_out, port);
+		line->sigio = 1;
+	}
+
+	chan_window_size(line, &tty->winsize.ws_row,
+		&tty->winsize.ws_col);
+
+	return 0;
+}
+
+static void unregister_winch(struct tty_struct *tty);
+
+static void line_destruct(struct tty_port *port)
+{
+	struct tty_struct *tty = tty_port_tty_get(port);
+	struct line *line = tty->driver_data;
+
+	if (line->sigio) {
+		unregister_winch(tty);
+		line->sigio = 0;
+	}
+}
+
+static const struct tty_port_operations line_port_ops = {
+	.activate = line_activate,
+	.destruct = line_destruct,
+};
+
+int line_open(struct tty_struct *tty, struct file *filp)
+{
+	struct line *line = tty->driver_data;
+
+	return tty_port_open(&line->port, tty, filp);
+}
+
+int line_install(struct tty_driver *driver, struct tty_struct *tty,
+		 struct line *line)
+{
+	int ret;
+
+	ret = tty_standard_install(driver, tty);
+	if (ret)
+		return ret;
+
+	tty->driver_data = line;
+
+	return 0;
+}
+
+void line_close(struct tty_struct *tty, struct file * filp)
+{
+	struct line *line = tty->driver_data;
+
+	tty_port_close(&line->port, tty, filp);
+}
+
+void line_hangup(struct tty_struct *tty)
+{
+	struct line *line = tty->driver_data;
+
+	tty_port_hangup(&line->port);
+}
+
+void close_lines(struct line *lines, int nlines)
+{
+	int i;
+
+	for(i = 0; i < nlines; i++)
+		close_chan(&lines[i]);
+}
+
+int setup_one_line(struct line *lines, int n, char *init,
+		   const struct chan_opts *opts, char **error_out)
+{
+	struct line *line = &lines[n];
+	struct tty_driver *driver = line->driver->driver;
+	int err = -EINVAL;
+
+	if (line->port.count) {
+		*error_out = "Device is already open";
+		goto out;
+	}
+
+	if (!strcmp(init, "none")) {
+		if (line->valid) {
+			line->valid = 0;
+			kfree(line->init_str);
+			tty_unregister_device(driver, n);
+			parse_chan_pair(NULL, line, n, opts, error_out);
+			err = 0;
+		}
+		*error_out = "configured as 'none'";
+	} else {
+		char *new = kstrdup(init, GFP_KERNEL);
+		if (!new) {
+			*error_out = "Failed to allocate memory";
+			return -ENOMEM;
+		}
+		if (line->valid) {
+			tty_unregister_device(driver, n);
+			kfree(line->init_str);
+		}
+		line->init_str = new;
+		line->valid = 1;
+		err = parse_chan_pair(new, line, n, opts, error_out);
+		if (!err) {
+			struct device *d = tty_port_register_device(&line->port,
+					driver, n, NULL);
+			if (IS_ERR(d)) {
+				*error_out = "Failed to register device";
+				err = PTR_ERR(d);
+				parse_chan_pair(NULL, line, n, opts, error_out);
+			}
+		}
+		if (err) {
+			*error_out = "failed to parse channel pair";
+			line->init_str = NULL;
+			line->valid = 0;
+			kfree(new);
+		}
+	}
+out:
+	return err;
+}
+
+/*
+ * Common setup code for both startup command line and mconsole initialization.
+ * @lines contains the array (of size @num) to modify;
+ * @init is the setup string;
+ * @error_out is an error string in the case of failure;
+ */
+
+int line_setup(char **conf, unsigned int num, char **def,
+	       char *init, char *name)
+{
+	char *error;
+
+	if (*init == '=') {
+		/*
+		 * We said con=/ssl= instead of con#=, so we are configuring all
+		 * consoles at once.
+		 */
+		*def = init + 1;
+	} else {
+		char *end;
+		unsigned n = simple_strtoul(init, &end, 0);
+
+		if (*end != '=') {
+			error = "Couldn't parse device number";
+			goto out;
+		}
+		if (n >= num) {
+			error = "Device number out of range";
+			goto out;
+		}
+		conf[n] = end + 1;
+	}
+	return 0;
+
+out:
+	printk(KERN_ERR "Failed to set up %s with "
+	       "configuration string \"%s\" : %s\n", name, init, error);
+	return -EINVAL;
+}
+
+int line_config(struct line *lines, unsigned int num, char *str,
+		const struct chan_opts *opts, char **error_out)
+{
+	char *end;
+	int n;
+
+	if (*str == '=') {
+		*error_out = "Can't configure all devices from mconsole";
+		return -EINVAL;
+	}
+
+	n = simple_strtoul(str, &end, 0);
+	if (*end++ != '=') {
+		*error_out = "Couldn't parse device number";
+		return -EINVAL;
+	}
+	if (n >= num) {
+		*error_out = "Device number out of range";
+		return -EINVAL;
+	}
+
+	return setup_one_line(lines, n, end, opts, error_out);
+}
+
+int line_get_config(char *name, struct line *lines, unsigned int num, char *str,
+		    int size, char **error_out)
+{
+	struct line *line;
+	char *end;
+	int dev, n = 0;
+
+	dev = simple_strtoul(name, &end, 0);
+	if ((*end != '\0') || (end == name)) {
+		*error_out = "line_get_config failed to parse device number";
+		return 0;
+	}
+
+	if ((dev < 0) || (dev >= num)) {
+		*error_out = "device number out of range";
+		return 0;
+	}
+
+	line = &lines[dev];
+
+	if (!line->valid)
+		CONFIG_CHUNK(str, size, n, "none", 1);
+	else {
+		struct tty_struct *tty = tty_port_tty_get(&line->port);
+		if (tty == NULL) {
+			CONFIG_CHUNK(str, size, n, line->init_str, 1);
+		} else {
+			n = chan_config_string(line, str, size, error_out);
+			tty_kref_put(tty);
+		}
+	}
+
+	return n;
+}
+
+int line_id(char **str, int *start_out, int *end_out)
+{
+	char *end;
+	int n;
+
+	n = simple_strtoul(*str, &end, 0);
+	if ((*end != '\0') || (end == *str))
+		return -1;
+
+	*str = end;
+	*start_out = n;
+	*end_out = n;
+	return n;
+}
+
+int line_remove(struct line *lines, unsigned int num, int n, char **error_out)
+{
+	if (n >= num) {
+		*error_out = "Device number out of range";
+		return -EINVAL;
+	}
+	return setup_one_line(lines, n, "none", NULL, error_out);
+}
+
+int register_lines(struct line_driver *line_driver,
+		   const struct tty_operations *ops,
+		   struct line *lines, int nlines)
+{
+	struct tty_driver *driver;
+	int err;
+	int i;
+
+	driver = tty_alloc_driver(nlines, TTY_DRIVER_REAL_RAW |
+			TTY_DRIVER_DYNAMIC_DEV);
+	if (IS_ERR(driver))
+		return PTR_ERR(driver);
+
+	driver->driver_name = line_driver->name;
+	driver->name = line_driver->device_name;
+	driver->major = line_driver->major;
+	driver->minor_start = line_driver->minor_start;
+	driver->type = line_driver->type;
+	driver->subtype = line_driver->subtype;
+	driver->init_termios = tty_std_termios;
+
+	for (i = 0; i < nlines; i++) {
+		tty_port_init(&lines[i].port);
+		lines[i].port.ops = &line_port_ops;
+		spin_lock_init(&lines[i].lock);
+		lines[i].driver = line_driver;
+		INIT_LIST_HEAD(&lines[i].chan_list);
+	}
+	tty_set_operations(driver, ops);
+
+	err = tty_register_driver(driver);
+	if (err) {
+		printk(KERN_ERR "register_lines : can't register %s driver\n",
+		       line_driver->name);
+		tty_driver_kref_put(driver);
+		for (i = 0; i < nlines; i++)
+			tty_port_destroy(&lines[i].port);
+		return err;
+	}
+
+	line_driver->driver = driver;
+	mconsole_register_dev(&line_driver->mc);
+	return 0;
+}
+
+static DEFINE_SPINLOCK(winch_handler_lock);
+static LIST_HEAD(winch_handlers);
+
+struct winch {
+	struct list_head list;
+	int fd;
+	int tty_fd;
+	int pid;
+	struct tty_port *port;
+	unsigned long stack;
+	struct work_struct work;
+};
+
+static void __free_winch(struct work_struct *work)
+{
+	struct winch *winch = container_of(work, struct winch, work);
+	um_free_irq(WINCH_IRQ, winch);
+
+	if (winch->pid != -1)
+		os_kill_process(winch->pid, 1);
+	if (winch->stack != 0)
+		free_stack(winch->stack, 0);
+	kfree(winch);
+}
+
+static void free_winch(struct winch *winch)
+{
+	int fd = winch->fd;
+	winch->fd = -1;
+	if (fd != -1)
+		os_close_file(fd);
+	__free_winch(&winch->work);
+}
+
+static irqreturn_t winch_interrupt(int irq, void *data)
+{
+	struct winch *winch = data;
+	struct tty_struct *tty;
+	struct line *line;
+	int fd = winch->fd;
+	int err;
+	char c;
+	struct pid *pgrp;
+
+	if (fd != -1) {
+		err = generic_read(fd, &c, NULL);
+		/* A read of 2 means the winch thread failed and has warned */
+		if (err < 0 || (err == 1 && c == 2)) {
+			if (err != -EAGAIN) {
+				winch->fd = -1;
+				list_del(&winch->list);
+				os_close_file(fd);
+				if (err < 0) {
+					printk(KERN_ERR "winch_interrupt : read failed, errno = %d\n",
+					       -err);
+					printk(KERN_ERR "fd %d is losing SIGWINCH support\n",
+					       winch->tty_fd);
+				}
+				INIT_WORK(&winch->work, __free_winch);
+				schedule_work(&winch->work);
+				return IRQ_HANDLED;
+			}
+			goto out;
+		}
+	}
+	tty = tty_port_tty_get(winch->port);
+	if (tty != NULL) {
+		line = tty->driver_data;
+		if (line != NULL) {
+			chan_window_size(line, &tty->winsize.ws_row,
+					 &tty->winsize.ws_col);
+			pgrp = tty_get_pgrp(tty);
+			if (pgrp)
+				kill_pgrp(pgrp, SIGWINCH, 1);
+			put_pid(pgrp);
+		}
+		tty_kref_put(tty);
+	}
+ out:
+	return IRQ_HANDLED;
+}
+
+void register_winch_irq(int fd, int tty_fd, int pid, struct tty_port *port,
+			unsigned long stack)
+{
+	struct winch *winch;
+
+	winch = kmalloc_obj(*winch);
+	if (winch == NULL) {
+		printk(KERN_ERR "register_winch_irq - kmalloc failed\n");
+		goto cleanup;
+	}
+
+	*winch = ((struct winch) { .fd  	= fd,
+				   .tty_fd 	= tty_fd,
+				   .pid  	= pid,
+				   .port 	= port,
+				   .stack	= stack });
+
+	spin_lock(&winch_handler_lock);
+	list_add(&winch->list, &winch_handlers);
+	spin_unlock(&winch_handler_lock);
+
+	if (um_request_irq(WINCH_IRQ, fd, IRQ_READ, winch_interrupt,
+			   IRQF_SHARED, "winch", winch) < 0) {
+		printk(KERN_ERR "register_winch_irq - failed to register "
+		       "IRQ\n");
+		spin_lock(&winch_handler_lock);
+		list_del(&winch->list);
+		spin_unlock(&winch_handler_lock);
+		goto out_free;
+	}
+
+	return;
+
+ out_free:
+	kfree(winch);
+ cleanup:
+	os_kill_process(pid, 1);
+	os_close_file(fd);
+	if (stack != 0)
+		free_stack(stack, 0);
+}
+
+static void unregister_winch(struct tty_struct *tty)
+{
+	struct list_head *ele, *next;
+	struct winch *winch;
+	struct tty_struct *wtty;
+
+	spin_lock(&winch_handler_lock);
+
+	list_for_each_safe(ele, next, &winch_handlers) {
+		winch = list_entry(ele, struct winch, list);
+		wtty = tty_port_tty_get(winch->port);
+		if (wtty == tty) {
+			list_del(&winch->list);
+			spin_unlock(&winch_handler_lock);
+			free_winch(winch);
+			break;
+		}
+		tty_kref_put(wtty);
+	}
+	spin_unlock(&winch_handler_lock);
+}
+
+static void winch_cleanup(void)
+{
+	struct winch *winch;
+
+	spin_lock(&winch_handler_lock);
+	while ((winch = list_first_entry_or_null(&winch_handlers,
+						 struct winch, list))) {
+		list_del(&winch->list);
+		spin_unlock(&winch_handler_lock);
+
+		free_winch(winch);
+
+		spin_lock(&winch_handler_lock);
+	}
+
+	spin_unlock(&winch_handler_lock);
+}
+__uml_exitcall(winch_cleanup);
+
+char *add_xterm_umid(char *base)
+{
+	char *umid, *title;
+	int len;
+
+	umid = get_umid();
+	if (*umid == '\0')
+		return base;
+
+	len = strlen(base) + strlen(" ()") + strlen(umid) + 1;
+	title = kmalloc(len, GFP_KERNEL);
+	if (title == NULL) {
+		printk(KERN_ERR "Failed to allocate buffer for xterm title\n");
+		return base;
+	}
+
+	snprintf(title, len, "%s (%s)", base, umid);
+	return title;
+}
diff --git a/arch/um/drivers/line.h b/arch/um/drivers/line.h
new file mode 100644
index 000000000..e8bd6f3df
--- /dev/null
+++ b/arch/um/drivers/line.h
@@ -0,0 +1,96 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2001, 2002 Jeff Dike (jdike@karaya.com)
+ */
+
+#ifndef __LINE_H__
+#define __LINE_H__
+
+#include <linux/list.h>
+#include <linux/workqueue.h>
+#include <linux/tty.h>
+#include <linux/interrupt.h>
+#include <linux/spinlock.h>
+#include <linux/mutex.h>
+#include "chan_user.h"
+#include "mconsole_kern.h"
+
+/* There's only two modifiable fields in this - .mc.list and .driver */
+struct line_driver {
+	const char *name;
+	const char *device_name;
+	const short major;
+	const short minor_start;
+	const short type;
+	const short subtype;
+	const char *read_irq_name;
+	const char *write_irq_name;
+	struct mc_device mc;
+	struct tty_driver *driver;
+};
+
+struct line {
+	struct tty_port port;
+	int valid;
+
+	int read_irq, write_irq;
+
+	char *init_str;
+	struct list_head chan_list;
+	struct chan *chan_in, *chan_out;
+
+	/*This lock is actually, mostly, local to*/
+	spinlock_t lock;
+	int throttled;
+	/* Yes, this is a real circular buffer.
+	 * XXX: And this should become a struct kfifo!
+	 *
+	 * buffer points to a buffer allocated on demand, of length
+	 * LINE_BUFSIZE, head to the start of the ring, tail to the end.*/
+	u8 *buffer;
+	u8 *head;
+	u8 *tail;
+
+	int sigio;
+	struct delayed_work task;
+	const struct line_driver *driver;
+};
+
+extern void line_close(struct tty_struct *tty, struct file * filp);
+extern int line_open(struct tty_struct *tty, struct file *filp);
+extern int line_install(struct tty_driver *driver, struct tty_struct *tty,
+	struct line *line);
+extern void line_cleanup(struct tty_struct *tty);
+extern void line_hangup(struct tty_struct *tty);
+extern int line_setup(char **conf, unsigned nlines, char **def,
+		      char *init, char *name);
+extern ssize_t line_write(struct tty_struct *tty, const u8 *buf, size_t len);
+extern unsigned int line_chars_in_buffer(struct tty_struct *tty);
+extern void line_flush_buffer(struct tty_struct *tty);
+extern void line_flush_chars(struct tty_struct *tty);
+extern unsigned int line_write_room(struct tty_struct *tty);
+extern void line_throttle(struct tty_struct *tty);
+extern void line_unthrottle(struct tty_struct *tty);
+
+extern char *add_xterm_umid(char *base);
+extern int line_setup_irq(int fd, int input, int output, struct line *line,
+			  void *data);
+extern void line_close_chan(struct line *line);
+extern int register_lines(struct line_driver *line_driver,
+			  const struct tty_operations *driver,
+			  struct line *lines, int nlines);
+extern int setup_one_line(struct line *lines, int n, char *init,
+			  const struct chan_opts *opts, char **error_out);
+extern void close_lines(struct line *lines, int nlines);
+
+extern int line_config(struct line *lines, unsigned int sizeof_lines,
+		       char *str, const struct chan_opts *opts,
+		       char **error_out);
+extern int line_id(char **str, int *start_out, int *end_out);
+extern int line_remove(struct line *lines, unsigned int sizeof_lines, int n,
+		       char **error_out);
+extern int line_get_config(char *dev, struct line *lines,
+			   unsigned int sizeof_lines, char *str,
+			   int size, char **error_out);
+
+#endif
diff --git a/arch/um/drivers/mconsole.h b/arch/um/drivers/mconsole.h
new file mode 100644
index 000000000..635637830
--- /dev/null
+++ b/arch/um/drivers/mconsole.h
@@ -0,0 +1,98 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2001 Lennert Buytenhek (buytenh@gnu.org)
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __MCONSOLE_H__
+#define __MCONSOLE_H__
+
+#ifdef __UM_HOST__
+#include <stdint.h>
+#define u32 uint32_t
+#endif
+
+#include <sysdep/ptrace.h>
+
+#define MCONSOLE_MAGIC (0xcafebabe)
+#define MCONSOLE_MAX_DATA (512)
+#define MCONSOLE_VERSION 2
+
+struct mconsole_request {
+	u32 magic;
+	u32 version;
+	u32 len;
+	char data[MCONSOLE_MAX_DATA];
+};
+
+struct mconsole_reply {
+	u32 err;
+	u32 more;
+	u32 len;
+	char data[MCONSOLE_MAX_DATA];
+};
+
+struct mconsole_notify {
+	u32 magic;
+	u32 version;
+	enum { MCONSOLE_SOCKET, MCONSOLE_PANIC, MCONSOLE_HANG,
+	       MCONSOLE_USER_NOTIFY } type;
+	u32 len;
+	char data[MCONSOLE_MAX_DATA];
+};
+
+struct mc_request;
+
+enum mc_context { MCONSOLE_INTR, MCONSOLE_PROC };
+
+struct mconsole_command
+{
+	char *command;
+	void (*handler)(struct mc_request *req);
+	enum mc_context context;
+};
+
+struct mc_request
+{
+	int len;
+	int as_interrupt;
+
+	int originating_fd;
+	unsigned int originlen;
+	unsigned char origin[128];			/* sockaddr_un */
+
+	struct mconsole_request request;
+	struct mconsole_command *cmd;
+	struct uml_pt_regs regs;
+};
+
+extern char mconsole_socket_name[];
+
+extern int mconsole_unlink_socket(void);
+extern int mconsole_reply_len(struct mc_request *req, const char *reply,
+			      int len, int err, int more);
+extern int mconsole_reply(struct mc_request *req, const char *str, int err,
+			  int more);
+
+extern void mconsole_version(struct mc_request *req);
+extern void mconsole_help(struct mc_request *req);
+extern void mconsole_halt(struct mc_request *req);
+extern void mconsole_reboot(struct mc_request *req);
+extern void mconsole_config(struct mc_request *req);
+extern void mconsole_remove(struct mc_request *req);
+extern void mconsole_sysrq(struct mc_request *req);
+extern void mconsole_cad(struct mc_request *req);
+extern void mconsole_stop(struct mc_request *req);
+extern void mconsole_go(struct mc_request *req);
+extern void mconsole_log(struct mc_request *req);
+extern void mconsole_proc(struct mc_request *req);
+extern void mconsole_stack(struct mc_request *req);
+
+extern int mconsole_get_request(int fd, struct mc_request *req);
+extern int mconsole_notify(char *sock_name, int type, const void *data,
+			   int len);
+extern char *mconsole_notify_socket(void);
+extern void lock_notify(void);
+extern void unlock_notify(void);
+
+#endif
diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
new file mode 100644
index 000000000..e2a9e8879
--- /dev/null
+++ b/arch/um/drivers/mconsole_kern.c
@@ -0,0 +1,871 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2001 Lennert Buytenhek (buytenh@gnu.org)
+ * Copyright (C) 2001 - 2008 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/console.h>
+#include <linux/ctype.h>
+#include <linux/string.h>
+#include <linux/interrupt.h>
+#include <linux/list.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/notifier.h>
+#include <linux/panic_notifier.h>
+#include <linux/reboot.h>
+#include <linux/sched/debug.h>
+#include <linux/proc_fs.h>
+#include <linux/slab.h>
+#include <linux/syscalls.h>
+#include <linux/utsname.h>
+#include <linux/socket.h>
+#include <linux/un.h>
+#include <linux/workqueue.h>
+#include <linux/mutex.h>
+#include <linux/fs.h>
+#include <linux/mount.h>
+#include <linux/file.h>
+#include <linux/uaccess.h>
+#include <asm/switch_to.h>
+
+#include <init.h>
+#include <irq_kern.h>
+#include <irq_user.h>
+#include <kern_util.h>
+#include "mconsole.h"
+#include "mconsole_kern.h"
+#include <os.h>
+
+static struct vfsmount *proc_mnt = NULL;
+
+static int do_unlink_socket(struct notifier_block *notifier,
+			    unsigned long what, void *data)
+{
+	return mconsole_unlink_socket();
+}
+
+
+static struct notifier_block reboot_notifier = {
+	.notifier_call		= do_unlink_socket,
+	.priority		= 0,
+};
+
+/* Safe without explicit locking for now.  Tasklets provide their own
+ * locking, and the interrupt handler is safe because it can't interrupt
+ * itself and it can only happen on CPU 0.
+ */
+
+static LIST_HEAD(mc_requests);
+
+static void mc_work_proc(struct work_struct *unused)
+{
+	struct mconsole_entry *req;
+	unsigned long flags;
+
+	while (!list_empty(&mc_requests)) {
+		local_irq_save(flags);
+		req = list_entry(mc_requests.next, struct mconsole_entry, list);
+		list_del(&req->list);
+		local_irq_restore(flags);
+		req->request.cmd->handler(&req->request);
+		kfree(req);
+	}
+}
+
+static DECLARE_WORK(mconsole_work, mc_work_proc);
+
+static irqreturn_t mconsole_interrupt(int irq, void *dev_id)
+{
+	/* long to avoid size mismatch warnings from gcc */
+	long fd;
+	struct mconsole_entry *new;
+	static struct mc_request req;	/* that's OK */
+
+	fd = (long) dev_id;
+	while (mconsole_get_request(fd, &req)) {
+		if (req.cmd->context == MCONSOLE_INTR)
+			(*req.cmd->handler)(&req);
+		else {
+			new = kmalloc_obj(*new, GFP_NOWAIT);
+			if (new == NULL)
+				mconsole_reply(&req, "Out of memory", 1, 0);
+			else {
+				new->request = req;
+				new->request.regs = get_irq_regs()->regs;
+				list_add(&new->list, &mc_requests);
+			}
+		}
+	}
+	if (!list_empty(&mc_requests))
+		schedule_work(&mconsole_work);
+	return IRQ_HANDLED;
+}
+
+void mconsole_version(struct mc_request *req)
+{
+	char version[256];
+
+	sprintf(version, "%s %s %s %s %s", utsname()->sysname,
+		utsname()->nodename, utsname()->release, utsname()->version,
+		utsname()->machine);
+	mconsole_reply(req, version, 0, 0);
+}
+
+void mconsole_log(struct mc_request *req)
+{
+	int len;
+	char *ptr = req->request.data;
+
+	ptr += strlen("log ");
+
+	len = req->len - (ptr - req->request.data);
+	printk(KERN_WARNING "%.*s", len, ptr);
+	mconsole_reply(req, "", 0, 0);
+}
+
+void mconsole_proc(struct mc_request *req)
+{
+	struct vfsmount *mnt = proc_mnt;
+	char *buf;
+	int len;
+	struct file *file;
+	int first_chunk = 1;
+	char *ptr = req->request.data;
+	loff_t pos = 0;
+
+	ptr += strlen("proc");
+	ptr = skip_spaces(ptr);
+
+	if (!mnt) {
+		mconsole_reply(req, "Proc not available", 1, 0);
+		goto out;
+	}
+	file = file_open_root_mnt(mnt, ptr, O_RDONLY, 0);
+	if (IS_ERR(file)) {
+		mconsole_reply(req, "Failed to open file", 1, 0);
+		printk(KERN_ERR "open /proc/%s: %ld\n", ptr, PTR_ERR(file));
+		goto out;
+	}
+
+	buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (buf == NULL) {
+		mconsole_reply(req, "Failed to allocate buffer", 1, 0);
+		goto out_fput;
+	}
+
+	do {
+		len = kernel_read(file, buf, PAGE_SIZE - 1, &pos);
+		if (len < 0) {
+			mconsole_reply(req, "Read of file failed", 1, 0);
+			goto out_free;
+		}
+		/* Begin the file content on his own line. */
+		if (first_chunk) {
+			mconsole_reply(req, "\n", 0, 1);
+			first_chunk = 0;
+		}
+		buf[len] = '\0';
+		mconsole_reply(req, buf, 0, (len > 0));
+	} while (len > 0);
+ out_free:
+	kfree(buf);
+ out_fput:
+	fput(file);
+ out: ;
+}
+
+#define UML_MCONSOLE_HELPTEXT \
+"Commands: \n\
+    version - Get kernel version \n\
+    help - Print this message \n\
+    halt - Halt UML \n\
+    reboot - Reboot UML \n\
+    config <dev>=<config> - Add a new device to UML;  \n\
+	same syntax as command line \n\
+    config <dev> - Query the configuration of a device \n\
+    remove <dev> - Remove a device from UML \n\
+    sysrq <letter> - Performs the SysRq action controlled by the letter \n\
+    cad - invoke the Ctrl-Alt-Del handler \n\
+    stop - pause the UML; it will do nothing until it receives a 'go' \n\
+    go - continue the UML after a 'stop' \n\
+    log <string> - make UML enter <string> into the kernel log\n\
+    proc <file> - returns the contents of the UML's /proc/<file>\n\
+    stack <pid> - returns the stack of the specified pid\n\
+"
+
+void mconsole_help(struct mc_request *req)
+{
+	mconsole_reply(req, UML_MCONSOLE_HELPTEXT, 0, 0);
+}
+
+void mconsole_halt(struct mc_request *req)
+{
+	mconsole_reply(req, "", 0, 0);
+	machine_halt();
+}
+
+void mconsole_reboot(struct mc_request *req)
+{
+	mconsole_reply(req, "", 0, 0);
+	machine_restart(NULL);
+}
+
+void mconsole_cad(struct mc_request *req)
+{
+	mconsole_reply(req, "", 0, 0);
+	ctrl_alt_del();
+}
+
+void mconsole_go(struct mc_request *req)
+{
+	mconsole_reply(req, "Not stopped", 1, 0);
+}
+
+void mconsole_stop(struct mc_request *req)
+{
+	block_signals();
+	os_set_fd_block(req->originating_fd, 1);
+	mconsole_reply(req, "stopped", 0, 0);
+	for (;;) {
+		if (!mconsole_get_request(req->originating_fd, req))
+			continue;
+		if (req->cmd->handler == mconsole_go)
+			break;
+		if (req->cmd->handler == mconsole_stop) {
+			mconsole_reply(req, "Already stopped", 1, 0);
+			continue;
+		}
+		if (req->cmd->handler == mconsole_sysrq) {
+			struct pt_regs *old_regs;
+			old_regs = set_irq_regs((struct pt_regs *)&req->regs);
+			mconsole_sysrq(req);
+			set_irq_regs(old_regs);
+			continue;
+		}
+		(*req->cmd->handler)(req);
+	}
+	os_set_fd_block(req->originating_fd, 0);
+	mconsole_reply(req, "", 0, 0);
+	unblock_signals();
+}
+
+static DEFINE_SPINLOCK(mc_devices_lock);
+static LIST_HEAD(mconsole_devices);
+
+void mconsole_register_dev(struct mc_device *new)
+{
+	spin_lock(&mc_devices_lock);
+	BUG_ON(!list_empty(&new->list));
+	list_add(&new->list, &mconsole_devices);
+	spin_unlock(&mc_devices_lock);
+}
+
+static struct mc_device *mconsole_find_dev(char *name)
+{
+	struct list_head *ele;
+	struct mc_device *dev;
+
+	list_for_each(ele, &mconsole_devices) {
+		dev = list_entry(ele, struct mc_device, list);
+		if (!strncmp(name, dev->name, strlen(dev->name)))
+			return dev;
+	}
+	return NULL;
+}
+
+#define UNPLUGGED_PER_PAGE \
+	((PAGE_SIZE - sizeof(struct list_head)) / sizeof(unsigned long))
+
+struct unplugged_pages {
+	struct list_head list;
+	void *pages[UNPLUGGED_PER_PAGE];
+};
+
+static DEFINE_MUTEX(plug_mem_mutex);
+static unsigned long long unplugged_pages_count;
+static LIST_HEAD(unplugged_pages);
+static int unplug_index = UNPLUGGED_PER_PAGE;
+
+static int mem_config(char *str, char **error_out)
+{
+	unsigned long long diff;
+	int err = -EINVAL, i, add;
+	char *ret;
+
+	if (str[0] != '=') {
+		*error_out = "Expected '=' after 'mem'";
+		goto out;
+	}
+
+	str++;
+	if (str[0] == '-')
+		add = 0;
+	else if (str[0] == '+') {
+		add = 1;
+	}
+	else {
+		*error_out = "Expected increment to start with '-' or '+'";
+		goto out;
+	}
+
+	str++;
+	diff = memparse(str, &ret);
+	if (*ret != '\0') {
+		*error_out = "Failed to parse memory increment";
+		goto out;
+	}
+
+	diff /= PAGE_SIZE;
+
+	mutex_lock(&plug_mem_mutex);
+	for (i = 0; i < diff; i++) {
+		struct unplugged_pages *unplugged;
+		void *addr;
+
+		if (add) {
+			if (list_empty(&unplugged_pages))
+				break;
+
+			unplugged = list_entry(unplugged_pages.next,
+					       struct unplugged_pages, list);
+			if (unplug_index > 0)
+				addr = unplugged->pages[--unplug_index];
+			else {
+				list_del(&unplugged->list);
+				addr = unplugged;
+				unplug_index = UNPLUGGED_PER_PAGE;
+			}
+
+			free_page((unsigned long) addr);
+			unplugged_pages_count--;
+		}
+		else {
+			struct page *page;
+
+			page = alloc_page(GFP_ATOMIC);
+			if (page == NULL)
+				break;
+
+			unplugged = page_address(page);
+			if (unplug_index == UNPLUGGED_PER_PAGE) {
+				list_add(&unplugged->list, &unplugged_pages);
+				unplug_index = 0;
+			}
+			else {
+				struct list_head *entry = unplugged_pages.next;
+				addr = unplugged;
+
+				unplugged = list_entry(entry,
+						       struct unplugged_pages,
+						       list);
+				err = os_drop_memory(addr, PAGE_SIZE);
+				if (err) {
+					printk(KERN_ERR "Failed to release "
+					       "memory - errno = %d\n", err);
+					*error_out = "Failed to release memory";
+					goto out_unlock;
+				}
+				unplugged->pages[unplug_index++] = addr;
+			}
+
+			unplugged_pages_count++;
+		}
+	}
+
+	err = 0;
+out_unlock:
+	mutex_unlock(&plug_mem_mutex);
+out:
+	return err;
+}
+
+static int mem_get_config(char *name, char *str, int size, char **error_out)
+{
+	char buf[sizeof("18446744073709551615")];
+	int len = 0;
+
+	sprintf(buf, "%ld", uml_physmem);
+	CONFIG_CHUNK(str, size, len, buf, 1);
+
+	return len;
+}
+
+static int mem_id(char **str, int *start_out, int *end_out)
+{
+	*start_out = 0;
+	*end_out = 0;
+
+	return 0;
+}
+
+static int mem_remove(int n, char **error_out)
+{
+	*error_out = "Memory doesn't support the remove operation";
+	return -EBUSY;
+}
+
+static struct mc_device mem_mc = {
+	.list		= LIST_HEAD_INIT(mem_mc.list),
+	.name		= "mem",
+	.config		= mem_config,
+	.get_config	= mem_get_config,
+	.id		= mem_id,
+	.remove		= mem_remove,
+};
+
+static int __init mem_mc_init(void)
+{
+	if (can_drop_memory())
+		mconsole_register_dev(&mem_mc);
+	else printk(KERN_ERR "Can't release memory to the host - memory "
+		    "hotplug won't be supported\n");
+	return 0;
+}
+
+__initcall(mem_mc_init);
+
+#define CONFIG_BUF_SIZE 64
+
+static void mconsole_get_config(int (*get_config)(char *, char *, int,
+						  char **),
+				struct mc_request *req, char *name)
+{
+	char default_buf[CONFIG_BUF_SIZE], *error, *buf;
+	int n, size;
+
+	if (get_config == NULL) {
+		mconsole_reply(req, "No get_config routine defined", 1, 0);
+		return;
+	}
+
+	error = NULL;
+	size = ARRAY_SIZE(default_buf);
+	buf = default_buf;
+
+	while (1) {
+		n = (*get_config)(name, buf, size, &error);
+		if (error != NULL) {
+			mconsole_reply(req, error, 1, 0);
+			goto out;
+		}
+
+		if (n <= size) {
+			mconsole_reply(req, buf, 0, 0);
+			goto out;
+		}
+
+		if (buf != default_buf)
+			kfree(buf);
+
+		size = n;
+		buf = kmalloc(size, GFP_KERNEL);
+		if (buf == NULL) {
+			mconsole_reply(req, "Failed to allocate buffer", 1, 0);
+			return;
+		}
+	}
+ out:
+	if (buf != default_buf)
+		kfree(buf);
+}
+
+void mconsole_config(struct mc_request *req)
+{
+	struct mc_device *dev;
+	char *ptr = req->request.data, *name, *error_string = "";
+	int err;
+
+	ptr += strlen("config");
+	ptr = skip_spaces(ptr);
+	dev = mconsole_find_dev(ptr);
+	if (dev == NULL) {
+		mconsole_reply(req, "Bad configuration option", 1, 0);
+		return;
+	}
+
+	name = &ptr[strlen(dev->name)];
+	ptr = name;
+	while ((*ptr != '=') && (*ptr != '\0'))
+		ptr++;
+
+	if (*ptr == '=') {
+		err = (*dev->config)(name, &error_string);
+		mconsole_reply(req, error_string, err, 0);
+	}
+	else mconsole_get_config(dev->get_config, req, name);
+}
+
+void mconsole_remove(struct mc_request *req)
+{
+	struct mc_device *dev;
+	char *ptr = req->request.data, *err_msg = "";
+	char error[256];
+	int err, start, end, n;
+
+	ptr += strlen("remove");
+	ptr = skip_spaces(ptr);
+	dev = mconsole_find_dev(ptr);
+	if (dev == NULL) {
+		mconsole_reply(req, "Bad remove option", 1, 0);
+		return;
+	}
+
+	ptr = &ptr[strlen(dev->name)];
+
+	err = 1;
+	n = (*dev->id)(&ptr, &start, &end);
+	if (n < 0) {
+		err_msg = "Couldn't parse device number";
+		goto out;
+	}
+	else if ((n < start) || (n > end)) {
+		sprintf(error, "Invalid device number - must be between "
+			"%d and %d", start, end);
+		err_msg = error;
+		goto out;
+	}
+
+	err_msg = NULL;
+	err = (*dev->remove)(n, &err_msg);
+	switch(err) {
+	case 0:
+		err_msg = "";
+		break;
+	case -ENODEV:
+		if (err_msg == NULL)
+			err_msg = "Device doesn't exist";
+		break;
+	case -EBUSY:
+		if (err_msg == NULL)
+			err_msg = "Device is currently open";
+		break;
+	default:
+		break;
+	}
+out:
+	mconsole_reply(req, err_msg, err, 0);
+}
+
+struct mconsole_output {
+	struct list_head list;
+	struct mc_request *req;
+};
+
+static DEFINE_SPINLOCK(client_lock);
+static LIST_HEAD(clients);
+static char console_buf[MCONSOLE_MAX_DATA] __nonstring;
+
+static void console_write(struct console *console, const char *string,
+			  unsigned int len)
+{
+	struct list_head *ele;
+	int n;
+
+	if (list_empty(&clients))
+		return;
+
+	while (len > 0) {
+		n = min((size_t) len, ARRAY_SIZE(console_buf));
+		memcpy(console_buf, string, n);
+		string += n;
+		len -= n;
+
+		list_for_each(ele, &clients) {
+			struct mconsole_output *entry;
+
+			entry = list_entry(ele, struct mconsole_output, list);
+			mconsole_reply_len(entry->req, console_buf, n, 0, 1);
+		}
+	}
+}
+
+static struct console mc_console = { .name	= "mc",
+				     .write	= console_write,
+				     .flags	= CON_ENABLED,
+				     .index	= -1 };
+
+static int mc_add_console(void)
+{
+	register_console(&mc_console);
+	return 0;
+}
+
+late_initcall(mc_add_console);
+
+static void with_console(struct mc_request *req, void (*proc)(void *),
+			 void *arg)
+{
+	struct mconsole_output entry;
+	unsigned long flags;
+
+	entry.req = req;
+	spin_lock_irqsave(&client_lock, flags);
+	list_add(&entry.list, &clients);
+	spin_unlock_irqrestore(&client_lock, flags);
+
+	(*proc)(arg);
+
+	mconsole_reply_len(req, "", 0, 0, 0);
+
+	spin_lock_irqsave(&client_lock, flags);
+	list_del(&entry.list);
+	spin_unlock_irqrestore(&client_lock, flags);
+}
+
+#ifdef CONFIG_MAGIC_SYSRQ
+
+#include <linux/sysrq.h>
+
+static void sysrq_proc(void *arg)
+{
+	char *op = arg;
+	handle_sysrq(*op);
+}
+
+void mconsole_sysrq(struct mc_request *req)
+{
+	char *ptr = req->request.data;
+
+	ptr += strlen("sysrq");
+	ptr = skip_spaces(ptr);
+
+	/*
+	 * With 'b', the system will shut down without a chance to reply,
+	 * so in this case, we reply first.
+	 */
+	if (*ptr == 'b')
+		mconsole_reply(req, "", 0, 0);
+
+	with_console(req, sysrq_proc, ptr);
+}
+#else
+void mconsole_sysrq(struct mc_request *req)
+{
+	mconsole_reply(req, "Sysrq not compiled in", 1, 0);
+}
+#endif
+
+static void stack_proc(void *arg)
+{
+	struct task_struct *task = arg;
+
+	show_stack(task, NULL, KERN_INFO);
+}
+
+/*
+ * Mconsole stack trace
+ *  Added by Allan Graves, Jeff Dike
+ *  Dumps a stacks registers to the linux console.
+ *  Usage stack <pid>.
+ */
+void mconsole_stack(struct mc_request *req)
+{
+	char *ptr = req->request.data;
+	int pid_requested= -1;
+	struct task_struct *to = NULL;
+
+	/*
+	 * Would be nice:
+	 * 1) Send showregs output to mconsole.
+	 * 2) Add a way to stack dump all pids.
+	 */
+
+	ptr += strlen("stack");
+	ptr = skip_spaces(ptr);
+
+	/*
+	 * Should really check for multiple pids or reject bad args here
+	 */
+	/* What do the arguments in mconsole_reply mean? */
+	if (sscanf(ptr, "%d", &pid_requested) == 0) {
+		mconsole_reply(req, "Please specify a pid", 1, 0);
+		return;
+	}
+
+	to = find_task_by_pid_ns(pid_requested, &init_pid_ns);
+	if ((to == NULL) || (pid_requested == 0)) {
+		mconsole_reply(req, "Couldn't find that pid", 1, 0);
+		return;
+	}
+	with_console(req, stack_proc, to);
+}
+
+static int __init mount_proc(void)
+{
+	struct file_system_type *proc_fs_type;
+	struct vfsmount *mnt;
+
+	proc_fs_type = get_fs_type("proc");
+	if (!proc_fs_type)
+		return -ENODEV;
+
+	mnt = kern_mount(proc_fs_type);
+	put_filesystem(proc_fs_type);
+	if (IS_ERR(mnt))
+		return PTR_ERR(mnt);
+
+	proc_mnt = mnt;
+	return 0;
+}
+
+/*
+ * Changed by mconsole_setup, which is __setup, and called before SMP is
+ * active.
+ */
+static char *notify_socket = NULL;
+
+static int __init mconsole_init(void)
+{
+	/* long to avoid size mismatch warnings from gcc */
+	long sock;
+	int err;
+	char file[UNIX_PATH_MAX];
+
+	mount_proc();
+
+	if (umid_file_name("mconsole", file, sizeof(file)))
+		return -1;
+	snprintf(mconsole_socket_name, sizeof(file), "%s", file);
+
+	sock = os_create_unix_socket(file, sizeof(file), 1);
+	if (sock < 0) {
+		printk(KERN_ERR "Failed to initialize management console\n");
+		return 1;
+	}
+	if (os_set_fd_block(sock, 0))
+		goto out;
+
+	register_reboot_notifier(&reboot_notifier);
+
+	err = um_request_irq(MCONSOLE_IRQ, sock, IRQ_READ, mconsole_interrupt,
+			     IRQF_SHARED, "mconsole", (void *)sock);
+	if (err < 0) {
+		printk(KERN_ERR "Failed to get IRQ for management console\n");
+		goto out;
+	}
+
+	if (notify_socket != NULL) {
+		notify_socket = kstrdup(notify_socket, GFP_KERNEL);
+		if (notify_socket != NULL)
+			mconsole_notify(notify_socket, MCONSOLE_SOCKET,
+					mconsole_socket_name,
+					strlen(mconsole_socket_name) + 1);
+		else printk(KERN_ERR "mconsole_setup failed to strdup "
+			    "string\n");
+	}
+
+	printk(KERN_INFO "mconsole (version %d) initialized on %s\n",
+	       MCONSOLE_VERSION, mconsole_socket_name);
+	return 0;
+
+ out:
+	os_close_file(sock);
+	return 1;
+}
+
+__initcall(mconsole_init);
+
+static ssize_t mconsole_proc_write(struct file *file,
+		const char __user *buffer, size_t count, loff_t *pos)
+{
+	char *buf;
+
+	buf = memdup_user_nul(buffer, count);
+	if (IS_ERR(buf))
+		return PTR_ERR(buf);
+
+	mconsole_notify(notify_socket, MCONSOLE_USER_NOTIFY, buf, count);
+	kfree(buf);
+	return count;
+}
+
+static const struct proc_ops mconsole_proc_ops = {
+	.proc_write	= mconsole_proc_write,
+	.proc_lseek	= noop_llseek,
+};
+
+static int create_proc_mconsole(void)
+{
+	struct proc_dir_entry *ent;
+
+	if (notify_socket == NULL)
+		return 0;
+
+	ent = proc_create("mconsole", 0200, NULL, &mconsole_proc_ops);
+	if (ent == NULL) {
+		printk(KERN_INFO "create_proc_mconsole : proc_create failed\n");
+		return 0;
+	}
+	return 0;
+}
+
+static DEFINE_SPINLOCK(notify_spinlock);
+
+void lock_notify(void)
+{
+	spin_lock(&notify_spinlock);
+}
+
+void unlock_notify(void)
+{
+	spin_unlock(&notify_spinlock);
+}
+
+__initcall(create_proc_mconsole);
+
+#define NOTIFY "notify:"
+
+static int mconsole_setup(char *str)
+{
+	if (!strncmp(str, NOTIFY, strlen(NOTIFY))) {
+		str += strlen(NOTIFY);
+		notify_socket = str;
+	}
+	else printk(KERN_ERR "mconsole_setup : Unknown option - '%s'\n", str);
+	return 1;
+}
+
+__setup("mconsole=", mconsole_setup);
+
+__uml_help(mconsole_setup,
+"mconsole=notify:<socket>\n"
+"    Requests that the mconsole driver send a message to the named Unix\n"
+"    socket containing the name of the mconsole socket.  This also serves\n"
+"    to notify outside processes when UML has booted far enough to respond\n"
+"    to mconsole requests.\n\n"
+);
+
+static int notify_panic(struct notifier_block *self, unsigned long unused1,
+			void *ptr)
+{
+	char *message = ptr;
+
+	if (notify_socket == NULL)
+		return 0;
+
+	mconsole_notify(notify_socket, MCONSOLE_PANIC, message,
+			strlen(message) + 1);
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block panic_exit_notifier = {
+	.notifier_call	= notify_panic,
+	.priority	= INT_MAX, /* run as soon as possible */
+};
+
+static int add_notifier(void)
+{
+	atomic_notifier_chain_register(&panic_notifier_list,
+			&panic_exit_notifier);
+	return 0;
+}
+
+__initcall(add_notifier);
+
+char *mconsole_notify_socket(void)
+{
+	return notify_socket;
+}
+
+EXPORT_SYMBOL(mconsole_notify_socket);
diff --git a/arch/um/drivers/mconsole_kern.h b/arch/um/drivers/mconsole_kern.h
new file mode 100644
index 000000000..56d8d6a3f
--- /dev/null
+++ b/arch/um/drivers/mconsole_kern.h
@@ -0,0 +1,52 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2001, 2002 Jeff Dike (jdike@karaya.com)
+ */
+
+#ifndef __MCONSOLE_KERN_H__
+#define __MCONSOLE_KERN_H__
+
+#include <linux/list.h>
+#include "mconsole.h"
+
+struct mconsole_entry {
+	struct list_head list;
+	struct mc_request request;
+};
+
+/* All these methods are called in process context. */
+struct mc_device {
+	struct list_head list;
+	char *name;
+	int (*config)(char *, char **);
+	int (*get_config)(char *, char *, int, char **);
+	int (*id)(char **, int *, int *);
+	int (*remove)(int, char **);
+};
+
+#define CONFIG_CHUNK(str, size, current, chunk, end) \
+do { \
+	current += strlen(chunk); \
+	if(current >= size) \
+		str = NULL; \
+	if(str != NULL){ \
+		strcpy(str, chunk); \
+		str += strlen(chunk); \
+	} \
+	if(end) \
+		current++; \
+} while(0)
+
+#ifdef CONFIG_MCONSOLE
+
+extern void mconsole_register_dev(struct mc_device *new);
+
+#else
+
+static inline void mconsole_register_dev(struct mc_device *new)
+{
+}
+
+#endif
+
+#endif
diff --git a/arch/um/drivers/mconsole_user.c b/arch/um/drivers/mconsole_user.c
new file mode 100644
index 000000000..a04cd13c6
--- /dev/null
+++ b/arch/um/drivers/mconsole_user.c
@@ -0,0 +1,221 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2001 Lennert Buytenhek (buytenh@gnu.org)
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <errno.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#include <sys/uio.h>
+#include <sys/un.h>
+#include "mconsole.h"
+
+static struct mconsole_command commands[] = {
+	/*
+	 * With uts namespaces, uts information becomes process-specific, so
+	 * we need a process context.  If we try handling this in interrupt
+	 * context, we may hit an exiting process without a valid uts
+	 * namespace.
+	 */
+	{ "version", mconsole_version, MCONSOLE_PROC },
+	{ "halt", mconsole_halt, MCONSOLE_PROC },
+	{ "reboot", mconsole_reboot, MCONSOLE_PROC },
+	{ "config", mconsole_config, MCONSOLE_PROC },
+	{ "remove", mconsole_remove, MCONSOLE_PROC },
+	{ "sysrq", mconsole_sysrq, MCONSOLE_INTR },
+	{ "help", mconsole_help, MCONSOLE_INTR },
+	{ "cad", mconsole_cad, MCONSOLE_INTR },
+	{ "stop", mconsole_stop, MCONSOLE_PROC },
+	{ "go", mconsole_go, MCONSOLE_INTR },
+	{ "log", mconsole_log, MCONSOLE_INTR },
+	{ "proc", mconsole_proc, MCONSOLE_PROC },
+	{ "stack", mconsole_stack, MCONSOLE_INTR },
+};
+
+/* Initialized in mconsole_init, which is an initcall */
+char mconsole_socket_name[256];
+
+static int mconsole_reply_v0(struct mc_request *req, char *reply)
+{
+	struct iovec iov;
+	struct msghdr msg;
+
+	iov.iov_base = reply;
+	iov.iov_len = strlen(reply);
+
+	msg.msg_name = &(req->origin);
+	msg.msg_namelen = req->originlen;
+	msg.msg_iov = &iov;
+	msg.msg_iovlen = 1;
+	msg.msg_control = NULL;
+	msg.msg_controllen = 0;
+	msg.msg_flags = 0;
+
+	return sendmsg(req->originating_fd, &msg, 0);
+}
+
+static struct mconsole_command *mconsole_parse(struct mc_request *req)
+{
+	struct mconsole_command *cmd;
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(commands); i++) {
+		cmd = &commands[i];
+		if (!strncmp(req->request.data, cmd->command,
+			    strlen(cmd->command))) {
+			return cmd;
+		}
+	}
+	return NULL;
+}
+
+#ifndef MIN
+#define MIN(a,b) ((a)<(b) ? (a):(b))
+#endif
+
+#define STRINGX(x) #x
+#define STRING(x) STRINGX(x)
+
+int mconsole_get_request(int fd, struct mc_request *req)
+{
+	int len;
+
+	req->originlen = sizeof(req->origin);
+	req->len = recvfrom(fd, &req->request, sizeof(req->request), 0,
+			    (struct sockaddr *) req->origin, &req->originlen);
+	if (req->len < 0)
+		return 0;
+
+	req->originating_fd = fd;
+
+	if (req->request.magic != MCONSOLE_MAGIC) {
+		/* Unversioned request */
+		len = MIN(sizeof(req->request.data) - 1,
+			  strlen((char *) &req->request));
+		memmove(req->request.data, &req->request, len);
+		req->request.data[len] = '\0';
+
+		req->request.magic = MCONSOLE_MAGIC;
+		req->request.version = 0;
+		req->request.len = len;
+
+		mconsole_reply_v0(req, "ERR Version 0 mconsole clients are "
+				  "not supported by this driver");
+		return 0;
+	}
+
+	if (req->request.len >= MCONSOLE_MAX_DATA) {
+		mconsole_reply(req, "Request too large", 1, 0);
+		return 0;
+	}
+	if (req->request.version != MCONSOLE_VERSION) {
+		mconsole_reply(req, "This driver only supports version "
+			       STRING(MCONSOLE_VERSION) " clients", 1, 0);
+	}
+
+	req->request.data[req->request.len] = '\0';
+	req->cmd = mconsole_parse(req);
+	if (req->cmd == NULL) {
+		mconsole_reply(req, "Unknown command", 1, 0);
+		return 0;
+	}
+
+	return 1;
+}
+
+int mconsole_reply_len(struct mc_request *req, const char *str, int total,
+		       int err, int more)
+{
+	/*
+	 * XXX This is a stack consumption problem.  It'd be nice to
+	 * make it global and serialize access to it, but there are a
+	 * ton of callers to this function.
+	 */
+	struct mconsole_reply reply;
+	int len, n;
+
+	do {
+		reply.err = err;
+
+		/* err can only be true on the first packet */
+		err = 0;
+
+		len = MIN(total, MCONSOLE_MAX_DATA - 1);
+
+		if (len == total) reply.more = more;
+		else reply.more = 1;
+
+		memcpy(reply.data, str, len);
+		reply.data[len] = '\0';
+		total -= len;
+		str += len;
+		reply.len = len + 1;
+
+		len = sizeof(reply) + reply.len - sizeof(reply.data);
+
+		n = sendto(req->originating_fd, &reply, len, 0,
+			   (struct sockaddr *) req->origin, req->originlen);
+
+		if (n < 0)
+			return -errno;
+	} while (total > 0);
+	return 0;
+}
+
+int mconsole_reply(struct mc_request *req, const char *str, int err, int more)
+{
+	return mconsole_reply_len(req, str, strlen(str), err, more);
+}
+
+
+int mconsole_unlink_socket(void)
+{
+	unlink(mconsole_socket_name);
+	return 0;
+}
+
+static int notify_sock = -1;
+
+int mconsole_notify(char *sock_name, int type, const void *data, int len)
+{
+	struct sockaddr_un target;
+	struct mconsole_notify packet;
+	int n, err = 0;
+
+	lock_notify();
+	if (notify_sock < 0) {
+		notify_sock = socket(PF_UNIX, SOCK_DGRAM, 0);
+		if (notify_sock < 0) {
+			err = -errno;
+			printk(UM_KERN_ERR "mconsole_notify - socket failed, "
+			       "errno = %d\n", errno);
+		}
+	}
+	unlock_notify();
+
+	if (err)
+		return err;
+
+	target.sun_family = AF_UNIX;
+	strcpy(target.sun_path, sock_name);
+
+	packet.magic = MCONSOLE_MAGIC;
+	packet.version = MCONSOLE_VERSION;
+	packet.type = type;
+	len = (len > sizeof(packet.data)) ? sizeof(packet.data) : len;
+	packet.len = len;
+	memcpy(packet.data, data, len);
+
+	err = 0;
+	len = sizeof(packet) + packet.len - sizeof(packet.data);
+	n = sendto(notify_sock, &packet, len, 0, (struct sockaddr *) &target,
+		   sizeof(target));
+	if (n < 0) {
+		err = -errno;
+		printk(UM_KERN_ERR "mconsole_notify - sendto failed, "
+		       "errno = %d\n", errno);
+	}
+	return err;
+}
diff --git a/arch/um/drivers/null.c b/arch/um/drivers/null.c
new file mode 100644
index 000000000..30d59b848
--- /dev/null
+++ b/arch/um/drivers/null.c
@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
+ */
+
+#include <stddef.h>
+#include <errno.h>
+#include <fcntl.h>
+#include "chan_user.h"
+#include <os.h>
+
+/* This address is used only as a unique identifier */
+static int null_chan;
+
+static void *null_init(char *str, int device, const struct chan_opts *opts)
+{
+	return &null_chan;
+}
+
+static int null_open(int input, int output, int primary, void *d,
+		     char **dev_out)
+{
+	int fd;
+
+	*dev_out = NULL;
+
+	fd = open(DEV_NULL, O_RDWR);
+	return (fd < 0) ? -errno : fd;
+}
+
+static int null_read(int fd, __u8 *c_out, void *unused)
+{
+	return -ENODEV;
+}
+
+static void null_free(void *data)
+{
+}
+
+const struct chan_ops null_ops = {
+	.type		= "null",
+	.init		= null_init,
+	.open		= null_open,
+	.close		= generic_close,
+	.read		= null_read,
+	.write		= generic_write,
+	.console_write	= generic_console_write,
+	.window_size	= generic_window_size,
+	.free		= null_free,
+	.winch		= 0,
+};
diff --git a/arch/um/drivers/port.h b/arch/um/drivers/port.h
new file mode 100644
index 000000000..9085b336e
--- /dev/null
+++ b/arch/um/drivers/port.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2001 Jeff Dike (jdike@karaya.com)
+ */
+
+#ifndef __PORT_H__
+#define __PORT_H__
+
+extern void *port_data(int port);
+extern int port_wait(void *data);
+extern void port_kern_close(void *d);
+extern int port_connection(int fd, int *socket_out, int *pid_out);
+extern int port_listen_fd(int port);
+extern void port_read(int fd, void *data);
+extern void port_kern_free(void *d);
+extern int port_rcv_fd(int fd);
+extern void port_remove_dev(void *d);
+
+#endif
+
diff --git a/arch/um/drivers/port_kern.c b/arch/um/drivers/port_kern.c
new file mode 100644
index 000000000..7b3ff4af1
--- /dev/null
+++ b/arch/um/drivers/port_kern.c
@@ -0,0 +1,305 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
+ */
+
+#include <linux/completion.h>
+#include <linux/interrupt.h>
+#include <linux/list.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/workqueue.h>
+#include <asm/atomic.h>
+#include <init.h>
+#include <irq_kern.h>
+#include <os.h>
+#include "port.h"
+
+struct port_list {
+	struct list_head list;
+	atomic_t wait_count;
+	int has_connection;
+	struct completion done;
+	int port;
+	int fd;
+	spinlock_t lock;
+	struct list_head pending;
+	struct list_head connections;
+};
+
+struct port_dev {
+	struct port_list *port;
+	int helper_pid;
+	int telnetd_pid;
+};
+
+struct connection {
+	struct list_head list;
+	int fd;
+	int helper_pid;
+	int socket[2];
+	int telnetd_pid;
+	struct port_list *port;
+};
+
+static irqreturn_t pipe_interrupt(int irq, void *data)
+{
+	struct connection *conn = data;
+	int n_fds = 1, fd = -1;
+	ssize_t ret;
+
+	ret = os_rcv_fd_msg(conn->socket[0], &fd, n_fds, &conn->helper_pid,
+			    sizeof(conn->helper_pid));
+	if (ret != sizeof(conn->helper_pid)) {
+		if (ret == -EAGAIN)
+			return IRQ_NONE;
+
+		printk(KERN_ERR "pipe_interrupt : os_rcv_fd_msg returned %zd\n",
+		       ret);
+		os_close_file(conn->fd);
+	}
+
+	list_del(&conn->list);
+
+	conn->fd = fd;
+	list_add(&conn->list, &conn->port->connections);
+
+	complete(&conn->port->done);
+	return IRQ_HANDLED;
+}
+
+#define NO_WAITER_MSG \
+    "****\n" \
+    "There are currently no UML consoles waiting for port connections.\n" \
+    "Either disconnect from one to make it available or activate some more\n" \
+    "by enabling more consoles in the UML /etc/inittab.\n" \
+    "****\n"
+
+static int port_accept(struct port_list *port)
+{
+	struct connection *conn;
+	int fd, socket[2], pid;
+
+	fd = port_connection(port->fd, socket, &pid);
+	if (fd < 0) {
+		if (fd != -EAGAIN)
+			printk(KERN_ERR "port_accept : port_connection "
+			       "returned %d\n", -fd);
+		goto out;
+	}
+
+	conn = kmalloc_obj(*conn, GFP_ATOMIC);
+	if (conn == NULL) {
+		printk(KERN_ERR "port_accept : failed to allocate "
+		       "connection\n");
+		goto out_close;
+	}
+	*conn = ((struct connection)
+		{ .list 	= LIST_HEAD_INIT(conn->list),
+		  .fd 		= fd,
+		  .socket  	= { socket[0], socket[1] },
+		  .telnetd_pid 	= pid,
+		  .port 	= port });
+
+	if (um_request_irq(TELNETD_IRQ, socket[0], IRQ_READ, pipe_interrupt,
+			  IRQF_SHARED, "telnetd", conn) < 0) {
+		printk(KERN_ERR "port_accept : failed to get IRQ for "
+		       "telnetd\n");
+		goto out_free;
+	}
+
+	if (atomic_read(&port->wait_count) == 0) {
+		os_write_file(fd, NO_WAITER_MSG, sizeof(NO_WAITER_MSG));
+		printk(KERN_ERR "No one waiting for port\n");
+	}
+	list_add(&conn->list, &port->pending);
+	return 1;
+
+ out_free:
+	kfree(conn);
+ out_close:
+	os_close_file(fd);
+	os_kill_process(pid, 1);
+ out:
+	return 0;
+}
+
+static DEFINE_MUTEX(ports_mutex);
+static LIST_HEAD(ports);
+
+static void port_work_proc(struct work_struct *unused)
+{
+	struct port_list *port;
+	struct list_head *ele;
+	unsigned long flags;
+
+	local_irq_save(flags);
+	list_for_each(ele, &ports) {
+		port = list_entry(ele, struct port_list, list);
+		if (!port->has_connection)
+			continue;
+
+		while (port_accept(port))
+			;
+		port->has_connection = 0;
+	}
+	local_irq_restore(flags);
+}
+
+static DECLARE_WORK(port_work, port_work_proc);
+
+static irqreturn_t port_interrupt(int irq, void *data)
+{
+	struct port_list *port = data;
+
+	port->has_connection = 1;
+	schedule_work(&port_work);
+	return IRQ_HANDLED;
+}
+
+void *port_data(int port_num)
+{
+	struct list_head *ele;
+	struct port_list *port;
+	struct port_dev *dev = NULL;
+	int fd;
+
+	mutex_lock(&ports_mutex);
+	list_for_each(ele, &ports) {
+		port = list_entry(ele, struct port_list, list);
+		if (port->port == port_num)
+			goto found;
+	}
+	port = kmalloc_obj(struct port_list);
+	if (port == NULL) {
+		printk(KERN_ERR "Allocation of port list failed\n");
+		goto out;
+	}
+
+	fd = port_listen_fd(port_num);
+	if (fd < 0) {
+		printk(KERN_ERR "binding to port %d failed, errno = %d\n",
+		       port_num, -fd);
+		goto out_free;
+	}
+
+	if (um_request_irq(ACCEPT_IRQ, fd, IRQ_READ, port_interrupt,
+			  IRQF_SHARED, "port", port) < 0) {
+		printk(KERN_ERR "Failed to get IRQ for port %d\n", port_num);
+		goto out_close;
+	}
+
+	*port = ((struct port_list)
+		{ .list 	 	= LIST_HEAD_INIT(port->list),
+		  .wait_count		= ATOMIC_INIT(0),
+		  .has_connection 	= 0,
+		  .port 	 	= port_num,
+		  .fd  			= fd,
+		  .pending 		= LIST_HEAD_INIT(port->pending),
+		  .connections 		= LIST_HEAD_INIT(port->connections) });
+	spin_lock_init(&port->lock);
+	init_completion(&port->done);
+	list_add(&port->list, &ports);
+
+ found:
+	dev = kmalloc_obj(struct port_dev);
+	if (dev == NULL) {
+		printk(KERN_ERR "Allocation of port device entry failed\n");
+		goto out;
+	}
+
+	*dev = ((struct port_dev) { .port  		= port,
+				    .helper_pid  	= -1,
+				    .telnetd_pid  	= -1 });
+	goto out;
+
+ out_close:
+	os_close_file(fd);
+ out_free:
+	kfree(port);
+ out:
+	mutex_unlock(&ports_mutex);
+	return dev;
+}
+
+int port_wait(void *data)
+{
+	struct port_dev *dev = data;
+	struct connection *conn;
+	struct port_list *port = dev->port;
+	int fd;
+
+	atomic_inc(&port->wait_count);
+	while (1) {
+		fd = -ERESTARTSYS;
+		if (wait_for_completion_interruptible(&port->done))
+			goto out;
+
+		spin_lock(&port->lock);
+
+		conn = list_entry(port->connections.next, struct connection,
+				  list);
+		list_del(&conn->list);
+		spin_unlock(&port->lock);
+
+		os_shutdown_socket(conn->socket[0], 1, 1);
+		os_close_file(conn->socket[0]);
+		os_shutdown_socket(conn->socket[1], 1, 1);
+		os_close_file(conn->socket[1]);
+
+		/* This is done here because freeing an IRQ can't be done
+		 * within the IRQ handler.  So, pipe_interrupt always ups
+		 * the semaphore regardless of whether it got a successful
+		 * connection.  Then we loop here throwing out failed
+		 * connections until a good one is found.
+		 */
+		um_free_irq(TELNETD_IRQ, conn);
+
+		if (conn->fd >= 0)
+			break;
+		os_close_file(conn->fd);
+		kfree(conn);
+	}
+
+	fd = conn->fd;
+	dev->helper_pid = conn->helper_pid;
+	dev->telnetd_pid = conn->telnetd_pid;
+	kfree(conn);
+ out:
+	atomic_dec(&port->wait_count);
+	return fd;
+}
+
+void port_remove_dev(void *d)
+{
+	struct port_dev *dev = d;
+
+	if (dev->helper_pid != -1)
+		os_kill_process(dev->helper_pid, 0);
+	if (dev->telnetd_pid != -1)
+		os_kill_process(dev->telnetd_pid, 1);
+	dev->helper_pid = -1;
+	dev->telnetd_pid = -1;
+}
+
+void port_kern_free(void *d)
+{
+	struct port_dev *dev = d;
+
+	port_remove_dev(dev);
+	kfree(dev);
+}
+
+static void free_port(void)
+{
+	struct list_head *ele;
+	struct port_list *port;
+
+	list_for_each(ele, &ports) {
+		port = list_entry(ele, struct port_list, list);
+		free_irq_by_fd(port->fd);
+		os_close_file(port->fd);
+	}
+}
+
+__uml_exitcall(free_port);
diff --git a/arch/um/drivers/port_user.c b/arch/um/drivers/port_user.c
new file mode 100644
index 000000000..3c62ae81d
--- /dev/null
+++ b/arch/um/drivers/port_user.c
@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <termios.h>
+#include <unistd.h>
+#include <netinet/in.h>
+#include "chan_user.h"
+#include <os.h>
+#include "port.h"
+#include <um_malloc.h>
+
+struct port_chan {
+	int raw;
+	struct termios tt;
+	void *kernel_data;
+	char dev[sizeof("32768\0")];
+};
+
+static void *port_init(char *str, int device, const struct chan_opts *opts)
+{
+	struct port_chan *data;
+	void *kern_data;
+	char *end;
+	int port;
+
+	if (*str != ':') {
+		printk(UM_KERN_ERR "port_init : channel type 'port' must "
+		       "specify a port number\n");
+		return NULL;
+	}
+	str++;
+	port = strtoul(str, &end, 0);
+	if ((*end != '\0') || (end == str)) {
+		printk(UM_KERN_ERR "port_init : couldn't parse port '%s'\n",
+		       str);
+		return NULL;
+	}
+
+	kern_data = port_data(port);
+	if (kern_data == NULL)
+		return NULL;
+
+	data = uml_kmalloc(sizeof(*data), UM_GFP_KERNEL);
+	if (data == NULL)
+		goto err;
+
+	*data = ((struct port_chan) { .raw  		= opts->raw,
+				      .kernel_data 	= kern_data });
+	sprintf(data->dev, "%d", port);
+
+	return data;
+ err:
+	port_kern_free(kern_data);
+	return NULL;
+}
+
+static void port_free(void *d)
+{
+	struct port_chan *data = d;
+
+	port_kern_free(data->kernel_data);
+	kfree(data);
+}
+
+static int port_open(int input, int output, int primary, void *d,
+		     char **dev_out)
+{
+	struct port_chan *data = d;
+	int fd, err;
+
+	fd = port_wait(data->kernel_data);
+	if ((fd >= 0) && data->raw) {
+		CATCH_EINTR(err = tcgetattr(fd, &data->tt));
+		if (err)
+			return err;
+
+		err = raw(fd);
+		if (err)
+			return err;
+	}
+	*dev_out = data->dev;
+	return fd;
+}
+
+static void port_close(int fd, void *d)
+{
+	struct port_chan *data = d;
+
+	port_remove_dev(data->kernel_data);
+	os_close_file(fd);
+}
+
+const struct chan_ops port_ops = {
+	.type		= "port",
+	.init		= port_init,
+	.open		= port_open,
+	.close		= port_close,
+	.read	        = generic_read,
+	.write		= generic_write,
+	.console_write	= generic_console_write,
+	.window_size	= generic_window_size,
+	.free		= port_free,
+	.winch		= 1,
+};
+
+int port_listen_fd(int port)
+{
+	struct sockaddr_in addr;
+	int fd, err, arg;
+
+	fd = socket(PF_INET, SOCK_STREAM, 0);
+	if (fd == -1)
+		return -errno;
+
+	arg = 1;
+	if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &arg, sizeof(arg)) < 0) {
+		err = -errno;
+		goto out;
+	}
+
+	addr.sin_family = AF_INET;
+	addr.sin_port = htons(port);
+	addr.sin_addr.s_addr = htonl(INADDR_ANY);
+	if (bind(fd, (struct sockaddr *) &addr, sizeof(addr)) < 0) {
+		err = -errno;
+		goto out;
+	}
+
+	if (listen(fd, 1) < 0) {
+		err = -errno;
+		goto out;
+	}
+
+	err = os_set_fd_block(fd, 0);
+	if (err < 0)
+		goto out;
+
+	return fd;
+ out:
+	close(fd);
+	return err;
+}
+
+struct port_pre_exec_data {
+	int sock_fd;
+	int pipe_fd;
+};
+
+static void port_pre_exec(void *arg)
+{
+	struct port_pre_exec_data *data = arg;
+
+	dup2(data->sock_fd, 0);
+	dup2(data->sock_fd, 1);
+	dup2(data->sock_fd, 2);
+	close(data->sock_fd);
+	dup2(data->pipe_fd, 3);
+	shutdown(3, SHUT_RD);
+	close(data->pipe_fd);
+}
+
+int port_connection(int fd, int *socket, int *pid_out)
+{
+	int new, err;
+	char *env;
+	char *argv[] = { "in.telnetd", "-L",
+			 OS_LIB_PATH "/uml/port-helper", NULL };
+	struct port_pre_exec_data data;
+
+	if ((env = getenv("UML_PORT_HELPER")))
+		argv[2] = env;
+
+	new = accept(fd, NULL, 0);
+	if (new < 0)
+		return -errno;
+
+	err = os_access(argv[2], X_OK);
+	if (err < 0) {
+		printk(UM_KERN_ERR "port_connection : error accessing port-helper "
+		       "executable at %s: %s\n", argv[2], strerror(-err));
+		if (env == NULL)
+			printk(UM_KERN_ERR "Set UML_PORT_HELPER environment "
+				"variable to path to uml-utilities port-helper "
+				"binary\n");
+		goto out_close;
+	}
+
+	err = os_pipe(socket, 0, 0);
+	if (err < 0)
+		goto out_close;
+
+	data = ((struct port_pre_exec_data)
+		{ .sock_fd  		= new,
+		  .pipe_fd 		= socket[1] });
+
+	err = run_helper(port_pre_exec, &data, argv);
+	if (err < 0)
+		goto out_shutdown;
+
+	*pid_out = err;
+	return new;
+
+ out_shutdown:
+	shutdown(socket[0], SHUT_RDWR);
+	close(socket[0]);
+	shutdown(socket[1], SHUT_RDWR);
+	close(socket[1]);
+ out_close:
+	close(new);
+	return err;
+}
diff --git a/arch/um/drivers/pty.c b/arch/um/drivers/pty.c
new file mode 100644
index 000000000..39c60068c
--- /dev/null
+++ b/arch/um/drivers/pty.c
@@ -0,0 +1,165 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <termios.h>
+#include <sys/stat.h>
+#include "chan_user.h"
+#include <os.h>
+#include <um_malloc.h>
+
+struct pty_chan {
+	void (*announce)(char *dev_name, int dev);
+	int dev;
+	int raw;
+	struct termios tt;
+	char dev_name[sizeof("/dev/pts/0123456\0")];
+};
+
+static void *pty_chan_init(char *str, int device, const struct chan_opts *opts)
+{
+	struct pty_chan *data;
+
+	data = uml_kmalloc(sizeof(*data), UM_GFP_KERNEL);
+	if (data == NULL)
+		return NULL;
+
+	*data = ((struct pty_chan) { .announce  	= opts->announce,
+				     .dev  		= device,
+				     .raw  		= opts->raw });
+	return data;
+}
+
+static int pts_open(int input, int output, int primary, void *d,
+		    char **dev_out)
+{
+	struct pty_chan *data = d;
+	char *dev;
+	int fd, err;
+
+	fd = get_pty();
+	if (fd < 0) {
+		err = -errno;
+		printk(UM_KERN_ERR "open_pts : Failed to open pts\n");
+		return err;
+	}
+
+	if (data->raw) {
+		CATCH_EINTR(err = tcgetattr(fd, &data->tt));
+		if (err)
+			goto out_close;
+
+		err = raw(fd);
+		if (err)
+			goto out_close;
+	}
+
+	dev = ptsname(fd);
+	sprintf(data->dev_name, "%s", dev);
+	*dev_out = data->dev_name;
+
+	if (data->announce)
+		(*data->announce)(dev, data->dev);
+
+	return fd;
+
+out_close:
+	close(fd);
+	return err;
+}
+
+static int getmaster(char *line)
+{
+	struct stat buf;
+	char *pty, *bank, *cp;
+	int master, err;
+
+	pty = &line[strlen("/dev/ptyp")];
+	for (bank = "pqrs"; *bank; bank++) {
+		line[strlen("/dev/pty")] = *bank;
+		*pty = '0';
+		/* Did we hit the end ? */
+		if ((stat(line, &buf) < 0) && (errno == ENOENT))
+			break;
+
+		for (cp = "0123456789abcdef"; *cp; cp++) {
+			*pty = *cp;
+			master = open(line, O_RDWR);
+			if (master >= 0) {
+				char *tp = &line[strlen("/dev/")];
+
+				/* verify slave side is usable */
+				*tp = 't';
+				err = access(line, R_OK | W_OK);
+				*tp = 'p';
+				if (!err)
+					return master;
+				close(master);
+			}
+		}
+	}
+
+	printk(UM_KERN_ERR "getmaster - no usable host pty devices\n");
+	return -ENOENT;
+}
+
+static int pty_open(int input, int output, int primary, void *d,
+		    char **dev_out)
+{
+	struct pty_chan *data = d;
+	int fd, err;
+	char dev[sizeof("/dev/ptyxx\0")] = "/dev/ptyxx";
+
+	fd = getmaster(dev);
+	if (fd < 0)
+		return fd;
+
+	if (data->raw) {
+		err = raw(fd);
+		if (err) {
+			close(fd);
+			return err;
+		}
+	}
+
+	if (data->announce)
+		(*data->announce)(dev, data->dev);
+
+	sprintf(data->dev_name, "%s", dev);
+	*dev_out = data->dev_name;
+
+	return fd;
+}
+
+const struct chan_ops pty_ops = {
+	.type		= "pty",
+	.init		= pty_chan_init,
+	.open		= pty_open,
+	.close		= generic_close,
+	.read		= generic_read,
+	.write		= generic_write,
+	.console_write	= generic_console_write,
+	.window_size	= generic_window_size,
+	.free		= generic_free,
+	.winch		= 0,
+};
+
+const struct chan_ops pts_ops = {
+	.type		= "pts",
+	.init		= pty_chan_init,
+	.open		= pts_open,
+	.close		= generic_close,
+	.read		= generic_read,
+	.write		= generic_write,
+	.console_write	= generic_console_write,
+	.window_size	= generic_window_size,
+	.free		= generic_free,
+	.winch		= 0,
+};
diff --git a/arch/um/drivers/random.c b/arch/um/drivers/random.c
new file mode 100644
index 000000000..ca08c91f4
--- /dev/null
+++ b/arch/um/drivers/random.c
@@ -0,0 +1,121 @@
+/* Copyright (C) 2005 - 2008 Jeff Dike <jdike@{linux.intel,addtoit}.com> */
+
+/* Much of this ripped from drivers/char/hw_random.c, see there for other
+ * copyright.
+ *
+ * This software may be used and distributed according to the terms
+ * of the GNU General Public License, incorporated herein by reference.
+ */
+#include <linux/sched/signal.h>
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/interrupt.h>
+#include <linux/miscdevice.h>
+#include <linux/hw_random.h>
+#include <linux/delay.h>
+#include <linux/uaccess.h>
+#include <init.h>
+#include <irq_kern.h>
+#include <os.h>
+
+/*
+ * core module information
+ */
+#define RNG_MODULE_NAME "hw_random"
+
+/* Changed at init time, in the non-modular case, and at module load
+ * time, in the module case.  Presumably, the module subsystem
+ * protects against a module being loaded twice at the same time.
+ */
+static int random_fd = -1;
+static struct hwrng hwrng;
+static DECLARE_COMPLETION(have_data);
+
+static int rng_dev_read(struct hwrng *rng, void *buf, size_t max, bool block)
+{
+	int ret;
+
+	for (;;) {
+		ret = os_read_file(random_fd, buf, max);
+		if (block && ret == -EAGAIN) {
+			add_sigio_fd(random_fd);
+
+			ret = wait_for_completion_killable(&have_data);
+
+			ignore_sigio_fd(random_fd);
+			deactivate_fd(random_fd, RANDOM_IRQ);
+
+			if (ret < 0)
+				break;
+		} else {
+			break;
+		}
+	}
+
+	return ret != -EAGAIN ? ret : 0;
+}
+
+static irqreturn_t random_interrupt(int irq, void *data)
+{
+	complete(&have_data);
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * rng_init - initialize RNG module
+ */
+static int __init rng_init (void)
+{
+	int err;
+
+	err = os_open_file("/dev/random", of_read(OPENFLAGS()), 0);
+	if (err < 0)
+		goto out;
+
+	random_fd = err;
+	err = um_request_irq(RANDOM_IRQ, random_fd, IRQ_READ, random_interrupt,
+			     0, "random", NULL);
+	if (err < 0)
+		goto err_out_cleanup_hw;
+
+	sigio_broken();
+	hwrng.name = RNG_MODULE_NAME;
+	hwrng.read = rng_dev_read;
+
+	err = hwrng_register(&hwrng);
+	if (err) {
+		pr_err(RNG_MODULE_NAME " registering failed (%d)\n", err);
+		goto err_out_cleanup_hw;
+	}
+out:
+	return err;
+
+err_out_cleanup_hw:
+	os_close_file(random_fd);
+	random_fd = -1;
+	goto out;
+}
+
+/*
+ * rng_cleanup - shutdown RNG module
+ */
+
+static void cleanup(void)
+{
+	free_irq_by_fd(random_fd);
+	os_close_file(random_fd);
+}
+
+static void __exit rng_cleanup(void)
+{
+	hwrng_unregister(&hwrng);
+	os_close_file(random_fd);
+}
+
+module_init (rng_init);
+module_exit (rng_cleanup);
+__uml_exitcall(cleanup);
+
+MODULE_DESCRIPTION("UML Host Random Number Generator (RNG) driver");
+MODULE_LICENSE("GPL");
diff --git a/arch/um/drivers/rtc.h b/arch/um/drivers/rtc.h
new file mode 100644
index 000000000..95e41c7d3
--- /dev/null
+++ b/arch/um/drivers/rtc.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2020 Intel Corporation
+ * Author: Johannes Berg <johannes@sipsolutions.net>
+ */
+#ifndef __UM_RTC_H__
+#define __UM_RTC_H__
+
+int uml_rtc_start(bool timetravel);
+int uml_rtc_enable_alarm(unsigned long long delta_seconds);
+void uml_rtc_disable_alarm(void);
+void uml_rtc_stop(bool timetravel);
+void uml_rtc_send_timetravel_alarm(void);
+
+#endif /* __UM_RTC_H__ */
diff --git a/arch/um/drivers/rtc_kern.c b/arch/um/drivers/rtc_kern.c
new file mode 100644
index 000000000..9158c936c
--- /dev/null
+++ b/arch/um/drivers/rtc_kern.c
@@ -0,0 +1,213 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020 Intel Corporation
+ * Author: Johannes Berg <johannes@sipsolutions.net>
+ */
+#include <linux/platform_device.h>
+#include <linux/time-internal.h>
+#include <linux/suspend.h>
+#include <linux/err.h>
+#include <linux/rtc.h>
+#include <kern_util.h>
+#include <irq_kern.h>
+#include <os.h>
+#include "rtc.h"
+
+static time64_t uml_rtc_alarm_time;
+static bool uml_rtc_alarm_enabled;
+static struct rtc_device *uml_rtc;
+static int uml_rtc_irq_fd, uml_rtc_irq;
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+
+static void uml_rtc_time_travel_alarm(struct time_travel_event *ev)
+{
+	uml_rtc_send_timetravel_alarm();
+}
+
+static struct time_travel_event uml_rtc_alarm_event = {
+	.fn = uml_rtc_time_travel_alarm,
+};
+#endif
+
+static int uml_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct timespec64 ts;
+
+	/* Use this to get correct time in time-travel mode */
+	read_persistent_clock64(&ts);
+	rtc_time64_to_tm(timespec64_to_ktime(ts) / NSEC_PER_SEC, tm);
+
+	return 0;
+}
+
+static int uml_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	rtc_time64_to_tm(uml_rtc_alarm_time, &alrm->time);
+	alrm->enabled = uml_rtc_alarm_enabled;
+
+	return 0;
+}
+
+static int uml_rtc_alarm_irq_enable(struct device *dev, unsigned int enable)
+{
+	struct timespec64 ts;
+	unsigned long long secs;
+
+	if (!enable && !uml_rtc_alarm_enabled)
+		return 0;
+
+	uml_rtc_alarm_enabled = enable;
+
+	read_persistent_clock64(&ts);
+	secs = uml_rtc_alarm_time - ts.tv_sec;
+
+	if (time_travel_mode == TT_MODE_OFF) {
+		if (!enable) {
+			uml_rtc_disable_alarm();
+			return 0;
+		}
+
+		/* enable or update */
+		return uml_rtc_enable_alarm(secs);
+	} else {
+		time_travel_del_event(&uml_rtc_alarm_event);
+
+		if (enable)
+			time_travel_add_event_rel(&uml_rtc_alarm_event,
+						  secs * NSEC_PER_SEC -
+						  ts.tv_nsec);
+	}
+
+	return 0;
+}
+
+static int uml_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	uml_rtc_alarm_irq_enable(dev, 0);
+	uml_rtc_alarm_time = rtc_tm_to_time64(&alrm->time);
+	uml_rtc_alarm_irq_enable(dev, alrm->enabled);
+
+	return 0;
+}
+
+static const struct rtc_class_ops uml_rtc_ops = {
+	.read_time = uml_rtc_read_time,
+	.read_alarm = uml_rtc_read_alarm,
+	.alarm_irq_enable = uml_rtc_alarm_irq_enable,
+	.set_alarm = uml_rtc_set_alarm,
+};
+
+static irqreturn_t uml_rtc_interrupt(int irq, void *data)
+{
+	unsigned long long c = 0;
+
+	/* alarm triggered, it's now off */
+	uml_rtc_alarm_enabled = false;
+
+	os_read_file(uml_rtc_irq_fd, &c, sizeof(c));
+	WARN_ON(c == 0);
+
+	pm_system_wakeup();
+	rtc_update_irq(uml_rtc, 1, RTC_IRQF | RTC_AF);
+
+	return IRQ_HANDLED;
+}
+
+static int uml_rtc_setup(void)
+{
+	int err;
+
+	err = uml_rtc_start(time_travel_mode != TT_MODE_OFF);
+	if (WARN(err < 0, "err = %d\n", err))
+		return err;
+
+	uml_rtc_irq_fd = err;
+
+	err = um_request_irq(UM_IRQ_ALLOC, uml_rtc_irq_fd, IRQ_READ,
+			     uml_rtc_interrupt, 0, "rtc", NULL);
+	if (err < 0) {
+		uml_rtc_stop(time_travel_mode != TT_MODE_OFF);
+		return err;
+	}
+
+	irq_set_irq_wake(err, 1);
+
+	uml_rtc_irq = err;
+	return 0;
+}
+
+static void uml_rtc_cleanup(void)
+{
+	um_free_irq(uml_rtc_irq, NULL);
+	uml_rtc_stop(time_travel_mode != TT_MODE_OFF);
+}
+
+static int uml_rtc_probe(struct platform_device *pdev)
+{
+	int err;
+
+	err = uml_rtc_setup();
+	if (err)
+		return err;
+
+	uml_rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(uml_rtc)) {
+		err = PTR_ERR(uml_rtc);
+		goto cleanup;
+	}
+
+	uml_rtc->ops = &uml_rtc_ops;
+
+	device_init_wakeup(&pdev->dev, 1);
+
+	err = devm_rtc_register_device(uml_rtc);
+	if (err)
+		goto cleanup;
+
+	return 0;
+cleanup:
+	uml_rtc_cleanup();
+	return err;
+}
+
+static void uml_rtc_remove(struct platform_device *pdev)
+{
+	device_init_wakeup(&pdev->dev, 0);
+	uml_rtc_cleanup();
+}
+
+static struct platform_driver uml_rtc_driver = {
+	.probe = uml_rtc_probe,
+	.remove = uml_rtc_remove,
+	.driver = {
+		.name = "uml-rtc",
+	},
+};
+
+static int __init uml_rtc_init(void)
+{
+	struct platform_device *pdev;
+	int err;
+
+	err = platform_driver_register(&uml_rtc_driver);
+	if (err)
+		return err;
+
+	pdev = platform_device_alloc("uml-rtc", 0);
+	if (!pdev) {
+		err = -ENOMEM;
+		goto unregister;
+	}
+
+	err = platform_device_add(pdev);
+	if (err)
+		goto unregister;
+	return 0;
+
+unregister:
+	platform_device_put(pdev);
+	platform_driver_unregister(&uml_rtc_driver);
+	return err;
+}
+device_initcall(uml_rtc_init);
diff --git a/arch/um/drivers/rtc_user.c b/arch/um/drivers/rtc_user.c
new file mode 100644
index 000000000..67912fcf7
--- /dev/null
+++ b/arch/um/drivers/rtc_user.c
@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020 Intel Corporation
+ * Author: Johannes Berg <johannes@sipsolutions.net>
+ */
+#include <stdbool.h>
+#include <os.h>
+#include <errno.h>
+#include <sched.h>
+#include <unistd.h>
+#include <kern_util.h>
+#include <sys/select.h>
+#include <stdio.h>
+#include <sys/timerfd.h>
+#include "rtc.h"
+
+static int uml_rtc_irq_fds[2];
+
+void uml_rtc_send_timetravel_alarm(void)
+{
+	unsigned long long c = 1;
+
+	CATCH_EINTR(write(uml_rtc_irq_fds[1], &c, sizeof(c)));
+}
+
+int uml_rtc_start(bool timetravel)
+{
+	int err;
+
+	if (timetravel) {
+		err = os_pipe(uml_rtc_irq_fds, 1, 1);
+		if (err)
+			goto fail;
+	} else {
+		uml_rtc_irq_fds[0] = timerfd_create(CLOCK_REALTIME, TFD_CLOEXEC);
+		if (uml_rtc_irq_fds[0] < 0) {
+			err = -errno;
+			goto fail;
+		}
+
+		/* apparently timerfd won't send SIGIO, use workaround */
+		sigio_broken();
+		err = add_sigio_fd(uml_rtc_irq_fds[0]);
+		if (err < 0) {
+			close(uml_rtc_irq_fds[0]);
+			goto fail;
+		}
+	}
+
+	return uml_rtc_irq_fds[0];
+fail:
+	uml_rtc_stop(timetravel);
+	return err;
+}
+
+int uml_rtc_enable_alarm(unsigned long long delta_seconds)
+{
+	struct itimerspec it = {
+		.it_value = {
+			.tv_sec = delta_seconds,
+		},
+	};
+
+	if (timerfd_settime(uml_rtc_irq_fds[0], 0, &it, NULL))
+		return -errno;
+	return 0;
+}
+
+void uml_rtc_disable_alarm(void)
+{
+	uml_rtc_enable_alarm(0);
+}
+
+void uml_rtc_stop(bool timetravel)
+{
+	if (timetravel)
+		os_close_file(uml_rtc_irq_fds[1]);
+	else
+		ignore_sigio_fd(uml_rtc_irq_fds[0]);
+	os_close_file(uml_rtc_irq_fds[0]);
+}
diff --git a/arch/um/drivers/ssl.c b/arch/um/drivers/ssl.c
new file mode 100644
index 000000000..8006a5bd5
--- /dev/null
+++ b/arch/um/drivers/ssl.c
@@ -0,0 +1,205 @@
+// SPDX-License-Identifier: GPL-2.0
+/* 
+ * Copyright (C) 2000, 2002 Jeff Dike (jdike@karaya.com)
+ */
+
+#include <linux/fs.h>
+#include <linux/tty.h>
+#include <linux/tty_driver.h>
+#include <linux/major.h>
+#include <linux/mm.h>
+#include <linux/init.h>
+#include <linux/console.h>
+#include <asm/termbits.h>
+#include <asm/irq.h>
+#include "chan.h"
+#include <init.h>
+#include <irq_user.h>
+#include "mconsole_kern.h"
+
+static const int ssl_version = 1;
+
+#define NR_PORTS 64
+
+static void ssl_announce(char *dev_name, int dev)
+{
+	printk(KERN_INFO "Serial line %d assigned device '%s'\n", dev,
+	       dev_name);
+}
+
+/* Almost const, except that xterm_title may be changed in an initcall */
+static struct chan_opts opts = {
+	.announce 	= ssl_announce,
+	.xterm_title	= "Serial Line #%d",
+	.raw		= 1,
+};
+
+static int ssl_config(char *str, char **error_out);
+static int ssl_get_config(char *dev, char *str, int size, char **error_out);
+static int ssl_remove(int n, char **error_out);
+
+
+/* Const, except for .mc.list */
+static struct line_driver driver = {
+	.name 			= "UML serial line",
+	.device_name 		= "ttyS",
+	.major 			= TTY_MAJOR,
+	.minor_start 		= 64,
+	.type 		 	= TTY_DRIVER_TYPE_SERIAL,
+	.subtype 	 	= 0,
+	.read_irq_name 		= "ssl",
+	.write_irq_name 	= "ssl-write",
+	.mc  = {
+		.list		= LIST_HEAD_INIT(driver.mc.list),
+		.name  		= "ssl",
+		.config 	= ssl_config,
+		.get_config 	= ssl_get_config,
+		.id		= line_id,
+		.remove 	= ssl_remove,
+	},
+};
+
+/* The array is initialized by line_init, at initcall time.  The
+ * elements are locked individually as needed.
+ */
+static char *conf[NR_PORTS];
+static char *def_conf = CONFIG_SSL_CHAN;
+static struct line serial_lines[NR_PORTS];
+
+static int ssl_config(char *str, char **error_out)
+{
+	return line_config(serial_lines, ARRAY_SIZE(serial_lines), str, &opts,
+			   error_out);
+}
+
+static int ssl_get_config(char *dev, char *str, int size, char **error_out)
+{
+	return line_get_config(dev, serial_lines, ARRAY_SIZE(serial_lines), str,
+			       size, error_out);
+}
+
+static int ssl_remove(int n, char **error_out)
+{
+	return line_remove(serial_lines, ARRAY_SIZE(serial_lines), n,
+			   error_out);
+}
+
+static int ssl_install(struct tty_driver *driver, struct tty_struct *tty)
+{
+	return line_install(driver, tty, &serial_lines[tty->index]);
+}
+
+static const struct tty_operations ssl_ops = {
+	.open 	 		= line_open,
+	.close 	 		= line_close,
+	.write 	 		= line_write,
+	.write_room		= line_write_room,
+	.chars_in_buffer 	= line_chars_in_buffer,
+	.flush_buffer 		= line_flush_buffer,
+	.flush_chars 		= line_flush_chars,
+	.throttle 		= line_throttle,
+	.unthrottle 		= line_unthrottle,
+	.install		= ssl_install,
+	.hangup			= line_hangup,
+};
+
+/* Changed by ssl_init and referenced by ssl_exit, which are both serialized
+ * by being an initcall and exitcall, respectively.
+ */
+static int ssl_init_done;
+
+static void ssl_console_write(struct console *c, const char *string,
+			      unsigned len)
+{
+	struct line *line = &serial_lines[c->index];
+	unsigned long flags;
+
+	spin_lock_irqsave(&line->lock, flags);
+	console_write_chan(line->chan_out, string, len);
+	spin_unlock_irqrestore(&line->lock, flags);
+}
+
+static struct tty_driver *ssl_console_device(struct console *c, int *index)
+{
+	*index = c->index;
+	return driver.driver;
+}
+
+static int ssl_console_setup(struct console *co, char *options)
+{
+	struct line *line = &serial_lines[co->index];
+
+	return console_open_chan(line, co);
+}
+
+/* No locking for register_console call - relies on single-threaded initcalls */
+static struct console ssl_cons = {
+	.name		= "ttyS",
+	.write		= ssl_console_write,
+	.device		= ssl_console_device,
+	.setup		= ssl_console_setup,
+	.flags		= CON_PRINTBUFFER|CON_ANYTIME,
+	.index		= -1,
+};
+
+static int ssl_init(void)
+{
+	char *new_title;
+	int err;
+	int i;
+
+	printk(KERN_INFO "Initializing software serial port version %d\n",
+	       ssl_version);
+
+	err = register_lines(&driver, &ssl_ops, serial_lines,
+				    ARRAY_SIZE(serial_lines));
+	if (err)
+		return err;
+
+	new_title = add_xterm_umid(opts.xterm_title);
+	if (new_title != NULL)
+		opts.xterm_title = new_title;
+
+	for (i = 0; i < NR_PORTS; i++) {
+		char *error;
+		char *s = conf[i];
+		if (!s)
+			s = def_conf;
+		if (setup_one_line(serial_lines, i, s, &opts, &error))
+			printk(KERN_ERR "setup_one_line failed for "
+			       "device %d : %s\n", i, error);
+	}
+
+	ssl_init_done = 1;
+	register_console(&ssl_cons);
+	return 0;
+}
+late_initcall(ssl_init);
+
+static void ssl_exit(void)
+{
+	if (!ssl_init_done)
+		return;
+	close_lines(serial_lines, ARRAY_SIZE(serial_lines));
+}
+__uml_exitcall(ssl_exit);
+
+static int ssl_chan_setup(char *str)
+{
+	line_setup(conf, NR_PORTS, &def_conf, str, "serial line");
+	return 1;
+}
+
+__setup("ssl", ssl_chan_setup);
+__channel_help(ssl_chan_setup, "ssl");
+
+static int ssl_non_raw_setup(char *str)
+{
+	opts.raw = 0;
+	return 1;
+}
+__setup("ssl-non-raw", ssl_non_raw_setup);
+__uml_help(ssl_non_raw_setup,
+"ssl-non-raw\n"
+"    Set serial lines to non-raw mode.\n\n"
+);
diff --git a/arch/um/drivers/stderr_console.c b/arch/um/drivers/stderr_console.c
new file mode 100644
index 000000000..ecc3a5814
--- /dev/null
+++ b/arch/um/drivers/stderr_console.c
@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/console.h>
+
+#include "chan_user.h"
+
+/* ----------------------------------------------------------------------------- */
+/* trivial console driver -- simply dump everything to stderr                    */
+
+/*
+ * Don't register by default -- as this registers very early in the
+ * boot process it becomes the default console.
+ *
+ * Initialized at init time.
+ */
+static int use_stderr_console = 0;
+
+static void stderr_console_write(struct console *console, const char *string,
+				 unsigned len)
+{
+	generic_write(2 /* stderr */, string, len, NULL);
+}
+
+static struct console stderr_console = {
+	.name		= "stderr",
+	.write		= stderr_console_write,
+	.flags		= CON_PRINTBUFFER,
+};
+
+static int __init stderr_console_init(void)
+{
+	if (use_stderr_console)
+		register_console(&stderr_console);
+	return 0;
+}
+console_initcall(stderr_console_init);
+
+static int stderr_setup(char *str)
+{
+	if (!str)
+		return 0;
+	use_stderr_console = simple_strtoul(str,&str,0);
+	return 1;
+}
+__setup("stderr=", stderr_setup);
+
+/* The previous behavior of not unregistering led to /dev/console being
+ * impossible to open.  My FC5 filesystem started having init die, and the
+ * system panicing because of this.  Unregistering causes the real
+ * console to become the default console, and /dev/console can then be
+ * opened.  Making this an initcall makes this happen late enough that
+ * there is no added value in dumping everything to stderr, and the
+ * normal console is good enough to show you all available output.
+ */
+static int __init unregister_stderr(void)
+{
+	unregister_console(&stderr_console);
+
+	return 0;
+}
+
+__initcall(unregister_stderr);
diff --git a/arch/um/drivers/stdio_console.c b/arch/um/drivers/stdio_console.c
new file mode 100644
index 000000000..1c239737d
--- /dev/null
+++ b/arch/um/drivers/stdio_console.c
@@ -0,0 +1,198 @@
+// SPDX-License-Identifier: GPL-2.0
+/* 
+ * Copyright (C) 2000, 2001 Jeff Dike (jdike@karaya.com)
+ */
+
+#include <linux/posix_types.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <linux/types.h>
+#include <linux/major.h>
+#include <linux/kdev_t.h>
+#include <linux/console.h>
+#include <linux/string.h>
+#include <linux/sched.h>
+#include <linux/list.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/slab.h>
+#include <linux/hardirq.h>
+#include <asm/current.h>
+#include <asm/irq.h>
+#include "stdio_console.h"
+#include "chan.h"
+#include <irq_user.h>
+#include "mconsole_kern.h"
+#include <init.h>
+
+#define MAX_TTYS (16)
+
+static void stdio_announce(char *dev_name, int dev)
+{
+	printk(KERN_INFO "Virtual console %d assigned device '%s'\n", dev,
+	       dev_name);
+}
+
+/* Almost const, except that xterm_title may be changed in an initcall */
+static struct chan_opts opts = {
+	.announce 	= stdio_announce,
+	.xterm_title	= "Virtual Console #%d",
+	.raw		= 1,
+};
+
+static int con_config(char *str, char **error_out);
+static int con_get_config(char *dev, char *str, int size, char **error_out);
+static int con_remove(int n, char **con_remove);
+
+
+/* Const, except for .mc.list */
+static struct line_driver driver = {
+	.name 			= "UML console",
+	.device_name 		= "tty",
+	.major 			= TTY_MAJOR,
+	.minor_start 		= 0,
+	.type 		 	= TTY_DRIVER_TYPE_CONSOLE,
+	.subtype 	 	= SYSTEM_TYPE_CONSOLE,
+	.read_irq_name 		= "console",
+	.write_irq_name 	= "console-write",
+	.mc  = {
+		.list		= LIST_HEAD_INIT(driver.mc.list),
+		.name  		= "con",
+		.config 	= con_config,
+		.get_config 	= con_get_config,
+		.id		= line_id,
+		.remove 	= con_remove,
+	},
+};
+
+/* The array is initialized by line_init, at initcall time.  The
+ * elements are locked individually as needed.
+ */
+static char *vt_conf[MAX_TTYS];
+static char *def_conf;
+static struct line vts[MAX_TTYS];
+
+static int con_config(char *str, char **error_out)
+{
+	return line_config(vts, ARRAY_SIZE(vts), str, &opts, error_out);
+}
+
+static int con_get_config(char *dev, char *str, int size, char **error_out)
+{
+	return line_get_config(dev, vts, ARRAY_SIZE(vts), str, size, error_out);
+}
+
+static int con_remove(int n, char **error_out)
+{
+	return line_remove(vts, ARRAY_SIZE(vts), n, error_out);
+}
+
+/* Set in an initcall, checked in an exitcall */
+static int con_init_done;
+
+static int con_install(struct tty_driver *driver, struct tty_struct *tty)
+{
+	return line_install(driver, tty, &vts[tty->index]);
+}
+
+static const struct tty_operations console_ops = {
+	.open 	 		= line_open,
+	.install		= con_install,
+	.close 	 		= line_close,
+	.write 	 		= line_write,
+	.write_room		= line_write_room,
+	.chars_in_buffer 	= line_chars_in_buffer,
+	.flush_buffer 		= line_flush_buffer,
+	.flush_chars 		= line_flush_chars,
+	.throttle 		= line_throttle,
+	.unthrottle 		= line_unthrottle,
+	.hangup			= line_hangup,
+};
+
+static void uml_console_write(struct console *console, const char *string,
+			      unsigned len)
+{
+	struct line *line = &vts[console->index];
+	unsigned long flags;
+
+	spin_lock_irqsave(&line->lock, flags);
+	console_write_chan(line->chan_out, string, len);
+	spin_unlock_irqrestore(&line->lock, flags);
+}
+
+static struct tty_driver *uml_console_device(struct console *c, int *index)
+{
+	*index = c->index;
+	return driver.driver;
+}
+
+static int uml_console_setup(struct console *co, char *options)
+{
+	struct line *line = &vts[co->index];
+
+	return console_open_chan(line, co);
+}
+
+/* No locking for register_console call - relies on single-threaded initcalls */
+static struct console stdiocons = {
+	.name		= "tty",
+	.write		= uml_console_write,
+	.device		= uml_console_device,
+	.setup		= uml_console_setup,
+	.flags		= CON_PRINTBUFFER|CON_ANYTIME,
+	.index		= -1,
+};
+
+static int stdio_init(void)
+{
+	char *new_title;
+	int err;
+	int i;
+
+	err = register_lines(&driver, &console_ops, vts,
+					ARRAY_SIZE(vts));
+	if (err)
+		return err;
+
+	printk(KERN_INFO "Initialized stdio console driver\n");
+
+	new_title = add_xterm_umid(opts.xterm_title);
+	if(new_title != NULL)
+		opts.xterm_title = new_title;
+
+	for (i = 0; i < MAX_TTYS; i++) {
+		char *error;
+		char *s = vt_conf[i];
+		if (!s)
+			s = def_conf;
+		if (!s)
+			s = i ? CONFIG_CON_CHAN : CONFIG_CON_ZERO_CHAN;
+		if (setup_one_line(vts, i, s, &opts, &error))
+			printk(KERN_ERR "setup_one_line failed for "
+			       "device %d : %s\n", i, error);
+	}
+
+	con_init_done = 1;
+	register_console(&stdiocons);
+	return 0;
+}
+late_initcall(stdio_init);
+
+static void console_exit(void)
+{
+	if (!con_init_done)
+		return;
+	close_lines(vts, ARRAY_SIZE(vts));
+}
+__uml_exitcall(console_exit);
+
+static int console_chan_setup(char *str)
+{
+	if (!strncmp(str, "sole=", 5))	/* console= option specifies tty */
+		return 0;
+
+	line_setup(vt_conf, MAX_TTYS, &def_conf, str, "console");
+	return 1;
+}
+__setup("con", console_chan_setup);
+__channel_help(console_chan_setup, "con");
diff --git a/arch/um/drivers/stdio_console.h b/arch/um/drivers/stdio_console.h
new file mode 100644
index 000000000..3a409ec23
--- /dev/null
+++ b/arch/um/drivers/stdio_console.h
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2000 Jeff Dike (jdike@karaya.com)
+ */
+
+#ifndef __STDIO_CONSOLE_H
+#define __STDIO_CONSOLE_H
+
+extern void save_console_flags(void);
+#endif
+
diff --git a/arch/um/drivers/tty.c b/arch/um/drivers/tty.c
new file mode 100644
index 000000000..884a762d2
--- /dev/null
+++ b/arch/um/drivers/tty.c
@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <termios.h>
+#include "chan_user.h"
+#include <os.h>
+#include <um_malloc.h>
+
+struct tty_chan {
+	char *dev;
+	int raw;
+	struct termios tt;
+};
+
+static void *tty_chan_init(char *str, int device, const struct chan_opts *opts)
+{
+	struct tty_chan *data;
+
+	if (*str != ':') {
+		printk(UM_KERN_ERR "tty_init : channel type 'tty' must specify "
+		       "a device\n");
+		return NULL;
+	}
+	str++;
+
+	data = uml_kmalloc(sizeof(*data), UM_GFP_KERNEL);
+	if (data == NULL)
+		return NULL;
+	*data = ((struct tty_chan) { .dev 	= str,
+				     .raw 	= opts->raw });
+
+	return data;
+}
+
+static int tty_open(int input, int output, int primary, void *d,
+		    char **dev_out)
+{
+	struct tty_chan *data = d;
+	int fd, err, mode = 0;
+
+	if (input && output)
+		mode = O_RDWR;
+	else if (input)
+		mode = O_RDONLY;
+	else if (output)
+		mode = O_WRONLY;
+
+	fd = open(data->dev, mode);
+	if (fd < 0)
+		return -errno;
+
+	if (data->raw) {
+		CATCH_EINTR(err = tcgetattr(fd, &data->tt));
+		if (err)
+			return err;
+
+		err = raw(fd);
+		if (err)
+			return err;
+	}
+
+	*dev_out = data->dev;
+	return fd;
+}
+
+const struct chan_ops tty_ops = {
+	.type		= "tty",
+	.init		= tty_chan_init,
+	.open		= tty_open,
+	.close		= generic_close,
+	.read		= generic_read,
+	.write		= generic_write,
+	.console_write	= generic_console_write,
+	.window_size	= generic_window_size,
+	.free		= generic_free,
+	.winch		= 0,
+};
diff --git a/arch/um/drivers/ubd.h b/arch/um/drivers/ubd.h
new file mode 100644
index 000000000..2985c1466
--- /dev/null
+++ b/arch/um/drivers/ubd.h
@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2000 Jeff Dike (jdike@karaya.com)
+ * Copyright (C) 2001 RidgeRun, Inc (glonnon@ridgerun.com)
+ */
+
+#ifndef __UM_UBD_USER_H
+#define __UM_UBD_USER_H
+
+#include <os.h>
+
+int start_io_thread(struct os_helper_thread **td_out, int *fd_out);
+void *io_thread(void *arg);
+extern int kernel_fd;
+
+extern int ubd_read_poll(int timeout);
+extern int ubd_write_poll(int timeout);
+
+#define UBD_REQ_BUFFER_SIZE 64
+
+#endif
+
diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
new file mode 100644
index 000000000..20fc33300
--- /dev/null
+++ b/arch/um/drivers/ubd_kern.c
@@ -0,0 +1,1540 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2018 Cambridge Greys Ltd
+ * Copyright (C) 2015-2016 Anton Ivanov (aivanov@brocade.com)
+ * Copyright (C) 2000 Jeff Dike (jdike@karaya.com)
+ */
+
+/* 2001-09-28...2002-04-17
+ * Partition stuff by James_McMechan@hotmail.com
+ * old style ubd by setting UBD_SHIFT to 0
+ * 2002-09-27...2002-10-18 massive tinkering for 2.5
+ * partitions have changed in 2.5
+ * 2003-01-29 more tinkering for 2.5.59-1
+ * This should now address the sysfs problems and has
+ * the symlink for devfs to allow for booting with
+ * the common /dev/ubd/discX/... names rather than
+ * only /dev/ubdN/discN this version also has lots of
+ * clean ups preparing for ubd-many.
+ * James McMechan
+ */
+
+#define UBD_SHIFT 4
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/blkdev.h>
+#include <linux/blk-mq.h>
+#include <linux/ata.h>
+#include <linux/hdreg.h>
+#include <linux/major.h>
+#include <linux/cdrom.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/ctype.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/platform_device.h>
+#include <linux/scatterlist.h>
+#include <kern_util.h>
+#include "mconsole_kern.h"
+#include <init.h>
+#include <irq_kern.h>
+#include "ubd.h"
+#include <os.h>
+#include "cow.h"
+
+/* Max request size is determined by sector mask - 32K */
+#define UBD_MAX_REQUEST (8 * sizeof(long))
+
+struct io_desc {
+	char *buffer;
+	unsigned long length;
+	unsigned long sector_mask;
+	unsigned long long cow_offset;
+	unsigned long bitmap_words[2];
+};
+
+struct io_thread_req {
+	struct request *req;
+	int fds[2];
+	unsigned long offsets[2];
+	unsigned long long offset;
+	int sectorsize;
+	int error;
+
+	int desc_cnt;
+	/* io_desc has to be the last element of the struct */
+	struct io_desc io_desc[];
+};
+
+
+static struct io_thread_req **irq_req_buffer;
+static struct io_thread_req *irq_remainder;
+static int irq_remainder_size;
+
+static struct io_thread_req **io_req_buffer;
+static struct io_thread_req *io_remainder;
+static int io_remainder_size;
+
+
+
+static inline int ubd_test_bit(__u64 bit, unsigned char *data)
+{
+	__u64 n;
+	int bits, off;
+
+	bits = sizeof(data[0]) * 8;
+	n = bit / bits;
+	off = bit % bits;
+	return (data[n] & (1 << off)) != 0;
+}
+
+static inline void ubd_set_bit(__u64 bit, unsigned char *data)
+{
+	__u64 n;
+	int bits, off;
+
+	bits = sizeof(data[0]) * 8;
+	n = bit / bits;
+	off = bit % bits;
+	data[n] |= (1 << off);
+}
+/*End stuff from ubd_user.h*/
+
+#define DRIVER_NAME "uml-blkdev"
+
+static DEFINE_MUTEX(ubd_lock);
+
+static int ubd_ioctl(struct block_device *bdev, blk_mode_t mode,
+		     unsigned int cmd, unsigned long arg);
+static int ubd_getgeo(struct gendisk *disk, struct hd_geometry *geo);
+
+#define MAX_DEV (16)
+
+static const struct block_device_operations ubd_blops = {
+        .owner		= THIS_MODULE,
+        .ioctl		= ubd_ioctl,
+        .compat_ioctl	= blkdev_compat_ptr_ioctl,
+	.getgeo		= ubd_getgeo,
+};
+
+#ifdef CONFIG_BLK_DEV_UBD_SYNC
+#define OPEN_FLAGS ((struct openflags) { .r = 1, .w = 1, .s = 1, .c = 0, \
+					 .cl = 1 })
+#else
+#define OPEN_FLAGS ((struct openflags) { .r = 1, .w = 1, .s = 0, .c = 0, \
+					 .cl = 1 })
+#endif
+static struct openflags global_openflags = OPEN_FLAGS;
+
+struct cow {
+	/* backing file name */
+	char *file;
+	/* backing file fd */
+	int fd;
+	unsigned long *bitmap;
+	unsigned long bitmap_len;
+	int bitmap_offset;
+	int data_offset;
+};
+
+#define MAX_SG 64
+
+struct ubd {
+	/* name (and fd, below) of the file opened for writing, either the
+	 * backing or the cow file. */
+	char *file;
+	char *serial;
+	int fd;
+	__u64 size;
+	struct openflags boot_openflags;
+	struct openflags openflags;
+	unsigned shared:1;
+	unsigned no_cow:1;
+	unsigned no_trim:1;
+	struct cow cow;
+	struct platform_device pdev;
+	struct gendisk *disk;
+	struct blk_mq_tag_set tag_set;
+	spinlock_t lock;
+};
+
+#define DEFAULT_COW { \
+	.file =			NULL, \
+	.fd =			-1,	\
+	.bitmap =		NULL, \
+	.bitmap_offset =	0, \
+	.data_offset =		0, \
+}
+
+#define DEFAULT_UBD { \
+	.file = 		NULL, \
+	.serial =		NULL, \
+	.fd =			-1, \
+	.size =			-1, \
+	.boot_openflags =	OPEN_FLAGS, \
+	.openflags =		OPEN_FLAGS, \
+	.no_cow =               0, \
+	.no_trim =		0, \
+	.shared =		0, \
+	.cow =			DEFAULT_COW, \
+	.lock =			__SPIN_LOCK_UNLOCKED(ubd_devs.lock), \
+}
+
+/* Protected by ubd_lock */
+static struct ubd ubd_devs[MAX_DEV] = { [0 ... MAX_DEV - 1] = DEFAULT_UBD };
+
+static blk_status_t ubd_queue_rq(struct blk_mq_hw_ctx *hctx,
+				 const struct blk_mq_queue_data *bd);
+
+static int fake_ide_setup(char *str)
+{
+	pr_warn("The fake_ide option has been removed\n");
+	return 1;
+}
+__setup("fake_ide", fake_ide_setup);
+
+__uml_help(fake_ide_setup,
+"fake_ide\n"
+"    Obsolete stub.\n\n"
+);
+
+static int parse_unit(char **ptr)
+{
+	char *str = *ptr, *end;
+	int n = -1;
+
+	if(isdigit(*str)) {
+		n = simple_strtoul(str, &end, 0);
+		if(end == str)
+			return -1;
+		*ptr = end;
+	}
+	else if (('a' <= *str) && (*str <= 'z')) {
+		n = *str - 'a';
+		str++;
+		*ptr = str;
+	}
+	return n;
+}
+
+/* If *index_out == -1 at exit, the passed option was a general one;
+ * otherwise, the str pointer is used (and owned) inside ubd_devs array, so it
+ * should not be freed on exit.
+ */
+static int ubd_setup_common(char *str, int *index_out, char **error_out)
+{
+	struct ubd *ubd_dev;
+	struct openflags flags = global_openflags;
+	char *file, *backing_file, *serial;
+	int n, err = 0, i;
+
+	if(index_out) *index_out = -1;
+	n = *str;
+	if(n == '='){
+		str++;
+		if(!strcmp(str, "sync")){
+			global_openflags = of_sync(global_openflags);
+			return err;
+		}
+
+		pr_warn("fake major not supported any more\n");
+		return 0;
+	}
+
+	n = parse_unit(&str);
+	if(n < 0){
+		*error_out = "Couldn't parse device number";
+		return -EINVAL;
+	}
+	if(n >= MAX_DEV){
+		*error_out = "Device number out of range";
+		return 1;
+	}
+
+	err = -EBUSY;
+	mutex_lock(&ubd_lock);
+
+	ubd_dev = &ubd_devs[n];
+	if(ubd_dev->file != NULL){
+		*error_out = "Device is already configured";
+		goto out;
+	}
+
+	if (index_out)
+		*index_out = n;
+
+	err = -EINVAL;
+	for (i = 0; i < sizeof("rscdt="); i++) {
+		switch (*str) {
+		case 'r':
+			flags.w = 0;
+			break;
+		case 's':
+			flags.s = 1;
+			break;
+		case 'd':
+			ubd_dev->no_cow = 1;
+			break;
+		case 'c':
+			ubd_dev->shared = 1;
+			break;
+		case 't':
+			ubd_dev->no_trim = 1;
+			break;
+		case '=':
+			str++;
+			goto break_loop;
+		default:
+			*error_out = "Expected '=' or flag letter "
+				"(r, s, c, t or d)";
+			goto out;
+		}
+		str++;
+	}
+
+	if (*str == '=')
+		*error_out = "Too many flags specified";
+	else
+		*error_out = "Missing '='";
+	goto out;
+
+break_loop:
+	file = strsep(&str, ",:");
+	if (*file == '\0')
+		file = NULL;
+
+	backing_file = strsep(&str, ",:");
+	if (backing_file && *backing_file == '\0')
+		backing_file = NULL;
+
+	serial = strsep(&str, ",:");
+	if (serial && *serial == '\0')
+		serial = NULL;
+
+	if (backing_file && ubd_dev->no_cow) {
+		*error_out = "Can't specify both 'd' and a cow file";
+		goto out;
+	}
+
+	err = 0;
+	ubd_dev->file = file;
+	ubd_dev->cow.file = backing_file;
+	ubd_dev->serial = serial;
+	ubd_dev->boot_openflags = flags;
+out:
+	mutex_unlock(&ubd_lock);
+	return err;
+}
+
+static int ubd_setup(char *str)
+{
+	char *error;
+	int err;
+
+	err = ubd_setup_common(str, NULL, &error);
+	if(err)
+		printk(KERN_ERR "Failed to initialize device with \"%s\" : "
+		       "%s\n", str, error);
+	return 1;
+}
+
+__setup("ubd", ubd_setup);
+__uml_help(ubd_setup,
+"ubd<n><flags>=<filename>[(:|,)<filename2>][(:|,)<serial>]\n"
+"    This is used to associate a device with a file in the underlying\n"
+"    filesystem. When specifying two filenames, the first one is the\n"
+"    COW name and the second is the backing file name. As separator you can\n"
+"    use either a ':' or a ',': the first one allows writing things like;\n"
+"	ubd0=~/Uml/root_cow:~/Uml/root_backing_file\n"
+"    while with a ',' the shell would not expand the 2nd '~'.\n"
+"    When using only one filename, UML will detect whether to treat it like\n"
+"    a COW file or a backing file. To override this detection, add the 'd'\n"
+"    flag:\n"
+"	ubd0d=BackingFile\n"
+"    Usually, there is a filesystem in the file, but \n"
+"    that's not required. Swap devices containing swap files can be\n"
+"    specified like this. Also, a file which doesn't contain a\n"
+"    filesystem can have its contents read in the virtual \n"
+"    machine by running 'dd' on the device. <n> must be in the range\n"
+"    0 to 7. Appending an 'r' to the number will cause that device\n"
+"    to be mounted read-only. For example ubd1r=./ext_fs. Appending\n"
+"    an 's' will cause data to be written to disk on the host immediately.\n"
+"    'c' will cause the device to be treated as being shared between multiple\n"
+"    UMLs and file locking will be turned off - this is appropriate for a\n"
+"    cluster filesystem and inappropriate at almost all other times.\n\n"
+"    't' will disable trim/discard support on the device (enabled by default).\n\n"
+"    An optional device serial number can be exposed using the serial parameter\n"
+"    on the cmdline which is exposed as a sysfs entry. This is particularly\n"
+"    useful when a unique number should be given to the device. Note when\n"
+"    specifying a label, the filename2 must be also presented. It can be\n"
+"    an empty string, in which case the backing file is not used:\n"
+"       ubd0=File,,Serial\n\n"
+);
+
+static int udb_setup(char *str)
+{
+	printk("udb%s specified on command line is almost certainly a ubd -> "
+	       "udb TYPO\n", str);
+	return 1;
+}
+
+__setup("udb", udb_setup);
+__uml_help(udb_setup,
+"udb\n"
+"    This option is here solely to catch ubd -> udb typos, which can be\n"
+"    to impossible to catch visually unless you specifically look for\n"
+"    them.  The only result of any option starting with 'udb' is an error\n"
+"    in the boot output.\n\n"
+);
+
+/* Only changed by ubd_init, which is an initcall. */
+static int thread_fd = -1;
+
+/* Function to read several request pointers at a time
+* handling fractional reads if (and as) needed
+*/
+
+static int bulk_req_safe_read(
+	int fd,
+	struct io_thread_req **request_buffer,
+	struct io_thread_req **remainder,
+	int *remainder_size,
+	int max_recs
+	)
+{
+	int n = 0;
+	int res = 0;
+
+	if (*remainder_size > 0) {
+		memmove(
+			(char *) request_buffer,
+			(char *) remainder, *remainder_size
+		);
+		n = *remainder_size;
+	}
+
+	res = os_read_file(
+			fd,
+			((char *) request_buffer) + *remainder_size,
+			sizeof(struct io_thread_req *)*max_recs
+				- *remainder_size
+		);
+	if (res > 0) {
+		n += res;
+		if ((n % sizeof(struct io_thread_req *)) > 0) {
+			/*
+			* Read somehow returned not a multiple of dword
+			* theoretically possible, but never observed in the
+			* wild, so read routine must be able to handle it
+			*/
+			*remainder_size = n % sizeof(struct io_thread_req *);
+			WARN(*remainder_size > 0, "UBD IPC read returned a partial result");
+			memmove(
+				remainder,
+				((char *) request_buffer) +
+					(n/sizeof(struct io_thread_req *))*sizeof(struct io_thread_req *),
+				*remainder_size
+			);
+			n = n - *remainder_size;
+		}
+	} else {
+		n = res;
+	}
+	return n;
+}
+
+static void ubd_end_request(struct io_thread_req *io_req)
+{
+	if (io_req->error == BLK_STS_NOTSUPP) {
+		if (req_op(io_req->req) == REQ_OP_DISCARD)
+			blk_queue_disable_discard(io_req->req->q);
+		else if (req_op(io_req->req) == REQ_OP_WRITE_ZEROES)
+			blk_queue_disable_write_zeroes(io_req->req->q);
+	}
+	blk_mq_end_request(io_req->req, io_req->error);
+	kfree(io_req);
+}
+
+static irqreturn_t ubd_intr(int irq, void *dev)
+{
+	int len, i;
+
+	while ((len = bulk_req_safe_read(thread_fd, irq_req_buffer,
+			&irq_remainder, &irq_remainder_size,
+			UBD_REQ_BUFFER_SIZE)) >= 0) {
+		for (i = 0; i < len / sizeof(struct io_thread_req *); i++)
+			ubd_end_request(irq_req_buffer[i]);
+	}
+
+	if (len < 0 && len != -EAGAIN)
+		pr_err("spurious interrupt in %s, err = %d\n", __func__, len);
+	return IRQ_HANDLED;
+}
+
+/* Only changed by ubd_init, which is an initcall. */
+static struct os_helper_thread *io_td;
+
+static void kill_io_thread(void)
+{
+	if (io_td)
+		os_kill_helper_thread(io_td);
+}
+
+__uml_exitcall(kill_io_thread);
+
+static inline int ubd_file_size(struct ubd *ubd_dev, __u64 *size_out)
+{
+	char *file;
+	int fd;
+	int err;
+
+	__u32 version;
+	__u32 align;
+	char *backing_file;
+	time64_t mtime;
+	unsigned long long size;
+	int sector_size;
+	int bitmap_offset;
+
+	if (ubd_dev->file && ubd_dev->cow.file) {
+		file = ubd_dev->cow.file;
+
+		goto out;
+	}
+
+	fd = os_open_file(ubd_dev->file, of_read(OPENFLAGS()), 0);
+	if (fd < 0)
+		return fd;
+
+	err = read_cow_header(file_reader, &fd, &version, &backing_file, \
+		&mtime, &size, &sector_size, &align, &bitmap_offset);
+	os_close_file(fd);
+
+	if(err == -EINVAL)
+		file = ubd_dev->file;
+	else
+		file = backing_file;
+
+out:
+	return os_file_size(file, size_out);
+}
+
+static int read_cow_bitmap(int fd, void *buf, int offset, int len)
+{
+	int err;
+
+	err = os_pread_file(fd, buf, len, offset);
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+static int backing_file_mismatch(char *file, __u64 size, time64_t mtime)
+{
+	time64_t modtime;
+	unsigned long long actual;
+	int err;
+
+	err = os_file_modtime(file, &modtime);
+	if (err < 0) {
+		printk(KERN_ERR "Failed to get modification time of backing "
+		       "file \"%s\", err = %d\n", file, -err);
+		return err;
+	}
+
+	err = os_file_size(file, &actual);
+	if (err < 0) {
+		printk(KERN_ERR "Failed to get size of backing file \"%s\", "
+		       "err = %d\n", file, -err);
+		return err;
+	}
+
+	if (actual != size) {
+		/*__u64 can be a long on AMD64 and with %lu GCC complains; so
+		 * the typecast.*/
+		printk(KERN_ERR "Size mismatch (%llu vs %llu) of COW header "
+		       "vs backing file\n", (unsigned long long) size, actual);
+		return -EINVAL;
+	}
+	if (modtime != mtime) {
+		printk(KERN_ERR "mtime mismatch (%lld vs %lld) of COW header vs "
+		       "backing file\n", mtime, modtime);
+		return -EINVAL;
+	}
+	return 0;
+}
+
+static int path_requires_switch(char *from_cmdline, char *from_cow, char *cow)
+{
+	struct uml_stat buf1, buf2;
+	int err;
+
+	if (from_cmdline == NULL)
+		return 0;
+	if (!strcmp(from_cmdline, from_cow))
+		return 0;
+
+	err = os_stat_file(from_cmdline, &buf1);
+	if (err < 0) {
+		printk(KERN_ERR "Couldn't stat '%s', err = %d\n", from_cmdline,
+		       -err);
+		return 0;
+	}
+	err = os_stat_file(from_cow, &buf2);
+	if (err < 0) {
+		printk(KERN_ERR "Couldn't stat '%s', err = %d\n", from_cow,
+		       -err);
+		return 1;
+	}
+	if ((buf1.ust_dev == buf2.ust_dev) && (buf1.ust_ino == buf2.ust_ino))
+		return 0;
+
+	printk(KERN_ERR "Backing file mismatch - \"%s\" requested, "
+	       "\"%s\" specified in COW header of \"%s\"\n",
+	       from_cmdline, from_cow, cow);
+	return 1;
+}
+
+static int open_ubd_file(char *file, struct openflags *openflags, int shared,
+		  char **backing_file_out, int *bitmap_offset_out,
+		  unsigned long *bitmap_len_out, int *data_offset_out,
+		  int *create_cow_out)
+{
+	time64_t mtime;
+	unsigned long long size;
+	__u32 version, align;
+	char *backing_file;
+	int fd, err, sectorsize, asked_switch, mode = 0644;
+
+	fd = os_open_file(file, *openflags, mode);
+	if (fd < 0) {
+		if ((fd == -ENOENT) && (create_cow_out != NULL))
+			*create_cow_out = 1;
+		if (!openflags->w ||
+		    ((fd != -EROFS) && (fd != -EACCES)))
+			return fd;
+		openflags->w = 0;
+		fd = os_open_file(file, *openflags, mode);
+		if (fd < 0)
+			return fd;
+	}
+
+	if (shared)
+		printk(KERN_INFO "Not locking \"%s\" on the host\n", file);
+	else {
+		err = os_lock_file(fd, openflags->w);
+		if (err < 0) {
+			printk(KERN_ERR "Failed to lock '%s', err = %d\n",
+			       file, -err);
+			goto out_close;
+		}
+	}
+
+	/* Successful return case! */
+	if (backing_file_out == NULL)
+		return fd;
+
+	err = read_cow_header(file_reader, &fd, &version, &backing_file, &mtime,
+			      &size, &sectorsize, &align, bitmap_offset_out);
+	if (err && (*backing_file_out != NULL)) {
+		printk(KERN_ERR "Failed to read COW header from COW file "
+		       "\"%s\", errno = %d\n", file, -err);
+		goto out_close;
+	}
+	if (err)
+		return fd;
+
+	asked_switch = path_requires_switch(*backing_file_out, backing_file,
+					    file);
+
+	/* Allow switching only if no mismatch. */
+	if (asked_switch && !backing_file_mismatch(*backing_file_out, size,
+						   mtime)) {
+		printk(KERN_ERR "Switching backing file to '%s'\n",
+		       *backing_file_out);
+		err = write_cow_header(file, fd, *backing_file_out,
+				       sectorsize, align, &size);
+		if (err) {
+			printk(KERN_ERR "Switch failed, errno = %d\n", -err);
+			goto out_close;
+		}
+	} else {
+		*backing_file_out = backing_file;
+		err = backing_file_mismatch(*backing_file_out, size, mtime);
+		if (err)
+			goto out_close;
+	}
+
+	cow_sizes(version, size, sectorsize, align, *bitmap_offset_out,
+		  bitmap_len_out, data_offset_out);
+
+	return fd;
+ out_close:
+	os_close_file(fd);
+	return err;
+}
+
+static int create_cow_file(char *cow_file, char *backing_file,
+		    struct openflags flags,
+		    int sectorsize, int alignment, int *bitmap_offset_out,
+		    unsigned long *bitmap_len_out, int *data_offset_out)
+{
+	int err, fd;
+
+	flags.c = 1;
+	fd = open_ubd_file(cow_file, &flags, 0, NULL, NULL, NULL, NULL, NULL);
+	if (fd < 0) {
+		err = fd;
+		printk(KERN_ERR "Open of COW file '%s' failed, errno = %d\n",
+		       cow_file, -err);
+		goto out;
+	}
+
+	err = init_cow_file(fd, cow_file, backing_file, sectorsize, alignment,
+			    bitmap_offset_out, bitmap_len_out,
+			    data_offset_out);
+	if (!err)
+		return fd;
+	os_close_file(fd);
+ out:
+	return err;
+}
+
+static void ubd_close_dev(struct ubd *ubd_dev)
+{
+	os_close_file(ubd_dev->fd);
+	if(ubd_dev->cow.file == NULL)
+		return;
+
+	os_close_file(ubd_dev->cow.fd);
+	vfree(ubd_dev->cow.bitmap);
+	ubd_dev->cow.bitmap = NULL;
+}
+
+static int ubd_open_dev(struct ubd *ubd_dev)
+{
+	struct openflags flags;
+	char **back_ptr;
+	int err, create_cow, *create_ptr;
+	int fd;
+
+	ubd_dev->openflags = ubd_dev->boot_openflags;
+	create_cow = 0;
+	create_ptr = (ubd_dev->cow.file != NULL) ? &create_cow : NULL;
+	back_ptr = ubd_dev->no_cow ? NULL : &ubd_dev->cow.file;
+
+	fd = open_ubd_file(ubd_dev->file, &ubd_dev->openflags, ubd_dev->shared,
+				back_ptr, &ubd_dev->cow.bitmap_offset,
+				&ubd_dev->cow.bitmap_len, &ubd_dev->cow.data_offset,
+				create_ptr);
+
+	if((fd == -ENOENT) && create_cow){
+		fd = create_cow_file(ubd_dev->file, ubd_dev->cow.file,
+					  ubd_dev->openflags, SECTOR_SIZE, PAGE_SIZE,
+					  &ubd_dev->cow.bitmap_offset,
+					  &ubd_dev->cow.bitmap_len,
+					  &ubd_dev->cow.data_offset);
+		if(fd >= 0){
+			printk(KERN_INFO "Creating \"%s\" as COW file for "
+			       "\"%s\"\n", ubd_dev->file, ubd_dev->cow.file);
+		}
+	}
+
+	if(fd < 0){
+		printk("Failed to open '%s', errno = %d\n", ubd_dev->file,
+		       -fd);
+		return fd;
+	}
+	ubd_dev->fd = fd;
+
+	if(ubd_dev->cow.file != NULL){
+		err = -ENOMEM;
+		ubd_dev->cow.bitmap = vmalloc(ubd_dev->cow.bitmap_len);
+		if(ubd_dev->cow.bitmap == NULL){
+			printk(KERN_ERR "Failed to vmalloc COW bitmap\n");
+			goto error;
+		}
+
+		err = read_cow_bitmap(ubd_dev->fd, ubd_dev->cow.bitmap,
+				      ubd_dev->cow.bitmap_offset,
+				      ubd_dev->cow.bitmap_len);
+		if(err < 0)
+			goto error;
+
+		flags = ubd_dev->openflags;
+		flags.w = 0;
+		err = open_ubd_file(ubd_dev->cow.file, &flags, ubd_dev->shared, NULL,
+				    NULL, NULL, NULL, NULL);
+		if(err < 0) goto error;
+		ubd_dev->cow.fd = err;
+	}
+	return 0;
+ error:
+	os_close_file(ubd_dev->fd);
+	return err;
+}
+
+static void ubd_device_release(struct device *dev)
+{
+	struct ubd *ubd_dev = container_of(dev, struct ubd, pdev.dev);
+
+	blk_mq_free_tag_set(&ubd_dev->tag_set);
+	*ubd_dev = ((struct ubd) DEFAULT_UBD);
+}
+
+static ssize_t serial_show(struct device *dev,
+			   struct device_attribute *attr, char *buf)
+{
+	struct gendisk *disk = dev_to_disk(dev);
+	struct ubd *ubd_dev = disk->private_data;
+
+	if (!ubd_dev)
+		return 0;
+
+	return sprintf(buf, "%s", ubd_dev->serial);
+}
+
+static DEVICE_ATTR_RO(serial);
+
+static struct attribute *ubd_attrs[] = {
+	&dev_attr_serial.attr,
+	NULL,
+};
+
+static umode_t ubd_attrs_are_visible(struct kobject *kobj,
+				     struct attribute *a, int n)
+{
+	return a->mode;
+}
+
+static const struct attribute_group ubd_attr_group = {
+	.attrs = ubd_attrs,
+	.is_visible = ubd_attrs_are_visible,
+};
+
+static const struct attribute_group *ubd_attr_groups[] = {
+	&ubd_attr_group,
+	NULL,
+};
+
+#define ROUND_BLOCK(n) ((n + (SECTOR_SIZE - 1)) & (-SECTOR_SIZE))
+
+static const struct blk_mq_ops ubd_mq_ops = {
+	.queue_rq = ubd_queue_rq,
+};
+
+static int ubd_add(int n, char **error_out)
+{
+	struct ubd *ubd_dev = &ubd_devs[n];
+	struct queue_limits lim = {
+		.max_segments		= MAX_SG,
+		.seg_boundary_mask	= PAGE_SIZE - 1,
+		.features		= BLK_FEAT_WRITE_CACHE,
+	};
+	struct gendisk *disk;
+	int err = 0;
+
+	if(ubd_dev->file == NULL)
+		goto out;
+
+	if (ubd_dev->cow.file)
+		lim.max_hw_sectors = 8 * sizeof(long);
+	if (!ubd_dev->no_trim) {
+		lim.max_hw_discard_sectors = UBD_MAX_REQUEST;
+		lim.max_write_zeroes_sectors = UBD_MAX_REQUEST;
+	}
+
+	err = ubd_file_size(ubd_dev, &ubd_dev->size);
+	if(err < 0){
+		*error_out = "Couldn't determine size of device's file";
+		goto out;
+	}
+
+	err = ubd_open_dev(ubd_dev);
+	if (err) {
+		pr_err("ubd%c: Can't open \"%s\": errno = %d\n",
+			'a' + n, ubd_dev->file, -err);
+		goto out;
+	}
+
+	ubd_dev->size = ROUND_BLOCK(ubd_dev->size);
+
+	ubd_dev->tag_set.ops = &ubd_mq_ops;
+	ubd_dev->tag_set.queue_depth = 64;
+	ubd_dev->tag_set.numa_node = NUMA_NO_NODE;
+	ubd_dev->tag_set.driver_data = ubd_dev;
+	ubd_dev->tag_set.nr_hw_queues = 1;
+
+	err = blk_mq_alloc_tag_set(&ubd_dev->tag_set);
+	if (err)
+		goto out_close;
+
+	disk = blk_mq_alloc_disk(&ubd_dev->tag_set, &lim, ubd_dev);
+	if (IS_ERR(disk)) {
+		err = PTR_ERR(disk);
+		goto out_cleanup_tags;
+	}
+
+	disk->major = UBD_MAJOR;
+	disk->first_minor = n << UBD_SHIFT;
+	disk->minors = 1 << UBD_SHIFT;
+	disk->fops = &ubd_blops;
+	set_capacity(disk, ubd_dev->size / 512);
+	sprintf(disk->disk_name, "ubd%c", 'a' + n);
+	disk->private_data = ubd_dev;
+	set_disk_ro(disk, !ubd_dev->openflags.w);
+
+	ubd_dev->pdev.id = n;
+	ubd_dev->pdev.name = DRIVER_NAME;
+	ubd_dev->pdev.dev.release = ubd_device_release;
+	dev_set_drvdata(&ubd_dev->pdev.dev, ubd_dev);
+	platform_device_register(&ubd_dev->pdev);
+
+	err = device_add_disk(&ubd_dev->pdev.dev, disk, ubd_attr_groups);
+	if (err)
+		goto out_cleanup_disk;
+
+	ubd_dev->disk = disk;
+
+	return 0;
+
+out_cleanup_disk:
+	put_disk(disk);
+out_cleanup_tags:
+	blk_mq_free_tag_set(&ubd_dev->tag_set);
+out_close:
+	ubd_close_dev(ubd_dev);
+out:
+	return err;
+}
+
+static int ubd_config(char *str, char **error_out)
+{
+	int n, ret;
+
+	/* This string is possibly broken up and stored, so it's only
+	 * freed if ubd_setup_common fails, or if only general options
+	 * were set.
+	 */
+	str = kstrdup(str, GFP_KERNEL);
+	if (str == NULL) {
+		*error_out = "Failed to allocate memory";
+		return -ENOMEM;
+	}
+
+	ret = ubd_setup_common(str, &n, error_out);
+	if (ret)
+		goto err_free;
+
+	if (n == -1) {
+		ret = 0;
+		goto err_free;
+	}
+
+	mutex_lock(&ubd_lock);
+	ret = ubd_add(n, error_out);
+	if (ret)
+		ubd_devs[n].file = NULL;
+	mutex_unlock(&ubd_lock);
+
+out:
+	return ret;
+
+err_free:
+	kfree(str);
+	goto out;
+}
+
+static int ubd_get_config(char *name, char *str, int size, char **error_out)
+{
+	struct ubd *ubd_dev;
+	int n, len = 0;
+
+	n = parse_unit(&name);
+	if((n >= MAX_DEV) || (n < 0)){
+		*error_out = "ubd_get_config : device number out of range";
+		return -1;
+	}
+
+	ubd_dev = &ubd_devs[n];
+	mutex_lock(&ubd_lock);
+
+	if(ubd_dev->file == NULL){
+		CONFIG_CHUNK(str, size, len, "", 1);
+		goto out;
+	}
+
+	CONFIG_CHUNK(str, size, len, ubd_dev->file, 0);
+
+	if(ubd_dev->cow.file != NULL){
+		CONFIG_CHUNK(str, size, len, ",", 0);
+		CONFIG_CHUNK(str, size, len, ubd_dev->cow.file, 1);
+	}
+	else CONFIG_CHUNK(str, size, len, "", 1);
+
+ out:
+	mutex_unlock(&ubd_lock);
+	return len;
+}
+
+static int ubd_id(char **str, int *start_out, int *end_out)
+{
+	int n;
+
+	n = parse_unit(str);
+	*start_out = 0;
+	*end_out = MAX_DEV - 1;
+	return n;
+}
+
+static int ubd_remove(int n, char **error_out)
+{
+	struct ubd *ubd_dev;
+	int err = -ENODEV;
+
+	mutex_lock(&ubd_lock);
+
+	ubd_dev = &ubd_devs[n];
+
+	if(ubd_dev->file == NULL)
+		goto out;
+
+	if (ubd_dev->disk) {
+		/* you cannot remove a open disk */
+		err = -EBUSY;
+		if (disk_openers(ubd_dev->disk))
+			goto out;
+
+		del_gendisk(ubd_dev->disk);
+		ubd_close_dev(ubd_dev);
+		put_disk(ubd_dev->disk);
+	}
+
+	err = 0;
+	platform_device_unregister(&ubd_dev->pdev);
+out:
+	mutex_unlock(&ubd_lock);
+	return err;
+}
+
+/* All these are called by mconsole in process context and without
+ * ubd-specific locks.  The structure itself is const except for .list.
+ */
+static struct mc_device ubd_mc = {
+	.list		= LIST_HEAD_INIT(ubd_mc.list),
+	.name		= "ubd",
+	.config		= ubd_config,
+	.get_config	= ubd_get_config,
+	.id		= ubd_id,
+	.remove		= ubd_remove,
+};
+
+static int __init ubd_mc_init(void)
+{
+	mconsole_register_dev(&ubd_mc);
+	return 0;
+}
+
+__initcall(ubd_mc_init);
+
+static int __init ubd0_init(void)
+{
+	struct ubd *ubd_dev = &ubd_devs[0];
+
+	mutex_lock(&ubd_lock);
+	if(ubd_dev->file == NULL)
+		ubd_dev->file = "root_fs";
+	mutex_unlock(&ubd_lock);
+
+	return 0;
+}
+
+__initcall(ubd0_init);
+
+/* Used in ubd_init, which is an initcall */
+static struct platform_driver ubd_driver = {
+	.driver = {
+		.name  = DRIVER_NAME,
+	},
+};
+
+static int __init ubd_init(void)
+{
+	char *error;
+	int i, err;
+
+	if (register_blkdev(UBD_MAJOR, "ubd"))
+		return -1;
+
+	irq_req_buffer = kmalloc_objs(struct io_thread_req *,
+				      UBD_REQ_BUFFER_SIZE);
+	irq_remainder = 0;
+
+	if (irq_req_buffer == NULL) {
+		printk(KERN_ERR "Failed to initialize ubd buffering\n");
+		return -ENOMEM;
+	}
+	io_req_buffer = kmalloc_objs(struct io_thread_req *,
+				     UBD_REQ_BUFFER_SIZE);
+
+	io_remainder = 0;
+
+	if (io_req_buffer == NULL) {
+		printk(KERN_ERR "Failed to initialize ubd buffering\n");
+		return -ENOMEM;
+	}
+	platform_driver_register(&ubd_driver);
+	mutex_lock(&ubd_lock);
+	for (i = 0; i < MAX_DEV; i++){
+		err = ubd_add(i, &error);
+		if(err)
+			printk(KERN_ERR "Failed to initialize ubd device %d :"
+			       "%s\n", i, error);
+	}
+	mutex_unlock(&ubd_lock);
+	return 0;
+}
+
+late_initcall(ubd_init);
+
+static int __init ubd_driver_init(void)
+{
+	int err;
+
+	/* Set by CONFIG_BLK_DEV_UBD_SYNC or ubd=sync.*/
+	if(global_openflags.s){
+		printk(KERN_INFO "ubd: Synchronous mode\n");
+		/* Letting ubd=sync be like using ubd#s= instead of ubd#= is
+		 * enough. So use anyway the io thread. */
+	}
+	err = start_io_thread(&io_td, &thread_fd);
+	if (err < 0) {
+		printk(KERN_ERR
+		       "ubd : Failed to start I/O thread (errno = %d) - "
+		       "falling back to synchronous I/O\n", -err);
+		return 0;
+	}
+	err = um_request_irq(UBD_IRQ, thread_fd, IRQ_READ, ubd_intr,
+			     0, "ubd", ubd_devs);
+	if(err < 0)
+		printk(KERN_ERR "um_request_irq failed - errno = %d\n", -err);
+	return 0;
+}
+
+device_initcall(ubd_driver_init);
+
+static void cowify_bitmap(__u64 io_offset, int length, unsigned long *cow_mask,
+			  __u64 *cow_offset, unsigned long *bitmap,
+			  __u64 bitmap_offset, unsigned long *bitmap_words,
+			  __u64 bitmap_len)
+{
+	__u64 sector = io_offset >> SECTOR_SHIFT;
+	int i, update_bitmap = 0;
+
+	for (i = 0; i < length >> SECTOR_SHIFT; i++) {
+		if(cow_mask != NULL)
+			ubd_set_bit(i, (unsigned char *) cow_mask);
+		if(ubd_test_bit(sector + i, (unsigned char *) bitmap))
+			continue;
+
+		update_bitmap = 1;
+		ubd_set_bit(sector + i, (unsigned char *) bitmap);
+	}
+
+	if(!update_bitmap)
+		return;
+
+	*cow_offset = sector / (sizeof(unsigned long) * 8);
+
+	/* This takes care of the case where we're exactly at the end of the
+	 * device, and *cow_offset + 1 is off the end.  So, just back it up
+	 * by one word.  Thanks to Lynn Kerby for the fix and James McMechan
+	 * for the original diagnosis.
+	 */
+	if (*cow_offset == (DIV_ROUND_UP(bitmap_len,
+					 sizeof(unsigned long)) - 1))
+		(*cow_offset)--;
+
+	bitmap_words[0] = bitmap[*cow_offset];
+	bitmap_words[1] = bitmap[*cow_offset + 1];
+
+	*cow_offset *= sizeof(unsigned long);
+	*cow_offset += bitmap_offset;
+}
+
+static void cowify_req(struct io_thread_req *req, struct io_desc *segment,
+		       unsigned long offset, unsigned long *bitmap,
+		       __u64 bitmap_offset, __u64 bitmap_len)
+{
+	__u64 sector = offset >> SECTOR_SHIFT;
+	int i;
+
+	if (segment->length > (sizeof(segment->sector_mask) * 8) << SECTOR_SHIFT)
+		panic("Operation too long");
+
+	if (req_op(req->req) == REQ_OP_READ) {
+		for (i = 0; i < segment->length >> SECTOR_SHIFT; i++) {
+			if(ubd_test_bit(sector + i, (unsigned char *) bitmap))
+				ubd_set_bit(i, (unsigned char *)
+					    &segment->sector_mask);
+		}
+	} else {
+		cowify_bitmap(offset, segment->length, &segment->sector_mask,
+			      &segment->cow_offset, bitmap, bitmap_offset,
+			      segment->bitmap_words, bitmap_len);
+	}
+}
+
+static void ubd_map_req(struct ubd *dev, struct io_thread_req *io_req,
+			struct request *req)
+{
+	struct bio_vec bvec;
+	struct req_iterator iter;
+	int i = 0;
+	unsigned long byte_offset = io_req->offset;
+	enum req_op op = req_op(req);
+
+	if (op == REQ_OP_WRITE_ZEROES || op == REQ_OP_DISCARD) {
+		io_req->io_desc[0].buffer = NULL;
+		io_req->io_desc[0].length = blk_rq_bytes(req);
+	} else {
+		rq_for_each_segment(bvec, req, iter) {
+			BUG_ON(i >= io_req->desc_cnt);
+
+			io_req->io_desc[i].buffer = bvec_virt(&bvec);
+			io_req->io_desc[i].length = bvec.bv_len;
+			i++;
+		}
+	}
+
+	if (dev->cow.file) {
+		for (i = 0; i < io_req->desc_cnt; i++) {
+			cowify_req(io_req, &io_req->io_desc[i], byte_offset,
+				   dev->cow.bitmap, dev->cow.bitmap_offset,
+				   dev->cow.bitmap_len);
+			byte_offset += io_req->io_desc[i].length;
+		}
+
+	}
+}
+
+static struct io_thread_req *ubd_alloc_req(struct ubd *dev, struct request *req,
+					   int desc_cnt)
+{
+	struct io_thread_req *io_req;
+	int i;
+
+	io_req = kmalloc(sizeof(*io_req) +
+			 (desc_cnt * sizeof(struct io_desc)),
+			 GFP_ATOMIC);
+	if (!io_req)
+		return NULL;
+
+	io_req->req = req;
+	if (dev->cow.file)
+		io_req->fds[0] = dev->cow.fd;
+	else
+		io_req->fds[0] = dev->fd;
+	io_req->error = 0;
+	io_req->sectorsize = SECTOR_SIZE;
+	io_req->fds[1] = dev->fd;
+	io_req->offset = (u64) blk_rq_pos(req) << SECTOR_SHIFT;
+	io_req->offsets[0] = 0;
+	io_req->offsets[1] = dev->cow.data_offset;
+
+	for (i = 0 ; i < desc_cnt; i++) {
+		io_req->io_desc[i].sector_mask = 0;
+		io_req->io_desc[i].cow_offset = -1;
+	}
+
+	return io_req;
+}
+
+static int ubd_submit_request(struct ubd *dev, struct request *req)
+{
+	int segs = 0;
+	struct io_thread_req *io_req;
+	int ret;
+	enum req_op op = req_op(req);
+
+	if (op == REQ_OP_FLUSH)
+		segs = 0;
+	else if (op == REQ_OP_WRITE_ZEROES || op == REQ_OP_DISCARD)
+		segs = 1;
+	else
+		segs = blk_rq_nr_phys_segments(req);
+
+	io_req = ubd_alloc_req(dev, req, segs);
+	if (!io_req)
+		return -ENOMEM;
+
+	io_req->desc_cnt = segs;
+	if (segs)
+		ubd_map_req(dev, io_req, req);
+
+	ret = os_write_file(thread_fd, &io_req, sizeof(io_req));
+	if (ret != sizeof(io_req)) {
+		if (ret != -EAGAIN)
+			pr_err("write to io thread failed: %d\n", -ret);
+		kfree(io_req);
+	}
+	return ret;
+}
+
+static blk_status_t ubd_queue_rq(struct blk_mq_hw_ctx *hctx,
+				 const struct blk_mq_queue_data *bd)
+{
+	struct ubd *ubd_dev = hctx->queue->queuedata;
+	struct request *req = bd->rq;
+	int ret = 0, res = BLK_STS_OK;
+
+	blk_mq_start_request(req);
+
+	spin_lock_irq(&ubd_dev->lock);
+
+	switch (req_op(req)) {
+	case REQ_OP_FLUSH:
+	case REQ_OP_READ:
+	case REQ_OP_WRITE:
+	case REQ_OP_DISCARD:
+	case REQ_OP_WRITE_ZEROES:
+		ret = ubd_submit_request(ubd_dev, req);
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		res = BLK_STS_NOTSUPP;
+	}
+
+	spin_unlock_irq(&ubd_dev->lock);
+
+	if (ret < 0) {
+		if (ret == -ENOMEM)
+			res = BLK_STS_RESOURCE;
+		else
+			res = BLK_STS_DEV_RESOURCE;
+	}
+
+	return res;
+}
+
+static int ubd_getgeo(struct gendisk *disk, struct hd_geometry *geo)
+{
+	struct ubd *ubd_dev = disk->private_data;
+
+	geo->heads = 128;
+	geo->sectors = 32;
+	geo->cylinders = ubd_dev->size / (128 * 32 * 512);
+	return 0;
+}
+
+static int ubd_ioctl(struct block_device *bdev, blk_mode_t mode,
+		     unsigned int cmd, unsigned long arg)
+{
+	struct ubd *ubd_dev = bdev->bd_disk->private_data;
+	u16 ubd_id[ATA_ID_WORDS];
+
+	switch (cmd) {
+		struct cdrom_volctrl volume;
+	case HDIO_GET_IDENTITY:
+		memset(&ubd_id, 0, ATA_ID_WORDS * 2);
+		ubd_id[ATA_ID_CYLS]	= ubd_dev->size / (128 * 32 * 512);
+		ubd_id[ATA_ID_HEADS]	= 128;
+		ubd_id[ATA_ID_SECTORS]	= 32;
+		if(copy_to_user((char __user *) arg, (char *) &ubd_id,
+				 sizeof(ubd_id)))
+			return -EFAULT;
+		return 0;
+
+	case CDROMVOLREAD:
+		if(copy_from_user(&volume, (char __user *) arg, sizeof(volume)))
+			return -EFAULT;
+		volume.channel0 = 255;
+		volume.channel1 = 255;
+		volume.channel2 = 255;
+		volume.channel3 = 255;
+		if(copy_to_user((char __user *) arg, &volume, sizeof(volume)))
+			return -EFAULT;
+		return 0;
+	}
+	return -EINVAL;
+}
+
+static int map_error(int error_code)
+{
+	switch (error_code) {
+	case 0:
+		return BLK_STS_OK;
+	case ENOSYS:
+	case EOPNOTSUPP:
+		return BLK_STS_NOTSUPP;
+	case ENOSPC:
+		return BLK_STS_NOSPC;
+	}
+	return BLK_STS_IOERR;
+}
+
+/*
+ * Everything from here onwards *IS NOT PART OF THE KERNEL*
+ *
+ * The following functions are part of UML hypervisor code.
+ * All functions from here onwards are executed as a helper
+ * thread and are not allowed to execute any kernel functions.
+ *
+ * Any communication must occur strictly via shared memory and IPC.
+ *
+ * Do not add printks, locks, kernel memory operations, etc - it
+ * will result in unpredictable behaviour and/or crashes.
+ */
+
+static int update_bitmap(struct io_thread_req *req, struct io_desc *segment)
+{
+	int n;
+
+	if (segment->cow_offset == -1)
+		return map_error(0);
+
+	n = os_pwrite_file(req->fds[1], &segment->bitmap_words,
+			  sizeof(segment->bitmap_words), segment->cow_offset);
+	if (n != sizeof(segment->bitmap_words))
+		return map_error(-n);
+
+	return map_error(0);
+}
+
+static void do_io(struct io_thread_req *req, struct io_desc *desc)
+{
+	char *buf = NULL;
+	unsigned long len;
+	int n, nsectors, start, end, bit;
+	__u64 off;
+
+	/* FLUSH is really a special case, we cannot "case" it with others */
+
+	if (req_op(req->req) == REQ_OP_FLUSH) {
+		/* fds[0] is always either the rw image or our cow file */
+		req->error = map_error(-os_sync_file(req->fds[0]));
+		return;
+	}
+
+	nsectors = desc->length / req->sectorsize;
+	start = 0;
+	do {
+		bit = ubd_test_bit(start, (unsigned char *) &desc->sector_mask);
+		end = start;
+		while((end < nsectors) &&
+		      (ubd_test_bit(end, (unsigned char *) &desc->sector_mask) == bit))
+			end++;
+
+		off = req->offset + req->offsets[bit] +
+			start * req->sectorsize;
+		len = (end - start) * req->sectorsize;
+		if (desc->buffer != NULL)
+			buf = &desc->buffer[start * req->sectorsize];
+
+		switch (req_op(req->req)) {
+		case REQ_OP_READ:
+			n = 0;
+			do {
+				buf = &buf[n];
+				len -= n;
+				n = os_pread_file(req->fds[bit], buf, len, off);
+				if (n < 0) {
+					req->error = map_error(-n);
+					return;
+				}
+			} while((n < len) && (n != 0));
+			if (n < len) memset(&buf[n], 0, len - n);
+			break;
+		case REQ_OP_WRITE:
+			n = os_pwrite_file(req->fds[bit], buf, len, off);
+			if(n != len){
+				req->error = map_error(-n);
+				return;
+			}
+			break;
+		case REQ_OP_DISCARD:
+			n = os_falloc_punch(req->fds[bit], off, len);
+			if (n) {
+				req->error = map_error(-n);
+				return;
+			}
+			break;
+		case REQ_OP_WRITE_ZEROES:
+			n = os_falloc_zeroes(req->fds[bit], off, len);
+			if (n) {
+				req->error = map_error(-n);
+				return;
+			}
+			break;
+		default:
+			WARN_ON_ONCE(1);
+			req->error = BLK_STS_NOTSUPP;
+			return;
+		}
+
+		start = end;
+	} while(start < nsectors);
+
+	req->offset += len;
+	req->error = update_bitmap(req, desc);
+}
+
+/* Changed in start_io_thread, which is serialized by being called only
+ * from ubd_init, which is an initcall.
+ */
+int kernel_fd = -1;
+
+/* Only changed by the io thread. XXX: currently unused. */
+static int io_count;
+
+void *io_thread(void *arg)
+{
+	int n, count, written, res;
+
+	os_fix_helper_thread_signals();
+
+	while(1){
+		n = bulk_req_safe_read(
+			kernel_fd,
+			io_req_buffer,
+			&io_remainder,
+			&io_remainder_size,
+			UBD_REQ_BUFFER_SIZE
+		);
+		if (n <= 0) {
+			if (n == -EAGAIN)
+				ubd_read_poll(-1);
+
+			continue;
+		}
+
+		for (count = 0; count < n/sizeof(struct io_thread_req *); count++) {
+			struct io_thread_req *req = io_req_buffer[count];
+			int i;
+
+			io_count++;
+			for (i = 0; !req->error && i < req->desc_cnt; i++)
+				do_io(req, &(req->io_desc[i]));
+
+		}
+
+		written = 0;
+
+		do {
+			res = os_write_file(kernel_fd,
+					    ((char *) io_req_buffer) + written,
+					    n - written);
+			if (res >= 0) {
+				written += res;
+			}
+			if (written < n) {
+				ubd_write_poll(-1);
+			}
+		} while (written < n);
+	}
+
+	return NULL;
+}
diff --git a/arch/um/drivers/ubd_user.c b/arch/um/drivers/ubd_user.c
new file mode 100644
index 000000000..8e8a8bf51
--- /dev/null
+++ b/arch/um/drivers/ubd_user.c
@@ -0,0 +1,78 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2016 Anton Ivanov (aivanov@brocade.com)
+ * Copyright (C) 2000, 2001, 2002 Jeff Dike (jdike@karaya.com)
+ * Copyright (C) 2001 Ridgerun,Inc (glonnon@ridgerun.com)
+ */
+
+#include <stddef.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sched.h>
+#include <signal.h>
+#include <string.h>
+#include <netinet/in.h>
+#include <sys/time.h>
+#include <sys/socket.h>
+#include <sys/mman.h>
+#include <sys/param.h>
+#include <endian.h>
+#include <byteswap.h>
+
+#include "ubd.h"
+#include <os.h>
+#include <poll.h>
+
+static struct pollfd kernel_pollfd;
+
+int start_io_thread(struct os_helper_thread **td_out, int *fd_out)
+{
+	int fds[2], err;
+
+	err = os_pipe(fds, 1, 1);
+	if(err < 0){
+		printk("start_io_thread - os_pipe failed, err = %d\n", -err);
+		goto out;
+	}
+
+	kernel_fd = fds[0];
+	kernel_pollfd.fd = kernel_fd;
+	kernel_pollfd.events = POLLIN;
+	*fd_out = fds[1];
+
+	err = os_set_fd_block(*fd_out, 0);
+	err |= os_set_fd_block(kernel_fd, 0);
+	if (err) {
+		printk("start_io_thread - failed to set nonblocking I/O.\n");
+		goto out_close;
+	}
+
+	err = os_run_helper_thread(td_out, io_thread, NULL);
+	if (err < 0) {
+		printk("%s - failed to run helper thread, err = %d\n",
+		       __func__, -err);
+		goto out_close;
+	}
+
+	return 0;
+
+ out_close:
+	os_close_file(fds[0]);
+	os_close_file(fds[1]);
+	kernel_fd = -1;
+	*fd_out = -1;
+ out:
+	return err;
+}
+
+int ubd_read_poll(int timeout)
+{
+	kernel_pollfd.events = POLLIN;
+	return poll(&kernel_pollfd, 1, timeout);
+}
+int ubd_write_poll(int timeout)
+{
+	kernel_pollfd.events = POLLOUT;
+	return poll(&kernel_pollfd, 1, timeout);
+}
+
diff --git a/arch/um/drivers/vector_kern.c b/arch/um/drivers/vector_kern.c
new file mode 100644
index 000000000..8a70b3a62
--- /dev/null
+++ b/arch/um/drivers/vector_kern.c
@@ -0,0 +1,1769 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2017 - 2019 Cambridge Greys Limited
+ * Copyright (C) 2011 - 2014 Cisco Systems Inc
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Copyright (C) 2001 Lennert Buytenhek (buytenh@gnu.org) and
+ * James Leu (jleu@mindspring.net).
+ * Copyright (C) 2001 by various other people who didn't put their name here.
+ */
+
+#define pr_fmt(fmt) "uml-vector: " fmt
+
+#include <linux/memblock.h>
+#include <linux/etherdevice.h>
+#include <linux/ethtool.h>
+#include <linux/hex.h>
+#include <linux/inetdevice.h>
+#include <linux/init.h>
+#include <linux/list.h>
+#include <linux/netdevice.h>
+#include <linux/platform_device.h>
+#include <linux/rtnetlink.h>
+#include <linux/skbuff.h>
+#include <linux/slab.h>
+#include <linux/interrupt.h>
+#include <linux/firmware.h>
+#include <linux/fs.h>
+#include <asm/atomic.h>
+#include <uapi/linux/filter.h>
+#include <init.h>
+#include <irq_kern.h>
+#include <irq_user.h>
+#include <os.h>
+#include "mconsole_kern.h"
+#include "vector_user.h"
+#include "vector_kern.h"
+
+/*
+ * Adapted from network devices with the following major changes:
+ * All transports are static - simplifies the code significantly
+ * Multiple FDs/IRQs per device
+ * Vector IO optionally used for read/write, falling back to legacy
+ * based on configuration and/or availability
+ * Configuration is no longer positional - L2TPv3 and GRE require up to
+ * 10 parameters, passing this as positional is not fit for purpose.
+ * Only socket transports are supported
+ */
+
+
+#define DRIVER_NAME "uml-vector"
+struct vector_cmd_line_arg {
+	struct list_head list;
+	int unit;
+	char *arguments;
+};
+
+struct vector_device {
+	struct list_head list;
+	struct net_device *dev;
+	struct platform_device pdev;
+	int unit;
+	int opened;
+};
+
+static LIST_HEAD(vec_cmd_line);
+
+static DEFINE_SPINLOCK(vector_devices_lock);
+static LIST_HEAD(vector_devices);
+
+static int driver_registered;
+
+static void vector_eth_configure(int n, struct arglist *def);
+static int vector_mmsg_rx(struct vector_private *vp, int budget);
+
+/* Argument accessors to set variables (and/or set default values)
+ * mtu, buffer sizing, default headroom, etc
+ */
+
+#define DEFAULT_HEADROOM 2
+#define SAFETY_MARGIN 32
+#define DEFAULT_VECTOR_SIZE 64
+#define TX_SMALL_PACKET 128
+#define MAX_IOV_SIZE (MAX_SKB_FRAGS + 1)
+
+static const struct {
+	const char string[ETH_GSTRING_LEN];
+} ethtool_stats_keys[] = {
+	{ "rx_queue_max" },
+	{ "rx_queue_running_average" },
+	{ "tx_queue_max" },
+	{ "tx_queue_running_average" },
+	{ "rx_encaps_errors" },
+	{ "tx_timeout_count" },
+	{ "tx_restart_queue" },
+	{ "tx_kicks" },
+	{ "tx_flow_control_xon" },
+	{ "tx_flow_control_xoff" },
+	{ "rx_csum_offload_good" },
+	{ "rx_csum_offload_errors"},
+	{ "sg_ok"},
+	{ "sg_linearized"},
+};
+
+#define VECTOR_NUM_STATS	ARRAY_SIZE(ethtool_stats_keys)
+
+static void vector_reset_stats(struct vector_private *vp)
+{
+	/* We reuse the existing queue locks for stats */
+
+	/* RX stats are modified with RX head_lock held
+	 * in vector_poll.
+	 */
+
+	spin_lock(&vp->rx_queue->head_lock);
+	vp->estats.rx_queue_max = 0;
+	vp->estats.rx_queue_running_average = 0;
+	vp->estats.rx_encaps_errors = 0;
+	vp->estats.sg_ok = 0;
+	vp->estats.sg_linearized = 0;
+	spin_unlock(&vp->rx_queue->head_lock);
+
+	/* TX stats are modified with TX head_lock held
+	 * in vector_send.
+	 */
+
+	spin_lock(&vp->tx_queue->head_lock);
+	vp->estats.tx_timeout_count = 0;
+	vp->estats.tx_restart_queue = 0;
+	vp->estats.tx_kicks = 0;
+	vp->estats.tx_flow_control_xon = 0;
+	vp->estats.tx_flow_control_xoff = 0;
+	vp->estats.tx_queue_max = 0;
+	vp->estats.tx_queue_running_average = 0;
+	spin_unlock(&vp->tx_queue->head_lock);
+}
+
+static int get_mtu(struct arglist *def)
+{
+	char *mtu = uml_vector_fetch_arg(def, "mtu");
+	long result;
+
+	if (mtu != NULL) {
+		if (kstrtoul(mtu, 10, &result) == 0)
+			if ((result < (1 << 16) - 1) && (result >= 576))
+				return result;
+	}
+	return ETH_MAX_PACKET;
+}
+
+static char *get_bpf_file(struct arglist *def)
+{
+	return uml_vector_fetch_arg(def, "bpffile");
+}
+
+static bool get_bpf_flash(struct arglist *def)
+{
+	char *allow = uml_vector_fetch_arg(def, "bpfflash");
+	long result;
+
+	if (allow != NULL) {
+		if (kstrtoul(allow, 10, &result) == 0)
+			return result > 0;
+	}
+	return false;
+}
+
+static int get_depth(struct arglist *def)
+{
+	char *mtu = uml_vector_fetch_arg(def, "depth");
+	long result;
+
+	if (mtu != NULL) {
+		if (kstrtoul(mtu, 10, &result) == 0)
+			return result;
+	}
+	return DEFAULT_VECTOR_SIZE;
+}
+
+static int get_headroom(struct arglist *def)
+{
+	char *mtu = uml_vector_fetch_arg(def, "headroom");
+	long result;
+
+	if (mtu != NULL) {
+		if (kstrtoul(mtu, 10, &result) == 0)
+			return result;
+	}
+	return DEFAULT_HEADROOM;
+}
+
+static int get_req_size(struct arglist *def)
+{
+	char *gro = uml_vector_fetch_arg(def, "gro");
+	long result;
+
+	if (gro != NULL) {
+		if (kstrtoul(gro, 10, &result) == 0) {
+			if (result > 0)
+				return 65536;
+		}
+	}
+	return get_mtu(def) + ETH_HEADER_OTHER +
+		get_headroom(def) + SAFETY_MARGIN;
+}
+
+
+static int get_transport_options(struct arglist *def)
+{
+	char *transport = uml_vector_fetch_arg(def, "transport");
+	char *vector = uml_vector_fetch_arg(def, "vec");
+
+	int vec_rx = VECTOR_RX;
+	int vec_tx = VECTOR_TX;
+	long parsed;
+	int result = 0;
+
+	if (transport == NULL)
+		return -EINVAL;
+
+	if (vector != NULL) {
+		if (kstrtoul(vector, 10, &parsed) == 0) {
+			if (parsed == 0) {
+				vec_rx = 0;
+				vec_tx = 0;
+			}
+		}
+	}
+
+	if (get_bpf_flash(def))
+		result = VECTOR_BPF_FLASH;
+
+	if (strncmp(transport, TRANS_TAP, TRANS_TAP_LEN) == 0)
+		return result;
+	if (strncmp(transport, TRANS_HYBRID, TRANS_HYBRID_LEN) == 0)
+		return (result | vec_rx | VECTOR_BPF);
+	if (strncmp(transport, TRANS_RAW, TRANS_RAW_LEN) == 0)
+		return (result | vec_rx | vec_tx | VECTOR_QDISC_BYPASS);
+	return (result | vec_rx | vec_tx);
+}
+
+
+/* A mini-buffer for packet drop read
+ * All of our supported transports are datagram oriented and we always
+ * read using recvmsg or recvmmsg. If we pass a buffer which is smaller
+ * than the packet size it still counts as full packet read and will
+ * clean the incoming stream to keep sigio/epoll happy
+ */
+
+#define DROP_BUFFER_SIZE 32
+
+static char *drop_buffer;
+
+
+/*
+ * Advance the mmsg queue head by n = advance. Resets the queue to
+ * maximum enqueue/dequeue-at-once capacity if possible. Called by
+ * dequeuers. Caller must hold the head_lock!
+ */
+
+static int vector_advancehead(struct vector_queue *qi, int advance)
+{
+	qi->head =
+		(qi->head + advance)
+			% qi->max_depth;
+
+
+	atomic_sub(advance, &qi->queue_depth);
+	return atomic_read(&qi->queue_depth);
+}
+
+/*	Advance the queue tail by n = advance.
+ *	This is called by enqueuers which should hold the
+ *	head lock already
+ */
+
+static int vector_advancetail(struct vector_queue *qi, int advance)
+{
+	qi->tail =
+		(qi->tail + advance)
+			% qi->max_depth;
+	atomic_add(advance, &qi->queue_depth);
+	return atomic_read(&qi->queue_depth);
+}
+
+static int prep_msg(struct vector_private *vp,
+	struct sk_buff *skb,
+	struct iovec *iov)
+{
+	int iov_index = 0;
+	int nr_frags, frag;
+	skb_frag_t *skb_frag;
+
+	nr_frags = skb_shinfo(skb)->nr_frags;
+	if (nr_frags > MAX_IOV_SIZE) {
+		if (skb_linearize(skb) != 0)
+			goto drop;
+	}
+	if (vp->header_size > 0) {
+		iov[iov_index].iov_len = vp->header_size;
+		vp->form_header(iov[iov_index].iov_base, skb, vp);
+		iov_index++;
+	}
+	iov[iov_index].iov_base = skb->data;
+	if (nr_frags > 0) {
+		iov[iov_index].iov_len = skb->len - skb->data_len;
+		vp->estats.sg_ok++;
+	} else
+		iov[iov_index].iov_len = skb->len;
+	iov_index++;
+	for (frag = 0; frag < nr_frags; frag++) {
+		skb_frag = &skb_shinfo(skb)->frags[frag];
+		iov[iov_index].iov_base = skb_frag_address_safe(skb_frag);
+		iov[iov_index].iov_len = skb_frag_size(skb_frag);
+		iov_index++;
+	}
+	return iov_index;
+drop:
+	return -1;
+}
+/*
+ * Generic vector enqueue with support for forming headers using transport
+ * specific callback. Allows GRE, L2TPv3, RAW and other transports
+ * to use a common enqueue procedure in vector mode
+ */
+
+static int vector_enqueue(struct vector_queue *qi, struct sk_buff *skb)
+{
+	struct vector_private *vp = netdev_priv(qi->dev);
+	int queue_depth;
+	int packet_len;
+	struct mmsghdr *mmsg_vector = qi->mmsg_vector;
+	int iov_count;
+
+	spin_lock(&qi->tail_lock);
+	queue_depth = atomic_read(&qi->queue_depth);
+
+	if (skb)
+		packet_len = skb->len;
+
+	if (queue_depth < qi->max_depth) {
+
+		*(qi->skbuff_vector + qi->tail) = skb;
+		mmsg_vector += qi->tail;
+		iov_count = prep_msg(
+			vp,
+			skb,
+			mmsg_vector->msg_hdr.msg_iov
+		);
+		if (iov_count < 1)
+			goto drop;
+		mmsg_vector->msg_hdr.msg_iovlen = iov_count;
+		mmsg_vector->msg_hdr.msg_name = vp->fds->remote_addr;
+		mmsg_vector->msg_hdr.msg_namelen = vp->fds->remote_addr_size;
+		wmb(); /* Make the packet visible to the NAPI poll thread */
+		queue_depth = vector_advancetail(qi, 1);
+	} else
+		goto drop;
+	spin_unlock(&qi->tail_lock);
+	return queue_depth;
+drop:
+	qi->dev->stats.tx_dropped++;
+	if (skb != NULL) {
+		packet_len = skb->len;
+		dev_consume_skb_any(skb);
+		netdev_completed_queue(qi->dev, 1, packet_len);
+	}
+	spin_unlock(&qi->tail_lock);
+	return queue_depth;
+}
+
+static int consume_vector_skbs(struct vector_queue *qi, int count)
+{
+	struct sk_buff *skb;
+	int skb_index;
+	int bytes_compl = 0;
+
+	for (skb_index = qi->head; skb_index < qi->head + count; skb_index++) {
+		skb = *(qi->skbuff_vector + skb_index);
+		/* mark as empty to ensure correct destruction if
+		 * needed
+		 */
+		bytes_compl += skb->len;
+		*(qi->skbuff_vector + skb_index) = NULL;
+		dev_consume_skb_any(skb);
+	}
+	qi->dev->stats.tx_bytes += bytes_compl;
+	qi->dev->stats.tx_packets += count;
+	netdev_completed_queue(qi->dev, count, bytes_compl);
+	return vector_advancehead(qi, count);
+}
+
+/*
+ * Generic vector dequeue via sendmmsg with support for forming headers
+ * using transport specific callback. Allows GRE, L2TPv3, RAW and
+ * other transports to use a common dequeue procedure in vector mode
+ */
+
+
+static int vector_send(struct vector_queue *qi)
+{
+	struct vector_private *vp = netdev_priv(qi->dev);
+	struct mmsghdr *send_from;
+	int result = 0, send_len;
+
+	if (spin_trylock(&qi->head_lock)) {
+		/* update queue_depth to current value */
+		while (atomic_read(&qi->queue_depth) > 0) {
+			/* Calculate the start of the vector */
+			send_len = atomic_read(&qi->queue_depth);
+			send_from = qi->mmsg_vector;
+			send_from += qi->head;
+			/* Adjust vector size if wraparound */
+			if (send_len + qi->head > qi->max_depth)
+				send_len = qi->max_depth - qi->head;
+			/* Try to TX as many packets as possible */
+			if (send_len > 0) {
+				result = uml_vector_sendmmsg(
+					 vp->fds->tx_fd,
+					 send_from,
+					 send_len,
+					 0
+				);
+				vp->in_write_poll =
+					(result != send_len);
+			}
+			/* For some of the sendmmsg error scenarios
+			 * we may end being unsure in the TX success
+			 * for all packets. It is safer to declare
+			 * them all TX-ed and blame the network.
+			 */
+			if (result < 0) {
+				if (net_ratelimit())
+					netdev_err(vp->dev, "sendmmsg err=%i\n",
+						result);
+				vp->in_error = true;
+				result = send_len;
+			}
+			if (result > 0) {
+				consume_vector_skbs(qi, result);
+				/* This is equivalent to an TX IRQ.
+				 * Restart the upper layers to feed us
+				 * more packets.
+				 */
+				if (result > vp->estats.tx_queue_max)
+					vp->estats.tx_queue_max = result;
+				vp->estats.tx_queue_running_average =
+					(vp->estats.tx_queue_running_average + result) >> 1;
+			}
+			netif_wake_queue(qi->dev);
+			/* if TX is busy, break out of the send loop,
+			 *  poll write IRQ will reschedule xmit for us.
+			 */
+			if (result != send_len) {
+				vp->estats.tx_restart_queue++;
+				break;
+			}
+		}
+		spin_unlock(&qi->head_lock);
+	}
+	return atomic_read(&qi->queue_depth);
+}
+
+/* Queue destructor. Deliberately stateless so we can use
+ * it in queue cleanup if initialization fails.
+ */
+
+static void destroy_queue(struct vector_queue *qi)
+{
+	int i;
+	struct iovec *iov;
+	struct vector_private *vp = netdev_priv(qi->dev);
+	struct mmsghdr *mmsg_vector;
+
+	if (qi == NULL)
+		return;
+	/* deallocate any skbuffs - we rely on any unused to be
+	 * set to NULL.
+	 */
+	if (qi->skbuff_vector != NULL) {
+		for (i = 0; i < qi->max_depth; i++) {
+			if (*(qi->skbuff_vector + i) != NULL)
+				dev_kfree_skb_any(*(qi->skbuff_vector + i));
+		}
+		kfree(qi->skbuff_vector);
+	}
+	/* deallocate matching IOV structures including header buffs */
+	if (qi->mmsg_vector != NULL) {
+		mmsg_vector = qi->mmsg_vector;
+		for (i = 0; i < qi->max_depth; i++) {
+			iov = mmsg_vector->msg_hdr.msg_iov;
+			if (iov != NULL) {
+				if ((vp->header_size > 0) &&
+					(iov->iov_base != NULL))
+					kfree(iov->iov_base);
+				kfree(iov);
+			}
+			mmsg_vector++;
+		}
+		kfree(qi->mmsg_vector);
+	}
+	kfree(qi);
+}
+
+/*
+ * Queue constructor. Create a queue with a given side.
+ */
+static struct vector_queue *create_queue(
+	struct vector_private *vp,
+	int max_size,
+	int header_size,
+	int num_extra_frags)
+{
+	struct vector_queue *result;
+	int i;
+	struct iovec *iov;
+	struct mmsghdr *mmsg_vector;
+
+	result = kmalloc_obj(struct vector_queue);
+	if (result == NULL)
+		return NULL;
+	result->max_depth = max_size;
+	result->dev = vp->dev;
+	result->mmsg_vector = kmalloc(
+		(sizeof(struct mmsghdr) * max_size), GFP_KERNEL);
+	if (result->mmsg_vector == NULL)
+		goto out_mmsg_fail;
+	result->skbuff_vector = kmalloc(
+		(sizeof(void *) * max_size), GFP_KERNEL);
+	if (result->skbuff_vector == NULL)
+		goto out_skb_fail;
+
+	/* further failures can be handled safely by destroy_queue*/
+
+	mmsg_vector = result->mmsg_vector;
+	for (i = 0; i < max_size; i++) {
+		/* Clear all pointers - we use non-NULL as marking on
+		 * what to free on destruction
+		 */
+		*(result->skbuff_vector + i) = NULL;
+		mmsg_vector->msg_hdr.msg_iov = NULL;
+		mmsg_vector++;
+	}
+	mmsg_vector = result->mmsg_vector;
+	result->max_iov_frags = num_extra_frags;
+	for (i = 0; i < max_size; i++) {
+		if (vp->header_size > 0)
+			iov = kmalloc_objs(struct iovec, 3 + num_extra_frags);
+		else
+			iov = kmalloc_objs(struct iovec, 2 + num_extra_frags);
+		if (iov == NULL)
+			goto out_fail;
+		mmsg_vector->msg_hdr.msg_iov = iov;
+		mmsg_vector->msg_hdr.msg_iovlen = 1;
+		mmsg_vector->msg_hdr.msg_control = NULL;
+		mmsg_vector->msg_hdr.msg_controllen = 0;
+		mmsg_vector->msg_hdr.msg_flags = MSG_DONTWAIT;
+		mmsg_vector->msg_hdr.msg_name = NULL;
+		mmsg_vector->msg_hdr.msg_namelen = 0;
+		if (vp->header_size > 0) {
+			iov->iov_base = kmalloc(header_size, GFP_KERNEL);
+			if (iov->iov_base == NULL)
+				goto out_fail;
+			iov->iov_len = header_size;
+			mmsg_vector->msg_hdr.msg_iovlen = 2;
+			iov++;
+		}
+		iov->iov_base = NULL;
+		iov->iov_len = 0;
+		mmsg_vector++;
+	}
+	spin_lock_init(&result->head_lock);
+	spin_lock_init(&result->tail_lock);
+	atomic_set(&result->queue_depth, 0);
+	result->head = 0;
+	result->tail = 0;
+	return result;
+out_skb_fail:
+	kfree(result->mmsg_vector);
+out_mmsg_fail:
+	kfree(result);
+	return NULL;
+out_fail:
+	destroy_queue(result);
+	return NULL;
+}
+
+/*
+ * We do not use the RX queue as a proper wraparound queue for now
+ * This is not necessary because the consumption via napi_gro_receive()
+ * happens in-line. While we can try using the return code of
+ * netif_rx() for flow control there are no drivers doing this today.
+ * For this RX specific use we ignore the tail/head locks and
+ * just read into a prepared queue filled with skbuffs.
+ */
+
+static struct sk_buff *prep_skb(
+	struct vector_private *vp,
+	struct user_msghdr *msg)
+{
+	int linear = vp->max_packet + vp->headroom + SAFETY_MARGIN;
+	struct sk_buff *result;
+	int iov_index = 0, len;
+	struct iovec *iov = msg->msg_iov;
+	int err, nr_frags, frag;
+	skb_frag_t *skb_frag;
+
+	if (vp->req_size <= linear)
+		len = linear;
+	else
+		len = vp->req_size;
+	result = alloc_skb_with_frags(
+		linear,
+		len - vp->max_packet,
+		3,
+		&err,
+		GFP_ATOMIC
+	);
+	if (vp->header_size > 0)
+		iov_index++;
+	if (result == NULL) {
+		iov[iov_index].iov_base = NULL;
+		iov[iov_index].iov_len = 0;
+		goto done;
+	}
+	skb_reserve(result, vp->headroom);
+	result->dev = vp->dev;
+	skb_put(result, vp->max_packet);
+	result->data_len = len - vp->max_packet;
+	result->len += len - vp->max_packet;
+	skb_reset_mac_header(result);
+	result->ip_summed = CHECKSUM_NONE;
+	iov[iov_index].iov_base = result->data;
+	iov[iov_index].iov_len = vp->max_packet;
+	iov_index++;
+
+	nr_frags = skb_shinfo(result)->nr_frags;
+	for (frag = 0; frag < nr_frags; frag++) {
+		skb_frag = &skb_shinfo(result)->frags[frag];
+		iov[iov_index].iov_base = skb_frag_address_safe(skb_frag);
+		if (iov[iov_index].iov_base != NULL)
+			iov[iov_index].iov_len = skb_frag_size(skb_frag);
+		else
+			iov[iov_index].iov_len = 0;
+		iov_index++;
+	}
+done:
+	msg->msg_iovlen = iov_index;
+	return result;
+}
+
+
+/* Prepare queue for recvmmsg one-shot rx - fill with fresh sk_buffs */
+
+static void prep_queue_for_rx(struct vector_queue *qi)
+{
+	struct vector_private *vp = netdev_priv(qi->dev);
+	struct mmsghdr *mmsg_vector = qi->mmsg_vector;
+	void **skbuff_vector = qi->skbuff_vector;
+	int i, queue_depth;
+
+	queue_depth = atomic_read(&qi->queue_depth);
+
+	if (queue_depth == 0)
+		return;
+
+	/* RX is always emptied 100% during each cycle, so we do not
+	 * have to do the tail wraparound math for it.
+	 */
+
+	qi->head = qi->tail = 0;
+
+	for (i = 0; i < queue_depth; i++) {
+		/* it is OK if allocation fails - recvmmsg with NULL data in
+		 * iov argument still performs an RX, just drops the packet
+		 * This allows us stop faffing around with a "drop buffer"
+		 */
+
+		*skbuff_vector = prep_skb(vp, &mmsg_vector->msg_hdr);
+		skbuff_vector++;
+		mmsg_vector++;
+	}
+	atomic_set(&qi->queue_depth, 0);
+}
+
+static struct vector_device *find_device(int n)
+{
+	struct vector_device *device;
+	struct list_head *ele;
+
+	spin_lock(&vector_devices_lock);
+	list_for_each(ele, &vector_devices) {
+		device = list_entry(ele, struct vector_device, list);
+		if (device->unit == n)
+			goto out;
+	}
+	device = NULL;
+ out:
+	spin_unlock(&vector_devices_lock);
+	return device;
+}
+
+static int vector_parse(char *str, int *index_out, char **str_out,
+			char **error_out)
+{
+	int n, err;
+	char *start = str;
+
+	while ((*str != ':') && (strlen(str) > 1))
+		str++;
+	if (*str != ':') {
+		*error_out = "Expected ':' after device number";
+		return -EINVAL;
+	}
+	*str = '\0';
+
+	err = kstrtouint(start, 0, &n);
+	if (err < 0) {
+		*error_out = "Bad device number";
+		return err;
+	}
+
+	str++;
+	if (find_device(n)) {
+		*error_out = "Device already configured";
+		return -EINVAL;
+	}
+
+	*index_out = n;
+	*str_out = str;
+	return 0;
+}
+
+static int vector_config(char *str, char **error_out)
+{
+	int err, n;
+	char *params;
+	struct arglist *parsed;
+
+	err = vector_parse(str, &n, &params, error_out);
+	if (err != 0)
+		return err;
+
+	/* This string is broken up and the pieces used by the underlying
+	 * driver. We should copy it to make sure things do not go wrong
+	 * later.
+	 */
+
+	params = kstrdup(params, GFP_KERNEL);
+	if (params == NULL) {
+		*error_out = "vector_config failed to strdup string";
+		return -ENOMEM;
+	}
+
+	parsed = uml_parse_vector_ifspec(params);
+
+	if (parsed == NULL) {
+		*error_out = "vector_config failed to parse parameters";
+		kfree(params);
+		return -EINVAL;
+	}
+
+	vector_eth_configure(n, parsed);
+	return 0;
+}
+
+static int vector_id(char **str, int *start_out, int *end_out)
+{
+	char *end;
+	int n;
+
+	n = simple_strtoul(*str, &end, 0);
+	if ((*end != '\0') || (end == *str))
+		return -1;
+
+	*start_out = n;
+	*end_out = n;
+	*str = end;
+	return n;
+}
+
+static int vector_remove(int n, char **error_out)
+{
+	struct vector_device *vec_d;
+	struct net_device *dev;
+	struct vector_private *vp;
+
+	vec_d = find_device(n);
+	if (vec_d == NULL)
+		return -ENODEV;
+	dev = vec_d->dev;
+	vp = netdev_priv(dev);
+	if (vp->fds != NULL)
+		return -EBUSY;
+	unregister_netdev(dev);
+	platform_device_unregister(&vec_d->pdev);
+	return 0;
+}
+
+/*
+ * There is no shared per-transport initialization code, so
+ * we will just initialize each interface one by one and
+ * add them to a list
+ */
+
+static struct platform_driver uml_net_driver = {
+	.driver = {
+		.name = DRIVER_NAME,
+	},
+};
+
+
+static void vector_device_release(struct device *dev)
+{
+	struct vector_device *device =
+		container_of(dev, struct vector_device, pdev.dev);
+	struct net_device *netdev = device->dev;
+
+	list_del(&device->list);
+	kfree(device);
+	free_netdev(netdev);
+}
+
+/* Bog standard recv using recvmsg - not used normally unless the user
+ * explicitly specifies not to use recvmmsg vector RX.
+ */
+
+static int vector_legacy_rx(struct vector_private *vp)
+{
+	int pkt_len;
+	struct user_msghdr hdr;
+	struct iovec iov[2 + MAX_IOV_SIZE]; /* header + data use case only */
+	int iovpos = 0;
+	struct sk_buff *skb;
+	int header_check;
+
+	hdr.msg_name = NULL;
+	hdr.msg_namelen = 0;
+	hdr.msg_iov = (struct iovec *) &iov;
+	hdr.msg_control = NULL;
+	hdr.msg_controllen = 0;
+	hdr.msg_flags = 0;
+
+	if (vp->header_size > 0) {
+		iov[0].iov_base = vp->header_rxbuffer;
+		iov[0].iov_len = vp->header_size;
+	}
+
+	skb = prep_skb(vp, &hdr);
+
+	if (skb == NULL) {
+		/* Read a packet into drop_buffer and don't do
+		 * anything with it.
+		 */
+		iov[iovpos].iov_base = drop_buffer;
+		iov[iovpos].iov_len = DROP_BUFFER_SIZE;
+		hdr.msg_iovlen = 1;
+		vp->dev->stats.rx_dropped++;
+	}
+
+	pkt_len = uml_vector_recvmsg(vp->fds->rx_fd, &hdr, 0);
+	if (pkt_len < 0) {
+		vp->in_error = true;
+		return pkt_len;
+	}
+
+	if (skb != NULL) {
+		if (pkt_len > vp->header_size) {
+			if (vp->header_size > 0) {
+				header_check = vp->verify_header(
+					vp->header_rxbuffer, skb, vp);
+				if (header_check < 0) {
+					dev_kfree_skb_irq(skb);
+					vp->dev->stats.rx_dropped++;
+					vp->estats.rx_encaps_errors++;
+					return 0;
+				}
+				if (header_check > 0) {
+					vp->estats.rx_csum_offload_good++;
+					skb->ip_summed = CHECKSUM_UNNECESSARY;
+				}
+			}
+			pskb_trim(skb, pkt_len - vp->rx_header_size);
+			skb->protocol = eth_type_trans(skb, skb->dev);
+			vp->dev->stats.rx_bytes += skb->len;
+			vp->dev->stats.rx_packets++;
+			napi_gro_receive(&vp->napi, skb);
+		} else {
+			dev_kfree_skb_irq(skb);
+		}
+	}
+	return pkt_len;
+}
+
+/*
+ * Packet at a time TX which falls back to vector TX if the
+ * underlying transport is busy.
+ */
+
+
+
+static int writev_tx(struct vector_private *vp, struct sk_buff *skb)
+{
+	struct iovec iov[3 + MAX_IOV_SIZE];
+	int iov_count, pkt_len = 0;
+
+	iov[0].iov_base = vp->header_txbuffer;
+	iov_count = prep_msg(vp, skb, (struct iovec *) &iov);
+
+	if (iov_count < 1)
+		goto drop;
+
+	pkt_len = uml_vector_writev(
+		vp->fds->tx_fd,
+		(struct iovec *) &iov,
+		iov_count
+	);
+
+	if (pkt_len < 0)
+		goto drop;
+
+	netif_trans_update(vp->dev);
+	netif_wake_queue(vp->dev);
+
+	if (pkt_len > 0) {
+		vp->dev->stats.tx_bytes += skb->len;
+		vp->dev->stats.tx_packets++;
+	} else {
+		vp->dev->stats.tx_dropped++;
+	}
+	consume_skb(skb);
+	return pkt_len;
+drop:
+	vp->dev->stats.tx_dropped++;
+	consume_skb(skb);
+	if (pkt_len < 0)
+		vp->in_error = true;
+	return pkt_len;
+}
+
+/*
+ * Receive as many messages as we can in one call using the special
+ * mmsg vector matched to an skb vector which we prepared earlier.
+ */
+
+static int vector_mmsg_rx(struct vector_private *vp, int budget)
+{
+	int packet_count, i;
+	struct vector_queue *qi = vp->rx_queue;
+	struct sk_buff *skb;
+	struct mmsghdr *mmsg_vector = qi->mmsg_vector;
+	void **skbuff_vector = qi->skbuff_vector;
+	int header_check;
+
+	/* Refresh the vector and make sure it is with new skbs and the
+	 * iovs are updated to point to them.
+	 */
+
+	prep_queue_for_rx(qi);
+
+	/* Fire the Lazy Gun - get as many packets as we can in one go. */
+
+	if (budget > qi->max_depth)
+		budget = qi->max_depth;
+
+	packet_count = uml_vector_recvmmsg(
+		vp->fds->rx_fd, qi->mmsg_vector, budget, 0);
+
+	if (packet_count < 0)
+		vp->in_error = true;
+
+	if (packet_count <= 0)
+		return packet_count;
+
+	/* We treat packet processing as enqueue, buffer refresh as dequeue
+	 * The queue_depth tells us how many buffers have been used and how
+	 * many do we need to prep the next time prep_queue_for_rx() is called.
+	 */
+
+	atomic_add(packet_count, &qi->queue_depth);
+
+	for (i = 0; i < packet_count; i++) {
+		skb = (*skbuff_vector);
+		if (mmsg_vector->msg_len > vp->header_size) {
+			if (vp->header_size > 0) {
+				header_check = vp->verify_header(
+					mmsg_vector->msg_hdr.msg_iov->iov_base,
+					skb,
+					vp
+				);
+				if (header_check < 0) {
+				/* Overlay header failed to verify - discard.
+				 * We can actually keep this skb and reuse it,
+				 * but that will make the prep logic too
+				 * complex.
+				 */
+					dev_kfree_skb_irq(skb);
+					vp->estats.rx_encaps_errors++;
+					(*skbuff_vector) = NULL;
+					mmsg_vector++;
+					skbuff_vector++;
+					continue;
+				}
+				if (header_check > 0) {
+					vp->estats.rx_csum_offload_good++;
+					skb->ip_summed = CHECKSUM_UNNECESSARY;
+				}
+			}
+			pskb_trim(skb,
+				mmsg_vector->msg_len - vp->rx_header_size);
+			skb->protocol = eth_type_trans(skb, skb->dev);
+			/*
+			 * We do not need to lock on updating stats here
+			 * The interrupt loop is non-reentrant.
+			 */
+			vp->dev->stats.rx_bytes += skb->len;
+			vp->dev->stats.rx_packets++;
+			napi_gro_receive(&vp->napi, skb);
+		} else {
+			/* Overlay header too short to do anything - discard.
+			 * We can actually keep this skb and reuse it,
+			 * but that will make the prep logic too complex.
+			 */
+			if (skb != NULL)
+				dev_kfree_skb_irq(skb);
+		}
+		(*skbuff_vector) = NULL;
+		/* Move to the next buffer element */
+		mmsg_vector++;
+		skbuff_vector++;
+	}
+	if (packet_count > 0) {
+		if (vp->estats.rx_queue_max < packet_count)
+			vp->estats.rx_queue_max = packet_count;
+		vp->estats.rx_queue_running_average =
+			(vp->estats.rx_queue_running_average + packet_count) >> 1;
+	}
+	return packet_count;
+}
+
+static int vector_net_start_xmit(struct sk_buff *skb, struct net_device *dev)
+{
+	struct vector_private *vp = netdev_priv(dev);
+	int queue_depth = 0;
+
+	if (vp->in_error) {
+		deactivate_fd(vp->fds->rx_fd, vp->rx_irq);
+		if ((vp->fds->rx_fd != vp->fds->tx_fd) && (vp->tx_irq != 0))
+			deactivate_fd(vp->fds->tx_fd, vp->tx_irq);
+		return NETDEV_TX_BUSY;
+	}
+
+	if ((vp->options & VECTOR_TX) == 0) {
+		writev_tx(vp, skb);
+		return NETDEV_TX_OK;
+	}
+
+	/* We do BQL only in the vector path, no point doing it in
+	 * packet at a time mode as there is no device queue
+	 */
+
+	netdev_sent_queue(vp->dev, skb->len);
+	queue_depth = vector_enqueue(vp->tx_queue, skb);
+
+	if (queue_depth < vp->tx_queue->max_depth && netdev_xmit_more()) {
+		mod_timer(&vp->tl, vp->coalesce);
+		return NETDEV_TX_OK;
+	} else {
+		queue_depth = vector_send(vp->tx_queue);
+		if (queue_depth > 0)
+			napi_schedule(&vp->napi);
+	}
+
+	return NETDEV_TX_OK;
+}
+
+static irqreturn_t vector_rx_interrupt(int irq, void *dev_id)
+{
+	struct net_device *dev = dev_id;
+	struct vector_private *vp = netdev_priv(dev);
+
+	if (!netif_running(dev))
+		return IRQ_NONE;
+	napi_schedule(&vp->napi);
+	return IRQ_HANDLED;
+
+}
+
+static irqreturn_t vector_tx_interrupt(int irq, void *dev_id)
+{
+	struct net_device *dev = dev_id;
+	struct vector_private *vp = netdev_priv(dev);
+
+	if (!netif_running(dev))
+		return IRQ_NONE;
+	/* We need to pay attention to it only if we got
+	 * -EAGAIN or -ENOBUFFS from sendmmsg. Otherwise
+	 * we ignore it. In the future, it may be worth
+	 * it to improve the IRQ controller a bit to make
+	 * tweaking the IRQ mask less costly
+	 */
+
+	napi_schedule(&vp->napi);
+	return IRQ_HANDLED;
+
+}
+
+static int irq_rr;
+
+static int vector_net_close(struct net_device *dev)
+{
+	struct vector_private *vp = netdev_priv(dev);
+
+	netif_stop_queue(dev);
+	timer_delete(&vp->tl);
+
+	vp->opened = false;
+
+	if (vp->fds == NULL)
+		return 0;
+
+	/* Disable and free all IRQS */
+	if (vp->rx_irq > 0) {
+		um_free_irq(vp->rx_irq, dev);
+		vp->rx_irq = 0;
+	}
+	if (vp->tx_irq > 0) {
+		um_free_irq(vp->tx_irq, dev);
+		vp->tx_irq = 0;
+	}
+	napi_disable(&vp->napi);
+	netif_napi_del(&vp->napi);
+	if (vp->fds->rx_fd > 0) {
+		if (vp->bpf)
+			uml_vector_detach_bpf(vp->fds->rx_fd, vp->bpf);
+		os_close_file(vp->fds->rx_fd);
+		vp->fds->rx_fd = -1;
+	}
+	if (vp->fds->tx_fd > 0) {
+		os_close_file(vp->fds->tx_fd);
+		vp->fds->tx_fd = -1;
+	}
+	if (vp->bpf != NULL)
+		kfree(vp->bpf->filter);
+	kfree(vp->bpf);
+	vp->bpf = NULL;
+	kfree(vp->fds->remote_addr);
+	kfree(vp->transport_data);
+	kfree(vp->header_rxbuffer);
+	kfree(vp->header_txbuffer);
+	if (vp->rx_queue != NULL)
+		destroy_queue(vp->rx_queue);
+	if (vp->tx_queue != NULL)
+		destroy_queue(vp->tx_queue);
+	kfree(vp->fds);
+	vp->fds = NULL;
+	vp->in_error = false;
+	return 0;
+}
+
+static int vector_poll(struct napi_struct *napi, int budget)
+{
+	struct vector_private *vp = container_of(napi, struct vector_private, napi);
+	int work_done = 0;
+	int err;
+	bool tx_enqueued = false;
+
+	if ((vp->options & VECTOR_TX) != 0)
+		tx_enqueued = (vector_send(vp->tx_queue) > 0);
+	spin_lock(&vp->rx_queue->head_lock);
+	if ((vp->options & VECTOR_RX) > 0)
+		err = vector_mmsg_rx(vp, budget);
+	else {
+		err = vector_legacy_rx(vp);
+		if (err > 0)
+			err = 1;
+	}
+	spin_unlock(&vp->rx_queue->head_lock);
+	if (err > 0)
+		work_done += err;
+
+	if (tx_enqueued || err > 0)
+		napi_schedule(napi);
+	if (work_done <= budget)
+		napi_complete_done(napi, work_done);
+	return work_done;
+}
+
+static void vector_reset_tx(struct work_struct *work)
+{
+	struct vector_private *vp =
+		container_of(work, struct vector_private, reset_tx);
+	netdev_reset_queue(vp->dev);
+	netif_start_queue(vp->dev);
+	netif_wake_queue(vp->dev);
+}
+
+static int vector_net_open(struct net_device *dev)
+{
+	struct vector_private *vp = netdev_priv(dev);
+	int err = -EINVAL;
+	struct vector_device *vdevice;
+
+	if (vp->opened)
+		return -ENXIO;
+	vp->opened = true;
+
+	vp->bpf = uml_vector_user_bpf(get_bpf_file(vp->parsed));
+
+	vp->fds = uml_vector_user_open(vp->unit, vp->parsed);
+
+	if (vp->fds == NULL)
+		goto out_close;
+
+	if (build_transport_data(vp) < 0)
+		goto out_close;
+
+	if ((vp->options & VECTOR_RX) > 0) {
+		vp->rx_queue = create_queue(
+			vp,
+			get_depth(vp->parsed),
+			vp->rx_header_size,
+			MAX_IOV_SIZE
+		);
+		atomic_set(&vp->rx_queue->queue_depth, get_depth(vp->parsed));
+	} else {
+		vp->header_rxbuffer = kmalloc(
+			vp->rx_header_size,
+			GFP_KERNEL
+		);
+		if (vp->header_rxbuffer == NULL)
+			goto out_close;
+	}
+	if ((vp->options & VECTOR_TX) > 0) {
+		vp->tx_queue = create_queue(
+			vp,
+			get_depth(vp->parsed),
+			vp->header_size,
+			MAX_IOV_SIZE
+		);
+	} else {
+		vp->header_txbuffer = kmalloc(vp->header_size, GFP_KERNEL);
+		if (vp->header_txbuffer == NULL)
+			goto out_close;
+	}
+
+	netif_napi_add_weight(vp->dev, &vp->napi, vector_poll,
+			      get_depth(vp->parsed));
+	napi_enable(&vp->napi);
+
+	/* READ IRQ */
+	err = um_request_irq(
+		irq_rr + VECTOR_BASE_IRQ, vp->fds->rx_fd,
+			IRQ_READ, vector_rx_interrupt,
+			IRQF_SHARED, dev->name, dev);
+	if (err < 0) {
+		netdev_err(dev, "vector_open: failed to get rx irq(%d)\n", err);
+		err = -ENETUNREACH;
+		goto out_close;
+	}
+	vp->rx_irq = irq_rr + VECTOR_BASE_IRQ;
+	dev->irq = irq_rr + VECTOR_BASE_IRQ;
+	irq_rr = (irq_rr + 1) % VECTOR_IRQ_SPACE;
+
+	/* WRITE IRQ - we need it only if we have vector TX */
+	if ((vp->options & VECTOR_TX) > 0) {
+		err = um_request_irq(
+			irq_rr + VECTOR_BASE_IRQ, vp->fds->tx_fd,
+				IRQ_WRITE, vector_tx_interrupt,
+				IRQF_SHARED, dev->name, dev);
+		if (err < 0) {
+			netdev_err(dev,
+				"vector_open: failed to get tx irq(%d)\n", err);
+			err = -ENETUNREACH;
+			goto out_close;
+		}
+		vp->tx_irq = irq_rr + VECTOR_BASE_IRQ;
+		irq_rr = (irq_rr + 1) % VECTOR_IRQ_SPACE;
+	}
+
+	if ((vp->options & VECTOR_QDISC_BYPASS) != 0) {
+		if (!uml_raw_enable_qdisc_bypass(vp->fds->rx_fd))
+			vp->options |= VECTOR_BPF;
+	}
+	if (((vp->options & VECTOR_BPF) != 0) && (vp->bpf == NULL))
+		vp->bpf = uml_vector_default_bpf(dev->dev_addr);
+
+	if (vp->bpf != NULL)
+		uml_vector_attach_bpf(vp->fds->rx_fd, vp->bpf);
+
+	netif_start_queue(dev);
+	vector_reset_stats(vp);
+
+	/* clear buffer - it can happen that the host side of the interface
+	 * is full when we get here. In this case, new data is never queued,
+	 * SIGIOs never arrive, and the net never works.
+	 */
+
+	napi_schedule(&vp->napi);
+
+	vdevice = find_device(vp->unit);
+	vdevice->opened = 1;
+
+	if ((vp->options & VECTOR_TX) != 0)
+		add_timer(&vp->tl);
+	return 0;
+out_close:
+	vector_net_close(dev);
+	return err;
+}
+
+
+static void vector_net_set_multicast_list(struct net_device *dev)
+{
+	/* TODO: - we can do some BPF games here */
+	return;
+}
+
+static void vector_net_tx_timeout(struct net_device *dev, unsigned int txqueue)
+{
+	struct vector_private *vp = netdev_priv(dev);
+
+	vp->estats.tx_timeout_count++;
+	netif_trans_update(dev);
+	schedule_work(&vp->reset_tx);
+}
+
+static netdev_features_t vector_fix_features(struct net_device *dev,
+	netdev_features_t features)
+{
+	features &= ~(NETIF_F_IP_CSUM|NETIF_F_IPV6_CSUM);
+	return features;
+}
+
+static int vector_set_features(struct net_device *dev,
+	netdev_features_t features)
+{
+	struct vector_private *vp = netdev_priv(dev);
+	/* Adjust buffer sizes for GSO/GRO. Unfortunately, there is
+	 * no way to negotiate it on raw sockets, so we can change
+	 * only our side.
+	 */
+	if (features & NETIF_F_GRO)
+		/* All new frame buffers will be GRO-sized */
+		vp->req_size = 65536;
+	else
+		/* All new frame buffers will be normal sized */
+		vp->req_size = vp->max_packet + vp->headroom + SAFETY_MARGIN;
+	return 0;
+}
+
+#ifdef CONFIG_NET_POLL_CONTROLLER
+static void vector_net_poll_controller(struct net_device *dev)
+{
+	disable_irq(dev->irq);
+	vector_rx_interrupt(dev->irq, dev);
+	enable_irq(dev->irq);
+}
+#endif
+
+static void vector_net_get_drvinfo(struct net_device *dev,
+				struct ethtool_drvinfo *info)
+{
+	strscpy(info->driver, DRIVER_NAME);
+}
+
+static int vector_net_load_bpf_flash(struct net_device *dev,
+				struct ethtool_flash *efl)
+{
+	struct vector_private *vp = netdev_priv(dev);
+	struct vector_device *vdevice;
+	const struct firmware *fw;
+	int result = 0;
+
+	if (!(vp->options & VECTOR_BPF_FLASH)) {
+		netdev_err(dev, "loading firmware not permitted: %s\n", efl->data);
+		return -1;
+	}
+
+	if (vp->bpf != NULL) {
+		if (vp->opened)
+			uml_vector_detach_bpf(vp->fds->rx_fd, vp->bpf);
+		kfree(vp->bpf->filter);
+		vp->bpf->filter = NULL;
+	} else {
+		vp->bpf = kmalloc_obj(struct sock_fprog, GFP_ATOMIC);
+		if (vp->bpf == NULL) {
+			netdev_err(dev, "failed to allocate memory for firmware\n");
+			goto flash_fail;
+		}
+	}
+
+	vdevice = find_device(vp->unit);
+
+	if (request_firmware(&fw, efl->data, &vdevice->pdev.dev))
+		goto flash_fail;
+
+	vp->bpf->filter = kmemdup(fw->data, fw->size, GFP_ATOMIC);
+	if (!vp->bpf->filter)
+		goto free_buffer;
+
+	vp->bpf->len = fw->size / sizeof(struct sock_filter);
+	release_firmware(fw);
+
+	if (vp->opened)
+		result = uml_vector_attach_bpf(vp->fds->rx_fd, vp->bpf);
+
+	return result;
+
+free_buffer:
+	release_firmware(fw);
+
+flash_fail:
+	if (vp->bpf != NULL)
+		kfree(vp->bpf->filter);
+	kfree(vp->bpf);
+	vp->bpf = NULL;
+	return -1;
+}
+
+static void vector_get_ringparam(struct net_device *netdev,
+				 struct ethtool_ringparam *ring,
+				 struct kernel_ethtool_ringparam *kernel_ring,
+				 struct netlink_ext_ack *extack)
+{
+	struct vector_private *vp = netdev_priv(netdev);
+
+	ring->rx_max_pending = vp->rx_queue->max_depth;
+	ring->tx_max_pending = vp->tx_queue->max_depth;
+	ring->rx_pending = vp->rx_queue->max_depth;
+	ring->tx_pending = vp->tx_queue->max_depth;
+}
+
+static void vector_get_strings(struct net_device *dev, u32 stringset, u8 *buf)
+{
+	switch (stringset) {
+	case ETH_SS_TEST:
+		*buf = '\0';
+		break;
+	case ETH_SS_STATS:
+		memcpy(buf, &ethtool_stats_keys, sizeof(ethtool_stats_keys));
+		break;
+	default:
+		WARN_ON(1);
+		break;
+	}
+}
+
+static int vector_get_sset_count(struct net_device *dev, int sset)
+{
+	switch (sset) {
+	case ETH_SS_TEST:
+		return 0;
+	case ETH_SS_STATS:
+		return VECTOR_NUM_STATS;
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static void vector_get_ethtool_stats(struct net_device *dev,
+	struct ethtool_stats *estats,
+	u64 *tmp_stats)
+{
+	struct vector_private *vp = netdev_priv(dev);
+
+	/* Stats are modified in the dequeue portions of
+	 * rx/tx which are protected by the head locks
+	 * grabbing these locks here ensures they are up
+	 * to date.
+	 */
+
+	spin_lock(&vp->tx_queue->head_lock);
+	spin_lock(&vp->rx_queue->head_lock);
+	memcpy(tmp_stats, &vp->estats, sizeof(struct vector_estats));
+	spin_unlock(&vp->rx_queue->head_lock);
+	spin_unlock(&vp->tx_queue->head_lock);
+}
+
+static int vector_get_coalesce(struct net_device *netdev,
+			       struct ethtool_coalesce *ec,
+			       struct kernel_ethtool_coalesce *kernel_coal,
+			       struct netlink_ext_ack *extack)
+{
+	struct vector_private *vp = netdev_priv(netdev);
+
+	ec->tx_coalesce_usecs = (vp->coalesce * 1000000) / HZ;
+	return 0;
+}
+
+static int vector_set_coalesce(struct net_device *netdev,
+			       struct ethtool_coalesce *ec,
+			       struct kernel_ethtool_coalesce *kernel_coal,
+			       struct netlink_ext_ack *extack)
+{
+	struct vector_private *vp = netdev_priv(netdev);
+
+	vp->coalesce = (ec->tx_coalesce_usecs * HZ) / 1000000;
+	if (vp->coalesce == 0)
+		vp->coalesce = 1;
+	return 0;
+}
+
+static const struct ethtool_ops vector_net_ethtool_ops = {
+	.supported_coalesce_params = ETHTOOL_COALESCE_TX_USECS,
+	.get_drvinfo	= vector_net_get_drvinfo,
+	.get_link	= ethtool_op_get_link,
+	.get_ts_info	= ethtool_op_get_ts_info,
+	.get_ringparam	= vector_get_ringparam,
+	.get_strings	= vector_get_strings,
+	.get_sset_count	= vector_get_sset_count,
+	.get_ethtool_stats = vector_get_ethtool_stats,
+	.get_coalesce	= vector_get_coalesce,
+	.set_coalesce	= vector_set_coalesce,
+	.flash_device	= vector_net_load_bpf_flash,
+};
+
+
+static const struct net_device_ops vector_netdev_ops = {
+	.ndo_open		= vector_net_open,
+	.ndo_stop		= vector_net_close,
+	.ndo_start_xmit		= vector_net_start_xmit,
+	.ndo_set_rx_mode	= vector_net_set_multicast_list,
+	.ndo_tx_timeout		= vector_net_tx_timeout,
+	.ndo_set_mac_address	= eth_mac_addr,
+	.ndo_validate_addr	= eth_validate_addr,
+	.ndo_fix_features	= vector_fix_features,
+	.ndo_set_features	= vector_set_features,
+#ifdef CONFIG_NET_POLL_CONTROLLER
+	.ndo_poll_controller = vector_net_poll_controller,
+#endif
+};
+
+static void vector_timer_expire(struct timer_list *t)
+{
+	struct vector_private *vp = timer_container_of(vp, t, tl);
+
+	vp->estats.tx_kicks++;
+	napi_schedule(&vp->napi);
+}
+
+static void vector_setup_etheraddr(struct net_device *dev, char *str)
+{
+	u8 addr[ETH_ALEN];
+
+	if (str == NULL)
+		goto random;
+
+	if (!mac_pton(str, addr)) {
+		netdev_err(dev,
+			"Failed to parse '%s' as an ethernet address\n", str);
+		goto random;
+	}
+	if (is_multicast_ether_addr(addr)) {
+		netdev_err(dev,
+			"Attempt to assign a multicast ethernet address to a device disallowed\n");
+		goto random;
+	}
+	if (!is_valid_ether_addr(addr)) {
+		netdev_err(dev,
+			"Attempt to assign an invalid ethernet address to a device disallowed\n");
+		goto random;
+	}
+	if (!is_local_ether_addr(addr)) {
+		netdev_warn(dev, "Warning: Assigning a globally valid ethernet address to a device\n");
+		netdev_warn(dev, "You should set the 2nd rightmost bit in the first byte of the MAC,\n");
+		netdev_warn(dev, "i.e. %02x:%02x:%02x:%02x:%02x:%02x\n",
+			addr[0] | 0x02, addr[1], addr[2], addr[3], addr[4], addr[5]);
+	}
+	eth_hw_addr_set(dev, addr);
+	return;
+
+random:
+	netdev_info(dev, "Choosing a random ethernet address\n");
+	eth_hw_addr_random(dev);
+}
+
+static void vector_eth_configure(
+		int n,
+		struct arglist *def
+	)
+{
+	struct vector_device *device;
+	struct net_device *dev;
+	struct vector_private *vp;
+	int err;
+
+	device = kzalloc_obj(*device);
+	if (device == NULL) {
+		pr_err("Failed to allocate struct vector_device for vec%d\n", n);
+		return;
+	}
+	dev = alloc_etherdev(sizeof(struct vector_private));
+	if (dev == NULL) {
+		pr_err("Failed to allocate struct net_device for vec%d\n", n);
+		goto out_free_device;
+	}
+
+	dev->mtu = get_mtu(def);
+
+	INIT_LIST_HEAD(&device->list);
+	device->unit = n;
+
+	/* If this name ends up conflicting with an existing registered
+	 * netdevice, that is OK, register_netdev{,ice}() will notice this
+	 * and fail.
+	 */
+	snprintf(dev->name, sizeof(dev->name), "vec%d", n);
+	vector_setup_etheraddr(dev, uml_vector_fetch_arg(def, "mac"));
+	vp = netdev_priv(dev);
+
+	/* sysfs register */
+	if (!driver_registered) {
+		platform_driver_register(&uml_net_driver);
+		driver_registered = 1;
+	}
+	device->pdev.id = n;
+	device->pdev.name = DRIVER_NAME;
+	device->pdev.dev.release = vector_device_release;
+	dev_set_drvdata(&device->pdev.dev, device);
+	if (platform_device_register(&device->pdev))
+		goto out_free_netdev;
+	SET_NETDEV_DEV(dev, &device->pdev.dev);
+
+	device->dev = dev;
+
+	INIT_LIST_HEAD(&vp->list);
+	vp->dev		= dev;
+	vp->unit	= n;
+	vp->options	= get_transport_options(def);
+	vp->parsed	= def;
+	vp->max_packet	= get_mtu(def) + ETH_HEADER_OTHER;
+	/*
+	 * TODO - we need to calculate headroom so that ip header
+	 * is 16 byte aligned all the time
+	 */
+	vp->headroom	= get_headroom(def);
+	vp->coalesce	= 2;
+	vp->req_size	= get_req_size(def);
+
+	dev->features = dev->hw_features = (NETIF_F_SG | NETIF_F_FRAGLIST);
+	INIT_WORK(&vp->reset_tx, vector_reset_tx);
+
+	timer_setup(&vp->tl, vector_timer_expire, 0);
+
+	/* FIXME */
+	dev->netdev_ops = &vector_netdev_ops;
+	dev->ethtool_ops = &vector_net_ethtool_ops;
+	dev->watchdog_timeo = (HZ >> 1);
+	/* primary IRQ - fixme */
+	dev->irq = 0; /* we will adjust this once opened */
+
+	rtnl_lock();
+	err = register_netdevice(dev);
+	rtnl_unlock();
+	if (err)
+		goto out_undo_user_init;
+
+	spin_lock(&vector_devices_lock);
+	list_add(&device->list, &vector_devices);
+	spin_unlock(&vector_devices_lock);
+
+	return;
+
+out_undo_user_init:
+	return;
+out_free_netdev:
+	free_netdev(dev);
+out_free_device:
+	kfree(device);
+}
+
+
+
+
+/*
+ * Invoked late in the init
+ */
+
+static int __init vector_init(void)
+{
+	struct list_head *ele;
+	struct vector_cmd_line_arg *def;
+	struct arglist *parsed;
+
+	list_for_each(ele, &vec_cmd_line) {
+		def = list_entry(ele, struct vector_cmd_line_arg, list);
+		parsed = uml_parse_vector_ifspec(def->arguments);
+		if (parsed != NULL)
+			vector_eth_configure(def->unit, parsed);
+	}
+	return 0;
+}
+
+
+/* Invoked at initial argument parsing, only stores
+ * arguments until a proper vector_init is called
+ * later
+ */
+
+static int __init vector_setup(char *str)
+{
+	char *error;
+	int n, err;
+	struct vector_cmd_line_arg *new;
+
+	err = vector_parse(str, &n, &str, &error);
+	if (err) {
+		pr_err("Couldn't parse '%s': %s\n", str, error);
+		return 1;
+	}
+	new = memblock_alloc_or_panic(sizeof(*new), SMP_CACHE_BYTES);
+	INIT_LIST_HEAD(&new->list);
+	new->unit = n;
+	new->arguments = str;
+	list_add_tail(&new->list, &vec_cmd_line);
+	return 1;
+}
+
+__setup("vec", vector_setup);
+__uml_help(vector_setup,
+"vec[0-9]+:<option>=<value>,<option>=<value>\n"
+"    Configure a vector io network device.\n\n"
+);
+
+late_initcall(vector_init);
+
+static struct mc_device vector_mc = {
+	.list		= LIST_HEAD_INIT(vector_mc.list),
+	.name		= "vec",
+	.config		= vector_config,
+	.get_config	= NULL,
+	.id		= vector_id,
+	.remove		= vector_remove,
+};
+
+#ifdef CONFIG_INET
+static int vector_inetaddr_event(
+	struct notifier_block *this,
+	unsigned long event,
+	void *ptr)
+{
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block vector_inetaddr_notifier = {
+	.notifier_call		= vector_inetaddr_event,
+};
+
+static void inet_register(void)
+{
+	register_inetaddr_notifier(&vector_inetaddr_notifier);
+}
+#else
+static inline void inet_register(void)
+{
+}
+#endif
+
+static int vector_net_init(void)
+{
+	mconsole_register_dev(&vector_mc);
+	inet_register();
+	return 0;
+}
+
+__initcall(vector_net_init);
+
+
+
diff --git a/arch/um/drivers/vector_kern.h b/arch/um/drivers/vector_kern.h
new file mode 100644
index 000000000..417834793
--- /dev/null
+++ b/arch/um/drivers/vector_kern.h
@@ -0,0 +1,139 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2002 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __UM_VECTOR_KERN_H
+#define __UM_VECTOR_KERN_H
+
+#include <linux/netdevice.h>
+#include <linux/platform_device.h>
+#include <linux/skbuff.h>
+#include <linux/socket.h>
+#include <linux/list.h>
+#include <linux/ctype.h>
+#include <linux/workqueue.h>
+#include <linux/interrupt.h>
+#include <asm/atomic.h>
+
+#include "vector_user.h"
+
+/* Queue structure specially adapted for multiple enqueue/dequeue
+ * in a mmsgrecv/mmsgsend context
+ */
+
+/* Dequeue method */
+
+#define QUEUE_SENDMSG 0
+#define QUEUE_SENDMMSG 1
+
+#define VECTOR_RX 1
+#define VECTOR_TX (1 << 1)
+#define VECTOR_BPF (1 << 2)
+#define VECTOR_QDISC_BYPASS (1 << 3)
+#define VECTOR_BPF_FLASH (1 << 4)
+
+#define ETH_MAX_PACKET 1500
+#define ETH_HEADER_OTHER 32 /* just in case someone decides to go mad on QnQ */
+
+#define MAX_FILTER_PROG (2 << 16)
+
+struct vector_queue {
+	struct mmsghdr *mmsg_vector;
+	void **skbuff_vector;
+	 /* backlink to device which owns us */
+	struct net_device *dev;
+	spinlock_t head_lock;
+	spinlock_t tail_lock;
+	atomic_t queue_depth;
+	int head, tail, max_depth, max_iov_frags;
+	short options;
+};
+
+struct vector_estats {
+	uint64_t rx_queue_max;
+	uint64_t rx_queue_running_average;
+	uint64_t tx_queue_max;
+	uint64_t tx_queue_running_average;
+	uint64_t rx_encaps_errors;
+	uint64_t tx_timeout_count;
+	uint64_t tx_restart_queue;
+	uint64_t tx_kicks;
+	uint64_t tx_flow_control_xon;
+	uint64_t tx_flow_control_xoff;
+	uint64_t rx_csum_offload_good;
+	uint64_t rx_csum_offload_errors;
+	uint64_t sg_ok;
+	uint64_t sg_linearized;
+};
+
+#define VERIFY_HEADER_NOK -1
+#define VERIFY_HEADER_OK 0
+#define VERIFY_CSUM_OK 1
+
+struct vector_private {
+	struct list_head list;
+	struct net_device *dev;
+	struct napi_struct		napi	____cacheline_aligned;
+
+	int unit;
+
+	/* Timeout timer in TX */
+
+	struct timer_list tl;
+
+	/* Scheduled "remove device" work */
+	struct work_struct reset_tx;
+	struct vector_fds *fds;
+
+	struct vector_queue *rx_queue;
+	struct vector_queue *tx_queue;
+
+	int rx_irq;
+	int tx_irq;
+
+	struct arglist *parsed;
+
+	void *transport_data; /* transport specific params if needed */
+
+	int max_packet;
+	int req_size; /* different from max packet - used for TSO */
+	int headroom;
+
+	int options;
+
+	/* remote address if any - some transports will leave this as null */
+
+	int header_size;
+	int rx_header_size;
+	int coalesce;
+
+	void *header_rxbuffer;
+	void *header_txbuffer;
+
+	int (*form_header)(uint8_t *header,
+		struct sk_buff *skb, struct vector_private *vp);
+	int (*verify_header)(uint8_t *header,
+		struct sk_buff *skb, struct vector_private *vp);
+
+	spinlock_t stats_lock;
+
+	bool rexmit_scheduled;
+	bool opened;
+	bool in_write_poll;
+	bool in_error;
+
+	/* guest allowed to use ethtool flash to load bpf */
+	bool bpf_via_flash;
+
+	/* ethtool stats */
+
+	struct vector_estats estats;
+	struct sock_fprog *bpf;
+
+	char user[];
+};
+
+extern int build_transport_data(struct vector_private *vp);
+
+#endif
diff --git a/arch/um/drivers/vector_transports.c b/arch/um/drivers/vector_transports.c
new file mode 100644
index 000000000..ddd127ee9
--- /dev/null
+++ b/arch/um/drivers/vector_transports.c
@@ -0,0 +1,494 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2017 - Cambridge Greys Limited
+ * Copyright (C) 2011 - 2014 Cisco Systems Inc
+ */
+
+#include <linux/etherdevice.h>
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+#include <linux/slab.h>
+#include <asm/byteorder.h>
+#include <uapi/linux/ip.h>
+#include <uapi/linux/virtio_net.h>
+#include <linux/virtio_net.h>
+#include <linux/virtio_byteorder.h>
+#include <linux/netdev_features.h>
+#include "vector_user.h"
+#include "vector_kern.h"
+
+#define GOOD_LINEAR 512
+#define GSO_ERROR "Incoming GSO frames and GRO disabled on the interface"
+
+struct gre_minimal_header {
+	uint16_t header;
+	uint16_t arptype;
+};
+
+
+struct uml_gre_data {
+	uint32_t rx_key;
+	uint32_t tx_key;
+	uint32_t sequence;
+
+	bool ipv6;
+	bool has_sequence;
+	bool pin_sequence;
+	bool checksum;
+	bool key;
+	struct gre_minimal_header expected_header;
+
+	uint32_t checksum_offset;
+	uint32_t key_offset;
+	uint32_t sequence_offset;
+
+};
+
+struct uml_l2tpv3_data {
+	uint64_t rx_cookie;
+	uint64_t tx_cookie;
+	uint64_t rx_session;
+	uint64_t tx_session;
+	uint32_t counter;
+
+	bool udp;
+	bool ipv6;
+	bool has_counter;
+	bool pin_counter;
+	bool cookie;
+	bool cookie_is_64;
+
+	uint32_t cookie_offset;
+	uint32_t session_offset;
+	uint32_t counter_offset;
+};
+
+static int l2tpv3_form_header(uint8_t *header,
+	struct sk_buff *skb, struct vector_private *vp)
+{
+	struct uml_l2tpv3_data *td = vp->transport_data;
+	uint32_t *counter;
+
+	if (td->udp)
+		*(uint32_t *) header = cpu_to_be32(L2TPV3_DATA_PACKET);
+	(*(uint32_t *) (header + td->session_offset)) = td->tx_session;
+
+	if (td->cookie) {
+		if (td->cookie_is_64)
+			(*(uint64_t *)(header + td->cookie_offset)) =
+				td->tx_cookie;
+		else
+			(*(uint32_t *)(header + td->cookie_offset)) =
+				td->tx_cookie;
+	}
+	if (td->has_counter) {
+		counter = (uint32_t *)(header + td->counter_offset);
+		if (td->pin_counter) {
+			*counter = 0;
+		} else {
+			td->counter++;
+			*counter = cpu_to_be32(td->counter);
+		}
+	}
+	return 0;
+}
+
+static int gre_form_header(uint8_t *header,
+		struct sk_buff *skb, struct vector_private *vp)
+{
+	struct uml_gre_data *td = vp->transport_data;
+	uint32_t *sequence;
+	*((uint32_t *) header) = *((uint32_t *) &td->expected_header);
+	if (td->key)
+		(*(uint32_t *) (header + td->key_offset)) = td->tx_key;
+	if (td->has_sequence) {
+		sequence = (uint32_t *)(header + td->sequence_offset);
+		if (td->pin_sequence)
+			*sequence = 0;
+		else
+			*sequence = cpu_to_be32(++td->sequence);
+	}
+	return 0;
+}
+
+static int raw_form_header(uint8_t *header,
+		struct sk_buff *skb, struct vector_private *vp)
+{
+	struct virtio_net_hdr *vheader = (struct virtio_net_hdr *) header;
+
+	virtio_net_hdr_from_skb(
+		skb,
+		vheader,
+		virtio_legacy_is_little_endian(),
+		false,
+		0
+	);
+
+	return 0;
+}
+
+static int l2tpv3_verify_header(
+	uint8_t *header, struct sk_buff *skb, struct vector_private *vp)
+{
+	struct uml_l2tpv3_data *td = vp->transport_data;
+	uint32_t *session;
+	uint64_t cookie;
+
+	if ((!td->udp) && (!td->ipv6))
+		header += sizeof(struct iphdr) /* fix for ipv4 raw */;
+
+	/* we do not do a strict check for "data" packets as per
+	 * the RFC spec because the pure IP spec does not have
+	 * that anyway.
+	 */
+
+	if (td->cookie) {
+		if (td->cookie_is_64)
+			cookie = *(uint64_t *)(header + td->cookie_offset);
+		else
+			cookie = *(uint32_t *)(header + td->cookie_offset);
+		if (cookie != td->rx_cookie) {
+			if (net_ratelimit())
+				netdev_err(vp->dev, "uml_l2tpv3: unknown cookie id");
+			return -1;
+		}
+	}
+	session = (uint32_t *) (header + td->session_offset);
+	if (*session != td->rx_session) {
+		if (net_ratelimit())
+			netdev_err(vp->dev, "uml_l2tpv3: session mismatch");
+		return -1;
+	}
+	return 0;
+}
+
+static int gre_verify_header(
+	uint8_t *header, struct sk_buff *skb, struct vector_private *vp)
+{
+
+	uint32_t key;
+	struct uml_gre_data *td = vp->transport_data;
+
+	if (!td->ipv6)
+		header += sizeof(struct iphdr) /* fix for ipv4 raw */;
+
+	if (*((uint32_t *) header) != *((uint32_t *) &td->expected_header)) {
+		if (net_ratelimit())
+			netdev_err(vp->dev, "header type disagreement, expecting %0x, got %0x",
+				*((uint32_t *) &td->expected_header),
+				*((uint32_t *) header)
+			);
+		return -1;
+	}
+
+	if (td->key) {
+		key = (*(uint32_t *)(header + td->key_offset));
+		if (key != td->rx_key) {
+			if (net_ratelimit())
+				netdev_err(vp->dev, "unknown key id %0x, expecting %0x",
+						key, td->rx_key);
+			return -1;
+		}
+	}
+	return 0;
+}
+
+static int raw_verify_header(
+	uint8_t *header, struct sk_buff *skb, struct vector_private *vp)
+{
+	struct virtio_net_hdr *vheader = (struct virtio_net_hdr *) header;
+
+	if ((vheader->gso_type != VIRTIO_NET_HDR_GSO_NONE) &&
+		(vp->req_size != 65536)) {
+		if (net_ratelimit())
+			netdev_err(
+				vp->dev,
+				GSO_ERROR
+		);
+	}
+	if ((vheader->flags & VIRTIO_NET_HDR_F_DATA_VALID) > 0)
+		return 1;
+
+	virtio_net_hdr_to_skb(skb, vheader, virtio_legacy_is_little_endian());
+	return 0;
+}
+
+static bool get_uint_param(
+	struct arglist *def, char *param, unsigned int *result)
+{
+	char *arg = uml_vector_fetch_arg(def, param);
+
+	if (arg != NULL) {
+		if (kstrtoint(arg, 0, result) == 0)
+			return true;
+	}
+	return false;
+}
+
+static bool get_ulong_param(
+	struct arglist *def, char *param, unsigned long *result)
+{
+	char *arg = uml_vector_fetch_arg(def, param);
+
+	if (arg != NULL) {
+		if (kstrtoul(arg, 0, result) == 0)
+			return true;
+		return true;
+	}
+	return false;
+}
+
+static int build_gre_transport_data(struct vector_private *vp)
+{
+	struct uml_gre_data *td;
+	int temp_int;
+	int temp_rx;
+	int temp_tx;
+
+	vp->transport_data = kmalloc_obj(struct uml_gre_data);
+	if (vp->transport_data == NULL)
+		return -ENOMEM;
+	td = vp->transport_data;
+	td->sequence = 0;
+
+	td->expected_header.arptype = GRE_IRB;
+	td->expected_header.header = 0;
+
+	vp->form_header = &gre_form_header;
+	vp->verify_header = &gre_verify_header;
+	vp->header_size = 4;
+	td->key_offset = 4;
+	td->sequence_offset = 4;
+	td->checksum_offset = 4;
+
+	td->ipv6 = false;
+	if (get_uint_param(vp->parsed, "v6", &temp_int)) {
+		if (temp_int > 0)
+			td->ipv6 = true;
+	}
+	td->key = false;
+	if (get_uint_param(vp->parsed, "rx_key", &temp_rx)) {
+		if (get_uint_param(vp->parsed, "tx_key", &temp_tx)) {
+			td->key = true;
+			td->expected_header.header |= GRE_MODE_KEY;
+			td->rx_key = cpu_to_be32(temp_rx);
+			td->tx_key = cpu_to_be32(temp_tx);
+			vp->header_size += 4;
+			td->sequence_offset += 4;
+		} else {
+			return -EINVAL;
+		}
+	}
+
+	td->sequence = false;
+	if (get_uint_param(vp->parsed, "sequence", &temp_int)) {
+		if (temp_int > 0) {
+			vp->header_size += 4;
+			td->has_sequence = true;
+			td->expected_header.header |= GRE_MODE_SEQUENCE;
+			if (get_uint_param(
+				vp->parsed, "pin_sequence", &temp_int)) {
+				if (temp_int > 0)
+					td->pin_sequence = true;
+			}
+		}
+	}
+	vp->rx_header_size = vp->header_size;
+	if (!td->ipv6)
+		vp->rx_header_size += sizeof(struct iphdr);
+	return 0;
+}
+
+static int build_l2tpv3_transport_data(struct vector_private *vp)
+{
+
+	struct uml_l2tpv3_data *td;
+	int temp_int, temp_rxs, temp_txs;
+	unsigned long temp_rx;
+	unsigned long temp_tx;
+
+	vp->transport_data = kmalloc_obj(struct uml_l2tpv3_data);
+
+	if (vp->transport_data == NULL)
+		return -ENOMEM;
+
+	td = vp->transport_data;
+
+	vp->form_header = &l2tpv3_form_header;
+	vp->verify_header = &l2tpv3_verify_header;
+	td->counter = 0;
+
+	vp->header_size = 4;
+	td->session_offset = 0;
+	td->cookie_offset = 4;
+	td->counter_offset = 4;
+
+
+	td->ipv6 = false;
+	if (get_uint_param(vp->parsed, "v6", &temp_int)) {
+		if (temp_int > 0)
+			td->ipv6 = true;
+	}
+
+	if (get_uint_param(vp->parsed, "rx_session", &temp_rxs)) {
+		if (get_uint_param(vp->parsed, "tx_session", &temp_txs)) {
+			td->tx_session = cpu_to_be32(temp_txs);
+			td->rx_session = cpu_to_be32(temp_rxs);
+		} else {
+			return -EINVAL;
+		}
+	} else {
+		return -EINVAL;
+	}
+
+	td->cookie_is_64  = false;
+	if (get_uint_param(vp->parsed, "cookie64", &temp_int)) {
+		if (temp_int > 0)
+			td->cookie_is_64  = true;
+	}
+	td->cookie = false;
+	if (get_ulong_param(vp->parsed, "rx_cookie", &temp_rx)) {
+		if (get_ulong_param(vp->parsed, "tx_cookie", &temp_tx)) {
+			td->cookie = true;
+			if (td->cookie_is_64) {
+				td->rx_cookie = cpu_to_be64(temp_rx);
+				td->tx_cookie = cpu_to_be64(temp_tx);
+				vp->header_size += 8;
+				td->counter_offset += 8;
+			} else {
+				td->rx_cookie = cpu_to_be32(temp_rx);
+				td->tx_cookie = cpu_to_be32(temp_tx);
+				vp->header_size += 4;
+				td->counter_offset += 4;
+			}
+		} else {
+			return -EINVAL;
+		}
+	}
+
+	td->has_counter = false;
+	if (get_uint_param(vp->parsed, "counter", &temp_int)) {
+		if (temp_int > 0) {
+			td->has_counter = true;
+			vp->header_size += 4;
+			if (get_uint_param(
+				vp->parsed, "pin_counter", &temp_int)) {
+				if (temp_int > 0)
+					td->pin_counter = true;
+			}
+		}
+	}
+
+	if (get_uint_param(vp->parsed, "udp", &temp_int)) {
+		if (temp_int > 0) {
+			td->udp = true;
+			vp->header_size += 4;
+			td->counter_offset += 4;
+			td->session_offset += 4;
+			td->cookie_offset += 4;
+		}
+	}
+
+	vp->rx_header_size = vp->header_size;
+	if ((!td->ipv6) && (!td->udp))
+		vp->rx_header_size += sizeof(struct iphdr);
+
+	return 0;
+}
+
+static int build_raw_transport_data(struct vector_private *vp)
+{
+	if (uml_raw_enable_vnet_headers(vp->fds->rx_fd)) {
+		if (!uml_raw_enable_vnet_headers(vp->fds->tx_fd))
+			return -1;
+		vp->form_header = &raw_form_header;
+		vp->verify_header = &raw_verify_header;
+		vp->header_size = sizeof(struct virtio_net_hdr);
+		vp->rx_header_size = sizeof(struct virtio_net_hdr);
+		vp->dev->hw_features |= (NETIF_F_TSO | NETIF_F_GRO);
+		vp->dev->features |=
+			(NETIF_F_RXCSUM | NETIF_F_HW_CSUM |
+				NETIF_F_TSO | NETIF_F_GRO);
+		netdev_info(
+			vp->dev,
+			"raw: using vnet headers for tso and tx/rx checksum"
+		);
+	}
+	return 0;
+}
+
+static int build_hybrid_transport_data(struct vector_private *vp)
+{
+	if (uml_raw_enable_vnet_headers(vp->fds->rx_fd)) {
+		vp->form_header = &raw_form_header;
+		vp->verify_header = &raw_verify_header;
+		vp->header_size = sizeof(struct virtio_net_hdr);
+		vp->rx_header_size = sizeof(struct virtio_net_hdr);
+		vp->dev->hw_features |=
+			(NETIF_F_TSO | NETIF_F_GSO | NETIF_F_GRO);
+		vp->dev->features |=
+			(NETIF_F_RXCSUM | NETIF_F_HW_CSUM |
+				NETIF_F_TSO | NETIF_F_GSO | NETIF_F_GRO);
+		netdev_info(
+			vp->dev,
+			"tap/raw hybrid: using vnet headers for tso and tx/rx checksum"
+		);
+	} else {
+		return 0; /* do not try to enable tap too if raw failed */
+	}
+	if (uml_tap_enable_vnet_headers(vp->fds->tx_fd))
+		return 0;
+	return -1;
+}
+
+static int build_tap_transport_data(struct vector_private *vp)
+{
+	/* "Pure" tap uses the same fd for rx and tx */
+	if (uml_tap_enable_vnet_headers(vp->fds->tx_fd)) {
+		vp->form_header = &raw_form_header;
+		vp->verify_header = &raw_verify_header;
+		vp->header_size = sizeof(struct virtio_net_hdr);
+		vp->rx_header_size = sizeof(struct virtio_net_hdr);
+		vp->dev->hw_features |=
+			(NETIF_F_TSO | NETIF_F_GSO | NETIF_F_GRO);
+		vp->dev->features |=
+			(NETIF_F_RXCSUM | NETIF_F_HW_CSUM |
+				NETIF_F_TSO | NETIF_F_GSO | NETIF_F_GRO);
+		netdev_info(
+			vp->dev,
+			"tap: using vnet headers for tso and tx/rx checksum"
+		);
+		return 0;
+	}
+	return -1;
+}
+
+
+static int build_bess_transport_data(struct vector_private *vp)
+{
+	vp->form_header = NULL;
+	vp->verify_header = NULL;
+	vp->header_size = 0;
+	vp->rx_header_size = 0;
+	return 0;
+}
+
+int build_transport_data(struct vector_private *vp)
+{
+	char *transport = uml_vector_fetch_arg(vp->parsed, "transport");
+
+	if (strncmp(transport, TRANS_GRE, TRANS_GRE_LEN) == 0)
+		return build_gre_transport_data(vp);
+	if (strncmp(transport, TRANS_L2TPV3, TRANS_L2TPV3_LEN) == 0)
+		return build_l2tpv3_transport_data(vp);
+	if (strncmp(transport, TRANS_RAW, TRANS_RAW_LEN) == 0)
+		return build_raw_transport_data(vp);
+	if (strncmp(transport, TRANS_TAP, TRANS_TAP_LEN) == 0)
+		return build_tap_transport_data(vp);
+	if (strncmp(transport, TRANS_HYBRID, TRANS_HYBRID_LEN) == 0)
+		return build_hybrid_transport_data(vp);
+	if (strncmp(transport, TRANS_BESS, TRANS_BESS_LEN) == 0)
+		return build_bess_transport_data(vp);
+	return 0;
+}
+
diff --git a/arch/um/drivers/vector_user.c b/arch/um/drivers/vector_user.c
new file mode 100644
index 000000000..2ea67e6fd
--- /dev/null
+++ b/arch/um/drivers/vector_user.c
@@ -0,0 +1,941 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stdbool.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <stdarg.h>
+#include <errno.h>
+#include <stddef.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <net/if.h>
+#include <linux/if_tun.h>
+#include <arpa/inet.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <netinet/ip.h>
+#include <linux/if_ether.h>
+#include <linux/if_packet.h>
+#include <sys/wait.h>
+#include <sys/uio.h>
+#include <linux/virtio_net.h>
+#include <netdb.h>
+#include <stdlib.h>
+#include <os.h>
+#include <limits.h>
+#include <um_malloc.h>
+#include "vector_user.h"
+
+#define ID_GRE 0
+#define ID_L2TPV3 1
+#define ID_BESS 2
+#define ID_MAX 2
+
+#define TOKEN_IFNAME "ifname"
+#define TOKEN_SCRIPT "ifup"
+
+#define TRANS_RAW "raw"
+#define TRANS_RAW_LEN strlen(TRANS_RAW)
+
+#define TRANS_FD "fd"
+#define TRANS_FD_LEN strlen(TRANS_FD)
+
+#define TRANS_VDE "vde"
+#define TRANS_VDE_LEN strlen(TRANS_VDE)
+
+#define VNET_HDR_FAIL "could not enable vnet headers on fd %d"
+#define TUN_GET_F_FAIL "tapraw: TUNGETFEATURES failed: %s"
+#define L2TPV3_BIND_FAIL "l2tpv3_open : could not bind socket err=%i"
+#define UNIX_BIND_FAIL "unix_open : could not bind socket err=%i"
+#define BPF_ATTACH_FAIL "Failed to attach filter size %d prog %px to %d, err %d\n"
+#define BPF_DETACH_FAIL "Failed to detach filter size %d prog %px to %d, err %d\n"
+
+#define MAX_UN_LEN 107
+
+static const char padchar[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+static const char *template = "tapXXXXXX";
+
+/* This is very ugly and brute force lookup, but it is done
+ * only once at initialization so not worth doing hashes or
+ * anything more intelligent
+ */
+
+char *uml_vector_fetch_arg(struct arglist *ifspec, char *token)
+{
+	int i;
+
+	for (i = 0; i < ifspec->numargs; i++) {
+		if (strcmp(ifspec->tokens[i], token) == 0)
+			return ifspec->values[i];
+	}
+	return NULL;
+
+}
+
+struct arglist *uml_parse_vector_ifspec(char *arg)
+{
+	struct arglist *result;
+	int pos, len;
+	bool parsing_token = true, next_starts = true;
+
+	if (arg == NULL)
+		return NULL;
+	result = uml_kmalloc(sizeof(struct arglist), UM_GFP_KERNEL);
+	if (result == NULL)
+		return NULL;
+	result->numargs = 0;
+	len = strlen(arg);
+	for (pos = 0; pos < len; pos++) {
+		if (next_starts) {
+			if (parsing_token) {
+				result->tokens[result->numargs] = arg + pos;
+			} else {
+				result->values[result->numargs] = arg + pos;
+				result->numargs++;
+			}
+			next_starts = false;
+		}
+		if (*(arg + pos) == '=') {
+			if (parsing_token)
+				parsing_token = false;
+			else
+				goto cleanup;
+			next_starts = true;
+			(*(arg + pos)) = '\0';
+		}
+		if (*(arg + pos) == ',') {
+			parsing_token = true;
+			next_starts = true;
+			(*(arg + pos)) = '\0';
+		}
+	}
+	return result;
+cleanup:
+	printk(UM_KERN_ERR "vector_setup - Couldn't parse '%s'\n", arg);
+	kfree(result);
+	return NULL;
+}
+
+/*
+ * Socket/FD configuration functions. These return an structure
+ * of rx and tx descriptors to cover cases where these are not
+ * the same (f.e. read via raw socket and write via tap).
+ */
+
+#define PATH_NET_TUN "/dev/net/tun"
+
+
+static int create_tap_fd(char *iface)
+{
+	struct ifreq ifr;
+	int fd = -1;
+	int err = -ENOMEM, offload;
+
+	fd = open(PATH_NET_TUN, O_RDWR);
+	if (fd < 0) {
+		printk(UM_KERN_ERR "uml_tap: failed to open tun device\n");
+		goto tap_fd_cleanup;
+	}
+	memset(&ifr, 0, sizeof(ifr));
+	ifr.ifr_flags = IFF_TAP | IFF_NO_PI | IFF_VNET_HDR;
+	strscpy(ifr.ifr_name, iface);
+
+	err = ioctl(fd, TUNSETIFF, (void *) &ifr);
+	if (err != 0) {
+		printk(UM_KERN_ERR "uml_tap: failed to select tap interface\n");
+		goto tap_fd_cleanup;
+	}
+
+	offload = TUN_F_CSUM | TUN_F_TSO4 | TUN_F_TSO6;
+	ioctl(fd, TUNSETOFFLOAD, offload);
+	return fd;
+tap_fd_cleanup:
+	if (fd >= 0)
+		os_close_file(fd);
+	return err;
+}
+
+static int create_raw_fd(char *iface, int flags, int proto)
+{
+	struct ifreq ifr;
+	int fd = -1;
+	struct sockaddr_ll sock;
+	int err = -ENOMEM;
+
+	fd = socket(AF_PACKET, SOCK_RAW, flags);
+	if (fd == -1) {
+		err = -errno;
+		goto raw_fd_cleanup;
+	}
+	memset(&ifr, 0, sizeof(ifr));
+	strscpy(ifr.ifr_name, iface);
+	if (ioctl(fd, SIOCGIFINDEX, (void *) &ifr) < 0) {
+		err = -errno;
+		goto raw_fd_cleanup;
+	}
+
+	sock.sll_family = AF_PACKET;
+	sock.sll_protocol = htons(proto);
+	sock.sll_ifindex = ifr.ifr_ifindex;
+
+	if (bind(fd,
+		(struct sockaddr *) &sock, sizeof(struct sockaddr_ll)) < 0) {
+		err = -errno;
+		goto raw_fd_cleanup;
+	}
+	return fd;
+raw_fd_cleanup:
+	printk(UM_KERN_ERR "user_init_raw: init failed, error %d", err);
+	if (fd >= 0)
+		os_close_file(fd);
+	return err;
+}
+
+
+static struct vector_fds *user_init_tap_fds(struct arglist *ifspec)
+{
+	int fd = -1, i;
+	char *iface;
+	struct vector_fds *result = NULL;
+	bool dynamic = false;
+	char dynamic_ifname[IFNAMSIZ];
+	char *argv[] = {NULL, NULL, NULL, NULL};
+
+	iface = uml_vector_fetch_arg(ifspec, TOKEN_IFNAME);
+	if (iface == NULL) {
+		dynamic = true;
+		iface = dynamic_ifname;
+		srand(getpid());
+	}
+
+	result = uml_kmalloc(sizeof(struct vector_fds), UM_GFP_KERNEL);
+	if (result == NULL) {
+		printk(UM_KERN_ERR "uml_tap: failed to allocate file descriptors\n");
+		goto tap_cleanup;
+	}
+	result->rx_fd = -1;
+	result->tx_fd = -1;
+	result->remote_addr = NULL;
+	result->remote_addr_size = 0;
+
+	/* TAP */
+	do {
+		if (dynamic) {
+			strcpy(iface, template);
+			for (i = 0; i < strlen(iface); i++) {
+				if (iface[i] == 'X') {
+					iface[i] = padchar[rand() % strlen(padchar)];
+				}
+			}
+		}
+		fd = create_tap_fd(iface);
+		if ((fd < 0) && (!dynamic)) {
+			printk(UM_KERN_ERR "uml_tap: failed to create tun interface\n");
+			goto tap_cleanup;
+		}
+		result->tx_fd = fd;
+		result->rx_fd = fd;
+	} while (fd < 0);
+
+	argv[0] = uml_vector_fetch_arg(ifspec, TOKEN_SCRIPT);
+	if (argv[0]) {
+		argv[1] = iface;
+		run_helper(NULL, NULL, argv);
+	}
+
+	return result;
+tap_cleanup:
+	printk(UM_KERN_ERR "user_init_tap: init failed, error %d", fd);
+	kfree(result);
+	return NULL;
+}
+
+static struct vector_fds *user_init_hybrid_fds(struct arglist *ifspec)
+{
+	char *iface;
+	struct vector_fds *result = NULL;
+	char *argv[] = {NULL, NULL, NULL, NULL};
+
+	iface = uml_vector_fetch_arg(ifspec, TOKEN_IFNAME);
+	if (iface == NULL) {
+		printk(UM_KERN_ERR "uml_tap: failed to parse interface spec\n");
+		goto hybrid_cleanup;
+	}
+
+	result = uml_kmalloc(sizeof(struct vector_fds), UM_GFP_KERNEL);
+	if (result == NULL) {
+		printk(UM_KERN_ERR "uml_tap: failed to allocate file descriptors\n");
+		goto hybrid_cleanup;
+	}
+	result->rx_fd = -1;
+	result->tx_fd = -1;
+	result->remote_addr = NULL;
+	result->remote_addr_size = 0;
+
+	/* TAP */
+
+	result->tx_fd = create_tap_fd(iface);
+	if (result->tx_fd < 0) {
+		printk(UM_KERN_ERR "uml_tap: failed to create tun interface: %i\n", result->tx_fd);
+		goto hybrid_cleanup;
+	}
+
+	/* RAW */
+
+	result->rx_fd = create_raw_fd(iface, ETH_P_ALL, ETH_P_ALL);
+	if (result->rx_fd == -1) {
+		printk(UM_KERN_ERR
+			"uml_tap: failed to create paired raw socket: %i\n", result->rx_fd);
+		goto hybrid_cleanup;
+	}
+
+	argv[0] = uml_vector_fetch_arg(ifspec, TOKEN_SCRIPT);
+	if (argv[0]) {
+		argv[1] = iface;
+		run_helper(NULL, NULL, argv);
+	}
+	return result;
+hybrid_cleanup:
+	printk(UM_KERN_ERR "user_init_hybrid: init failed");
+	kfree(result);
+	return NULL;
+}
+
+static struct vector_fds *user_init_unix_fds(struct arglist *ifspec, int id)
+{
+	int fd = -1;
+	int socktype;
+	char *src, *dst;
+	struct vector_fds *result = NULL;
+	struct sockaddr_un *local_addr = NULL, *remote_addr = NULL;
+
+	src = uml_vector_fetch_arg(ifspec, "src");
+	dst = uml_vector_fetch_arg(ifspec, "dst");
+	result = uml_kmalloc(sizeof(struct vector_fds), UM_GFP_KERNEL);
+	if (result == NULL) {
+		printk(UM_KERN_ERR "unix open:cannot allocate remote addr");
+		goto unix_cleanup;
+	}
+	remote_addr = uml_kmalloc(sizeof(struct sockaddr_un), UM_GFP_KERNEL);
+	if (remote_addr == NULL) {
+		printk(UM_KERN_ERR "unix open:cannot allocate remote addr");
+		goto unix_cleanup;
+	}
+
+	switch (id) {
+	case ID_BESS:
+		socktype = SOCK_SEQPACKET;
+		if ((src != NULL) && (strlen(src) <= MAX_UN_LEN)) {
+			local_addr = uml_kmalloc(sizeof(struct sockaddr_un), UM_GFP_KERNEL);
+			if (local_addr == NULL) {
+				printk(UM_KERN_ERR "bess open:cannot allocate local addr");
+				goto unix_cleanup;
+			}
+			local_addr->sun_family = AF_UNIX;
+			memcpy(local_addr->sun_path, src, strlen(src) + 1);
+		}
+		if ((dst == NULL) || (strlen(dst) > MAX_UN_LEN))
+			goto unix_cleanup;
+		remote_addr->sun_family = AF_UNIX;
+		memcpy(remote_addr->sun_path, dst, strlen(dst) + 1);
+		break;
+	default:
+		printk(KERN_ERR "Unsupported unix socket type\n");
+		return NULL;
+	}
+
+	fd = socket(AF_UNIX, socktype, 0);
+	if (fd == -1) {
+		printk(UM_KERN_ERR
+			"unix open: could not open socket, error = %d",
+			-errno
+		);
+		goto unix_cleanup;
+	}
+	if (local_addr != NULL) {
+		if (bind(fd, (struct sockaddr *) local_addr, sizeof(struct sockaddr_un))) {
+			printk(UM_KERN_ERR UNIX_BIND_FAIL, errno);
+			goto unix_cleanup;
+		}
+	}
+	switch (id) {
+	case ID_BESS:
+		if (connect(fd, (const struct sockaddr *) remote_addr, sizeof(struct sockaddr_un)) < 0) {
+			printk(UM_KERN_ERR "bess open:cannot connect to %s %i", remote_addr->sun_path, -errno);
+			goto unix_cleanup;
+		}
+		break;
+	}
+	result->rx_fd = fd;
+	result->tx_fd = fd;
+	result->remote_addr_size = sizeof(struct sockaddr_un);
+	result->remote_addr = remote_addr;
+	return result;
+unix_cleanup:
+	if (fd >= 0)
+		os_close_file(fd);
+	kfree(remote_addr);
+	kfree(result);
+	return NULL;
+}
+
+static int strtofd(const char *nptr)
+{
+	long fd;
+	char *endptr;
+
+	if (nptr == NULL)
+		return -1;
+
+	errno = 0;
+	fd = strtol(nptr, &endptr, 10);
+	if (nptr == endptr ||
+		errno != 0 ||
+		*endptr != '\0' ||
+		fd < 0 ||
+		fd > INT_MAX) {
+		return -1;
+	}
+	return fd;
+}
+
+static struct vector_fds *user_init_fd_fds(struct arglist *ifspec)
+{
+	int fd = -1;
+	char *fdarg = NULL;
+	struct vector_fds *result = NULL;
+
+	fdarg = uml_vector_fetch_arg(ifspec, "fd");
+	fd = strtofd(fdarg);
+	if (fd == -1) {
+		printk(UM_KERN_ERR "fd open: bad or missing fd argument");
+		goto fd_cleanup;
+	}
+
+	result = uml_kmalloc(sizeof(struct vector_fds), UM_GFP_KERNEL);
+	if (result == NULL) {
+		printk(UM_KERN_ERR "fd open: allocation failed");
+		goto fd_cleanup;
+	}
+
+	result->rx_fd = fd;
+	result->tx_fd = fd;
+	result->remote_addr_size = 0;
+	result->remote_addr = NULL;
+	return result;
+
+fd_cleanup:
+	if (fd >= 0)
+		os_close_file(fd);
+	kfree(result);
+	return NULL;
+}
+
+/* enough char to store an int type */
+#define ENOUGH(type) ((CHAR_BIT * sizeof(type) - 1) / 3 + 2)
+#define ENOUGH_OCTAL(type) ((CHAR_BIT * sizeof(type) + 2) / 3)
+/* vde_plug --descr xx --port2 xx --mod2 xx --group2 xx seqpacket://NN vnl (NULL) */
+#define VDE_MAX_ARGC 12
+#define VDE_SEQPACKET_HEAD "seqpacket://"
+#define VDE_SEQPACKET_HEAD_LEN (sizeof(VDE_SEQPACKET_HEAD) - 1)
+#define VDE_DEFAULT_DESCRIPTION "UML"
+
+static struct vector_fds *user_init_vde_fds(struct arglist *ifspec)
+{
+	char seqpacketvnl[VDE_SEQPACKET_HEAD_LEN + ENOUGH(int) + 1];
+	char *argv[VDE_MAX_ARGC] = {"vde_plug"};
+	int argc = 1;
+	int rv;
+	int sv[2];
+	struct vector_fds *result = NULL;
+
+	char *vnl = uml_vector_fetch_arg(ifspec,"vnl");
+	char *descr = uml_vector_fetch_arg(ifspec,"descr");
+	char *port = uml_vector_fetch_arg(ifspec,"port");
+	char *mode = uml_vector_fetch_arg(ifspec,"mode");
+	char *group = uml_vector_fetch_arg(ifspec,"group");
+	if (descr == NULL) descr = VDE_DEFAULT_DESCRIPTION;
+
+	argv[argc++] = "--descr";
+	argv[argc++] = descr;
+	if (port != NULL) {
+		argv[argc++] = "--port2";
+		argv[argc++] = port;
+	}
+	if (mode != NULL) {
+		argv[argc++] = "--mod2";
+		argv[argc++] = mode;
+	}
+	if (group != NULL) {
+		argv[argc++] = "--group2";
+		argv[argc++] = group;
+	}
+	argv[argc++] = seqpacketvnl;
+	argv[argc++] = vnl;
+	argv[argc++] = NULL;
+
+	rv = socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sv);
+	if (rv  < 0) {
+		printk(UM_KERN_ERR "vde: seqpacket socketpair err %d", -errno);
+		return NULL;
+	}
+	rv = os_set_exec_close(sv[0]);
+	if (rv  < 0) {
+		printk(UM_KERN_ERR "vde: seqpacket socketpair cloexec err %d", -errno);
+		goto vde_cleanup_sv;
+	}
+	snprintf(seqpacketvnl, sizeof(seqpacketvnl), VDE_SEQPACKET_HEAD "%d", sv[1]);
+
+	run_helper(NULL, NULL, argv);
+
+	close(sv[1]);
+
+	result = uml_kmalloc(sizeof(struct vector_fds), UM_GFP_KERNEL);
+	if (result == NULL) {
+		printk(UM_KERN_ERR "fd open: allocation failed");
+		goto vde_cleanup;
+	}
+
+	result->rx_fd = sv[0];
+	result->tx_fd = sv[0];
+	result->remote_addr_size = 0;
+	result->remote_addr = NULL;
+	return result;
+
+vde_cleanup_sv:
+	close(sv[1]);
+vde_cleanup:
+	close(sv[0]);
+	return NULL;
+}
+
+static struct vector_fds *user_init_raw_fds(struct arglist *ifspec)
+{
+	int rxfd = -1, txfd = -1;
+	int err = -ENOMEM;
+	char *iface;
+	struct vector_fds *result = NULL;
+	char *argv[] = {NULL, NULL, NULL, NULL};
+
+	iface = uml_vector_fetch_arg(ifspec, TOKEN_IFNAME);
+	if (iface == NULL)
+		goto raw_cleanup;
+
+	rxfd = create_raw_fd(iface, ETH_P_ALL, ETH_P_ALL);
+	if (rxfd == -1) {
+		err = -errno;
+		goto raw_cleanup;
+	}
+	txfd = create_raw_fd(iface, 0, ETH_P_IP); /* Turn off RX on this fd */
+	if (txfd == -1) {
+		err = -errno;
+		goto raw_cleanup;
+	}
+	result = uml_kmalloc(sizeof(struct vector_fds), UM_GFP_KERNEL);
+	if (result != NULL) {
+		result->rx_fd = rxfd;
+		result->tx_fd = txfd;
+		result->remote_addr = NULL;
+		result->remote_addr_size = 0;
+	}
+	argv[0] = uml_vector_fetch_arg(ifspec, TOKEN_SCRIPT);
+	if (argv[0]) {
+		argv[1] = iface;
+		run_helper(NULL, NULL, argv);
+	}
+	return result;
+raw_cleanup:
+	printk(UM_KERN_ERR "user_init_raw: init failed, error %d", err);
+	kfree(result);
+	return NULL;
+}
+
+
+bool uml_raw_enable_qdisc_bypass(int fd)
+{
+	int optval = 1;
+
+	if (setsockopt(fd,
+		SOL_PACKET, PACKET_QDISC_BYPASS,
+		&optval, sizeof(optval)) != 0) {
+		return false;
+	}
+	return true;
+}
+
+bool uml_raw_enable_vnet_headers(int fd)
+{
+	int optval = 1;
+
+	if (setsockopt(fd,
+		SOL_PACKET, PACKET_VNET_HDR,
+		&optval, sizeof(optval)) != 0) {
+		printk(UM_KERN_INFO VNET_HDR_FAIL, fd);
+		return false;
+	}
+	return true;
+}
+bool uml_tap_enable_vnet_headers(int fd)
+{
+	unsigned int features;
+	int len = sizeof(struct virtio_net_hdr);
+
+	if (ioctl(fd, TUNGETFEATURES, &features) == -1) {
+		printk(UM_KERN_INFO TUN_GET_F_FAIL, strerror(errno));
+		return false;
+	}
+	if ((features & IFF_VNET_HDR) == 0) {
+		printk(UM_KERN_INFO "tapraw: No VNET HEADER support");
+		return false;
+	}
+	ioctl(fd, TUNSETVNETHDRSZ, &len);
+	return true;
+}
+
+static struct vector_fds *user_init_socket_fds(struct arglist *ifspec, int id)
+{
+	int err = -ENOMEM;
+	int fd = -1, gairet;
+	struct addrinfo srchints;
+	struct addrinfo dsthints;
+	bool v6, udp;
+	char *value;
+	char *src, *dst, *srcport, *dstport;
+	struct addrinfo *gairesult = NULL;
+	struct vector_fds *result = NULL;
+
+
+	value = uml_vector_fetch_arg(ifspec, "v6");
+	v6 = false;
+	udp = false;
+	if (value != NULL) {
+		if (strtol((const char *) value, NULL, 10) > 0)
+			v6 = true;
+	}
+
+	value = uml_vector_fetch_arg(ifspec, "udp");
+	if (value != NULL) {
+		if (strtol((const char *) value, NULL, 10) > 0)
+			udp = true;
+	}
+	src = uml_vector_fetch_arg(ifspec, "src");
+	dst = uml_vector_fetch_arg(ifspec, "dst");
+	srcport = uml_vector_fetch_arg(ifspec, "srcport");
+	dstport = uml_vector_fetch_arg(ifspec, "dstport");
+
+	memset(&dsthints, 0, sizeof(dsthints));
+
+	if (v6)
+		dsthints.ai_family = AF_INET6;
+	else
+		dsthints.ai_family = AF_INET;
+
+	switch (id) {
+	case ID_GRE:
+		dsthints.ai_socktype = SOCK_RAW;
+		dsthints.ai_protocol = IPPROTO_GRE;
+		break;
+	case ID_L2TPV3:
+		if (udp) {
+			dsthints.ai_socktype = SOCK_DGRAM;
+			dsthints.ai_protocol = 0;
+		} else {
+			dsthints.ai_socktype = SOCK_RAW;
+			dsthints.ai_protocol = IPPROTO_L2TP;
+		}
+		break;
+	default:
+		printk(KERN_ERR "Unsupported socket type\n");
+		return NULL;
+	}
+	memcpy(&srchints, &dsthints, sizeof(struct addrinfo));
+
+	gairet = getaddrinfo(src, srcport, &dsthints, &gairesult);
+	if ((gairet != 0) || (gairesult == NULL)) {
+		printk(UM_KERN_ERR
+			"socket_open : could not resolve src, error = %s",
+			gai_strerror(gairet)
+		);
+		return NULL;
+	}
+	fd = socket(gairesult->ai_family,
+		gairesult->ai_socktype, gairesult->ai_protocol);
+	if (fd == -1) {
+		printk(UM_KERN_ERR
+			"socket_open : could not open socket, error = %d",
+			-errno
+		);
+		goto cleanup;
+	}
+	if (bind(fd,
+		(struct sockaddr *) gairesult->ai_addr,
+		gairesult->ai_addrlen)) {
+		printk(UM_KERN_ERR L2TPV3_BIND_FAIL, errno);
+		goto cleanup;
+	}
+
+	if (gairesult != NULL)
+		freeaddrinfo(gairesult);
+
+	gairesult = NULL;
+
+	gairet = getaddrinfo(dst, dstport, &dsthints, &gairesult);
+	if ((gairet != 0) || (gairesult == NULL)) {
+		printk(UM_KERN_ERR
+			"socket_open : could not resolve dst, error = %s",
+			gai_strerror(gairet)
+		);
+		return NULL;
+	}
+
+	result = uml_kmalloc(sizeof(struct vector_fds), UM_GFP_KERNEL);
+	if (result != NULL) {
+		result->rx_fd = fd;
+		result->tx_fd = fd;
+		result->remote_addr = uml_kmalloc(
+			gairesult->ai_addrlen, UM_GFP_KERNEL);
+		if (result->remote_addr == NULL)
+			goto cleanup;
+		result->remote_addr_size = gairesult->ai_addrlen;
+		memcpy(
+			result->remote_addr,
+			gairesult->ai_addr,
+			gairesult->ai_addrlen
+		);
+	}
+	freeaddrinfo(gairesult);
+	return result;
+cleanup:
+	if (gairesult != NULL)
+		freeaddrinfo(gairesult);
+	printk(UM_KERN_ERR "user_init_socket: init failed, error %d", err);
+	if (fd >= 0)
+		os_close_file(fd);
+	if (result != NULL) {
+		kfree(result->remote_addr);
+		kfree(result);
+	}
+	return NULL;
+}
+
+struct vector_fds *uml_vector_user_open(
+	int unit,
+	struct arglist *parsed
+)
+{
+	char *transport;
+
+	if (parsed == NULL) {
+		printk(UM_KERN_ERR "no parsed config for unit %d\n", unit);
+		return NULL;
+	}
+	transport = uml_vector_fetch_arg(parsed, "transport");
+	if (transport == NULL) {
+		printk(UM_KERN_ERR "missing transport for unit %d\n", unit);
+		return NULL;
+	}
+	if (strncmp(transport, TRANS_RAW, TRANS_RAW_LEN) == 0)
+		return user_init_raw_fds(parsed);
+	if (strncmp(transport, TRANS_HYBRID, TRANS_HYBRID_LEN) == 0)
+		return user_init_hybrid_fds(parsed);
+	if (strncmp(transport, TRANS_TAP, TRANS_TAP_LEN) == 0)
+		return user_init_tap_fds(parsed);
+	if (strncmp(transport, TRANS_GRE, TRANS_GRE_LEN) == 0)
+		return user_init_socket_fds(parsed, ID_GRE);
+	if (strncmp(transport, TRANS_L2TPV3, TRANS_L2TPV3_LEN) == 0)
+		return user_init_socket_fds(parsed, ID_L2TPV3);
+	if (strncmp(transport, TRANS_BESS, TRANS_BESS_LEN) == 0)
+		return user_init_unix_fds(parsed, ID_BESS);
+	if (strncmp(transport, TRANS_FD, TRANS_FD_LEN) == 0)
+		return user_init_fd_fds(parsed);
+	if (strncmp(transport, TRANS_VDE, TRANS_VDE_LEN) == 0)
+		return user_init_vde_fds(parsed);
+	return NULL;
+}
+
+
+int uml_vector_sendmsg(int fd, void *hdr, int flags)
+{
+	int n;
+
+	CATCH_EINTR(n = sendmsg(fd, (struct msghdr *) hdr,  flags));
+	if ((n < 0) && (errno == EAGAIN))
+		return 0;
+	if (n >= 0)
+		return n;
+	else
+		return -errno;
+}
+
+int uml_vector_recvmsg(int fd, void *hdr, int flags)
+{
+	int n;
+	struct msghdr *msg = (struct msghdr *) hdr;
+
+	CATCH_EINTR(n = readv(fd, msg->msg_iov, msg->msg_iovlen));
+	if ((n < 0) && (errno == EAGAIN))
+		return 0;
+	if (n >= 0)
+		return n;
+	else
+		return -errno;
+}
+
+int uml_vector_writev(int fd, void *hdr, int iovcount)
+{
+	int n;
+
+	CATCH_EINTR(n = writev(fd, (struct iovec *) hdr,  iovcount));
+	if ((n < 0) && ((errno == EAGAIN) || (errno == ENOBUFS)))
+		return 0;
+	if (n >= 0)
+		return n;
+	else
+		return -errno;
+}
+
+int uml_vector_sendmmsg(
+	int fd,
+	void *msgvec,
+	unsigned int vlen,
+	unsigned int flags)
+{
+	int n;
+
+	CATCH_EINTR(n = sendmmsg(fd, (struct mmsghdr *) msgvec, vlen, flags));
+	if ((n < 0) && ((errno == EAGAIN) || (errno == ENOBUFS)))
+		return 0;
+	if (n >= 0)
+		return n;
+	else
+		return -errno;
+}
+
+int uml_vector_recvmmsg(
+	int fd,
+	void *msgvec,
+	unsigned int vlen,
+	unsigned int flags)
+{
+	int n;
+
+	CATCH_EINTR(
+		n = recvmmsg(fd, (struct mmsghdr *) msgvec, vlen, flags, 0));
+	if ((n < 0) && (errno == EAGAIN))
+		return 0;
+	if (n >= 0)
+		return n;
+	else
+		return -errno;
+}
+int uml_vector_attach_bpf(int fd, void *bpf)
+{
+	struct sock_fprog *prog = bpf;
+
+	int err = setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, bpf, sizeof(struct sock_fprog));
+
+	if (err < 0)
+		printk(KERN_ERR BPF_ATTACH_FAIL, prog->len, prog->filter, fd, -errno);
+	return err;
+}
+
+int uml_vector_detach_bpf(int fd, void *bpf)
+{
+	struct sock_fprog *prog = bpf;
+
+	int err = setsockopt(fd, SOL_SOCKET, SO_DETACH_FILTER, bpf, sizeof(struct sock_fprog));
+	if (err < 0)
+		printk(KERN_ERR BPF_DETACH_FAIL, prog->len, prog->filter, fd, -errno);
+	return err;
+}
+void *uml_vector_default_bpf(const void *mac)
+{
+	struct sock_filter *bpf;
+	uint32_t *mac1 = (uint32_t *)(mac + 2);
+	uint16_t *mac2 = (uint16_t *) mac;
+	struct sock_fprog *bpf_prog;
+
+	bpf_prog = uml_kmalloc(sizeof(struct sock_fprog), UM_GFP_KERNEL);
+	if (bpf_prog) {
+		bpf_prog->len = DEFAULT_BPF_LEN;
+		bpf_prog->filter = NULL;
+	} else {
+		return NULL;
+	}
+	bpf = uml_kmalloc(
+		sizeof(struct sock_filter) * DEFAULT_BPF_LEN, UM_GFP_KERNEL);
+	if (bpf) {
+		bpf_prog->filter = bpf;
+		/* ld	[8] */
+		bpf[0] = (struct sock_filter){ 0x20, 0, 0, 0x00000008 };
+		/* jeq	#0xMAC[2-6] jt 2 jf 5*/
+		bpf[1] = (struct sock_filter){ 0x15, 0, 3, ntohl(*mac1)};
+		/* ldh	[6] */
+		bpf[2] = (struct sock_filter){ 0x28, 0, 0, 0x00000006 };
+		/* jeq	#0xMAC[0-1] jt 4 jf 5 */
+		bpf[3] = (struct sock_filter){ 0x15, 0, 1, ntohs(*mac2)};
+		/* ret	#0 */
+		bpf[4] = (struct sock_filter){ 0x6, 0, 0, 0x00000000 };
+		/* ret	#0x40000 */
+		bpf[5] = (struct sock_filter){ 0x6, 0, 0, 0x00040000 };
+	} else {
+		kfree(bpf_prog);
+		bpf_prog = NULL;
+	}
+	return bpf_prog;
+}
+
+/* Note - this function requires a valid mac being passed as an arg */
+
+void *uml_vector_user_bpf(char *filename)
+{
+	struct sock_filter *bpf;
+	struct sock_fprog *bpf_prog;
+	struct stat statbuf;
+	int res, ffd = -1;
+
+	if (filename == NULL)
+		return NULL;
+
+	if (stat(filename, &statbuf) < 0) {
+		printk(KERN_ERR "Error %d reading bpf file", -errno);
+		return false;
+	}
+	bpf_prog = uml_kmalloc(sizeof(struct sock_fprog), UM_GFP_KERNEL);
+	if (bpf_prog == NULL) {
+		printk(KERN_ERR "Failed to allocate bpf prog buffer");
+		return NULL;
+	}
+	bpf_prog->len = statbuf.st_size / sizeof(struct sock_filter);
+	bpf_prog->filter = NULL;
+	ffd = os_open_file(filename, of_read(OPENFLAGS()), 0);
+	if (ffd < 0) {
+		printk(KERN_ERR "Error %d opening bpf file", -errno);
+		goto bpf_failed;
+	}
+	bpf = uml_kmalloc(statbuf.st_size, UM_GFP_KERNEL);
+	if (bpf == NULL) {
+		printk(KERN_ERR "Failed to allocate bpf buffer");
+		goto bpf_failed;
+	}
+	bpf_prog->filter = bpf;
+	res = os_read_file(ffd, bpf, statbuf.st_size);
+	if (res < statbuf.st_size) {
+		printk(KERN_ERR "Failed to read bpf program %s, error %d", filename, res);
+		kfree(bpf);
+		goto bpf_failed;
+	}
+	os_close_file(ffd);
+	return bpf_prog;
+bpf_failed:
+	if (ffd > 0)
+		os_close_file(ffd);
+	kfree(bpf_prog);
+	return NULL;
+}
diff --git a/arch/um/drivers/vector_user.h b/arch/um/drivers/vector_user.h
new file mode 100644
index 000000000..59ed5f9e6
--- /dev/null
+++ b/arch/um/drivers/vector_user.h
@@ -0,0 +1,107 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2002 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __UM_VECTOR_USER_H
+#define __UM_VECTOR_USER_H
+
+#define MAXVARGS	20
+
+#define TOKEN_IFNAME "ifname"
+
+#define TRANS_RAW "raw"
+#define TRANS_RAW_LEN strlen(TRANS_RAW)
+
+#define TRANS_TAP "tap"
+#define TRANS_TAP_LEN strlen(TRANS_TAP)
+
+#define TRANS_GRE "gre"
+#define TRANS_GRE_LEN strlen(TRANS_GRE)
+
+#define TRANS_L2TPV3 "l2tpv3"
+#define TRANS_L2TPV3_LEN strlen(TRANS_L2TPV3)
+
+#define TRANS_HYBRID "hybrid"
+#define TRANS_HYBRID_LEN strlen(TRANS_HYBRID)
+
+#define TRANS_BESS "bess"
+#define TRANS_BESS_LEN strlen(TRANS_BESS)
+
+#define DEFAULT_BPF_LEN 6
+
+#ifndef IPPROTO_GRE
+#define IPPROTO_GRE 0x2F
+#endif
+
+#define GRE_MODE_CHECKSUM	cpu_to_be16(8 << 12)	/* checksum */
+#define GRE_MODE_RESERVED	cpu_to_be16(4 << 12)	/* unused */
+#define GRE_MODE_KEY		cpu_to_be16(2 << 12)	/* KEY present */
+#define GRE_MODE_SEQUENCE	cpu_to_be16(1 << 12)	/* sequence */
+
+#define GRE_IRB cpu_to_be16(0x6558)
+
+#define L2TPV3_DATA_PACKET 0x30000
+
+/* IANA-assigned IP protocol ID for L2TPv3 */
+
+#ifndef IPPROTO_L2TP
+#define IPPROTO_L2TP 0x73
+#endif
+
+struct arglist {
+	int	numargs;
+	char	*tokens[MAXVARGS];
+	char	*values[MAXVARGS];
+};
+
+/* Separating read and write FDs allows us to have different
+ * rx and tx method. Example - read tap via raw socket using
+ * recvmmsg, write using legacy tap write calls
+ */
+
+struct vector_fds {
+	int rx_fd;
+	int tx_fd;
+	void *remote_addr;
+	int remote_addr_size;
+};
+
+#define VECTOR_READ	1
+
+extern struct arglist *uml_parse_vector_ifspec(char *arg);
+
+extern struct vector_fds *uml_vector_user_open(
+	int unit,
+	struct arglist *parsed
+);
+
+extern char *uml_vector_fetch_arg(
+	struct arglist *ifspec,
+	char *token
+);
+
+extern int uml_vector_recvmsg(int fd, void *hdr, int flags);
+extern int uml_vector_sendmsg(int fd, void *hdr, int flags);
+extern int uml_vector_writev(int fd, void *hdr, int iovcount);
+extern int uml_vector_sendmmsg(
+	int fd, void *msgvec,
+	unsigned int vlen,
+	unsigned int flags
+);
+extern int uml_vector_recvmmsg(
+	int fd,
+	void *msgvec,
+	unsigned int vlen,
+	unsigned int flags
+);
+extern void *uml_vector_default_bpf(const void *mac);
+extern void *uml_vector_user_bpf(char *filename);
+extern int uml_vector_attach_bpf(int fd, void *bpf);
+extern int uml_vector_detach_bpf(int fd, void *bpf);
+extern bool uml_raw_enable_qdisc_bypass(int fd);
+extern bool uml_raw_enable_vnet_headers(int fd);
+extern bool uml_tap_enable_vnet_headers(int fd);
+
+
+#endif
diff --git a/arch/um/drivers/vfio_kern.c b/arch/um/drivers/vfio_kern.c
new file mode 100644
index 000000000..e6dab473c
--- /dev/null
+++ b/arch/um/drivers/vfio_kern.c
@@ -0,0 +1,707 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2025 Ant Group
+ * Author: Tiwei Bie <tiwei.btw@antgroup.com>
+ */
+
+#define pr_fmt(fmt) "vfio-uml: " fmt
+
+#include <linux/module.h>
+#include <linux/logic_iomem.h>
+#include <linux/mutex.h>
+#include <linux/list.h>
+#include <linux/string.h>
+#include <linux/unaligned.h>
+#include <irq_kern.h>
+#include <init.h>
+#include <os.h>
+
+#include "mconsole_kern.h"
+#include "virt-pci.h"
+#include "vfio_user.h"
+
+#define to_vdev(_pdev) container_of(_pdev, struct uml_vfio_device, pdev)
+
+struct uml_vfio_intr_ctx {
+	struct uml_vfio_device *dev;
+	int irq;
+};
+
+struct uml_vfio_device {
+	const char *name;
+	int group;
+
+	struct um_pci_device pdev;
+	struct uml_vfio_user_device udev;
+	struct uml_vfio_intr_ctx *intr_ctx;
+
+	int msix_cap;
+	int msix_bar;
+	int msix_offset;
+	int msix_size;
+	u32 *msix_data;
+
+	struct list_head list;
+};
+
+struct uml_vfio_group {
+	int id;
+	int fd;
+	int users;
+	struct list_head list;
+};
+
+static struct {
+	int fd;
+	int users;
+} uml_vfio_container = { .fd = -1 };
+static DEFINE_MUTEX(uml_vfio_container_mtx);
+
+static LIST_HEAD(uml_vfio_groups);
+static DEFINE_MUTEX(uml_vfio_groups_mtx);
+
+static LIST_HEAD(uml_vfio_devices);
+static DEFINE_MUTEX(uml_vfio_devices_mtx);
+
+static int uml_vfio_set_container(int group_fd)
+{
+	int err;
+
+	guard(mutex)(&uml_vfio_container_mtx);
+
+	err = uml_vfio_user_set_container(uml_vfio_container.fd, group_fd);
+	if (err)
+		return err;
+
+	uml_vfio_container.users++;
+	if (uml_vfio_container.users > 1)
+		return 0;
+
+	err = uml_vfio_user_setup_iommu(uml_vfio_container.fd);
+	if (err) {
+		uml_vfio_user_unset_container(uml_vfio_container.fd, group_fd);
+		uml_vfio_container.users--;
+	}
+	return err;
+}
+
+static void uml_vfio_unset_container(int group_fd)
+{
+	guard(mutex)(&uml_vfio_container_mtx);
+
+	uml_vfio_user_unset_container(uml_vfio_container.fd, group_fd);
+	uml_vfio_container.users--;
+}
+
+static int uml_vfio_open_group(int group_id)
+{
+	struct uml_vfio_group *group;
+	int err;
+
+	guard(mutex)(&uml_vfio_groups_mtx);
+
+	list_for_each_entry(group, &uml_vfio_groups, list) {
+		if (group->id == group_id) {
+			group->users++;
+			return group->fd;
+		}
+	}
+
+	group = kzalloc_obj(*group);
+	if (!group)
+		return -ENOMEM;
+
+	group->fd = uml_vfio_user_open_group(group_id);
+	if (group->fd < 0) {
+		err = group->fd;
+		goto free_group;
+	}
+
+	err = uml_vfio_set_container(group->fd);
+	if (err)
+		goto close_group;
+
+	group->id = group_id;
+	group->users = 1;
+
+	list_add(&group->list, &uml_vfio_groups);
+
+	return group->fd;
+
+close_group:
+	os_close_file(group->fd);
+free_group:
+	kfree(group);
+	return err;
+}
+
+static int uml_vfio_release_group(int group_fd)
+{
+	struct uml_vfio_group *group;
+
+	guard(mutex)(&uml_vfio_groups_mtx);
+
+	list_for_each_entry(group, &uml_vfio_groups, list) {
+		if (group->fd == group_fd) {
+			group->users--;
+			if (group->users == 0) {
+				uml_vfio_unset_container(group_fd);
+				os_close_file(group_fd);
+				list_del(&group->list);
+				kfree(group);
+			}
+			return 0;
+		}
+	}
+
+	return -ENOENT;
+}
+
+static irqreturn_t uml_vfio_interrupt(int unused, void *opaque)
+{
+	struct uml_vfio_intr_ctx *ctx = opaque;
+	struct uml_vfio_device *dev = ctx->dev;
+	int index = ctx - dev->intr_ctx;
+	int irqfd = dev->udev.irqfd[index];
+	int irq = dev->msix_data[index];
+	uint64_t v;
+	int r;
+
+	do {
+		r = os_read_file(irqfd, &v, sizeof(v));
+		if (r == sizeof(v))
+			generic_handle_irq(irq);
+	} while (r == sizeof(v) || r == -EINTR);
+	WARN(r != -EAGAIN, "read returned %d\n", r);
+
+	return IRQ_HANDLED;
+}
+
+static int uml_vfio_activate_irq(struct uml_vfio_device *dev, int index)
+{
+	struct uml_vfio_intr_ctx *ctx = &dev->intr_ctx[index];
+	int err, irqfd;
+
+	if (ctx->irq >= 0)
+		return 0;
+
+	irqfd = uml_vfio_user_activate_irq(&dev->udev, index);
+	if (irqfd < 0)
+		return irqfd;
+
+	ctx->irq = um_request_irq(UM_IRQ_ALLOC, irqfd, IRQ_READ,
+				  uml_vfio_interrupt, 0,
+				  "vfio-uml", ctx);
+	if (ctx->irq < 0) {
+		err = ctx->irq;
+		goto deactivate;
+	}
+
+	err = add_sigio_fd(irqfd);
+	if (err)
+		goto free_irq;
+
+	return 0;
+
+free_irq:
+	um_free_irq(ctx->irq, ctx);
+	ctx->irq = -1;
+deactivate:
+	uml_vfio_user_deactivate_irq(&dev->udev, index);
+	return err;
+}
+
+static int uml_vfio_deactivate_irq(struct uml_vfio_device *dev, int index)
+{
+	struct uml_vfio_intr_ctx *ctx = &dev->intr_ctx[index];
+
+	if (ctx->irq >= 0) {
+		ignore_sigio_fd(dev->udev.irqfd[index]);
+		um_free_irq(ctx->irq, ctx);
+		uml_vfio_user_deactivate_irq(&dev->udev, index);
+		ctx->irq = -1;
+	}
+	return 0;
+}
+
+static int uml_vfio_update_msix_cap(struct uml_vfio_device *dev,
+				    unsigned int offset, int size,
+				    unsigned long val)
+{
+	/*
+	 * Here, we handle only the operations we care about,
+	 * ignoring the rest.
+	 */
+	if (size == 2 && offset == dev->msix_cap + PCI_MSIX_FLAGS) {
+		switch (val & ~PCI_MSIX_FLAGS_QSIZE) {
+		case PCI_MSIX_FLAGS_ENABLE:
+		case 0:
+			return uml_vfio_user_update_irqs(&dev->udev);
+		}
+	}
+	return 0;
+}
+
+static int uml_vfio_update_msix_table(struct uml_vfio_device *dev,
+				      unsigned int offset, int size,
+				      unsigned long val)
+{
+	int index;
+
+	/*
+	 * Here, we handle only the operations we care about,
+	 * ignoring the rest.
+	 */
+	offset -= dev->msix_offset + PCI_MSIX_ENTRY_DATA;
+
+	if (size != 4 || offset % PCI_MSIX_ENTRY_SIZE != 0)
+		return 0;
+
+	index = offset / PCI_MSIX_ENTRY_SIZE;
+	if (index >= dev->udev.irq_count)
+		return -EINVAL;
+
+	dev->msix_data[index] = val;
+
+	return val ? uml_vfio_activate_irq(dev, index) :
+		uml_vfio_deactivate_irq(dev, index);
+}
+
+static unsigned long __uml_vfio_cfgspace_read(struct uml_vfio_device *dev,
+					      unsigned int offset, int size)
+{
+	u8 data[8];
+
+	memset(data, 0xff, sizeof(data));
+
+	if (uml_vfio_user_cfgspace_read(&dev->udev, offset, data, size))
+		return ULONG_MAX;
+
+	switch (size) {
+	case 1:
+		return data[0];
+	case 2:
+		return le16_to_cpup((void *)data);
+	case 4:
+		return le32_to_cpup((void *)data);
+#ifdef CONFIG_64BIT
+	case 8:
+		return le64_to_cpup((void *)data);
+#endif
+	default:
+		return ULONG_MAX;
+	}
+}
+
+static unsigned long uml_vfio_cfgspace_read(struct um_pci_device *pdev,
+					    unsigned int offset, int size)
+{
+	struct uml_vfio_device *dev = to_vdev(pdev);
+
+	return __uml_vfio_cfgspace_read(dev, offset, size);
+}
+
+static void __uml_vfio_cfgspace_write(struct uml_vfio_device *dev,
+				      unsigned int offset, int size,
+				      unsigned long val)
+{
+	u8 data[8];
+
+	switch (size) {
+	case 1:
+		data[0] = (u8)val;
+		break;
+	case 2:
+		put_unaligned_le16(val, (void *)data);
+		break;
+	case 4:
+		put_unaligned_le32(val, (void *)data);
+		break;
+#ifdef CONFIG_64BIT
+	case 8:
+		put_unaligned_le64(val, (void *)data);
+		break;
+#endif
+	}
+
+	WARN_ON(uml_vfio_user_cfgspace_write(&dev->udev, offset, data, size));
+}
+
+static void uml_vfio_cfgspace_write(struct um_pci_device *pdev,
+				    unsigned int offset, int size,
+				    unsigned long val)
+{
+	struct uml_vfio_device *dev = to_vdev(pdev);
+
+	if (offset < dev->msix_cap + PCI_CAP_MSIX_SIZEOF &&
+	    offset + size > dev->msix_cap)
+		WARN_ON(uml_vfio_update_msix_cap(dev, offset, size, val));
+
+	__uml_vfio_cfgspace_write(dev, offset, size, val);
+}
+
+static void uml_vfio_bar_copy_from(struct um_pci_device *pdev, int bar,
+				   void *buffer, unsigned int offset, int size)
+{
+	struct uml_vfio_device *dev = to_vdev(pdev);
+
+	memset(buffer, 0xff, size);
+	uml_vfio_user_bar_read(&dev->udev, bar, offset, buffer, size);
+}
+
+static unsigned long uml_vfio_bar_read(struct um_pci_device *pdev, int bar,
+				       unsigned int offset, int size)
+{
+	u8 data[8];
+
+	uml_vfio_bar_copy_from(pdev, bar, data, offset, size);
+
+	switch (size) {
+	case 1:
+		return data[0];
+	case 2:
+		return le16_to_cpup((void *)data);
+	case 4:
+		return le32_to_cpup((void *)data);
+#ifdef CONFIG_64BIT
+	case 8:
+		return le64_to_cpup((void *)data);
+#endif
+	default:
+		return ULONG_MAX;
+	}
+}
+
+static void uml_vfio_bar_copy_to(struct um_pci_device *pdev, int bar,
+				 unsigned int offset, const void *buffer,
+				 int size)
+{
+	struct uml_vfio_device *dev = to_vdev(pdev);
+
+	uml_vfio_user_bar_write(&dev->udev, bar, offset, buffer, size);
+}
+
+static void uml_vfio_bar_write(struct um_pci_device *pdev, int bar,
+			       unsigned int offset, int size,
+			       unsigned long val)
+{
+	struct uml_vfio_device *dev = to_vdev(pdev);
+	u8 data[8];
+
+	if (bar == dev->msix_bar && offset + size > dev->msix_offset &&
+	    offset < dev->msix_offset + dev->msix_size)
+		WARN_ON(uml_vfio_update_msix_table(dev, offset, size, val));
+
+	switch (size) {
+	case 1:
+		data[0] = (u8)val;
+		break;
+	case 2:
+		put_unaligned_le16(val, (void *)data);
+		break;
+	case 4:
+		put_unaligned_le32(val, (void *)data);
+		break;
+#ifdef CONFIG_64BIT
+	case 8:
+		put_unaligned_le64(val, (void *)data);
+		break;
+#endif
+	}
+
+	uml_vfio_bar_copy_to(pdev, bar, offset, data, size);
+}
+
+static void uml_vfio_bar_set(struct um_pci_device *pdev, int bar,
+			     unsigned int offset, u8 value, int size)
+{
+	struct uml_vfio_device *dev = to_vdev(pdev);
+	int i;
+
+	for (i = 0; i < size; i++)
+		uml_vfio_user_bar_write(&dev->udev, bar, offset + i, &value, 1);
+}
+
+static const struct um_pci_ops uml_vfio_um_pci_ops = {
+	.cfgspace_read	= uml_vfio_cfgspace_read,
+	.cfgspace_write	= uml_vfio_cfgspace_write,
+	.bar_read	= uml_vfio_bar_read,
+	.bar_write	= uml_vfio_bar_write,
+	.bar_copy_from	= uml_vfio_bar_copy_from,
+	.bar_copy_to	= uml_vfio_bar_copy_to,
+	.bar_set	= uml_vfio_bar_set,
+};
+
+static u8 uml_vfio_find_capability(struct uml_vfio_device *dev, u8 cap)
+{
+	u8 id, pos;
+	u16 ent;
+	int ttl = 48; /* PCI_FIND_CAP_TTL */
+
+	pos = __uml_vfio_cfgspace_read(dev, PCI_CAPABILITY_LIST, sizeof(pos));
+
+	while (pos && ttl--) {
+		ent = __uml_vfio_cfgspace_read(dev, pos, sizeof(ent));
+
+		id = ent & 0xff;
+		if (id == 0xff)
+			break;
+		if (id == cap)
+			return pos;
+
+		pos = ent >> 8;
+	}
+
+	return 0;
+}
+
+static int uml_vfio_read_msix_table(struct uml_vfio_device *dev)
+{
+	unsigned int off;
+	u16 flags;
+	u32 tbl;
+
+	off = uml_vfio_find_capability(dev, PCI_CAP_ID_MSIX);
+	if (!off)
+		return -ENOTSUPP;
+
+	dev->msix_cap = off;
+
+	tbl = __uml_vfio_cfgspace_read(dev, off + PCI_MSIX_TABLE, sizeof(tbl));
+	flags = __uml_vfio_cfgspace_read(dev, off + PCI_MSIX_FLAGS, sizeof(flags));
+
+	dev->msix_bar = tbl & PCI_MSIX_TABLE_BIR;
+	dev->msix_offset = tbl & PCI_MSIX_TABLE_OFFSET;
+	dev->msix_size = ((flags & PCI_MSIX_FLAGS_QSIZE) + 1) * PCI_MSIX_ENTRY_SIZE;
+
+	dev->msix_data = kzalloc(dev->msix_size, GFP_KERNEL);
+	if (!dev->msix_data)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static void uml_vfio_open_device(struct uml_vfio_device *dev)
+{
+	struct uml_vfio_intr_ctx *ctx;
+	int err, group_id, i;
+
+	group_id = uml_vfio_user_get_group_id(dev->name);
+	if (group_id < 0) {
+		pr_err("Failed to get group id (%s), error %d\n",
+		       dev->name, group_id);
+		goto free_dev;
+	}
+
+	dev->group = uml_vfio_open_group(group_id);
+	if (dev->group < 0) {
+		pr_err("Failed to open group %d (%s), error %d\n",
+		       group_id, dev->name, dev->group);
+		goto free_dev;
+	}
+
+	err = uml_vfio_user_setup_device(&dev->udev, dev->group, dev->name);
+	if (err) {
+		pr_err("Failed to setup device (%s), error %d\n",
+		       dev->name, err);
+		goto release_group;
+	}
+
+	err = uml_vfio_read_msix_table(dev);
+	if (err) {
+		pr_err("Failed to read MSI-X table (%s), error %d\n",
+		       dev->name, err);
+		goto teardown_udev;
+	}
+
+	dev->intr_ctx = kmalloc_objs(struct uml_vfio_intr_ctx,
+				     dev->udev.irq_count);
+	if (!dev->intr_ctx) {
+		pr_err("Failed to allocate interrupt context (%s)\n",
+		       dev->name);
+		goto free_msix;
+	}
+
+	for (i = 0; i < dev->udev.irq_count; i++) {
+		ctx = &dev->intr_ctx[i];
+		ctx->dev = dev;
+		ctx->irq = -1;
+	}
+
+	dev->pdev.ops = &uml_vfio_um_pci_ops;
+
+	err = um_pci_device_register(&dev->pdev);
+	if (err) {
+		pr_err("Failed to register UM PCI device (%s), error %d\n",
+		       dev->name, err);
+		goto free_intr_ctx;
+	}
+
+	return;
+
+free_intr_ctx:
+	kfree(dev->intr_ctx);
+free_msix:
+	kfree(dev->msix_data);
+teardown_udev:
+	uml_vfio_user_teardown_device(&dev->udev);
+release_group:
+	uml_vfio_release_group(dev->group);
+free_dev:
+	list_del(&dev->list);
+	kfree(dev->name);
+	kfree(dev);
+}
+
+static void uml_vfio_release_device(struct uml_vfio_device *dev)
+{
+	int i;
+
+	for (i = 0; i < dev->udev.irq_count; i++)
+		uml_vfio_deactivate_irq(dev, i);
+	uml_vfio_user_update_irqs(&dev->udev);
+
+	um_pci_device_unregister(&dev->pdev);
+	kfree(dev->intr_ctx);
+	kfree(dev->msix_data);
+	uml_vfio_user_teardown_device(&dev->udev);
+	uml_vfio_release_group(dev->group);
+	list_del(&dev->list);
+	kfree(dev->name);
+	kfree(dev);
+}
+
+static struct uml_vfio_device *uml_vfio_find_device(const char *device)
+{
+	struct uml_vfio_device *dev;
+
+	list_for_each_entry(dev, &uml_vfio_devices, list) {
+		if (!strcmp(dev->name, device))
+			return dev;
+	}
+	return NULL;
+}
+
+static struct uml_vfio_device *uml_vfio_add_device(const char *device)
+{
+	struct uml_vfio_device *dev;
+	int fd;
+
+	guard(mutex)(&uml_vfio_devices_mtx);
+
+	if (uml_vfio_container.fd < 0) {
+		fd = uml_vfio_user_open_container();
+		if (fd < 0)
+			return ERR_PTR(fd);
+		uml_vfio_container.fd = fd;
+	}
+
+	if (uml_vfio_find_device(device))
+		return ERR_PTR(-EEXIST);
+
+	dev = kzalloc_obj(*dev);
+	if (!dev)
+		return ERR_PTR(-ENOMEM);
+
+	dev->name = kstrdup(device, GFP_KERNEL);
+	if (!dev->name) {
+		kfree(dev);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	list_add_tail(&dev->list, &uml_vfio_devices);
+	return dev;
+}
+
+static int uml_vfio_cmdline_set(const char *device, const struct kernel_param *kp)
+{
+	struct uml_vfio_device *dev;
+
+	dev = uml_vfio_add_device(device);
+	if (IS_ERR(dev))
+		return PTR_ERR(dev);
+	return 0;
+}
+
+static int uml_vfio_cmdline_get(char *buffer, const struct kernel_param *kp)
+{
+	return 0;
+}
+
+static const struct kernel_param_ops uml_vfio_cmdline_param_ops = {
+	.set = uml_vfio_cmdline_set,
+	.get = uml_vfio_cmdline_get,
+};
+
+device_param_cb(device, &uml_vfio_cmdline_param_ops, NULL, 0400);
+__uml_help(uml_vfio_cmdline_param_ops,
+"vfio_uml.device=<domain:bus:slot.function>\n"
+"    Pass through a PCI device to UML via VFIO. Currently, only MSI-X\n"
+"    capable devices are supported, and it is assumed that drivers will\n"
+"    use MSI-X. This parameter can be specified multiple times to pass\n"
+"    through multiple PCI devices to UML.\n\n"
+);
+
+static int uml_vfio_mc_config(char *str, char **error_out)
+{
+	struct uml_vfio_device *dev;
+
+	if (*str != '=') {
+		*error_out = "Invalid config";
+		return -EINVAL;
+	}
+	str += 1;
+
+	dev = uml_vfio_add_device(str);
+	if (IS_ERR(dev))
+		return PTR_ERR(dev);
+	uml_vfio_open_device(dev);
+	return 0;
+}
+
+static int uml_vfio_mc_id(char **str, int *start_out, int *end_out)
+{
+	return -EOPNOTSUPP;
+}
+
+static int uml_vfio_mc_remove(int n, char **error_out)
+{
+	return -EOPNOTSUPP;
+}
+
+static struct mc_device uml_vfio_mc = {
+	.list           = LIST_HEAD_INIT(uml_vfio_mc.list),
+	.name           = "vfio_uml.device",
+	.config         = uml_vfio_mc_config,
+	.get_config     = NULL,
+	.id             = uml_vfio_mc_id,
+	.remove         = uml_vfio_mc_remove,
+};
+
+static int __init uml_vfio_init(void)
+{
+	struct uml_vfio_device *dev, *n;
+
+	sigio_broken();
+
+	/* If the opening fails, the device will be released. */
+	list_for_each_entry_safe(dev, n, &uml_vfio_devices, list)
+		uml_vfio_open_device(dev);
+
+	mconsole_register_dev(&uml_vfio_mc);
+
+	return 0;
+}
+late_initcall(uml_vfio_init);
+
+static void __exit uml_vfio_exit(void)
+{
+	struct uml_vfio_device *dev, *n;
+
+	list_for_each_entry_safe(dev, n, &uml_vfio_devices, list)
+		uml_vfio_release_device(dev);
+
+	if (uml_vfio_container.fd >= 0)
+		os_close_file(uml_vfio_container.fd);
+}
+module_exit(uml_vfio_exit);
diff --git a/arch/um/drivers/vfio_user.c b/arch/um/drivers/vfio_user.c
new file mode 100644
index 000000000..6a45d8e14
--- /dev/null
+++ b/arch/um/drivers/vfio_user.c
@@ -0,0 +1,327 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2025 Ant Group
+ * Author: Tiwei Bie <tiwei.btw@antgroup.com>
+ */
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/eventfd.h>
+#include <linux/limits.h>
+#include <linux/vfio.h>
+#include <linux/pci_regs.h>
+#include <as-layout.h>
+#include <um_malloc.h>
+
+#include "vfio_user.h"
+
+int uml_vfio_user_open_container(void)
+{
+	int r, fd;
+
+	fd = open("/dev/vfio/vfio", O_RDWR);
+	if (fd < 0)
+		return -errno;
+
+	r = ioctl(fd, VFIO_GET_API_VERSION);
+	if (r != VFIO_API_VERSION) {
+		r = r < 0 ? -errno : -EINVAL;
+		goto error;
+	}
+
+	r = ioctl(fd, VFIO_CHECK_EXTENSION, VFIO_TYPE1_IOMMU);
+	if (r <= 0) {
+		r = r < 0 ? -errno : -EINVAL;
+		goto error;
+	}
+
+	return fd;
+
+error:
+	close(fd);
+	return r;
+}
+
+int uml_vfio_user_setup_iommu(int container)
+{
+	/*
+	 * This is a bit tricky. See the big comment in
+	 * vhost_user_set_mem_table() in virtio_uml.c.
+	 */
+	unsigned long reserved = uml_reserved - uml_physmem;
+	struct vfio_iommu_type1_dma_map dma_map = {
+		.argsz = sizeof(dma_map),
+		.flags = VFIO_DMA_MAP_FLAG_READ | VFIO_DMA_MAP_FLAG_WRITE,
+		.vaddr = uml_reserved,
+		.iova = reserved,
+		.size = physmem_size - reserved,
+	};
+
+	if (ioctl(container, VFIO_SET_IOMMU, VFIO_TYPE1_IOMMU) < 0)
+		return -errno;
+
+	if (ioctl(container, VFIO_IOMMU_MAP_DMA, &dma_map) < 0)
+		return -errno;
+
+	return 0;
+}
+
+int uml_vfio_user_get_group_id(const char *device)
+{
+	char *path, *buf, *end;
+	const char *name;
+	int r;
+
+	path = uml_kmalloc(PATH_MAX, UM_GFP_KERNEL);
+	if (!path)
+		return -ENOMEM;
+
+	sprintf(path, "/sys/bus/pci/devices/%s/iommu_group", device);
+
+	buf = uml_kmalloc(PATH_MAX + 1, UM_GFP_KERNEL);
+	if (!buf) {
+		r = -ENOMEM;
+		goto free_path;
+	}
+
+	r = readlink(path, buf, PATH_MAX);
+	if (r < 0) {
+		r = -errno;
+		goto free_buf;
+	}
+	buf[r] = '\0';
+
+	name = basename(buf);
+
+	r = strtoul(name, &end, 10);
+	if (*end != '\0' || end == name) {
+		r = -EINVAL;
+		goto free_buf;
+	}
+
+free_buf:
+	kfree(buf);
+free_path:
+	kfree(path);
+	return r;
+}
+
+int uml_vfio_user_open_group(int group_id)
+{
+	char *path;
+	int fd;
+
+	path = uml_kmalloc(PATH_MAX, UM_GFP_KERNEL);
+	if (!path)
+		return -ENOMEM;
+
+	sprintf(path, "/dev/vfio/%d", group_id);
+
+	fd = open(path, O_RDWR);
+	if (fd < 0) {
+		fd = -errno;
+		goto out;
+	}
+
+out:
+	kfree(path);
+	return fd;
+}
+
+int uml_vfio_user_set_container(int container, int group)
+{
+	if (ioctl(group, VFIO_GROUP_SET_CONTAINER, &container) < 0)
+		return -errno;
+	return 0;
+}
+
+int uml_vfio_user_unset_container(int container, int group)
+{
+	if (ioctl(group, VFIO_GROUP_UNSET_CONTAINER, &container) < 0)
+		return -errno;
+	return 0;
+}
+
+static int vfio_set_irqs(int device, int start, int count, int *irqfd)
+{
+	struct vfio_irq_set *irq_set;
+	int argsz = sizeof(*irq_set) + sizeof(*irqfd) * count;
+	int err = 0;
+
+	irq_set = uml_kmalloc(argsz, UM_GFP_KERNEL);
+	if (!irq_set)
+		return -ENOMEM;
+
+	irq_set->argsz = argsz;
+	irq_set->flags = VFIO_IRQ_SET_DATA_EVENTFD | VFIO_IRQ_SET_ACTION_TRIGGER;
+	irq_set->index = VFIO_PCI_MSIX_IRQ_INDEX;
+	irq_set->start = start;
+	irq_set->count = count;
+	memcpy(irq_set->data, irqfd, sizeof(*irqfd) * count);
+
+	if (ioctl(device, VFIO_DEVICE_SET_IRQS, irq_set) < 0) {
+		err = -errno;
+		goto out;
+	}
+
+out:
+	kfree(irq_set);
+	return err;
+}
+
+int uml_vfio_user_setup_device(struct uml_vfio_user_device *dev,
+			       int group, const char *device)
+{
+	struct vfio_device_info device_info = { .argsz = sizeof(device_info) };
+	struct vfio_irq_info irq_info = { .argsz = sizeof(irq_info) };
+	int err, i;
+
+	dev->device = ioctl(group, VFIO_GROUP_GET_DEVICE_FD, device);
+	if (dev->device < 0)
+		return -errno;
+
+	if (ioctl(dev->device, VFIO_DEVICE_GET_INFO, &device_info) < 0) {
+		err = -errno;
+		goto close_device;
+	}
+
+	dev->num_regions = device_info.num_regions;
+	if (dev->num_regions > VFIO_PCI_CONFIG_REGION_INDEX + 1)
+		dev->num_regions = VFIO_PCI_CONFIG_REGION_INDEX + 1;
+
+	dev->region = uml_kmalloc(sizeof(*dev->region) * dev->num_regions,
+				  UM_GFP_KERNEL);
+	if (!dev->region) {
+		err = -ENOMEM;
+		goto close_device;
+	}
+
+	for (i = 0; i < dev->num_regions; i++) {
+		struct vfio_region_info region = {
+			.argsz = sizeof(region),
+			.index = i,
+		};
+		if (ioctl(dev->device, VFIO_DEVICE_GET_REGION_INFO, &region) < 0) {
+			err = -errno;
+			goto free_region;
+		}
+		dev->region[i].size = region.size;
+		dev->region[i].offset = region.offset;
+	}
+
+	/* Only MSI-X is supported currently. */
+	irq_info.index = VFIO_PCI_MSIX_IRQ_INDEX;
+	if (ioctl(dev->device, VFIO_DEVICE_GET_IRQ_INFO, &irq_info) < 0) {
+		err = -errno;
+		goto free_region;
+	}
+
+	dev->irq_count = irq_info.count;
+
+	dev->irqfd = uml_kmalloc(sizeof(int) * dev->irq_count, UM_GFP_KERNEL);
+	if (!dev->irqfd) {
+		err = -ENOMEM;
+		goto free_region;
+	}
+
+	memset(dev->irqfd, -1, sizeof(int) * dev->irq_count);
+
+	err = vfio_set_irqs(dev->device, 0, dev->irq_count, dev->irqfd);
+	if (err)
+		goto free_irqfd;
+
+	return 0;
+
+free_irqfd:
+	kfree(dev->irqfd);
+free_region:
+	kfree(dev->region);
+close_device:
+	close(dev->device);
+	return err;
+}
+
+void uml_vfio_user_teardown_device(struct uml_vfio_user_device *dev)
+{
+	kfree(dev->irqfd);
+	kfree(dev->region);
+	close(dev->device);
+}
+
+int uml_vfio_user_activate_irq(struct uml_vfio_user_device *dev, int index)
+{
+	int irqfd;
+
+	irqfd = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
+	if (irqfd < 0)
+		return -errno;
+
+	dev->irqfd[index] = irqfd;
+	return irqfd;
+}
+
+void uml_vfio_user_deactivate_irq(struct uml_vfio_user_device *dev, int index)
+{
+	close(dev->irqfd[index]);
+	dev->irqfd[index] = -1;
+}
+
+int uml_vfio_user_update_irqs(struct uml_vfio_user_device *dev)
+{
+	return vfio_set_irqs(dev->device, 0, dev->irq_count, dev->irqfd);
+}
+
+static int vfio_region_read(struct uml_vfio_user_device *dev, unsigned int index,
+			    uint64_t offset, void *buf, uint64_t size)
+{
+	if (index >= dev->num_regions || offset + size > dev->region[index].size)
+		return -EINVAL;
+
+	if (pread(dev->device, buf, size, dev->region[index].offset + offset) < 0)
+		return -errno;
+
+	return 0;
+}
+
+static int vfio_region_write(struct uml_vfio_user_device *dev, unsigned int index,
+			     uint64_t offset, const void *buf, uint64_t size)
+{
+	if (index >= dev->num_regions || offset + size > dev->region[index].size)
+		return -EINVAL;
+
+	if (pwrite(dev->device, buf, size, dev->region[index].offset + offset) < 0)
+		return -errno;
+
+	return 0;
+}
+
+int uml_vfio_user_cfgspace_read(struct uml_vfio_user_device *dev,
+				unsigned int offset, void *buf, int size)
+{
+	return vfio_region_read(dev, VFIO_PCI_CONFIG_REGION_INDEX,
+				offset, buf, size);
+}
+
+int uml_vfio_user_cfgspace_write(struct uml_vfio_user_device *dev,
+				 unsigned int offset, const void *buf, int size)
+{
+	return vfio_region_write(dev, VFIO_PCI_CONFIG_REGION_INDEX,
+				 offset, buf, size);
+}
+
+int uml_vfio_user_bar_read(struct uml_vfio_user_device *dev, int bar,
+			   unsigned int offset, void *buf, int size)
+{
+	return vfio_region_read(dev, bar, offset, buf, size);
+}
+
+int uml_vfio_user_bar_write(struct uml_vfio_user_device *dev, int bar,
+			    unsigned int offset, const void *buf, int size)
+{
+	return vfio_region_write(dev, bar, offset, buf, size);
+}
diff --git a/arch/um/drivers/vfio_user.h b/arch/um/drivers/vfio_user.h
new file mode 100644
index 000000000..75535e050
--- /dev/null
+++ b/arch/um/drivers/vfio_user.h
@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UM_VFIO_USER_H
+#define __UM_VFIO_USER_H
+
+struct uml_vfio_user_device {
+	int device;
+
+	struct {
+		uint64_t size;
+		uint64_t offset;
+	} *region;
+	int num_regions;
+
+	int32_t *irqfd;
+	int irq_count;
+};
+
+int uml_vfio_user_open_container(void);
+int uml_vfio_user_setup_iommu(int container);
+
+int uml_vfio_user_get_group_id(const char *device);
+int uml_vfio_user_open_group(int group_id);
+int uml_vfio_user_set_container(int container, int group);
+int uml_vfio_user_unset_container(int container, int group);
+
+int uml_vfio_user_setup_device(struct uml_vfio_user_device *dev,
+			       int group, const char *device);
+void uml_vfio_user_teardown_device(struct uml_vfio_user_device *dev);
+
+int uml_vfio_user_activate_irq(struct uml_vfio_user_device *dev, int index);
+void uml_vfio_user_deactivate_irq(struct uml_vfio_user_device *dev, int index);
+int uml_vfio_user_update_irqs(struct uml_vfio_user_device *dev);
+
+int uml_vfio_user_cfgspace_read(struct uml_vfio_user_device *dev,
+				unsigned int offset, void *buf, int size);
+int uml_vfio_user_cfgspace_write(struct uml_vfio_user_device *dev,
+				 unsigned int offset, const void *buf, int size);
+
+int uml_vfio_user_bar_read(struct uml_vfio_user_device *dev, int bar,
+			   unsigned int offset, void *buf, int size);
+int uml_vfio_user_bar_write(struct uml_vfio_user_device *dev, int bar,
+			    unsigned int offset, const void *buf, int size);
+
+#endif /* __UM_VFIO_USER_H */
diff --git a/arch/um/drivers/vhost_user.h b/arch/um/drivers/vhost_user.h
new file mode 100644
index 000000000..fcfa3b7e0
--- /dev/null
+++ b/arch/um/drivers/vhost_user.h
@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Vhost-user protocol */
+
+#ifndef __VHOST_USER_H__
+#define __VHOST_USER_H__
+
+/* Message flags */
+#define VHOST_USER_FLAG_REPLY		BIT(2)
+#define VHOST_USER_FLAG_NEED_REPLY	BIT(3)
+/* Feature bits */
+#define VHOST_USER_F_PROTOCOL_FEATURES	30
+/* Protocol feature bits */
+#define VHOST_USER_PROTOCOL_F_MQ			0
+#define VHOST_USER_PROTOCOL_F_REPLY_ACK			3
+#define VHOST_USER_PROTOCOL_F_SLAVE_REQ			5
+#define VHOST_USER_PROTOCOL_F_CONFIG			9
+#define VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS	14
+/* Vring state index masks */
+#define VHOST_USER_VRING_INDEX_MASK	0xff
+#define VHOST_USER_VRING_POLL_MASK	BIT(8)
+
+/* Supported version */
+#define VHOST_USER_VERSION		1
+/* Supported transport features */
+#define VHOST_USER_SUPPORTED_F		BIT_ULL(VHOST_USER_F_PROTOCOL_FEATURES)
+/* Supported protocol features */
+#define VHOST_USER_SUPPORTED_PROTOCOL_F	(BIT_ULL(VHOST_USER_PROTOCOL_F_MQ) | \
+					 BIT_ULL(VHOST_USER_PROTOCOL_F_REPLY_ACK) | \
+					 BIT_ULL(VHOST_USER_PROTOCOL_F_SLAVE_REQ) | \
+					 BIT_ULL(VHOST_USER_PROTOCOL_F_CONFIG) | \
+					 BIT_ULL(VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS))
+
+enum vhost_user_request {
+	VHOST_USER_GET_FEATURES = 1,
+	VHOST_USER_SET_FEATURES = 2,
+	VHOST_USER_SET_OWNER = 3,
+	VHOST_USER_RESET_OWNER = 4,
+	VHOST_USER_SET_MEM_TABLE = 5,
+	VHOST_USER_SET_LOG_BASE = 6,
+	VHOST_USER_SET_LOG_FD = 7,
+	VHOST_USER_SET_VRING_NUM = 8,
+	VHOST_USER_SET_VRING_ADDR = 9,
+	VHOST_USER_SET_VRING_BASE = 10,
+	VHOST_USER_GET_VRING_BASE = 11,
+	VHOST_USER_SET_VRING_KICK = 12,
+	VHOST_USER_SET_VRING_CALL = 13,
+	VHOST_USER_SET_VRING_ERR = 14,
+	VHOST_USER_GET_PROTOCOL_FEATURES = 15,
+	VHOST_USER_SET_PROTOCOL_FEATURES = 16,
+	VHOST_USER_GET_QUEUE_NUM = 17,
+	VHOST_USER_SET_VRING_ENABLE = 18,
+	VHOST_USER_SEND_RARP = 19,
+	VHOST_USER_NET_SEND_MTU = 20,
+	VHOST_USER_SET_SLAVE_REQ_FD = 21,
+	VHOST_USER_IOTLB_MSG = 22,
+	VHOST_USER_SET_VRING_ENDIAN = 23,
+	VHOST_USER_GET_CONFIG = 24,
+	VHOST_USER_SET_CONFIG = 25,
+	VHOST_USER_VRING_KICK = 35,
+};
+
+enum vhost_user_slave_request {
+	VHOST_USER_SLAVE_IOTLB_MSG = 1,
+	VHOST_USER_SLAVE_CONFIG_CHANGE_MSG = 2,
+	VHOST_USER_SLAVE_VRING_HOST_NOTIFIER_MSG = 3,
+	VHOST_USER_SLAVE_VRING_CALL = 4,
+};
+
+struct vhost_user_header {
+	/*
+	 * Use enum vhost_user_request for outgoing messages,
+	 * uses enum vhost_user_slave_request for incoming ones.
+	 */
+	u32 request;
+	u32 flags;
+	u32 size;
+} __packed;
+
+struct vhost_user_config {
+	u32 offset;
+	u32 size;
+	u32 flags;
+	u8 payload[]; /* Variable length */
+} __packed;
+
+struct vhost_user_vring_state {
+	u32 index;
+	u32 num;
+} __packed;
+
+struct vhost_user_vring_addr {
+	u32 index;
+	u32 flags;
+	u64 desc, used, avail, log;
+} __packed;
+
+struct vhost_user_mem_region {
+	u64 guest_addr;
+	u64 size;
+	u64 user_addr;
+	u64 mmap_offset;
+} __packed;
+
+struct vhost_user_mem_regions {
+	u32 num;
+	u32 padding;
+	struct vhost_user_mem_region regions[2]; /* Currently supporting 2 */
+} __packed;
+
+union vhost_user_payload {
+	u64 integer;
+	struct vhost_user_config config;
+	struct vhost_user_vring_state vring_state;
+	struct vhost_user_vring_addr vring_addr;
+	struct vhost_user_mem_regions mem_regions;
+};
+
+struct vhost_user_msg {
+	struct vhost_user_header header;
+	union vhost_user_payload payload;
+} __packed;
+
+#endif
diff --git a/arch/um/drivers/virt-pci.c b/arch/um/drivers/virt-pci.c
new file mode 100644
index 000000000..557d93aea
--- /dev/null
+++ b/arch/um/drivers/virt-pci.c
@@ -0,0 +1,618 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020 Intel Corporation
+ * Author: Johannes Berg <johannes@sipsolutions.net>
+ */
+#include <linux/module.h>
+#include <linux/pci.h>
+#include <linux/logic_iomem.h>
+#include <linux/of_platform.h>
+#include <linux/irqchip/irq-msi-lib.h>
+#include <linux/irqdomain.h>
+#include <linux/msi.h>
+#include <linux/unaligned.h>
+#include <irq_kern.h>
+
+#include "virt-pci.h"
+
+#define MAX_DEVICES 8
+#define MAX_MSI_VECTORS 32
+#define CFG_SPACE_SIZE 4096
+
+struct um_pci_device_reg {
+	struct um_pci_device *dev;
+	void __iomem *iomem;
+};
+
+static struct pci_host_bridge *bridge;
+static DEFINE_MUTEX(um_pci_mtx);
+static struct um_pci_device *um_pci_platform_device;
+static struct um_pci_device_reg um_pci_devices[MAX_DEVICES];
+static struct fwnode_handle *um_pci_fwnode;
+static struct irq_domain *um_pci_inner_domain;
+static unsigned long um_pci_msi_used[BITS_TO_LONGS(MAX_MSI_VECTORS)];
+
+static unsigned long um_pci_cfgspace_read(void *priv, unsigned int offset,
+					  int size)
+{
+	struct um_pci_device_reg *reg = priv;
+	struct um_pci_device *dev = reg->dev;
+
+	if (!dev)
+		return ULONG_MAX;
+
+	switch (size) {
+	case 1:
+	case 2:
+	case 4:
+#ifdef CONFIG_64BIT
+	case 8:
+#endif
+		break;
+	default:
+		WARN(1, "invalid config space read size %d\n", size);
+		return ULONG_MAX;
+	}
+
+	return dev->ops->cfgspace_read(dev, offset, size);
+}
+
+static void um_pci_cfgspace_write(void *priv, unsigned int offset, int size,
+				  unsigned long val)
+{
+	struct um_pci_device_reg *reg = priv;
+	struct um_pci_device *dev = reg->dev;
+
+	if (!dev)
+		return;
+
+	switch (size) {
+	case 1:
+	case 2:
+	case 4:
+#ifdef CONFIG_64BIT
+	case 8:
+#endif
+		break;
+	default:
+		WARN(1, "invalid config space write size %d\n", size);
+		return;
+	}
+
+	dev->ops->cfgspace_write(dev, offset, size, val);
+}
+
+static const struct logic_iomem_ops um_pci_device_cfgspace_ops = {
+	.read = um_pci_cfgspace_read,
+	.write = um_pci_cfgspace_write,
+};
+
+static unsigned long um_pci_bar_read(void *priv, unsigned int offset,
+				     int size)
+{
+	u8 *resptr = priv;
+	struct um_pci_device *dev = container_of(resptr - *resptr,
+						 struct um_pci_device,
+						 resptr[0]);
+	u8 bar = *resptr;
+
+	switch (size) {
+	case 1:
+	case 2:
+	case 4:
+#ifdef CONFIG_64BIT
+	case 8:
+#endif
+		break;
+	default:
+		WARN(1, "invalid bar read size %d\n", size);
+		return ULONG_MAX;
+	}
+
+	return dev->ops->bar_read(dev, bar, offset, size);
+}
+
+static void um_pci_bar_write(void *priv, unsigned int offset, int size,
+			     unsigned long val)
+{
+	u8 *resptr = priv;
+	struct um_pci_device *dev = container_of(resptr - *resptr,
+						 struct um_pci_device,
+						 resptr[0]);
+	u8 bar = *resptr;
+
+	switch (size) {
+	case 1:
+	case 2:
+	case 4:
+#ifdef CONFIG_64BIT
+	case 8:
+#endif
+		break;
+	default:
+		WARN(1, "invalid bar write size %d\n", size);
+		return;
+	}
+
+	dev->ops->bar_write(dev, bar, offset, size, val);
+}
+
+static void um_pci_bar_copy_from(void *priv, void *buffer,
+				 unsigned int offset, int size)
+{
+	u8 *resptr = priv;
+	struct um_pci_device *dev = container_of(resptr - *resptr,
+						 struct um_pci_device,
+						 resptr[0]);
+	u8 bar = *resptr;
+
+	dev->ops->bar_copy_from(dev, bar, buffer, offset, size);
+}
+
+static void um_pci_bar_copy_to(void *priv, unsigned int offset,
+			       const void *buffer, int size)
+{
+	u8 *resptr = priv;
+	struct um_pci_device *dev = container_of(resptr - *resptr,
+						 struct um_pci_device,
+						 resptr[0]);
+	u8 bar = *resptr;
+
+	dev->ops->bar_copy_to(dev, bar, offset, buffer, size);
+}
+
+static void um_pci_bar_set(void *priv, unsigned int offset, u8 value, int size)
+{
+	u8 *resptr = priv;
+	struct um_pci_device *dev = container_of(resptr - *resptr,
+						 struct um_pci_device,
+						 resptr[0]);
+	u8 bar = *resptr;
+
+	dev->ops->bar_set(dev, bar, offset, value, size);
+}
+
+static const struct logic_iomem_ops um_pci_device_bar_ops = {
+	.read = um_pci_bar_read,
+	.write = um_pci_bar_write,
+	.set = um_pci_bar_set,
+	.copy_from = um_pci_bar_copy_from,
+	.copy_to = um_pci_bar_copy_to,
+};
+
+static void __iomem *um_pci_map_bus(struct pci_bus *bus, unsigned int devfn,
+				    int where)
+{
+	struct um_pci_device_reg *dev;
+	unsigned int busn = bus->number;
+
+	if (busn > 0)
+		return NULL;
+
+	/* not allowing functions for now ... */
+	if (devfn % 8)
+		return NULL;
+
+	if (devfn / 8 >= ARRAY_SIZE(um_pci_devices))
+		return NULL;
+
+	dev = &um_pci_devices[devfn / 8];
+	if (!dev)
+		return NULL;
+
+	return (void __iomem *)((unsigned long)dev->iomem + where);
+}
+
+static struct pci_ops um_pci_ops = {
+	.map_bus = um_pci_map_bus,
+	.read = pci_generic_config_read,
+	.write = pci_generic_config_write,
+};
+
+static void um_pci_rescan(void)
+{
+	pci_lock_rescan_remove();
+	pci_rescan_bus(bridge->bus);
+	pci_unlock_rescan_remove();
+}
+
+#ifdef CONFIG_OF
+/* Copied from arch/x86/kernel/devicetree.c */
+struct device_node *pcibios_get_phb_of_node(struct pci_bus *bus)
+{
+	struct device_node *np;
+
+	for_each_node_by_type(np, "pci") {
+		const void *prop;
+		unsigned int bus_min;
+
+		prop = of_get_property(np, "bus-range", NULL);
+		if (!prop)
+			continue;
+		bus_min = be32_to_cpup(prop);
+		if (bus->number == bus_min)
+			return np;
+	}
+	return NULL;
+}
+#endif
+
+static struct resource virt_cfgspace_resource = {
+	.name = "PCI config space",
+	.start = 0xf0000000 - MAX_DEVICES * CFG_SPACE_SIZE,
+	.end = 0xf0000000 - 1,
+	.flags = IORESOURCE_MEM,
+};
+
+static long um_pci_map_cfgspace(unsigned long offset, size_t size,
+				const struct logic_iomem_ops **ops,
+				void **priv)
+{
+	if (WARN_ON(size > CFG_SPACE_SIZE || offset % CFG_SPACE_SIZE))
+		return -EINVAL;
+
+	if (offset / CFG_SPACE_SIZE < MAX_DEVICES) {
+		*ops = &um_pci_device_cfgspace_ops;
+		*priv = &um_pci_devices[offset / CFG_SPACE_SIZE];
+		return 0;
+	}
+
+	WARN(1, "cannot map offset 0x%lx/0x%zx\n", offset, size);
+	return -ENOENT;
+}
+
+static const struct logic_iomem_region_ops um_pci_cfgspace_ops = {
+	.map = um_pci_map_cfgspace,
+};
+
+static struct resource virt_iomem_resource = {
+	.name = "PCI iomem",
+	.start = 0xf0000000,
+	.end = 0xffffffff,
+	.flags = IORESOURCE_MEM,
+};
+
+struct um_pci_map_iomem_data {
+	unsigned long offset;
+	size_t size;
+	const struct logic_iomem_ops **ops;
+	void **priv;
+	long ret;
+};
+
+static int um_pci_map_iomem_walk(struct pci_dev *pdev, void *_data)
+{
+	struct um_pci_map_iomem_data *data = _data;
+	struct um_pci_device_reg *reg = &um_pci_devices[pdev->devfn / 8];
+	struct um_pci_device *dev;
+	int i;
+
+	if (!reg->dev)
+		return 0;
+
+	for (i = 0; i < ARRAY_SIZE(dev->resptr); i++) {
+		struct resource *r = &pdev->resource[i];
+
+		if ((r->flags & IORESOURCE_TYPE_BITS) != IORESOURCE_MEM)
+			continue;
+
+		/*
+		 * must be the whole or part of the resource,
+		 * not allowed to only overlap
+		 */
+		if (data->offset < r->start || data->offset > r->end)
+			continue;
+		if (data->offset + data->size - 1 > r->end)
+			continue;
+
+		dev = reg->dev;
+		*data->ops = &um_pci_device_bar_ops;
+		dev->resptr[i] = i;
+		*data->priv = &dev->resptr[i];
+		data->ret = data->offset - r->start;
+
+		/* no need to continue */
+		return 1;
+	}
+
+	return 0;
+}
+
+static long um_pci_map_iomem(unsigned long offset, size_t size,
+			     const struct logic_iomem_ops **ops,
+			     void **priv)
+{
+	struct um_pci_map_iomem_data data = {
+		/* we want the full address here */
+		.offset = offset + virt_iomem_resource.start,
+		.size = size,
+		.ops = ops,
+		.priv = priv,
+		.ret = -ENOENT,
+	};
+
+	pci_walk_bus(bridge->bus, um_pci_map_iomem_walk, &data);
+	return data.ret;
+}
+
+static const struct logic_iomem_region_ops um_pci_iomem_ops = {
+	.map = um_pci_map_iomem,
+};
+
+static void um_pci_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
+{
+	/*
+	 * This is a very low address and not actually valid 'physical' memory
+	 * in UML, so we can simply map MSI(-X) vectors to there, it cannot be
+	 * legitimately written to by the device in any other way.
+	 * We use the (virtual) IRQ number here as the message to simplify the
+	 * code that receives the message, where for now we simply trust the
+	 * device to send the correct message.
+	 */
+	msg->address_hi = 0;
+	msg->address_lo = 0xa0000;
+	msg->data = data->irq;
+}
+
+static struct irq_chip um_pci_msi_bottom_irq_chip = {
+	.name = "UM virtual MSI",
+	.irq_compose_msi_msg = um_pci_compose_msi_msg,
+};
+
+static int um_pci_inner_domain_alloc(struct irq_domain *domain,
+				     unsigned int virq, unsigned int nr_irqs,
+				     void *args)
+{
+	unsigned long bit;
+
+	WARN_ON(nr_irqs != 1);
+
+	mutex_lock(&um_pci_mtx);
+	bit = find_first_zero_bit(um_pci_msi_used, MAX_MSI_VECTORS);
+	if (bit >= MAX_MSI_VECTORS) {
+		mutex_unlock(&um_pci_mtx);
+		return -ENOSPC;
+	}
+
+	set_bit(bit, um_pci_msi_used);
+	mutex_unlock(&um_pci_mtx);
+
+	irq_domain_set_info(domain, virq, bit, &um_pci_msi_bottom_irq_chip,
+			    domain->host_data, handle_simple_irq,
+			    NULL, NULL);
+
+	return 0;
+}
+
+static void um_pci_inner_domain_free(struct irq_domain *domain,
+				     unsigned int virq, unsigned int nr_irqs)
+{
+	struct irq_data *d = irq_domain_get_irq_data(domain, virq);
+
+	mutex_lock(&um_pci_mtx);
+
+	if (!test_bit(d->hwirq, um_pci_msi_used))
+		pr_err("trying to free unused MSI#%lu\n", d->hwirq);
+	else
+		__clear_bit(d->hwirq, um_pci_msi_used);
+
+	mutex_unlock(&um_pci_mtx);
+}
+
+static const struct irq_domain_ops um_pci_inner_domain_ops = {
+	.select = msi_lib_irq_domain_select,
+	.alloc = um_pci_inner_domain_alloc,
+	.free = um_pci_inner_domain_free,
+};
+
+#define UM_PCI_MSI_FLAGS_REQUIRED (MSI_FLAG_USE_DEF_DOM_OPS		| \
+				   MSI_FLAG_USE_DEF_CHIP_OPS		| \
+				   MSI_FLAG_NO_AFFINITY)
+#define UM_PCI_MSI_FLAGS_SUPPORTED (MSI_GENERIC_FLAGS_MASK		| \
+				    MSI_FLAG_PCI_MSIX)
+
+static const struct msi_parent_ops um_pci_msi_parent_ops = {
+	.required_flags		= UM_PCI_MSI_FLAGS_REQUIRED,
+	.supported_flags	= UM_PCI_MSI_FLAGS_SUPPORTED,
+	.bus_select_token	= DOMAIN_BUS_NEXUS,
+	.bus_select_mask	= MATCH_PCI_MSI,
+	.prefix			= "UM-virtual-",
+	.init_dev_msi_info	= msi_lib_init_dev_msi_info,
+};
+
+static struct resource busn_resource = {
+	.name	= "PCI busn",
+	.start	= 0,
+	.end	= 0,
+	.flags	= IORESOURCE_BUS,
+};
+
+static int um_pci_map_irq(const struct pci_dev *pdev, u8 slot, u8 pin)
+{
+	struct um_pci_device_reg *reg = &um_pci_devices[pdev->devfn / 8];
+
+	if (WARN_ON(!reg->dev))
+		return -EINVAL;
+
+	/* Yes, we map all pins to the same IRQ ... doesn't matter for now. */
+	return reg->dev->irq;
+}
+
+void *pci_root_bus_fwnode(struct pci_bus *bus)
+{
+	return um_pci_fwnode;
+}
+
+static long um_pci_map_platform(unsigned long offset, size_t size,
+				const struct logic_iomem_ops **ops,
+				void **priv)
+{
+	if (!um_pci_platform_device)
+		return -ENOENT;
+
+	*ops = &um_pci_device_bar_ops;
+	*priv = &um_pci_platform_device->resptr[0];
+
+	return offset;
+}
+
+static const struct logic_iomem_region_ops um_pci_platform_ops = {
+	.map = um_pci_map_platform,
+};
+
+static struct resource virt_platform_resource = {
+	.name = "platform",
+	.start = 0x10000000,
+	.end = 0x1fffffff,
+	.flags = IORESOURCE_MEM,
+};
+
+int um_pci_device_register(struct um_pci_device *dev)
+{
+	int i, free = -1;
+	int err = 0;
+
+	mutex_lock(&um_pci_mtx);
+	for (i = 0; i < MAX_DEVICES; i++) {
+		if (um_pci_devices[i].dev)
+			continue;
+		free = i;
+		break;
+	}
+
+	if (free < 0) {
+		err = -ENOSPC;
+		goto out;
+	}
+
+	dev->irq = irq_alloc_desc(numa_node_id());
+	if (dev->irq < 0) {
+		err = dev->irq;
+		goto out;
+	}
+
+	um_pci_devices[free].dev = dev;
+
+out:
+	mutex_unlock(&um_pci_mtx);
+	if (!err)
+		um_pci_rescan();
+	return err;
+}
+
+void um_pci_device_unregister(struct um_pci_device *dev)
+{
+	int i;
+
+	mutex_lock(&um_pci_mtx);
+	for (i = 0; i < MAX_DEVICES; i++) {
+		if (um_pci_devices[i].dev != dev)
+			continue;
+		um_pci_devices[i].dev = NULL;
+		irq_free_desc(dev->irq);
+		break;
+	}
+	mutex_unlock(&um_pci_mtx);
+
+	if (i < MAX_DEVICES) {
+		struct pci_dev *pci_dev;
+
+		pci_dev = pci_get_slot(bridge->bus, i);
+		if (pci_dev)
+			pci_stop_and_remove_bus_device_locked(pci_dev);
+	}
+}
+
+int um_pci_platform_device_register(struct um_pci_device *dev)
+{
+	guard(mutex)(&um_pci_mtx);
+	if (um_pci_platform_device)
+		return -EBUSY;
+	um_pci_platform_device = dev;
+	return 0;
+}
+
+void um_pci_platform_device_unregister(struct um_pci_device *dev)
+{
+	guard(mutex)(&um_pci_mtx);
+	if (um_pci_platform_device == dev)
+		um_pci_platform_device = NULL;
+}
+
+static int __init um_pci_init(void)
+{
+	int err, i;
+
+	WARN_ON(logic_iomem_add_region(&virt_cfgspace_resource,
+				       &um_pci_cfgspace_ops));
+	WARN_ON(logic_iomem_add_region(&virt_iomem_resource,
+				       &um_pci_iomem_ops));
+	WARN_ON(logic_iomem_add_region(&virt_platform_resource,
+				       &um_pci_platform_ops));
+
+	bridge = pci_alloc_host_bridge(0);
+	if (!bridge) {
+		err = -ENOMEM;
+		goto free;
+	}
+
+	um_pci_fwnode = irq_domain_alloc_named_fwnode("um-pci");
+	if (!um_pci_fwnode) {
+		err = -ENOMEM;
+		goto free;
+	}
+
+	struct irq_domain_info info = {
+		.fwnode		= um_pci_fwnode,
+		.ops		= &um_pci_inner_domain_ops,
+		.size		= MAX_MSI_VECTORS,
+	};
+
+	um_pci_inner_domain = msi_create_parent_irq_domain(&info, &um_pci_msi_parent_ops);
+	if (!um_pci_inner_domain) {
+		err = -ENOMEM;
+		goto free;
+	}
+
+	pci_add_resource(&bridge->windows, &virt_iomem_resource);
+	pci_add_resource(&bridge->windows, &busn_resource);
+	bridge->ops = &um_pci_ops;
+	bridge->map_irq = um_pci_map_irq;
+
+	for (i = 0; i < MAX_DEVICES; i++) {
+		resource_size_t start;
+
+		start = virt_cfgspace_resource.start + i * CFG_SPACE_SIZE;
+		um_pci_devices[i].iomem = ioremap(start, CFG_SPACE_SIZE);
+		if (WARN(!um_pci_devices[i].iomem, "failed to map %d\n", i)) {
+			err = -ENOMEM;
+			goto free;
+		}
+	}
+
+	err = pci_host_probe(bridge);
+	if (err)
+		goto free;
+
+	return 0;
+
+free:
+	if (um_pci_inner_domain)
+		irq_domain_remove(um_pci_inner_domain);
+	if (um_pci_fwnode)
+		irq_domain_free_fwnode(um_pci_fwnode);
+	if (bridge) {
+		pci_free_resource_list(&bridge->windows);
+		pci_free_host_bridge(bridge);
+	}
+	return err;
+}
+device_initcall(um_pci_init);
+
+static void __exit um_pci_exit(void)
+{
+	irq_domain_remove(um_pci_inner_domain);
+	pci_free_resource_list(&bridge->windows);
+	pci_free_host_bridge(bridge);
+}
+module_exit(um_pci_exit);
diff --git a/arch/um/drivers/virt-pci.h b/arch/um/drivers/virt-pci.h
new file mode 100644
index 000000000..b20d1475d
--- /dev/null
+++ b/arch/um/drivers/virt-pci.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UM_VIRT_PCI_H
+#define __UM_VIRT_PCI_H
+
+#include <linux/pci.h>
+
+struct um_pci_device {
+	const struct um_pci_ops *ops;
+
+	/* for now just standard BARs */
+	u8 resptr[PCI_STD_NUM_BARS];
+
+	int irq;
+};
+
+struct um_pci_ops {
+	unsigned long (*cfgspace_read)(struct um_pci_device *dev,
+				       unsigned int offset, int size);
+	void (*cfgspace_write)(struct um_pci_device *dev, unsigned int offset,
+			       int size, unsigned long val);
+
+	unsigned long (*bar_read)(struct um_pci_device *dev, int bar,
+				  unsigned int offset, int size);
+	void (*bar_write)(struct um_pci_device *dev, int bar,
+			  unsigned int offset, int size, unsigned long val);
+
+	void (*bar_copy_from)(struct um_pci_device *dev, int bar, void *buffer,
+			      unsigned int offset, int size);
+	void (*bar_copy_to)(struct um_pci_device *dev, int bar,
+			    unsigned int offset, const void *buffer, int size);
+	void (*bar_set)(struct um_pci_device *dev, int bar,
+			unsigned int offset, u8 value, int size);
+};
+
+int um_pci_device_register(struct um_pci_device *dev);
+void um_pci_device_unregister(struct um_pci_device *dev);
+
+int um_pci_platform_device_register(struct um_pci_device *dev);
+void um_pci_platform_device_unregister(struct um_pci_device *dev);
+
+#endif /* __UM_VIRT_PCI_H */
diff --git a/arch/um/drivers/virtio_pcidev.c b/arch/um/drivers/virtio_pcidev.c
new file mode 100644
index 000000000..2bf5a645d
--- /dev/null
+++ b/arch/um/drivers/virtio_pcidev.c
@@ -0,0 +1,634 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2020 Intel Corporation
+ * Author: Johannes Berg <johannes@sipsolutions.net>
+ */
+#include <linux/module.h>
+#include <linux/pci.h>
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <linux/logic_iomem.h>
+#include <linux/of_platform.h>
+#include <linux/irqdomain.h>
+#include <linux/virtio_pcidev.h>
+#include <linux/virtio-uml.h>
+#include <linux/delay.h>
+#include <linux/msi.h>
+#include <linux/unaligned.h>
+#include <irq_kern.h>
+
+#include "virt-pci.h"
+
+#define to_virtio_pcidev(_pdev) \
+	container_of(_pdev, struct virtio_pcidev_device, pdev)
+
+/* for MSI-X we have a 32-bit payload */
+#define MAX_IRQ_MSG_SIZE (sizeof(struct virtio_pcidev_msg) + sizeof(u32))
+#define NUM_IRQ_MSGS	10
+
+struct virtio_pcidev_message_buffer {
+	struct virtio_pcidev_msg hdr;
+	u8 data[8];
+};
+
+struct virtio_pcidev_device {
+	struct um_pci_device pdev;
+	struct virtio_device *vdev;
+
+	struct virtqueue *cmd_vq, *irq_vq;
+
+#define VIRTIO_PCIDEV_WRITE_BUFS	20
+	struct virtio_pcidev_message_buffer bufs[VIRTIO_PCIDEV_WRITE_BUFS + 1];
+	void *extra_ptrs[VIRTIO_PCIDEV_WRITE_BUFS + 1];
+	DECLARE_BITMAP(used_bufs, VIRTIO_PCIDEV_WRITE_BUFS);
+
+#define VIRTIO_PCIDEV_STAT_WAITING	0
+	unsigned long status;
+
+	bool platform;
+};
+
+static unsigned int virtio_pcidev_max_delay_us = 40000;
+module_param_named(max_delay_us, virtio_pcidev_max_delay_us, uint, 0644);
+
+static int virtio_pcidev_get_buf(struct virtio_pcidev_device *dev, bool *posted)
+{
+	int i;
+
+	for (i = 0; i < VIRTIO_PCIDEV_WRITE_BUFS; i++) {
+		if (!test_and_set_bit(i, dev->used_bufs))
+			return i;
+	}
+
+	*posted = false;
+	return VIRTIO_PCIDEV_WRITE_BUFS;
+}
+
+static void virtio_pcidev_free_buf(struct virtio_pcidev_device *dev, void *buf)
+{
+	int i;
+
+	if (buf == &dev->bufs[VIRTIO_PCIDEV_WRITE_BUFS]) {
+		kfree(dev->extra_ptrs[VIRTIO_PCIDEV_WRITE_BUFS]);
+		dev->extra_ptrs[VIRTIO_PCIDEV_WRITE_BUFS] = NULL;
+		return;
+	}
+
+	for (i = 0; i < VIRTIO_PCIDEV_WRITE_BUFS; i++) {
+		if (buf == &dev->bufs[i]) {
+			kfree(dev->extra_ptrs[i]);
+			dev->extra_ptrs[i] = NULL;
+			WARN_ON(!test_and_clear_bit(i, dev->used_bufs));
+			return;
+		}
+	}
+
+	WARN_ON(1);
+}
+
+static int virtio_pcidev_send_cmd(struct virtio_pcidev_device *dev,
+				  struct virtio_pcidev_msg *cmd,
+				  unsigned int cmd_size,
+				  const void *extra, unsigned int extra_size,
+				  void *out, unsigned int out_size)
+{
+	struct scatterlist out_sg, extra_sg, in_sg;
+	struct scatterlist *sgs_list[] = {
+		[0] = &out_sg,
+		[1] = extra ? &extra_sg : &in_sg,
+		[2] = extra ? &in_sg : NULL,
+	};
+	struct virtio_pcidev_message_buffer *buf;
+	int delay_count = 0;
+	bool bounce_out;
+	int ret, len;
+	int buf_idx;
+	bool posted;
+
+	if (WARN_ON(cmd_size < sizeof(*cmd) || cmd_size > sizeof(*buf)))
+		return -EINVAL;
+
+	switch (cmd->op) {
+	case VIRTIO_PCIDEV_OP_CFG_WRITE:
+	case VIRTIO_PCIDEV_OP_MMIO_WRITE:
+	case VIRTIO_PCIDEV_OP_MMIO_MEMSET:
+		/* in PCI, writes are posted, so don't wait */
+		posted = !out;
+		WARN_ON(!posted);
+		break;
+	default:
+		posted = false;
+		break;
+	}
+
+	bounce_out = !posted && cmd_size <= sizeof(*cmd) &&
+		     out && out_size <= sizeof(buf->data);
+
+	buf_idx = virtio_pcidev_get_buf(dev, &posted);
+	buf = &dev->bufs[buf_idx];
+	memcpy(buf, cmd, cmd_size);
+
+	if (posted && extra && extra_size > sizeof(buf) - cmd_size) {
+		dev->extra_ptrs[buf_idx] = kmemdup(extra, extra_size,
+						   GFP_ATOMIC);
+
+		if (!dev->extra_ptrs[buf_idx]) {
+			virtio_pcidev_free_buf(dev, buf);
+			return -ENOMEM;
+		}
+		extra = dev->extra_ptrs[buf_idx];
+	} else if (extra && extra_size <= sizeof(buf) - cmd_size) {
+		memcpy((u8 *)buf + cmd_size, extra, extra_size);
+		cmd_size += extra_size;
+		extra_size = 0;
+		extra = NULL;
+		cmd = (void *)buf;
+	} else {
+		cmd = (void *)buf;
+	}
+
+	sg_init_one(&out_sg, cmd, cmd_size);
+	if (extra)
+		sg_init_one(&extra_sg, extra, extra_size);
+	/* allow stack for small buffers */
+	if (bounce_out)
+		sg_init_one(&in_sg, buf->data, out_size);
+	else if (out)
+		sg_init_one(&in_sg, out, out_size);
+
+	/* add to internal virtio queue */
+	ret = virtqueue_add_sgs(dev->cmd_vq, sgs_list,
+				extra ? 2 : 1,
+				out ? 1 : 0,
+				cmd, GFP_ATOMIC);
+	if (ret) {
+		virtio_pcidev_free_buf(dev, buf);
+		return ret;
+	}
+
+	if (posted) {
+		virtqueue_kick(dev->cmd_vq);
+		return 0;
+	}
+
+	/* kick and poll for getting a response on the queue */
+	set_bit(VIRTIO_PCIDEV_STAT_WAITING, &dev->status);
+	virtqueue_kick(dev->cmd_vq);
+	ret = 0;
+
+	while (1) {
+		void *completed = virtqueue_get_buf(dev->cmd_vq, &len);
+
+		if (completed == buf)
+			break;
+
+		if (completed)
+			virtio_pcidev_free_buf(dev, completed);
+
+		if (WARN_ONCE(virtqueue_is_broken(dev->cmd_vq) ||
+			      ++delay_count > virtio_pcidev_max_delay_us,
+			      "um virt-pci delay: %d", delay_count)) {
+			ret = -EIO;
+			break;
+		}
+		udelay(1);
+	}
+	clear_bit(VIRTIO_PCIDEV_STAT_WAITING, &dev->status);
+
+	if (bounce_out)
+		memcpy(out, buf->data, out_size);
+
+	virtio_pcidev_free_buf(dev, buf);
+
+	return ret;
+}
+
+static unsigned long virtio_pcidev_cfgspace_read(struct um_pci_device *pdev,
+						 unsigned int offset, int size)
+{
+	struct virtio_pcidev_device *dev = to_virtio_pcidev(pdev);
+	struct virtio_pcidev_msg hdr = {
+		.op = VIRTIO_PCIDEV_OP_CFG_READ,
+		.size = size,
+		.addr = offset,
+	};
+	/* max 8, we might not use it all */
+	u8 data[8];
+
+	memset(data, 0xff, sizeof(data));
+
+	/* size has been checked in um_pci_cfgspace_read() */
+	if (virtio_pcidev_send_cmd(dev, &hdr, sizeof(hdr), NULL, 0, data, size))
+		return ULONG_MAX;
+
+	switch (size) {
+	case 1:
+		return data[0];
+	case 2:
+		return le16_to_cpup((void *)data);
+	case 4:
+		return le32_to_cpup((void *)data);
+#ifdef CONFIG_64BIT
+	case 8:
+		return le64_to_cpup((void *)data);
+#endif
+	default:
+		return ULONG_MAX;
+	}
+}
+
+static void virtio_pcidev_cfgspace_write(struct um_pci_device *pdev,
+					 unsigned int offset, int size,
+					 unsigned long val)
+{
+	struct virtio_pcidev_device *dev = to_virtio_pcidev(pdev);
+	struct {
+		struct virtio_pcidev_msg hdr;
+		/* maximum size - we may only use parts of it */
+		u8 data[8];
+	} msg = {
+		.hdr = {
+			.op = VIRTIO_PCIDEV_OP_CFG_WRITE,
+			.size = size,
+			.addr = offset,
+		},
+	};
+
+	/* size has been checked in um_pci_cfgspace_write() */
+	switch (size) {
+	case 1:
+		msg.data[0] = (u8)val;
+		break;
+	case 2:
+		put_unaligned_le16(val, (void *)msg.data);
+		break;
+	case 4:
+		put_unaligned_le32(val, (void *)msg.data);
+		break;
+#ifdef CONFIG_64BIT
+	case 8:
+		put_unaligned_le64(val, (void *)msg.data);
+		break;
+#endif
+	}
+
+	WARN_ON(virtio_pcidev_send_cmd(dev, &msg.hdr, sizeof(msg), NULL, 0, NULL, 0));
+}
+
+static void virtio_pcidev_bar_copy_from(struct um_pci_device *pdev,
+					int bar, void *buffer,
+					unsigned int offset, int size)
+{
+	struct virtio_pcidev_device *dev = to_virtio_pcidev(pdev);
+	struct virtio_pcidev_msg hdr = {
+		.op = VIRTIO_PCIDEV_OP_MMIO_READ,
+		.bar = bar,
+		.size = size,
+		.addr = offset,
+	};
+
+	memset(buffer, 0xff, size);
+
+	virtio_pcidev_send_cmd(dev, &hdr, sizeof(hdr), NULL, 0, buffer, size);
+}
+
+static unsigned long virtio_pcidev_bar_read(struct um_pci_device *pdev, int bar,
+					    unsigned int offset, int size)
+{
+	/* 8 is maximum size - we may only use parts of it */
+	u8 data[8];
+
+	/* size has been checked in um_pci_bar_read() */
+	virtio_pcidev_bar_copy_from(pdev, bar, data, offset, size);
+
+	switch (size) {
+	case 1:
+		return data[0];
+	case 2:
+		return le16_to_cpup((void *)data);
+	case 4:
+		return le32_to_cpup((void *)data);
+#ifdef CONFIG_64BIT
+	case 8:
+		return le64_to_cpup((void *)data);
+#endif
+	default:
+		return ULONG_MAX;
+	}
+}
+
+static void virtio_pcidev_bar_copy_to(struct um_pci_device *pdev,
+				      int bar, unsigned int offset,
+				      const void *buffer, int size)
+{
+	struct virtio_pcidev_device *dev = to_virtio_pcidev(pdev);
+	struct virtio_pcidev_msg hdr = {
+		.op = VIRTIO_PCIDEV_OP_MMIO_WRITE,
+		.bar = bar,
+		.size = size,
+		.addr = offset,
+	};
+
+	virtio_pcidev_send_cmd(dev, &hdr, sizeof(hdr), buffer, size, NULL, 0);
+}
+
+static void virtio_pcidev_bar_write(struct um_pci_device *pdev, int bar,
+				    unsigned int offset, int size,
+				    unsigned long val)
+{
+	/* maximum size - we may only use parts of it */
+	u8 data[8];
+
+	/* size has been checked in um_pci_bar_write() */
+	switch (size) {
+	case 1:
+		data[0] = (u8)val;
+		break;
+	case 2:
+		put_unaligned_le16(val, (void *)data);
+		break;
+	case 4:
+		put_unaligned_le32(val, (void *)data);
+		break;
+#ifdef CONFIG_64BIT
+	case 8:
+		put_unaligned_le64(val, (void *)data);
+		break;
+#endif
+	}
+
+	virtio_pcidev_bar_copy_to(pdev, bar, offset, data, size);
+}
+
+static void virtio_pcidev_bar_set(struct um_pci_device *pdev, int bar,
+				  unsigned int offset, u8 value, int size)
+{
+	struct virtio_pcidev_device *dev = to_virtio_pcidev(pdev);
+	struct {
+		struct virtio_pcidev_msg hdr;
+		u8 data;
+	} msg = {
+		.hdr = {
+			.op = VIRTIO_PCIDEV_OP_CFG_WRITE,
+			.bar = bar,
+			.size = size,
+			.addr = offset,
+		},
+		.data = value,
+	};
+
+	virtio_pcidev_send_cmd(dev, &msg.hdr, sizeof(msg), NULL, 0, NULL, 0);
+}
+
+static const struct um_pci_ops virtio_pcidev_um_pci_ops = {
+	.cfgspace_read	= virtio_pcidev_cfgspace_read,
+	.cfgspace_write	= virtio_pcidev_cfgspace_write,
+	.bar_read	= virtio_pcidev_bar_read,
+	.bar_write	= virtio_pcidev_bar_write,
+	.bar_copy_from	= virtio_pcidev_bar_copy_from,
+	.bar_copy_to	= virtio_pcidev_bar_copy_to,
+	.bar_set	= virtio_pcidev_bar_set,
+};
+
+static void virtio_pcidev_irq_vq_addbuf(struct virtqueue *vq, void *buf, bool kick)
+{
+	struct scatterlist sg[1];
+
+	sg_init_one(sg, buf, MAX_IRQ_MSG_SIZE);
+	if (virtqueue_add_inbuf(vq, sg, 1, buf, GFP_ATOMIC))
+		kfree(buf);
+	else if (kick)
+		virtqueue_kick(vq);
+}
+
+static void virtio_pcidev_handle_irq_message(struct virtqueue *vq,
+					     struct virtio_pcidev_msg *msg)
+{
+	struct virtio_device *vdev = vq->vdev;
+	struct virtio_pcidev_device *dev = vdev->priv;
+
+	if (!dev->pdev.irq)
+		return;
+
+	/* we should properly chain interrupts, but on ARCH=um we don't care */
+
+	switch (msg->op) {
+	case VIRTIO_PCIDEV_OP_INT:
+		generic_handle_irq(dev->pdev.irq);
+		break;
+	case VIRTIO_PCIDEV_OP_MSI:
+		/* our MSI message is just the interrupt number */
+		if (msg->size == sizeof(u32))
+			generic_handle_irq(le32_to_cpup((void *)msg->data));
+		else
+			generic_handle_irq(le16_to_cpup((void *)msg->data));
+		break;
+	case VIRTIO_PCIDEV_OP_PME:
+		/* nothing to do - we already woke up due to the message */
+		break;
+	default:
+		dev_err(&vdev->dev, "unexpected virt-pci message %d\n", msg->op);
+		break;
+	}
+}
+
+static void virtio_pcidev_cmd_vq_cb(struct virtqueue *vq)
+{
+	struct virtio_device *vdev = vq->vdev;
+	struct virtio_pcidev_device *dev = vdev->priv;
+	void *cmd;
+	int len;
+
+	if (test_bit(VIRTIO_PCIDEV_STAT_WAITING, &dev->status))
+		return;
+
+	while ((cmd = virtqueue_get_buf(vq, &len)))
+		virtio_pcidev_free_buf(dev, cmd);
+}
+
+static void virtio_pcidev_irq_vq_cb(struct virtqueue *vq)
+{
+	struct virtio_pcidev_msg *msg;
+	int len;
+
+	while ((msg = virtqueue_get_buf(vq, &len))) {
+		if (len >= sizeof(*msg))
+			virtio_pcidev_handle_irq_message(vq, msg);
+
+		/* recycle the message buffer */
+		virtio_pcidev_irq_vq_addbuf(vq, msg, true);
+	}
+}
+
+static int virtio_pcidev_init_vqs(struct virtio_pcidev_device *dev)
+{
+	struct virtqueue_info vqs_info[] = {
+		{ "cmd", virtio_pcidev_cmd_vq_cb },
+		{ "irq", virtio_pcidev_irq_vq_cb },
+	};
+	struct virtqueue *vqs[2];
+	int err, i;
+
+	err = virtio_find_vqs(dev->vdev, 2, vqs, vqs_info, NULL);
+	if (err)
+		return err;
+
+	dev->cmd_vq = vqs[0];
+	dev->irq_vq = vqs[1];
+
+	virtio_device_ready(dev->vdev);
+
+	for (i = 0; i < NUM_IRQ_MSGS; i++) {
+		void *msg = kzalloc(MAX_IRQ_MSG_SIZE, GFP_KERNEL);
+
+		if (msg)
+			virtio_pcidev_irq_vq_addbuf(dev->irq_vq, msg, false);
+	}
+
+	virtqueue_kick(dev->irq_vq);
+
+	return 0;
+}
+
+static void __virtio_pcidev_virtio_platform_remove(struct virtio_device *vdev,
+						   struct virtio_pcidev_device *dev)
+{
+	um_pci_platform_device_unregister(&dev->pdev);
+
+	virtio_reset_device(vdev);
+	vdev->config->del_vqs(vdev);
+
+	kfree(dev);
+}
+
+static int virtio_pcidev_virtio_platform_probe(struct virtio_device *vdev,
+					       struct virtio_pcidev_device *dev)
+{
+	int err;
+
+	dev->platform = true;
+
+	err = virtio_pcidev_init_vqs(dev);
+	if (err)
+		goto err_free;
+
+	err = um_pci_platform_device_register(&dev->pdev);
+	if (err)
+		goto err_reset;
+
+	err = of_platform_default_populate(vdev->dev.of_node, NULL, &vdev->dev);
+	if (err)
+		goto err_unregister;
+
+	return 0;
+
+err_unregister:
+	um_pci_platform_device_unregister(&dev->pdev);
+err_reset:
+	virtio_reset_device(vdev);
+	vdev->config->del_vqs(vdev);
+err_free:
+	kfree(dev);
+	return err;
+}
+
+static int virtio_pcidev_virtio_probe(struct virtio_device *vdev)
+{
+	struct virtio_pcidev_device *dev;
+	int err;
+
+	dev = kzalloc_obj(*dev);
+	if (!dev)
+		return -ENOMEM;
+
+	dev->vdev = vdev;
+	vdev->priv = dev;
+
+	dev->pdev.ops = &virtio_pcidev_um_pci_ops;
+
+	if (of_device_is_compatible(vdev->dev.of_node, "simple-bus"))
+		return virtio_pcidev_virtio_platform_probe(vdev, dev);
+
+	err = virtio_pcidev_init_vqs(dev);
+	if (err)
+		goto err_free;
+
+	err = um_pci_device_register(&dev->pdev);
+	if (err)
+		goto err_reset;
+
+	device_set_wakeup_enable(&vdev->dev, true);
+
+	/*
+	 * In order to do suspend-resume properly, don't allow VQs
+	 * to be suspended.
+	 */
+	virtio_uml_set_no_vq_suspend(vdev, true);
+
+	return 0;
+
+err_reset:
+	virtio_reset_device(vdev);
+	vdev->config->del_vqs(vdev);
+err_free:
+	kfree(dev);
+	return err;
+}
+
+static void virtio_pcidev_virtio_remove(struct virtio_device *vdev)
+{
+	struct virtio_pcidev_device *dev = vdev->priv;
+
+	if (dev->platform) {
+		of_platform_depopulate(&vdev->dev);
+		__virtio_pcidev_virtio_platform_remove(vdev, dev);
+		return;
+	}
+
+	device_set_wakeup_enable(&vdev->dev, false);
+
+	um_pci_device_unregister(&dev->pdev);
+
+	/* Stop all virtqueues */
+	virtio_reset_device(vdev);
+	dev->cmd_vq = NULL;
+	dev->irq_vq = NULL;
+	vdev->config->del_vqs(vdev);
+
+	kfree(dev);
+}
+
+static void virtio_pcidev_virtio_shutdown(struct virtio_device *vdev)
+{
+	/* nothing to do, we just don't want queue shutdown */
+}
+
+static struct virtio_device_id id_table[] = {
+	{ CONFIG_UML_PCI_OVER_VIRTIO_DEVICE_ID, VIRTIO_DEV_ANY_ID },
+	{ 0 },
+};
+MODULE_DEVICE_TABLE(virtio, id_table);
+
+static struct virtio_driver virtio_pcidev_virtio_driver = {
+	.driver.name = "virtio-pci",
+	.id_table = id_table,
+	.probe = virtio_pcidev_virtio_probe,
+	.remove = virtio_pcidev_virtio_remove,
+	.shutdown = virtio_pcidev_virtio_shutdown,
+};
+
+static int __init virtio_pcidev_init(void)
+{
+	if (WARN(CONFIG_UML_PCI_OVER_VIRTIO_DEVICE_ID < 0,
+		 "No virtio device ID configured for PCI - no PCI support\n"))
+		return 0;
+
+	return register_virtio_driver(&virtio_pcidev_virtio_driver);
+}
+late_initcall(virtio_pcidev_init);
+
+static void __exit virtio_pcidev_exit(void)
+{
+	unregister_virtio_driver(&virtio_pcidev_virtio_driver);
+}
+module_exit(virtio_pcidev_exit);
diff --git a/arch/um/drivers/virtio_uml.c b/arch/um/drivers/virtio_uml.c
new file mode 100644
index 000000000..7425a8548
--- /dev/null
+++ b/arch/um/drivers/virtio_uml.c
@@ -0,0 +1,1544 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Virtio vhost-user driver
+ *
+ * Copyright(c) 2019 Intel Corporation
+ *
+ * This driver allows virtio devices to be used over a vhost-user socket.
+ *
+ * Guest devices can be instantiated by kernel module or command line
+ * parameters. One device will be created for each parameter. Syntax:
+ *
+ *		virtio_uml.device=<socket>:<virtio_id>[:<platform_id>]
+ * where:
+ *		<socket>	:= vhost-user socket path to connect
+ *		<virtio_id>	:= virtio device id (as in virtio_ids.h)
+ *		<platform_id>	:= (optional) platform device id
+ *
+ * example:
+ *		virtio_uml.device=/var/uml.socket:1
+ *
+ * Based on Virtio MMIO driver by Pawel Moll, copyright 2011-2014, ARM Ltd.
+ */
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/string_choices.h>
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <linux/virtio_ring.h>
+#include <linux/time-internal.h>
+#include <linux/virtio-uml.h>
+#include <shared/as-layout.h>
+#include <irq_kern.h>
+#include <init.h>
+#include <os.h>
+#include "mconsole_kern.h"
+#include "vhost_user.h"
+
+#define MAX_SUPPORTED_QUEUE_SIZE	256
+
+#define to_virtio_uml_device(_vdev) \
+	container_of(_vdev, struct virtio_uml_device, vdev)
+
+struct virtio_uml_platform_data {
+	u32 virtio_device_id;
+	const char *socket_path;
+	struct work_struct conn_broken_wk;
+	struct platform_device *pdev;
+};
+
+struct virtio_uml_device {
+	struct virtio_device vdev;
+	struct platform_device *pdev;
+	struct virtio_uml_platform_data *pdata;
+
+	raw_spinlock_t sock_lock;
+	int sock, req_fd, irq;
+	u64 features;
+	u64 protocol_features;
+	u64 max_vqs;
+	u8 status;
+	u8 registered:1;
+	u8 suspended:1;
+	u8 no_vq_suspend:1;
+
+	u8 config_changed_irq:1;
+	uint64_t vq_irq_vq_map;
+	int recv_rc;
+};
+
+struct virtio_uml_vq_info {
+	int kick_fd, call_fd;
+	char name[32];
+	bool suspended;
+};
+
+#define vu_err(vu_dev, ...)	dev_err(&(vu_dev)->pdev->dev, ##__VA_ARGS__)
+
+/* Vhost-user protocol */
+
+static int full_sendmsg_fds(int fd, const void *buf, unsigned int len,
+			    const int *fds, unsigned int fds_num)
+{
+	int rc;
+
+	do {
+		rc = os_sendmsg_fds(fd, buf, len, fds, fds_num);
+		if (rc > 0) {
+			buf += rc;
+			len -= rc;
+			fds = NULL;
+			fds_num = 0;
+		}
+	} while (len && (rc >= 0 || rc == -EINTR));
+
+	if (rc < 0)
+		return rc;
+	return 0;
+}
+
+static int full_read(int fd, void *buf, int len, bool abortable)
+{
+	int rc;
+
+	if (!len)
+		return 0;
+
+	do {
+		rc = os_read_file(fd, buf, len);
+		if (rc > 0) {
+			buf += rc;
+			len -= rc;
+		}
+	} while (len && (rc > 0 || rc == -EINTR || (!abortable && rc == -EAGAIN)));
+
+	if (rc < 0)
+		return rc;
+	if (rc == 0)
+		return -ECONNRESET;
+	return 0;
+}
+
+static int vhost_user_recv_header(int fd, struct vhost_user_msg *msg)
+{
+	return full_read(fd, msg, sizeof(msg->header), true);
+}
+
+static int vhost_user_recv(struct virtio_uml_device *vu_dev,
+			   int fd, struct vhost_user_msg *msg,
+			   size_t max_payload_size, bool wait)
+{
+	size_t size;
+	int rc;
+
+	/*
+	 * In virtio time-travel mode, we're handling all the vhost-user
+	 * FDs by polling them whenever appropriate. However, we may get
+	 * into a situation where we're sending out an interrupt message
+	 * to a device (e.g. a net device) and need to handle a simulation
+	 * time message while doing so, e.g. one that tells us to update
+	 * our idea of how long we can run without scheduling.
+	 *
+	 * Thus, we need to not just read() from the given fd, but need
+	 * to also handle messages for the simulation time - this function
+	 * does that for us while waiting for the given fd to be readable.
+	 */
+	if (wait)
+		time_travel_wait_readable(fd);
+
+	rc = vhost_user_recv_header(fd, msg);
+
+	if (rc)
+		return rc;
+	size = msg->header.size;
+	if (size > max_payload_size)
+		return -EPROTO;
+	return full_read(fd, &msg->payload, size, false);
+}
+
+static void vhost_user_check_reset(struct virtio_uml_device *vu_dev,
+				   int rc)
+{
+	struct virtio_uml_platform_data *pdata = vu_dev->pdata;
+
+	if (rc != -ECONNRESET)
+		return;
+
+	if (!vu_dev->registered)
+		return;
+
+	vu_dev->registered = 0;
+
+	schedule_work(&pdata->conn_broken_wk);
+}
+
+static int vhost_user_recv_resp(struct virtio_uml_device *vu_dev,
+				struct vhost_user_msg *msg,
+				size_t max_payload_size)
+{
+	int rc = vhost_user_recv(vu_dev, vu_dev->sock, msg,
+				 max_payload_size, true);
+
+	if (rc) {
+		vhost_user_check_reset(vu_dev, rc);
+		return rc;
+	}
+
+	if (msg->header.flags != (VHOST_USER_FLAG_REPLY | VHOST_USER_VERSION))
+		return -EPROTO;
+
+	return 0;
+}
+
+static int vhost_user_recv_u64(struct virtio_uml_device *vu_dev,
+			       u64 *value)
+{
+	struct vhost_user_msg msg;
+	int rc = vhost_user_recv_resp(vu_dev, &msg,
+				      sizeof(msg.payload.integer));
+
+	if (rc)
+		return rc;
+	if (msg.header.size != sizeof(msg.payload.integer))
+		return -EPROTO;
+	*value = msg.payload.integer;
+	return 0;
+}
+
+static int vhost_user_recv_req(struct virtio_uml_device *vu_dev,
+			       struct vhost_user_msg *msg,
+			       size_t max_payload_size)
+{
+	int rc = vhost_user_recv(vu_dev, vu_dev->req_fd, msg,
+				 max_payload_size, false);
+
+	if (rc)
+		return rc;
+
+	if ((msg->header.flags & ~VHOST_USER_FLAG_NEED_REPLY) !=
+			VHOST_USER_VERSION)
+		return -EPROTO;
+
+	return 0;
+}
+
+static int vhost_user_send(struct virtio_uml_device *vu_dev,
+			   bool need_response, struct vhost_user_msg *msg,
+			   int *fds, size_t num_fds)
+{
+	size_t size = sizeof(msg->header) + msg->header.size;
+	unsigned long flags;
+	bool request_ack;
+	int rc;
+
+	msg->header.flags |= VHOST_USER_VERSION;
+
+	/*
+	 * The need_response flag indicates that we already need a response,
+	 * e.g. to read the features. In these cases, don't request an ACK as
+	 * it is meaningless. Also request an ACK only if supported.
+	 */
+	request_ack = !need_response;
+	if (!(vu_dev->protocol_features &
+			BIT_ULL(VHOST_USER_PROTOCOL_F_REPLY_ACK)))
+		request_ack = false;
+
+	if (request_ack)
+		msg->header.flags |= VHOST_USER_FLAG_NEED_REPLY;
+
+	raw_spin_lock_irqsave(&vu_dev->sock_lock, flags);
+	rc = full_sendmsg_fds(vu_dev->sock, msg, size, fds, num_fds);
+	if (rc < 0)
+		goto out;
+
+	if (request_ack) {
+		uint64_t status;
+
+		rc = vhost_user_recv_u64(vu_dev, &status);
+		if (rc)
+			goto out;
+
+		if (status) {
+			vu_err(vu_dev, "slave reports error: %llu\n", status);
+			rc = -EIO;
+			goto out;
+		}
+	}
+
+out:
+	raw_spin_unlock_irqrestore(&vu_dev->sock_lock, flags);
+	return rc;
+}
+
+static int vhost_user_send_no_payload(struct virtio_uml_device *vu_dev,
+				      bool need_response, u32 request)
+{
+	struct vhost_user_msg msg = {
+		.header.request = request,
+	};
+
+	return vhost_user_send(vu_dev, need_response, &msg, NULL, 0);
+}
+
+static int vhost_user_send_no_payload_fd(struct virtio_uml_device *vu_dev,
+					 u32 request, int fd)
+{
+	struct vhost_user_msg msg = {
+		.header.request = request,
+	};
+
+	return vhost_user_send(vu_dev, false, &msg, &fd, 1);
+}
+
+static int vhost_user_send_u64(struct virtio_uml_device *vu_dev,
+			       u32 request, u64 value)
+{
+	struct vhost_user_msg msg = {
+		.header.request = request,
+		.header.size = sizeof(msg.payload.integer),
+		.payload.integer = value,
+	};
+
+	return vhost_user_send(vu_dev, false, &msg, NULL, 0);
+}
+
+static int vhost_user_set_owner(struct virtio_uml_device *vu_dev)
+{
+	return vhost_user_send_no_payload(vu_dev, false, VHOST_USER_SET_OWNER);
+}
+
+static int vhost_user_get_features(struct virtio_uml_device *vu_dev,
+				   u64 *features)
+{
+	int rc = vhost_user_send_no_payload(vu_dev, true,
+					    VHOST_USER_GET_FEATURES);
+
+	if (rc)
+		return rc;
+	return vhost_user_recv_u64(vu_dev, features);
+}
+
+static int vhost_user_set_features(struct virtio_uml_device *vu_dev,
+				   u64 features)
+{
+	return vhost_user_send_u64(vu_dev, VHOST_USER_SET_FEATURES, features);
+}
+
+static int vhost_user_get_protocol_features(struct virtio_uml_device *vu_dev,
+					    u64 *protocol_features)
+{
+	int rc = vhost_user_send_no_payload(vu_dev, true,
+			VHOST_USER_GET_PROTOCOL_FEATURES);
+
+	if (rc)
+		return rc;
+	return vhost_user_recv_u64(vu_dev, protocol_features);
+}
+
+static int vhost_user_set_protocol_features(struct virtio_uml_device *vu_dev,
+					    u64 protocol_features)
+{
+	return vhost_user_send_u64(vu_dev, VHOST_USER_SET_PROTOCOL_FEATURES,
+				   protocol_features);
+}
+
+static int vhost_user_get_queue_num(struct virtio_uml_device *vu_dev,
+				    u64 *queue_num)
+{
+	int rc = vhost_user_send_no_payload(vu_dev, true,
+			VHOST_USER_GET_QUEUE_NUM);
+
+	if (rc)
+		return rc;
+	return vhost_user_recv_u64(vu_dev, queue_num);
+}
+
+static void vhost_user_reply(struct virtio_uml_device *vu_dev,
+			     struct vhost_user_msg *msg, int response)
+{
+	struct vhost_user_msg reply = {
+		.payload.integer = response,
+	};
+	size_t size = sizeof(reply.header) + sizeof(reply.payload.integer);
+	int rc;
+
+	reply.header = msg->header;
+	reply.header.flags &= ~VHOST_USER_FLAG_NEED_REPLY;
+	reply.header.flags |= VHOST_USER_FLAG_REPLY;
+	reply.header.size = sizeof(reply.payload.integer);
+
+	rc = full_sendmsg_fds(vu_dev->req_fd, &reply, size, NULL, 0);
+
+	if (rc)
+		vu_err(vu_dev,
+		       "sending reply to slave request failed: %d (size %zu)\n",
+		       rc, size);
+}
+
+static irqreturn_t vu_req_read_message(struct virtio_uml_device *vu_dev,
+				       struct time_travel_event *ev)
+{
+	struct virtqueue *vq;
+	int response = 1;
+	struct {
+		struct vhost_user_msg msg;
+		u8 extra_payload[512];
+	} msg;
+	int rc;
+	irqreturn_t irq_rc = IRQ_NONE;
+
+	while (1) {
+		rc = vhost_user_recv_req(vu_dev, &msg.msg,
+					 sizeof(msg.msg.payload) +
+					 sizeof(msg.extra_payload));
+		if (rc)
+			break;
+
+		switch (msg.msg.header.request) {
+		case VHOST_USER_SLAVE_CONFIG_CHANGE_MSG:
+			vu_dev->config_changed_irq = true;
+			response = 0;
+			break;
+		case VHOST_USER_SLAVE_VRING_CALL:
+			virtio_device_for_each_vq((&vu_dev->vdev), vq) {
+				if (vq->index == msg.msg.payload.vring_state.index) {
+					response = 0;
+					vu_dev->vq_irq_vq_map |= BIT_ULL(vq->index);
+					break;
+				}
+			}
+			break;
+		case VHOST_USER_SLAVE_IOTLB_MSG:
+			/* not supported - VIRTIO_F_ACCESS_PLATFORM */
+		case VHOST_USER_SLAVE_VRING_HOST_NOTIFIER_MSG:
+			/* not supported - VHOST_USER_PROTOCOL_F_HOST_NOTIFIER */
+		default:
+			vu_err(vu_dev, "unexpected slave request %d\n",
+			       msg.msg.header.request);
+		}
+
+		if (ev && !vu_dev->suspended)
+			time_travel_add_irq_event(ev);
+
+		if (msg.msg.header.flags & VHOST_USER_FLAG_NEED_REPLY)
+			vhost_user_reply(vu_dev, &msg.msg, response);
+		irq_rc = IRQ_HANDLED;
+	}
+	/* mask EAGAIN as we try non-blocking read until socket is empty */
+	vu_dev->recv_rc = (rc == -EAGAIN) ? 0 : rc;
+	return irq_rc;
+}
+
+static irqreturn_t vu_req_interrupt(int irq, void *data)
+{
+	struct virtio_uml_device *vu_dev = data;
+	irqreturn_t ret = IRQ_HANDLED;
+
+	if (!um_irq_timetravel_handler_used())
+		ret = vu_req_read_message(vu_dev, NULL);
+
+	if (vu_dev->recv_rc) {
+		vhost_user_check_reset(vu_dev, vu_dev->recv_rc);
+	} else if (vu_dev->vq_irq_vq_map) {
+		struct virtqueue *vq;
+
+		virtio_device_for_each_vq((&vu_dev->vdev), vq) {
+			if (vu_dev->vq_irq_vq_map & BIT_ULL(vq->index))
+				vring_interrupt(0 /* ignored */, vq);
+		}
+		vu_dev->vq_irq_vq_map = 0;
+	} else if (vu_dev->config_changed_irq) {
+		virtio_config_changed(&vu_dev->vdev);
+		vu_dev->config_changed_irq = false;
+	}
+
+	return ret;
+}
+
+static void vu_req_interrupt_comm_handler(int irq, int fd, void *data,
+					  struct time_travel_event *ev)
+{
+	vu_req_read_message(data, ev);
+}
+
+static int vhost_user_init_slave_req(struct virtio_uml_device *vu_dev)
+{
+	int rc, req_fds[2];
+
+	/* Use a pipe for slave req fd, SIGIO is not supported for eventfd */
+	rc = os_pipe(req_fds, true, true);
+	if (rc < 0)
+		return rc;
+	vu_dev->req_fd = req_fds[0];
+
+	rc = um_request_irq_tt(UM_IRQ_ALLOC, vu_dev->req_fd, IRQ_READ,
+			       vu_req_interrupt, IRQF_SHARED,
+			       vu_dev->pdev->name, vu_dev,
+			       vu_req_interrupt_comm_handler);
+	if (rc < 0)
+		goto err_close;
+
+	vu_dev->irq = rc;
+
+	rc = vhost_user_send_no_payload_fd(vu_dev, VHOST_USER_SET_SLAVE_REQ_FD,
+					   req_fds[1]);
+	if (rc)
+		goto err_free_irq;
+
+	goto out;
+
+err_free_irq:
+	um_free_irq(vu_dev->irq, vu_dev);
+err_close:
+	os_close_file(req_fds[0]);
+out:
+	/* Close unused write end of request fds */
+	os_close_file(req_fds[1]);
+	return rc;
+}
+
+static int vhost_user_init(struct virtio_uml_device *vu_dev)
+{
+	int rc = vhost_user_set_owner(vu_dev);
+
+	if (rc)
+		return rc;
+	rc = vhost_user_get_features(vu_dev, &vu_dev->features);
+	if (rc)
+		return rc;
+
+	if (vu_dev->features & BIT_ULL(VHOST_USER_F_PROTOCOL_FEATURES)) {
+		rc = vhost_user_get_protocol_features(vu_dev,
+				&vu_dev->protocol_features);
+		if (rc)
+			return rc;
+		vu_dev->protocol_features &= VHOST_USER_SUPPORTED_PROTOCOL_F;
+		rc = vhost_user_set_protocol_features(vu_dev,
+				vu_dev->protocol_features);
+		if (rc)
+			return rc;
+	}
+
+	if (vu_dev->protocol_features &
+			BIT_ULL(VHOST_USER_PROTOCOL_F_SLAVE_REQ)) {
+		rc = vhost_user_init_slave_req(vu_dev);
+		if (rc)
+			return rc;
+	}
+
+	if (vu_dev->protocol_features &
+			BIT_ULL(VHOST_USER_PROTOCOL_F_MQ)) {
+		rc = vhost_user_get_queue_num(vu_dev, &vu_dev->max_vqs);
+		if (rc)
+			return rc;
+	} else {
+		vu_dev->max_vqs = U64_MAX;
+	}
+
+	return 0;
+}
+
+static void vhost_user_get_config(struct virtio_uml_device *vu_dev,
+				  u32 offset, void *buf, u32 len)
+{
+	u32 cfg_size = offset + len;
+	struct vhost_user_msg *msg;
+	size_t payload_size = sizeof(msg->payload.config) + cfg_size;
+	size_t msg_size = sizeof(msg->header) + payload_size;
+	int rc;
+
+	if (!(vu_dev->protocol_features &
+	      BIT_ULL(VHOST_USER_PROTOCOL_F_CONFIG)))
+		return;
+
+	msg = kzalloc(msg_size, GFP_KERNEL);
+	if (!msg)
+		return;
+	msg->header.request = VHOST_USER_GET_CONFIG;
+	msg->header.size = payload_size;
+	msg->payload.config.offset = 0;
+	msg->payload.config.size = cfg_size;
+
+	rc = vhost_user_send(vu_dev, true, msg, NULL, 0);
+	if (rc) {
+		vu_err(vu_dev, "sending VHOST_USER_GET_CONFIG failed: %d\n",
+		       rc);
+		goto free;
+	}
+
+	rc = vhost_user_recv_resp(vu_dev, msg, msg_size);
+	if (rc) {
+		vu_err(vu_dev,
+		       "receiving VHOST_USER_GET_CONFIG response failed: %d\n",
+		       rc);
+		goto free;
+	}
+
+	if (msg->header.size != payload_size ||
+	    msg->payload.config.size != cfg_size) {
+		rc = -EPROTO;
+		vu_err(vu_dev,
+		       "Invalid VHOST_USER_GET_CONFIG sizes (payload %d expected %zu, config %u expected %u)\n",
+		       msg->header.size, payload_size,
+		       msg->payload.config.size, cfg_size);
+		goto free;
+	}
+	memcpy(buf, msg->payload.config.payload + offset, len);
+
+free:
+	kfree(msg);
+}
+
+static void vhost_user_set_config(struct virtio_uml_device *vu_dev,
+				  u32 offset, const void *buf, u32 len)
+{
+	struct vhost_user_msg *msg;
+	size_t payload_size = sizeof(msg->payload.config) + len;
+	size_t msg_size = sizeof(msg->header) + payload_size;
+	int rc;
+
+	if (!(vu_dev->protocol_features &
+	      BIT_ULL(VHOST_USER_PROTOCOL_F_CONFIG)))
+		return;
+
+	msg = kzalloc(msg_size, GFP_KERNEL);
+	if (!msg)
+		return;
+	msg->header.request = VHOST_USER_SET_CONFIG;
+	msg->header.size = payload_size;
+	msg->payload.config.offset = offset;
+	msg->payload.config.size = len;
+	memcpy(msg->payload.config.payload, buf, len);
+
+	rc = vhost_user_send(vu_dev, false, msg, NULL, 0);
+	if (rc)
+		vu_err(vu_dev, "sending VHOST_USER_SET_CONFIG failed: %d\n",
+		       rc);
+
+	kfree(msg);
+}
+
+static int vhost_user_init_mem_region(u64 addr, u64 size, int *fd_out,
+				      struct vhost_user_mem_region *region_out)
+{
+	unsigned long long mem_offset;
+	int rc = phys_mapping(addr, &mem_offset);
+
+	if (WARN(rc < 0, "phys_mapping of 0x%llx returned %d\n", addr, rc))
+		return -EFAULT;
+	*fd_out = rc;
+	region_out->guest_addr = addr;
+	region_out->user_addr = addr;
+	region_out->size = size;
+	region_out->mmap_offset = mem_offset;
+
+	/* Ensure mapping is valid for the entire region */
+	rc = phys_mapping(addr + size - 1, &mem_offset);
+	if (WARN(rc != *fd_out, "phys_mapping of 0x%llx failed: %d != %d\n",
+		 addr + size - 1, rc, *fd_out))
+		return -EFAULT;
+	return 0;
+}
+
+static int vhost_user_set_mem_table(struct virtio_uml_device *vu_dev)
+{
+	struct vhost_user_msg msg = {
+		.header.request = VHOST_USER_SET_MEM_TABLE,
+		.header.size = offsetof(typeof(msg.payload.mem_regions), regions[1]),
+		.payload.mem_regions.num = 1,
+	};
+	unsigned long reserved = uml_reserved - uml_physmem;
+	int fds[2];
+	int rc;
+
+	/*
+	 * This is a bit tricky, see also the comment with setup_physmem().
+	 *
+	 * Essentially, setup_physmem() uses a file to mmap() our physmem,
+	 * but the code and data we *already* have is omitted. To us, this
+	 * is no difference, since they both become part of our address
+	 * space and memory consumption. To somebody looking in from the
+	 * outside, however, it is different because the part of our memory
+	 * consumption that's already part of the binary (code/data) is not
+	 * mapped from the file, so it's not visible to another mmap from
+	 * the file descriptor.
+	 *
+	 * Thus, don't advertise this space to the vhost-user slave. This
+	 * means that the slave will likely abort or similar when we give
+	 * it an address from the hidden range, since it's not marked as
+	 * a valid address, but at least that way we detect the issue and
+	 * don't just have the slave read an all-zeroes buffer from the
+	 * shared memory file, or write something there that we can never
+	 * see (depending on the direction of the virtqueue traffic.)
+	 *
+	 * Since we usually don't want to use .text for virtio buffers,
+	 * this effectively means that you cannot use
+	 *  1) global variables, which are in the .bss and not in the shm
+	 *     file-backed memory
+	 *  2) the stack in some processes, depending on where they have
+	 *     their stack (or maybe only no interrupt stack?)
+	 *
+	 * The stack is already not typically valid for DMA, so this isn't
+	 * much of a restriction, but global variables might be encountered.
+	 *
+	 * It might be possible to fix it by copying around the data that's
+	 * between bss_start and where we map the file now, but it's not
+	 * something that you typically encounter with virtio drivers, so
+	 * it didn't seem worthwhile.
+	 */
+	rc = vhost_user_init_mem_region(reserved, physmem_size - reserved,
+					&fds[0],
+					&msg.payload.mem_regions.regions[0]);
+
+	if (rc < 0)
+		return rc;
+
+	return vhost_user_send(vu_dev, false, &msg, fds,
+			       msg.payload.mem_regions.num);
+}
+
+static int vhost_user_set_vring_state(struct virtio_uml_device *vu_dev,
+				      u32 request, u32 index, u32 num)
+{
+	struct vhost_user_msg msg = {
+		.header.request = request,
+		.header.size = sizeof(msg.payload.vring_state),
+		.payload.vring_state.index = index,
+		.payload.vring_state.num = num,
+	};
+
+	return vhost_user_send(vu_dev, false, &msg, NULL, 0);
+}
+
+static int vhost_user_set_vring_num(struct virtio_uml_device *vu_dev,
+				    u32 index, u32 num)
+{
+	return vhost_user_set_vring_state(vu_dev, VHOST_USER_SET_VRING_NUM,
+					  index, num);
+}
+
+static int vhost_user_set_vring_base(struct virtio_uml_device *vu_dev,
+				     u32 index, u32 offset)
+{
+	return vhost_user_set_vring_state(vu_dev, VHOST_USER_SET_VRING_BASE,
+					  index, offset);
+}
+
+static int vhost_user_set_vring_addr(struct virtio_uml_device *vu_dev,
+				     u32 index, u64 desc, u64 used, u64 avail,
+				     u64 log)
+{
+	struct vhost_user_msg msg = {
+		.header.request = VHOST_USER_SET_VRING_ADDR,
+		.header.size = sizeof(msg.payload.vring_addr),
+		.payload.vring_addr.index = index,
+		.payload.vring_addr.desc = desc,
+		.payload.vring_addr.used = used,
+		.payload.vring_addr.avail = avail,
+		.payload.vring_addr.log = log,
+	};
+
+	return vhost_user_send(vu_dev, false, &msg, NULL, 0);
+}
+
+static int vhost_user_set_vring_fd(struct virtio_uml_device *vu_dev,
+				   u32 request, int index, int fd)
+{
+	struct vhost_user_msg msg = {
+		.header.request = request,
+		.header.size = sizeof(msg.payload.integer),
+		.payload.integer = index,
+	};
+
+	if (index & ~VHOST_USER_VRING_INDEX_MASK)
+		return -EINVAL;
+	if (fd < 0) {
+		msg.payload.integer |= VHOST_USER_VRING_POLL_MASK;
+		return vhost_user_send(vu_dev, false, &msg, NULL, 0);
+	}
+	return vhost_user_send(vu_dev, false, &msg, &fd, 1);
+}
+
+static int vhost_user_set_vring_call(struct virtio_uml_device *vu_dev,
+				     int index, int fd)
+{
+	return vhost_user_set_vring_fd(vu_dev, VHOST_USER_SET_VRING_CALL,
+				       index, fd);
+}
+
+static int vhost_user_set_vring_kick(struct virtio_uml_device *vu_dev,
+				     int index, int fd)
+{
+	return vhost_user_set_vring_fd(vu_dev, VHOST_USER_SET_VRING_KICK,
+				       index, fd);
+}
+
+static int vhost_user_set_vring_enable(struct virtio_uml_device *vu_dev,
+				       u32 index, bool enable)
+{
+	if (!(vu_dev->features & BIT_ULL(VHOST_USER_F_PROTOCOL_FEATURES)))
+		return 0;
+
+	return vhost_user_set_vring_state(vu_dev, VHOST_USER_SET_VRING_ENABLE,
+					  index, enable);
+}
+
+
+/* Virtio interface */
+
+static bool vu_notify(struct virtqueue *vq)
+{
+	struct virtio_uml_vq_info *info = vq->priv;
+	const uint64_t n = 1;
+	int rc;
+
+	if (info->suspended)
+		return true;
+
+	time_travel_propagate_time();
+
+	if (info->kick_fd < 0) {
+		struct virtio_uml_device *vu_dev;
+
+		vu_dev = to_virtio_uml_device(vq->vdev);
+
+		return vhost_user_set_vring_state(vu_dev, VHOST_USER_VRING_KICK,
+						  vq->index, 0) == 0;
+	}
+
+	do {
+		rc = os_write_file(info->kick_fd, &n, sizeof(n));
+	} while (rc == -EINTR);
+	return !WARN(rc != sizeof(n), "write returned %d\n", rc);
+}
+
+static irqreturn_t vu_interrupt(int irq, void *opaque)
+{
+	struct virtqueue *vq = opaque;
+	struct virtio_uml_vq_info *info = vq->priv;
+	uint64_t n;
+	int rc;
+	irqreturn_t ret = IRQ_NONE;
+
+	do {
+		rc = os_read_file(info->call_fd, &n, sizeof(n));
+		if (rc == sizeof(n))
+			ret |= vring_interrupt(irq, vq);
+	} while (rc == sizeof(n) || rc == -EINTR);
+	WARN(rc != -EAGAIN, "read returned %d\n", rc);
+	return ret;
+}
+
+
+static void vu_get(struct virtio_device *vdev, unsigned offset,
+		   void *buf, unsigned len)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	vhost_user_get_config(vu_dev, offset, buf, len);
+}
+
+static void vu_set(struct virtio_device *vdev, unsigned offset,
+		   const void *buf, unsigned len)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	vhost_user_set_config(vu_dev, offset, buf, len);
+}
+
+static u8 vu_get_status(struct virtio_device *vdev)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	return vu_dev->status;
+}
+
+static void vu_set_status(struct virtio_device *vdev, u8 status)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	vu_dev->status = status;
+}
+
+static void vu_reset(struct virtio_device *vdev)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	vu_dev->status = 0;
+}
+
+static void vu_del_vq(struct virtqueue *vq)
+{
+	struct virtio_uml_vq_info *info = vq->priv;
+
+	if (info->call_fd >= 0) {
+		struct virtio_uml_device *vu_dev;
+
+		vu_dev = to_virtio_uml_device(vq->vdev);
+
+		um_free_irq(vu_dev->irq, vq);
+		os_close_file(info->call_fd);
+	}
+
+	if (info->kick_fd >= 0)
+		os_close_file(info->kick_fd);
+
+	vring_del_virtqueue(vq);
+	kfree(info);
+}
+
+static void vu_del_vqs(struct virtio_device *vdev)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+	struct virtqueue *vq, *n;
+	u64 features;
+
+	/* Note: reverse order as a workaround to a decoding bug in snabb */
+	list_for_each_entry_reverse(vq, &vdev->vqs, list)
+		WARN_ON(vhost_user_set_vring_enable(vu_dev, vq->index, false));
+
+	/* Ensure previous messages have been processed */
+	WARN_ON(vhost_user_get_features(vu_dev, &features));
+
+	list_for_each_entry_safe(vq, n, &vdev->vqs, list)
+		vu_del_vq(vq);
+}
+
+static int vu_setup_vq_call_fd(struct virtio_uml_device *vu_dev,
+			       struct virtqueue *vq)
+{
+	struct virtio_uml_vq_info *info = vq->priv;
+	int call_fds[2];
+	int rc, irq;
+
+	/* no call FD needed/desired in this case */
+	if (vu_dev->protocol_features &
+			BIT_ULL(VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS) &&
+	    vu_dev->protocol_features &
+			BIT_ULL(VHOST_USER_PROTOCOL_F_SLAVE_REQ)) {
+		info->call_fd = -1;
+		return 0;
+	}
+
+	/* Use a pipe for call fd, since SIGIO is not supported for eventfd */
+	rc = os_pipe(call_fds, true, true);
+	if (rc < 0)
+		return rc;
+
+	info->call_fd = call_fds[0];
+	irq = um_request_irq(vu_dev->irq, info->call_fd, IRQ_READ,
+			     vu_interrupt, IRQF_SHARED, info->name, vq);
+	if (irq < 0) {
+		rc = irq;
+		goto close_both;
+	}
+
+	rc = vhost_user_set_vring_call(vu_dev, vq->index, call_fds[1]);
+	if (rc)
+		goto release_irq;
+
+	vu_dev->irq = irq;
+
+	goto out;
+
+release_irq:
+	um_free_irq(irq, vq);
+close_both:
+	os_close_file(call_fds[0]);
+out:
+	/* Close (unused) write end of call fds */
+	os_close_file(call_fds[1]);
+
+	return rc;
+}
+
+static struct virtqueue *vu_setup_vq(struct virtio_device *vdev,
+				     unsigned index, vq_callback_t *callback,
+				     const char *name, bool ctx)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+	struct platform_device *pdev = vu_dev->pdev;
+	struct virtio_uml_vq_info *info;
+	struct virtqueue *vq;
+	int num = MAX_SUPPORTED_QUEUE_SIZE;
+	int rc;
+
+	info = kzalloc_obj(*info);
+	if (!info) {
+		rc = -ENOMEM;
+		goto error_kzalloc;
+	}
+	snprintf(info->name, sizeof(info->name), "%s.%d-%s", pdev->name,
+		 pdev->id, name);
+
+	vq = vring_create_virtqueue(index, num, PAGE_SIZE, vdev, true, true,
+				    ctx, vu_notify, callback, info->name);
+	if (!vq) {
+		rc = -ENOMEM;
+		goto error_create;
+	}
+	vq->priv = info;
+	vq->num_max = num;
+	num = virtqueue_get_vring_size(vq);
+
+	if (vu_dev->protocol_features &
+			BIT_ULL(VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS)) {
+		info->kick_fd = -1;
+	} else {
+		rc = os_eventfd(0, 0);
+		if (rc < 0)
+			goto error_kick;
+		info->kick_fd = rc;
+	}
+
+	rc = vu_setup_vq_call_fd(vu_dev, vq);
+	if (rc)
+		goto error_call;
+
+	rc = vhost_user_set_vring_num(vu_dev, index, num);
+	if (rc)
+		goto error_setup;
+
+	rc = vhost_user_set_vring_base(vu_dev, index, 0);
+	if (rc)
+		goto error_setup;
+
+	rc = vhost_user_set_vring_addr(vu_dev, index,
+				       virtqueue_get_desc_addr(vq),
+				       virtqueue_get_used_addr(vq),
+				       virtqueue_get_avail_addr(vq),
+				       (u64) -1);
+	if (rc)
+		goto error_setup;
+
+	return vq;
+
+error_setup:
+	if (info->call_fd >= 0) {
+		um_free_irq(vu_dev->irq, vq);
+		os_close_file(info->call_fd);
+	}
+error_call:
+	if (info->kick_fd >= 0)
+		os_close_file(info->kick_fd);
+error_kick:
+	vring_del_virtqueue(vq);
+error_create:
+	kfree(info);
+error_kzalloc:
+	return ERR_PTR(rc);
+}
+
+static int vu_find_vqs(struct virtio_device *vdev, unsigned nvqs,
+		       struct virtqueue *vqs[],
+		       struct virtqueue_info vqs_info[],
+		       struct irq_affinity *desc)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+	int i, queue_idx = 0, rc;
+	struct virtqueue *vq;
+
+	/* not supported for now */
+	if (WARN(nvqs > 64 || nvqs > vu_dev->max_vqs,
+		 "%d VQs requested, only up to 64 or %lld supported\n",
+		 nvqs, vu_dev->max_vqs))
+		return -EINVAL;
+
+	rc = vhost_user_set_mem_table(vu_dev);
+	if (rc)
+		return rc;
+
+	for (i = 0; i < nvqs; ++i) {
+		struct virtqueue_info *vqi = &vqs_info[i];
+
+		if (!vqi->name) {
+			vqs[i] = NULL;
+			continue;
+		}
+
+		vqs[i] = vu_setup_vq(vdev, queue_idx++, vqi->callback,
+				     vqi->name, vqi->ctx);
+		if (IS_ERR(vqs[i])) {
+			rc = PTR_ERR(vqs[i]);
+			goto error_setup;
+		}
+	}
+
+	list_for_each_entry(vq, &vdev->vqs, list) {
+		struct virtio_uml_vq_info *info = vq->priv;
+
+		if (info->kick_fd >= 0) {
+			rc = vhost_user_set_vring_kick(vu_dev, vq->index,
+						       info->kick_fd);
+			if (rc)
+				goto error_setup;
+		}
+
+		rc = vhost_user_set_vring_enable(vu_dev, vq->index, true);
+		if (rc)
+			goto error_setup;
+	}
+
+	return 0;
+
+error_setup:
+	vu_del_vqs(vdev);
+	return rc;
+}
+
+static u64 vu_get_features(struct virtio_device *vdev)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	return vu_dev->features;
+}
+
+static int vu_finalize_features(struct virtio_device *vdev)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+	u64 supported = vdev->features & VHOST_USER_SUPPORTED_F;
+
+	vring_transport_features(vdev);
+	vu_dev->features = vdev->features | supported;
+
+	return vhost_user_set_features(vu_dev, vu_dev->features);
+}
+
+static const char *vu_bus_name(struct virtio_device *vdev)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	return vu_dev->pdev->name;
+}
+
+static const struct virtio_config_ops virtio_uml_config_ops = {
+	.get = vu_get,
+	.set = vu_set,
+	.get_status = vu_get_status,
+	.set_status = vu_set_status,
+	.reset = vu_reset,
+	.find_vqs = vu_find_vqs,
+	.del_vqs = vu_del_vqs,
+	.get_features = vu_get_features,
+	.finalize_features = vu_finalize_features,
+	.bus_name = vu_bus_name,
+};
+
+static void virtio_uml_release_dev(struct device *d)
+{
+	struct virtio_device *vdev =
+			container_of(d, struct virtio_device, dev);
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	time_travel_propagate_time();
+
+	/* might not have been opened due to not negotiating the feature */
+	if (vu_dev->req_fd >= 0) {
+		um_free_irq(vu_dev->irq, vu_dev);
+		os_close_file(vu_dev->req_fd);
+	}
+
+	os_close_file(vu_dev->sock);
+	kfree(vu_dev);
+}
+
+void virtio_uml_set_no_vq_suspend(struct virtio_device *vdev,
+				  bool no_vq_suspend)
+{
+	struct virtio_uml_device *vu_dev = to_virtio_uml_device(vdev);
+
+	if (WARN_ON(vdev->config != &virtio_uml_config_ops))
+		return;
+
+	vu_dev->no_vq_suspend = no_vq_suspend;
+	dev_info(&vdev->dev, "%s VQ suspend\n", str_disabled_enabled(no_vq_suspend));
+}
+
+static void vu_of_conn_broken(struct work_struct *wk)
+{
+	struct virtio_uml_platform_data *pdata;
+	struct virtio_uml_device *vu_dev;
+
+	pdata = container_of(wk, struct virtio_uml_platform_data, conn_broken_wk);
+
+	vu_dev = platform_get_drvdata(pdata->pdev);
+
+	virtio_break_device(&vu_dev->vdev);
+
+	/*
+	 * We can't remove the device from the devicetree so the only thing we
+	 * can do is warn.
+	 */
+	WARN_ON(1);
+}
+
+/* Platform device */
+
+static struct virtio_uml_platform_data *
+virtio_uml_create_pdata(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct virtio_uml_platform_data *pdata;
+	int ret;
+
+	if (!np)
+		return ERR_PTR(-EINVAL);
+
+	pdata = devm_kzalloc(&pdev->dev, sizeof(*pdata), GFP_KERNEL);
+	if (!pdata)
+		return ERR_PTR(-ENOMEM);
+
+	INIT_WORK(&pdata->conn_broken_wk, vu_of_conn_broken);
+	pdata->pdev = pdev;
+
+	ret = of_property_read_string(np, "socket-path", &pdata->socket_path);
+	if (ret)
+		return ERR_PTR(ret);
+
+	ret = of_property_read_u32(np, "virtio-device-id",
+				   &pdata->virtio_device_id);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return pdata;
+}
+
+static int virtio_uml_probe(struct platform_device *pdev)
+{
+	struct virtio_uml_platform_data *pdata = pdev->dev.platform_data;
+	struct virtio_uml_device *vu_dev;
+	int rc;
+
+	if (!pdata) {
+		pdata = virtio_uml_create_pdata(pdev);
+		if (IS_ERR(pdata))
+			return PTR_ERR(pdata);
+	}
+
+	vu_dev = kzalloc_obj(*vu_dev);
+	if (!vu_dev)
+		return -ENOMEM;
+
+	vu_dev->pdata = pdata;
+	vu_dev->vdev.dev.parent = &pdev->dev;
+	vu_dev->vdev.dev.release = virtio_uml_release_dev;
+	vu_dev->vdev.config = &virtio_uml_config_ops;
+	vu_dev->vdev.id.device = pdata->virtio_device_id;
+	vu_dev->vdev.id.vendor = VIRTIO_DEV_ANY_ID;
+	vu_dev->pdev = pdev;
+	vu_dev->req_fd = -1;
+	vu_dev->irq = UM_IRQ_ALLOC;
+
+	time_travel_propagate_time();
+
+	do {
+		rc = os_connect_socket(pdata->socket_path);
+	} while (rc == -EINTR);
+	if (rc < 0)
+		goto error_free;
+	vu_dev->sock = rc;
+
+	raw_spin_lock_init(&vu_dev->sock_lock);
+
+	rc = vhost_user_init(vu_dev);
+	if (rc)
+		goto error_init;
+
+	platform_set_drvdata(pdev, vu_dev);
+
+	device_set_wakeup_capable(&vu_dev->vdev.dev, true);
+
+	rc = register_virtio_device(&vu_dev->vdev);
+	if (rc) {
+		put_device(&vu_dev->vdev.dev);
+		return rc;
+	}
+	vu_dev->registered = 1;
+	return 0;
+
+error_init:
+	os_close_file(vu_dev->sock);
+error_free:
+	kfree(vu_dev);
+	return rc;
+}
+
+static void virtio_uml_remove(struct platform_device *pdev)
+{
+	struct virtio_uml_device *vu_dev = platform_get_drvdata(pdev);
+
+	unregister_virtio_device(&vu_dev->vdev);
+}
+
+/* Command line device list */
+
+static void vu_cmdline_release_dev(struct device *d)
+{
+}
+
+static struct device vu_cmdline_parent = {
+	.init_name = "virtio-uml-cmdline",
+	.release = vu_cmdline_release_dev,
+};
+
+static DEFINE_MUTEX(vu_cmdline_lock);
+static bool vu_cmdline_parent_registered;
+static int vu_cmdline_id;
+
+static int vu_unregister_cmdline_device(struct device *dev, void *data)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct virtio_uml_platform_data *pdata = pdev->dev.platform_data;
+
+	kfree(pdata->socket_path);
+	platform_device_unregister(pdev);
+	return 0;
+}
+
+static void vu_conn_broken(struct work_struct *wk)
+{
+	struct virtio_uml_platform_data *pdata;
+	struct virtio_uml_device *vu_dev;
+
+	pdata = container_of(wk, struct virtio_uml_platform_data, conn_broken_wk);
+
+	vu_dev = platform_get_drvdata(pdata->pdev);
+
+	virtio_break_device(&vu_dev->vdev);
+
+	vu_unregister_cmdline_device(&pdata->pdev->dev, NULL);
+}
+
+static int vu_cmdline_set_device(const char *device)
+{
+	const char *ids = strchr(device, ':');
+	unsigned int virtio_device_id;
+	int processed, consumed, err;
+	char *socket_path;
+	struct virtio_uml_platform_data pdata, *ppdata;
+	struct platform_device *pdev;
+
+	if (!ids || ids == device)
+		return -EINVAL;
+
+	guard(mutex)(&vu_cmdline_lock);
+
+	processed = sscanf(ids, ":%u%n:%d%n",
+			   &virtio_device_id, &consumed,
+			   &vu_cmdline_id, &consumed);
+
+	if (processed < 1 || ids[consumed])
+		return -EINVAL;
+
+	if (!vu_cmdline_parent_registered) {
+		err = device_register(&vu_cmdline_parent);
+		if (err) {
+			pr_err("Failed to register parent device!\n");
+			put_device(&vu_cmdline_parent);
+			return err;
+		}
+		vu_cmdline_parent_registered = true;
+	}
+
+	socket_path = kmemdup_nul(device, ids - device, GFP_KERNEL);
+	if (!socket_path)
+		return -ENOMEM;
+
+	pdata.virtio_device_id = (u32) virtio_device_id;
+	pdata.socket_path = socket_path;
+
+	pr_info("Registering device virtio-uml.%d id=%d at %s\n",
+		vu_cmdline_id, virtio_device_id, socket_path);
+
+	pdev = platform_device_register_data(&vu_cmdline_parent, "virtio-uml",
+					     vu_cmdline_id++, &pdata,
+					     sizeof(pdata));
+	err = PTR_ERR_OR_ZERO(pdev);
+	if (err)
+		goto free;
+
+	ppdata = pdev->dev.platform_data;
+	ppdata->pdev = pdev;
+	INIT_WORK(&ppdata->conn_broken_wk, vu_conn_broken);
+
+	return 0;
+
+free:
+	kfree(socket_path);
+	return err;
+}
+
+static int vu_cmdline_set(const char *device, const struct kernel_param *kp)
+{
+	return vu_cmdline_set_device(device);
+}
+
+static int vu_cmdline_get_device(struct device *dev, void *data)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct virtio_uml_platform_data *pdata = pdev->dev.platform_data;
+	char *buffer = data;
+	unsigned int len = strlen(buffer);
+
+	snprintf(buffer + len, PAGE_SIZE - len, "%s:%d:%d\n",
+		 pdata->socket_path, pdata->virtio_device_id, pdev->id);
+	return 0;
+}
+
+static int vu_cmdline_get(char *buffer, const struct kernel_param *kp)
+{
+	guard(mutex)(&vu_cmdline_lock);
+
+	buffer[0] = '\0';
+	if (vu_cmdline_parent_registered)
+		device_for_each_child(&vu_cmdline_parent, buffer,
+				      vu_cmdline_get_device);
+	return strlen(buffer) + 1;
+}
+
+static const struct kernel_param_ops vu_cmdline_param_ops = {
+	.set = vu_cmdline_set,
+	.get = vu_cmdline_get,
+};
+
+device_param_cb(device, &vu_cmdline_param_ops, NULL, S_IRUSR);
+__uml_help(vu_cmdline_param_ops,
+"virtio_uml.device=<socket>:<virtio_id>[:<platform_id>]\n"
+"    Configure a virtio device over a vhost-user socket.\n"
+"    See virtio_ids.h for a list of possible virtio device id values.\n"
+"    Optionally use a specific platform_device id.\n\n"
+);
+
+
+static void vu_unregister_cmdline_devices(void)
+{
+	guard(mutex)(&vu_cmdline_lock);
+
+	if (vu_cmdline_parent_registered) {
+		device_for_each_child(&vu_cmdline_parent, NULL,
+				      vu_unregister_cmdline_device);
+		device_unregister(&vu_cmdline_parent);
+		vu_cmdline_parent_registered = false;
+	}
+}
+
+static int vu_mc_config(char *str, char **error_out)
+{
+	if (*str != '=') {
+		*error_out = "Invalid config";
+		return -EINVAL;
+	}
+	str += 1;
+	return vu_cmdline_set_device(str);
+}
+
+static int vu_mc_id(char **str, int *start_out, int *end_out)
+{
+	return -EOPNOTSUPP;
+}
+
+static int vu_mc_remove(int n, char **error_out)
+{
+	return -EOPNOTSUPP;
+}
+
+static struct mc_device virtio_uml_mc = {
+	.list		= LIST_HEAD_INIT(virtio_uml_mc.list),
+	.name		= "virtio_uml.device",
+	.config		= vu_mc_config,
+	.get_config	= NULL,
+	.id		= vu_mc_id,
+	.remove		= vu_mc_remove,
+};
+
+static int __init virtio_uml_mc_init(void)
+{
+	mconsole_register_dev(&virtio_uml_mc);
+	return 0;
+}
+late_initcall(virtio_uml_mc_init);
+
+/* Platform driver */
+
+static const struct of_device_id virtio_uml_match[] = {
+	{ .compatible = "virtio,uml", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, virtio_uml_match);
+
+static int virtio_uml_suspend(struct platform_device *pdev, pm_message_t state)
+{
+	struct virtio_uml_device *vu_dev = platform_get_drvdata(pdev);
+
+	if (!vu_dev->no_vq_suspend) {
+		struct virtqueue *vq;
+
+		virtio_device_for_each_vq((&vu_dev->vdev), vq) {
+			struct virtio_uml_vq_info *info = vq->priv;
+
+			info->suspended = true;
+			vhost_user_set_vring_enable(vu_dev, vq->index, false);
+		}
+	}
+
+	if (!device_may_wakeup(&vu_dev->vdev.dev)) {
+		vu_dev->suspended = true;
+		return 0;
+	}
+
+	return irq_set_irq_wake(vu_dev->irq, 1);
+}
+
+static int virtio_uml_resume(struct platform_device *pdev)
+{
+	struct virtio_uml_device *vu_dev = platform_get_drvdata(pdev);
+
+	if (!vu_dev->no_vq_suspend) {
+		struct virtqueue *vq;
+
+		virtio_device_for_each_vq((&vu_dev->vdev), vq) {
+			struct virtio_uml_vq_info *info = vq->priv;
+
+			info->suspended = false;
+			vhost_user_set_vring_enable(vu_dev, vq->index, true);
+		}
+	}
+
+	vu_dev->suspended = false;
+
+	if (!device_may_wakeup(&vu_dev->vdev.dev))
+		return 0;
+
+	return irq_set_irq_wake(vu_dev->irq, 0);
+}
+
+static struct platform_driver virtio_uml_driver = {
+	.probe = virtio_uml_probe,
+	.remove = virtio_uml_remove,
+	.driver = {
+		.name = "virtio-uml",
+		.of_match_table = virtio_uml_match,
+	},
+	.suspend = virtio_uml_suspend,
+	.resume = virtio_uml_resume,
+};
+
+static int __init virtio_uml_init(void)
+{
+	return platform_driver_register(&virtio_uml_driver);
+}
+
+static void __exit virtio_uml_exit(void)
+{
+	platform_driver_unregister(&virtio_uml_driver);
+	vu_unregister_cmdline_devices();
+}
+
+module_init(virtio_uml_init);
+module_exit(virtio_uml_exit);
+__uml_exitcall(virtio_uml_exit);
+
+MODULE_DESCRIPTION("UML driver for vhost-user virtio devices");
+MODULE_LICENSE("GPL");
diff --git a/arch/um/drivers/xterm.c b/arch/um/drivers/xterm.c
new file mode 100644
index 000000000..d05918e42
--- /dev/null
+++ b/arch/um/drivers/xterm.c
@@ -0,0 +1,226 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <termios.h>
+#include "chan_user.h"
+#include <os.h>
+#include <um_malloc.h>
+#include "xterm.h"
+
+struct xterm_chan {
+	int pid;
+	int helper_pid;
+	int chan_fd;
+	char *title;
+	int device;
+	int raw;
+	struct termios tt;
+};
+
+static void *xterm_init(char *str, int device, const struct chan_opts *opts)
+{
+	struct xterm_chan *data;
+
+	data = uml_kmalloc(sizeof(*data), UM_GFP_KERNEL);
+	if (data == NULL)
+		return NULL;
+	*data = ((struct xterm_chan) { .pid 		= -1,
+				       .helper_pid 	= -1,
+				       .chan_fd		= -1,
+				       .device 		= device,
+				       .title 		= opts->xterm_title,
+				       .raw  		= opts->raw } );
+	return data;
+}
+
+/* Only changed by xterm_setup, which is a setup */
+static char *terminal_emulator = CONFIG_XTERM_CHAN_DEFAULT_EMULATOR;
+static char *title_switch = "-T";
+static char *exec_switch = "-e";
+
+static int __init xterm_setup(char *line, int *add)
+{
+	*add = 0;
+	terminal_emulator = line;
+
+	line = strchr(line, ',');
+	if (line == NULL)
+		return 0;
+
+	*line++ = '\0';
+	if (*line)
+		title_switch = line;
+
+	line = strchr(line, ',');
+	if (line == NULL)
+		return 0;
+
+	*line++ = '\0';
+	if (*line)
+		exec_switch = line;
+
+	return 0;
+}
+
+__uml_setup("xterm=", xterm_setup,
+"xterm=<terminal emulator>,<title switch>,<exec switch>\n"
+"    Specifies an alternate terminal emulator to use for the debugger,\n"
+"    consoles, and serial lines when they are attached to the xterm channel.\n"
+"    The values are the terminal emulator binary, the switch it uses to set\n"
+"    its title, and the switch it uses to execute a subprocess,\n"
+"    respectively.  The title switch must have the form '<switch> title',\n"
+"    not '<switch>=title'.  Similarly, the exec switch must have the form\n"
+"    '<switch> command arg1 arg2 ...'.\n"
+"    The default values are 'xterm=" CONFIG_XTERM_CHAN_DEFAULT_EMULATOR
+     ",-T,-e'.\n"
+"    Values for gnome-terminal are 'xterm=gnome-terminal,-t,--'.\n\n"
+);
+
+static int xterm_open(int input, int output, int primary, void *d,
+		      char **dev_out)
+{
+	struct xterm_chan *data = d;
+	int pid, fd, new, err;
+	char title[256], file[] = "/tmp/xterm-pipeXXXXXX";
+	char *argv[] = { terminal_emulator, title_switch, title, exec_switch,
+			 OS_LIB_PATH "/uml/port-helper", "-uml-socket",
+			 file, NULL };
+
+	if (access(argv[4], X_OK) < 0)
+		argv[4] = "port-helper";
+
+	/* Ensure we are running on Xorg or Wayland. */
+	if (!getenv("DISPLAY") && !getenv("WAYLAND_DISPLAY")) {
+		printk(UM_KERN_ERR "xterm_open : neither $DISPLAY nor $WAYLAND_DISPLAY is set.\n");
+		return -ENODEV;
+	}
+
+	/*
+	 * This business of getting a descriptor to a temp file,
+	 * deleting the file and closing the descriptor is just to get
+	 * a known-unused name for the Unix socket that we really
+	 * want.
+	 */
+	fd = mkstemp(file);
+	if (fd < 0) {
+		err = -errno;
+		printk(UM_KERN_ERR "xterm_open : mkstemp failed, errno = %d\n",
+		       errno);
+		return err;
+	}
+
+	if (unlink(file)) {
+		err = -errno;
+		printk(UM_KERN_ERR "xterm_open : unlink failed, errno = %d\n",
+		       errno);
+		close(fd);
+		return err;
+	}
+	close(fd);
+
+	fd = os_create_unix_socket(file, sizeof(file), 1);
+	if (fd < 0) {
+		printk(UM_KERN_ERR "xterm_open : create_unix_socket failed, "
+		       "errno = %d\n", -fd);
+		return fd;
+	}
+
+	sprintf(title, data->title, data->device);
+	pid = run_helper(NULL, NULL, argv);
+	if (pid < 0) {
+		err = pid;
+		printk(UM_KERN_ERR "xterm_open : run_helper failed, "
+		       "errno = %d\n", -err);
+		goto out_close1;
+	}
+
+	err = os_set_fd_block(fd, 0);
+	if (err < 0) {
+		printk(UM_KERN_ERR "xterm_open : failed to set descriptor "
+		       "non-blocking, err = %d\n", -err);
+		goto out_kill;
+	}
+
+	data->chan_fd = fd;
+	new = xterm_fd(fd, &data->helper_pid);
+	if (new < 0) {
+		err = new;
+		printk(UM_KERN_ERR "xterm_open : xterm_fd failed, err = %d\n",
+		       -err);
+		goto out_kill;
+	}
+
+	err = os_set_fd_block(new, 0);
+	if (err) {
+		printk(UM_KERN_ERR "xterm_open : failed to set xterm "
+		       "descriptor non-blocking, err = %d\n", -err);
+		goto out_close2;
+	}
+
+	CATCH_EINTR(err = tcgetattr(new, &data->tt));
+	if (err) {
+		new = err;
+		goto out_close2;
+	}
+
+	if (data->raw) {
+		err = raw(new);
+		if (err) {
+			new = err;
+			goto out_close2;
+		}
+	}
+
+	unlink(file);
+	data->pid = pid;
+	*dev_out = NULL;
+
+	return new;
+
+ out_close2:
+	close(new);
+ out_kill:
+	os_kill_process(pid, 1);
+ out_close1:
+	close(fd);
+
+	return err;
+}
+
+static void xterm_close(int fd, void *d)
+{
+	struct xterm_chan *data = d;
+
+	if (data->pid != -1)
+		os_kill_process(data->pid, 1);
+	data->pid = -1;
+
+	if (data->helper_pid != -1)
+		os_kill_process(data->helper_pid, 0);
+	data->helper_pid = -1;
+
+	if (data->chan_fd != -1)
+		os_close_file(data->chan_fd);
+	os_close_file(fd);
+}
+
+const struct chan_ops xterm_ops = {
+	.type		= "xterm",
+	.init		= xterm_init,
+	.open		= xterm_open,
+	.close		= xterm_close,
+	.read		= generic_read,
+	.write		= generic_write,
+	.console_write	= generic_console_write,
+	.window_size	= generic_window_size,
+	.free		= generic_free,
+	.winch		= 1,
+};
diff --git a/arch/um/drivers/xterm.h b/arch/um/drivers/xterm.h
new file mode 100644
index 000000000..5968da3a6
--- /dev/null
+++ b/arch/um/drivers/xterm.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
+ */
+
+#ifndef __XTERM_H__
+#define __XTERM_H__
+
+extern int xterm_fd(int socket, int *pid_out);
+
+#endif
+
diff --git a/arch/um/drivers/xterm_kern.c b/arch/um/drivers/xterm_kern.c
new file mode 100644
index 000000000..d630cb19e
--- /dev/null
+++ b/arch/um/drivers/xterm_kern.c
@@ -0,0 +1,83 @@
+// SPDX-License-Identifier: GPL-2.0
+/* 
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/slab.h>
+#include <linux/completion.h>
+#include <linux/irqreturn.h>
+#include <asm/irq.h>
+#include <irq_kern.h>
+#include <os.h>
+#include "xterm.h"
+
+struct xterm_wait {
+	struct completion ready;
+	int fd;
+	int pid;
+	int new_fd;
+};
+
+static irqreturn_t xterm_interrupt(int irq, void *data)
+{
+	struct xterm_wait *xterm = data;
+	int fd = -1, n_fds = 1;
+	ssize_t ret;
+
+	ret = os_rcv_fd_msg(xterm->fd, &fd, n_fds,
+			    &xterm->pid, sizeof(xterm->pid));
+	if (ret == -EAGAIN)
+		return IRQ_NONE;
+
+	if (ret < 0)
+		fd = ret;
+	else if (ret != sizeof(xterm->pid))
+		fd = -EMSGSIZE;
+
+	xterm->new_fd = fd;
+	complete(&xterm->ready);
+
+	return IRQ_HANDLED;
+}
+
+int xterm_fd(int socket, int *pid_out)
+{
+	struct xterm_wait *data;
+	int err, ret;
+
+	data = kmalloc_obj(*data);
+	if (data == NULL) {
+		printk(KERN_ERR "xterm_fd : failed to allocate xterm_wait\n");
+		return -ENOMEM;
+	}
+
+	/* This is a locked semaphore... */
+	*data = ((struct xterm_wait) { .fd 		= socket,
+				       .pid 		= -1,
+				       .new_fd	 	= -1 });
+	init_completion(&data->ready);
+
+	err = um_request_irq(XTERM_IRQ, socket, IRQ_READ, xterm_interrupt,
+			     IRQF_SHARED, "xterm", data);
+	if (err < 0) {
+		printk(KERN_ERR "xterm_fd : failed to get IRQ for xterm, "
+		       "err = %d\n",  err);
+		ret = err;
+		goto out;
+	}
+
+	/* ... so here we wait for an xterm interrupt.
+	 *
+	 * XXX Note, if the xterm doesn't work for some reason (eg. DISPLAY
+	 * isn't set) this will hang... */
+	wait_for_completion(&data->ready);
+
+	um_free_irq(XTERM_IRQ, data);
+
+	ret = data->new_fd;
+	*pid_out = data->pid;
+ out:
+	kfree(data);
+
+	return ret;
+}
diff --git a/arch/um/include/asm/Kbuild b/arch/um/include/asm/Kbuild
new file mode 100644
index 000000000..8fdc0bd9a
--- /dev/null
+++ b/arch/um/include/asm/Kbuild
@@ -0,0 +1,30 @@
+# SPDX-License-Identifier: GPL-2.0
+generic-y += bug.h
+generic-y += compat.h
+generic-y += device.h
+generic-y += dma-mapping.h
+generic-y += emergency-restart.h
+generic-y += exec.h
+generic-y += ftrace.h
+generic-y += hw_irq.h
+generic-y += irq_regs.h
+generic-y += irq_work.h
+generic-y += kdebug.h
+generic-y += mcs_spinlock.h
+generic-y += mmiowb.h
+generic-y += module.h
+generic-y += module.lds.h
+generic-y += parport.h
+generic-y += percpu.h
+generic-y += percpu_types.h
+generic-y += preempt.h
+generic-y += ring_buffer.h
+generic-y += runtime-const.h
+generic-y += softirq_stack.h
+generic-y += switch_to.h
+generic-y += topology.h
+generic-y += trace_clock.h
+generic-y += kprobes.h
+generic-y += mm_hooks.h
+generic-y += vga.h
+generic-y += video.h
diff --git a/arch/um/include/asm/archrandom.h b/arch/um/include/asm/archrandom.h
new file mode 100644
index 000000000..24e16c979
--- /dev/null
+++ b/arch/um/include/asm/archrandom.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_UM_ARCHRANDOM_H__
+#define __ASM_UM_ARCHRANDOM_H__
+
+#include <linux/types.h>
+
+/* This is from <os.h>, but better not to #include that in a global header here. */
+ssize_t os_getrandom(void *buf, size_t len, unsigned int flags);
+
+static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs)
+{
+	ssize_t ret;
+
+	ret = os_getrandom(v, max_longs * sizeof(*v), 0);
+	if (ret < 0)
+		return 0;
+	return ret / sizeof(*v);
+}
+
+static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, size_t max_longs)
+{
+	return 0;
+}
+
+#endif
diff --git a/arch/um/include/asm/asm-prototypes.h b/arch/um/include/asm/asm-prototypes.h
new file mode 100644
index 000000000..408b31d59
--- /dev/null
+++ b/arch/um/include/asm/asm-prototypes.h
@@ -0,0 +1,6 @@
+#include <asm-generic/asm-prototypes.h>
+#include <asm/checksum.h>
+
+#ifdef CONFIG_UML_X86
+extern void cmpxchg8b_emu(void);
+#endif
diff --git a/arch/um/include/asm/bpf_perf_event.h b/arch/um/include/asm/bpf_perf_event.h
new file mode 100644
index 000000000..287221342
--- /dev/null
+++ b/arch/um/include/asm/bpf_perf_event.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * asm-generic/bpf_perf_event.h is part of the uapi headers, but since
+ * arch/um has no uapi of its on, we can't use the "generic-y"
+ * Kbuild rule to generate the wrapper
+ */
+
+#include <asm-generic/bpf_perf_event.h>
diff --git a/arch/um/include/asm/cache.h b/arch/um/include/asm/cache.h
new file mode 100644
index 000000000..5c1562734
--- /dev/null
+++ b/arch/um/include/asm/cache.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UM_CACHE_H
+#define __UM_CACHE_H
+
+
+#if defined(CONFIG_UML_X86) && !defined(CONFIG_64BIT)
+# define L1_CACHE_SHIFT		(CONFIG_X86_L1_CACHE_SHIFT)
+#elif defined(CONFIG_UML_X86) /* 64-bit */
+# define L1_CACHE_SHIFT		6 /* Should be 7 on Intel */
+#else
+/* XXX: this was taken from x86, now it's completely random. Luckily only
+ * affects SMP padding. */
+# define L1_CACHE_SHIFT		5
+#endif
+
+#define L1_CACHE_BYTES		(1 << L1_CACHE_SHIFT)
+
+#endif
diff --git a/arch/um/include/asm/cacheflush.h b/arch/um/include/asm/cacheflush.h
new file mode 100644
index 000000000..4c9858cd3
--- /dev/null
+++ b/arch/um/include/asm/cacheflush.h
@@ -0,0 +1,9 @@
+#ifndef __UM_ASM_CACHEFLUSH_H
+#define __UM_ASM_CACHEFLUSH_H
+
+#include <asm/tlbflush.h>
+#define flush_cache_vmap flush_tlb_kernel_range
+#define flush_cache_vunmap flush_tlb_kernel_range
+
+#include <asm-generic/cacheflush.h>
+#endif /* __UM_ASM_CACHEFLUSH_H */
diff --git a/arch/um/include/asm/common.lds.S b/arch/um/include/asm/common.lds.S
new file mode 100644
index 000000000..fd481ac37
--- /dev/null
+++ b/arch/um/include/asm/common.lds.S
@@ -0,0 +1,101 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <asm-generic/vmlinux.lds.h>
+
+  .fini      : { *(.fini)    } =0x9090
+  _etext = .;
+  PROVIDE (etext = .);
+
+  . = ALIGN(4096);
+  _sdata = .;
+  PROVIDE (sdata = .);
+
+  RO_DATA(4096)
+
+  .unprotected : { *(.unprotected) }
+  . = ALIGN(4096);
+  PROVIDE (_unprotected_end = .);
+
+  . = ALIGN(4096);
+  EXCEPTION_TABLE(0)
+
+  BUG_TABLE
+
+  .uml.setup.init : {
+	__uml_setup_start = .;
+	*(.uml.setup.init)
+	__uml_setup_end = .;
+  }
+	
+  .uml.help.init : {
+	__uml_help_start = .;
+	*(.uml.help.init)
+	__uml_help_end = .;
+  }
+	
+  .uml.postsetup.init : {
+	__uml_postsetup_start = .;
+	*(.uml.postsetup.init)
+	__uml_postsetup_end = .;
+  }
+	
+  .init.setup : {
+	INIT_SETUP(0)
+  }
+
+  PERCPU_SECTION(32)
+	
+  .initcall.init : {
+	INIT_CALLS
+  }
+
+  .con_initcall.init : {
+	CON_INITCALL
+  }
+
+  .exitcall : {
+	__exitcall_begin = .;
+	*(.exitcall.exit)
+	__exitcall_end = .;
+  }
+
+  .uml.exitcall : {
+	__uml_exitcall_begin = .;
+	*(.uml.exitcall.exit)
+	__uml_exitcall_end = .;
+  }
+
+  . = ALIGN(4);
+  .altinstructions : {
+	__alt_instructions = .;
+	*(.altinstructions)
+	__alt_instructions_end = .;
+  }
+  .altinstr_replacement : { *(.altinstr_replacement) }
+  /* .exit.text is discard at runtime, not link time, to deal with references
+     from .altinstructions and .eh_frame */
+  .exit.text : { EXIT_TEXT }
+  .exit.data : { *(.exit.data) }
+
+  .preinit_array : {
+	__preinit_array_start = .;
+	*(.preinit_array)
+	__preinit_array_end = .;
+  }
+  .init_array : {
+	__init_array_start = .;
+	*(.kasan_init)
+	*(.init_array.*)
+	*(.init_array)
+	__init_array_end = .;
+  }
+  .fini_array : {
+	__fini_array_start = .;
+	*(.fini_array)
+	__fini_array_end = .;
+  }
+
+   . = ALIGN(4096);
+  .init.ramfs : {
+	INIT_RAM_FS
+  }
+
diff --git a/arch/um/include/asm/cpufeature.h b/arch/um/include/asm/cpufeature.h
new file mode 100644
index 000000000..f7770083c
--- /dev/null
+++ b/arch/um/include/asm/cpufeature.h
@@ -0,0 +1,133 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_UM_CPUFEATURE_H
+#define _ASM_UM_CPUFEATURE_H
+
+#include <asm/processor.h>
+
+#if defined(__KERNEL__) && !defined(__ASSEMBLER__)
+
+#include <asm/asm.h>
+#include <linux/bitops.h>
+
+extern const char * const x86_cap_flags[NCAPINTS*32];
+extern const char * const x86_power_flags[32];
+#define X86_CAP_FMT "%s"
+#define x86_cap_flag(flag) x86_cap_flags[flag]
+
+/*
+ * In order to save room, we index into this array by doing
+ * X86_BUG_<name> - NCAPINTS*32.
+ */
+extern const char * const x86_bug_flags[NBUGINTS*32];
+
+#define test_cpu_cap(c, bit)						\
+	 test_bit(bit, (unsigned long *)((c)->x86_capability))
+
+/*
+ * There are 32 bits/features in each mask word.  The high bits
+ * (selected with (bit>>5) give us the word number and the low 5
+ * bits give us the bit/feature number inside the word.
+ * (1UL<<((bit)&31) gives us a mask for the feature_bit so we can
+ * see if it is set in the mask word.
+ */
+#define CHECK_BIT_IN_MASK_WORD(maskname, word, bit)	\
+	(((bit)>>5)==(word) && (1UL<<((bit)&31) & maskname##word ))
+
+#define cpu_has(c, bit)							\
+	 test_cpu_cap(c, bit)
+
+#define this_cpu_has(bit)						\
+	(__builtin_constant_p(bit) && REQUIRED_MASK_BIT_SET(bit) ? 1 :	\
+	 x86_this_cpu_test_bit(bit, cpu_info.x86_capability))
+
+/*
+ * This macro is for detection of features which need kernel
+ * infrastructure to be used.  It may *not* directly test the CPU
+ * itself.  Use the cpu_has() family if you want true runtime
+ * testing of CPU features, like in hypervisor code where you are
+ * supporting a possible guest feature where host support for it
+ * is not relevant.
+ */
+#define cpu_feature_enabled(bit)	\
+	(__builtin_constant_p(bit) && DISABLED_MASK_BIT_SET(bit) ? 0 : _static_cpu_has(bit))
+
+#define boot_cpu_has(bit)	cpu_has(&boot_cpu_data, bit)
+
+#define set_cpu_cap(c, bit)	set_bit(bit, (unsigned long *)((c)->x86_capability))
+
+extern void setup_clear_cpu_cap(unsigned int bit);
+
+#define setup_force_cpu_cap(bit) do { \
+	set_cpu_cap(&boot_cpu_data, bit);	\
+	set_bit(bit, (unsigned long *)cpu_caps_set);	\
+} while (0)
+
+#define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
+
+static __always_inline bool __static_cpu_has(u16 bit)
+{
+	asm goto("1: jmp 6f\n"
+		 "2:\n"
+		 ".skip -(((5f-4f) - (2b-1b)) > 0) * "
+			 "((5f-4f) - (2b-1b)),0x90\n"
+		 "3:\n"
+		 ".section .altinstructions,\"a\"\n"
+		 " .long 1b - .\n"		/* src offset */
+		 " .long 4f - .\n"		/* repl offset */
+		 " .word %P[always]\n"		/* always replace */
+		 " .byte 3b - 1b\n"		/* src len */
+		 " .byte 5f - 4f\n"		/* repl len */
+		 " .byte 3b - 2b\n"		/* pad len */
+		 ".previous\n"
+		 ".section .altinstr_replacement,\"ax\"\n"
+		 "4: jmp %l[t_no]\n"
+		 "5:\n"
+		 ".previous\n"
+		 ".section .altinstructions,\"a\"\n"
+		 " .long 1b - .\n"		/* src offset */
+		 " .long 0\n"			/* no replacement */
+		 " .word %P[feature]\n"		/* feature bit */
+		 " .byte 3b - 1b\n"		/* src len */
+		 " .byte 0\n"			/* repl len */
+		 " .byte 0\n"			/* pad len */
+		 ".previous\n"
+		 ".section .altinstr_aux,\"ax\"\n"
+		 "6:\n"
+		 " testb %[bitnum],%[cap_byte]\n"
+		 " jnz %l[t_yes]\n"
+		 " jmp %l[t_no]\n"
+		 ".previous\n"
+		 : : [feature]  "i" (bit),
+		     [always]   "i" (X86_FEATURE_ALWAYS),
+		     [bitnum]   "i" (1 << (bit & 7)),
+		     [cap_byte] "m" (((const char *)boot_cpu_data.x86_capability)[bit >> 3])
+		 : : t_yes, t_no);
+t_yes:
+	return true;
+t_no:
+	return false;
+}
+
+#define _static_cpu_has(bit)					\
+(								\
+	__builtin_constant_p(boot_cpu_has(bit)) ?		\
+		boot_cpu_has(bit) :				\
+		_static_cpu_has(bit)				\
+)
+
+#define cpu_has_bug(c, bit)		cpu_has(c, (bit))
+#define set_cpu_bug(c, bit)		set_cpu_cap(c, (bit))
+
+#define static_cpu_has_bug(bit)		_static_cpu_has((bit))
+#define boot_cpu_has_bug(bit)		cpu_has_bug(&boot_cpu_data, (bit))
+#define boot_cpu_set_bug(bit)		set_cpu_cap(&boot_cpu_data, (bit))
+
+#define MAX_CPU_FEATURES		(NCAPINTS * 32)
+#define cpu_have_feature		boot_cpu_has
+
+#define CPU_FEATURE_TYPEFMT		"x86,ven%04Xfam%04Xmod%04X"
+#define CPU_FEATURE_TYPEVAL		boot_cpu_data.x86_vendor, boot_cpu_data.x86, \
+					boot_cpu_data.x86_model
+
+#endif /* defined(__KERNEL__) && !defined(__ASSEMBLER__) */
+#endif /* _ASM_UM_CPUFEATURE_H */
diff --git a/arch/um/include/asm/current.h b/arch/um/include/asm/current.h
new file mode 100644
index 000000000..159a29b3d
--- /dev/null
+++ b/arch/um/include/asm/current.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_CURRENT_H
+#define __ASM_CURRENT_H
+
+#include <linux/compiler.h>
+#include <linux/threads.h>
+
+#ifndef __ASSEMBLER__
+
+#include <shared/smp.h>
+
+struct task_struct;
+extern struct task_struct *cpu_tasks[NR_CPUS];
+
+static __always_inline struct task_struct *get_current(void)
+{
+	return cpu_tasks[uml_curr_cpu()];
+}
+
+#define current get_current()
+
+#endif /* __ASSEMBLER__ */
+
+#endif /* __ASM_CURRENT_H */
diff --git a/arch/um/include/asm/delay.h b/arch/um/include/asm/delay.h
new file mode 100644
index 000000000..e79b2ab6f
--- /dev/null
+++ b/arch/um/include/asm/delay.h
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UM_DELAY_H
+#define __UM_DELAY_H
+#include <asm-generic/delay.h>
+#include <linux/time-internal.h>
+
+static inline void um_ndelay(unsigned long nsecs)
+{
+	if (time_travel_mode == TT_MODE_INFCPU ||
+	    time_travel_mode == TT_MODE_EXTERNAL) {
+		time_travel_ndelay(nsecs);
+		return;
+	}
+	ndelay(nsecs);
+}
+#undef ndelay
+#define ndelay(n) um_ndelay(n)
+
+static inline void um_udelay(unsigned long usecs)
+{
+	if (time_travel_mode == TT_MODE_INFCPU ||
+	    time_travel_mode == TT_MODE_EXTERNAL) {
+		time_travel_ndelay(1000 * usecs);
+		return;
+	}
+	udelay(usecs);
+}
+#undef udelay
+#define udelay(n) um_udelay(n)
+#endif /* __UM_DELAY_H */
diff --git a/arch/um/include/asm/dma.h b/arch/um/include/asm/dma.h
new file mode 100644
index 000000000..fdc53642c
--- /dev/null
+++ b/arch/um/include/asm/dma.h
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UM_DMA_H
+#define __UM_DMA_H
+
+#include <asm/io.h>
+
+extern unsigned long uml_physmem;
+
+#define MAX_DMA_ADDRESS (uml_physmem)
+
+#endif
diff --git a/arch/um/include/asm/fpu/api.h b/arch/um/include/asm/fpu/api.h
new file mode 100644
index 000000000..3abf67c83
--- /dev/null
+++ b/arch/um/include/asm/fpu/api.h
@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _ASM_UM_FPU_API_H
+#define _ASM_UM_FPU_API_H
+
+#include <linux/types.h>
+
+/* Copyright (c) 2020 Cambridge Greys Ltd
+ * Copyright (c) 2020 Red Hat Inc.
+ * A set of "dummy" defines to allow the direct inclusion
+ * of x86 optimized copy, xor, etc routines into the
+ * UML code tree. */
+
+#define kernel_fpu_begin() (void)0
+#define kernel_fpu_end() (void)0
+
+static inline bool irq_fpu_usable(void)
+{
+	return true;
+}
+
+
+#endif
diff --git a/arch/um/include/asm/futex.h b/arch/um/include/asm/futex.h
new file mode 100644
index 000000000..780aa6bfc
--- /dev/null
+++ b/arch/um/include/asm/futex.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_UM_FUTEX_H
+#define _ASM_UM_FUTEX_H
+
+#include <linux/futex.h>
+#include <linux/uaccess.h>
+#include <asm/errno.h>
+
+
+int arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr);
+int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
+			      u32 oldval, u32 newval);
+
+#endif
diff --git a/arch/um/include/asm/hardirq.h b/arch/um/include/asm/hardirq.h
new file mode 100644
index 000000000..8de71752a
--- /dev/null
+++ b/arch/um/include/asm/hardirq.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_UM_HARDIRQ_H
+#define __ASM_UM_HARDIRQ_H
+
+#include <linux/cache.h>
+#include <linux/threads.h>
+
+#define __ARCH_IRQ_EXIT_IRQS_DISABLED 1
+
+typedef struct {
+	unsigned int __softirq_pending;
+#if IS_ENABLED(CONFIG_SMP)
+	unsigned int irq_resched_count;
+	unsigned int irq_call_count;
+#endif
+} ____cacheline_aligned irq_cpustat_t;
+
+DECLARE_PER_CPU_SHARED_ALIGNED(irq_cpustat_t, irq_stat);
+
+#define __ARCH_IRQ_STAT
+
+#define inc_irq_stat(member)	this_cpu_inc(irq_stat.member)
+
+#include <linux/irq.h>
+
+static inline void ack_bad_irq(unsigned int irq)
+{
+	pr_crit("unexpected IRQ trap at vector %02x\n", irq);
+}
+
+#endif /* __ASM_UM_HARDIRQ_H */
diff --git a/arch/um/include/asm/io.h b/arch/um/include/asm/io.h
new file mode 100644
index 000000000..9ea42cc74
--- /dev/null
+++ b/arch/um/include/asm/io.h
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_UM_IO_H
+#define _ASM_UM_IO_H
+#include <linux/types.h>
+
+/* get emulated iomem (if desired) */
+#include <asm-generic/logic_io.h>
+
+#ifndef ioremap
+#define ioremap ioremap
+static inline void __iomem *ioremap(phys_addr_t offset, size_t size)
+{
+	return NULL;
+}
+#endif /* ioremap */
+
+#ifndef iounmap
+#define iounmap iounmap
+static inline void iounmap(void __iomem *addr)
+{
+}
+#endif /* iounmap */
+
+#include <asm-generic/io.h>
+
+#endif
diff --git a/arch/um/include/asm/irq.h b/arch/um/include/asm/irq.h
new file mode 100644
index 000000000..36dbedd1a
--- /dev/null
+++ b/arch/um/include/asm/irq.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UM_IRQ_H
+#define __UM_IRQ_H
+
+#define TIMER_IRQ		0
+#define UMN_IRQ			1
+#define UBD_IRQ			2
+#define UM_ETH_IRQ		3
+#define ACCEPT_IRQ		4
+#define MCONSOLE_IRQ		5
+#define WINCH_IRQ		6
+#define SIGIO_WRITE_IRQ 	7
+#define TELNETD_IRQ 		8
+#define XTERM_IRQ 		9
+#define RANDOM_IRQ 		10
+#define SIGCHLD_IRQ		11
+
+#ifdef CONFIG_UML_NET_VECTOR
+
+#define VECTOR_BASE_IRQ		(SIGCHLD_IRQ + 1)
+#define VECTOR_IRQ_SPACE	8
+
+#define UM_FIRST_DYN_IRQ (VECTOR_IRQ_SPACE + VECTOR_BASE_IRQ)
+
+#else
+
+#define UM_FIRST_DYN_IRQ (SIGCHLD_IRQ + 1)
+
+#endif
+
+#define UM_LAST_SIGNAL_IRQ	64
+/* If we have (simulated) PCI MSI, allow 64 more interrupt numbers for it */
+#ifdef CONFIG_PCI_MSI
+#define NR_IRQS			(UM_LAST_SIGNAL_IRQ + 64)
+#else
+#define NR_IRQS			UM_LAST_SIGNAL_IRQ
+#endif /* CONFIG_PCI_MSI */
+
+#include <asm-generic/irq.h>
+#endif
diff --git a/arch/um/include/asm/irqflags.h b/arch/um/include/asm/irqflags.h
new file mode 100644
index 000000000..31e49e089
--- /dev/null
+++ b/arch/um/include/asm/irqflags.h
@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UM_IRQFLAGS_H
+#define __UM_IRQFLAGS_H
+
+int um_get_signals(void);
+int um_set_signals(int enable);
+void block_signals(void);
+void unblock_signals(void);
+
+#define arch_local_save_flags arch_local_save_flags
+static inline unsigned long arch_local_save_flags(void)
+{
+	return um_get_signals();
+}
+
+#define arch_local_irq_restore arch_local_irq_restore
+static inline void arch_local_irq_restore(unsigned long flags)
+{
+	um_set_signals(flags);
+}
+
+#define arch_local_irq_enable arch_local_irq_enable
+static inline void arch_local_irq_enable(void)
+{
+	unblock_signals();
+}
+
+#define arch_local_irq_disable arch_local_irq_disable
+static inline void arch_local_irq_disable(void)
+{
+	block_signals();
+}
+
+#define ARCH_IRQ_DISABLED	0
+
+#include <asm-generic/irqflags.h>
+
+#endif
diff --git a/arch/um/include/asm/kasan.h b/arch/um/include/asm/kasan.h
new file mode 100644
index 000000000..81bcdc0f9
--- /dev/null
+++ b/arch/um/include/asm/kasan.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_UM_KASAN_H
+#define __ASM_UM_KASAN_H
+
+#include <linux/init.h>
+#include <linux/const.h>
+
+#define KASAN_SHADOW_OFFSET _AC(CONFIG_KASAN_SHADOW_OFFSET, UL)
+
+/* used in kasan_mem_to_shadow to divide by 8 */
+#define KASAN_SHADOW_SCALE_SHIFT 3
+
+#ifdef CONFIG_X86_64
+#define KASAN_HOST_USER_SPACE_END_ADDR 0x00007fffffffffffUL
+/* KASAN_SHADOW_SIZE is the size of total address space divided by 8 */
+#define KASAN_SHADOW_SIZE ((KASAN_HOST_USER_SPACE_END_ADDR + 1) >> \
+			KASAN_SHADOW_SCALE_SHIFT)
+#else
+#error "KASAN_SHADOW_SIZE is not defined for this sub-architecture"
+#endif /* CONFIG_X86_64 */
+
+#define KASAN_SHADOW_START (KASAN_SHADOW_OFFSET)
+#define KASAN_SHADOW_END (KASAN_SHADOW_START + KASAN_SHADOW_SIZE)
+
+#ifdef CONFIG_KASAN
+void kasan_init(void);
+#else
+static inline void kasan_init(void) { }
+#endif /* CONFIG_KASAN */
+
+#endif /* __ASM_UM_KASAN_H */
diff --git a/arch/um/include/asm/kvm_para.h b/arch/um/include/asm/kvm_para.h
new file mode 100644
index 000000000..14fab8f0b
--- /dev/null
+++ b/arch/um/include/asm/kvm_para.h
@@ -0,0 +1 @@
+#include <asm-generic/kvm_para.h>
diff --git a/arch/um/include/asm/mmu.h b/arch/um/include/asm/mmu.h
new file mode 100644
index 000000000..07d48738b
--- /dev/null
+++ b/arch/um/include/asm/mmu.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __ARCH_UM_MMU_H
+#define __ARCH_UM_MMU_H
+
+#include "linux/types.h"
+#include <linux/mutex.h>
+#include <linux/spinlock.h>
+#include <mm_id.h>
+
+typedef struct mm_context {
+	struct mm_id id;
+	struct mutex turnstile;
+
+	struct list_head list;
+
+	/* Address range in need of a TLB sync */
+	spinlock_t sync_tlb_lock;
+	unsigned long sync_tlb_range_from;
+	unsigned long sync_tlb_range_to;
+} mm_context_t;
+
+#define INIT_MM_CONTEXT(mm)						\
+	.context = {							\
+		.turnstile = __MUTEX_INITIALIZER(mm.context.turnstile),	\
+		.sync_tlb_lock = __SPIN_LOCK_INITIALIZER(mm.context.sync_tlb_lock), \
+	}
+
+#endif
diff --git a/arch/um/include/asm/mmu_context.h b/arch/um/include/asm/mmu_context.h
new file mode 100644
index 000000000..c727e56ba
--- /dev/null
+++ b/arch/um/include/asm/mmu_context.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __UM_MMU_CONTEXT_H
+#define __UM_MMU_CONTEXT_H
+
+#include <linux/sched.h>
+#include <linux/mm_types.h>
+#include <linux/mmap_lock.h>
+
+#include <asm/mm_hooks.h>
+#include <asm/mmu.h>
+
+static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, 
+			     struct task_struct *tsk)
+{
+}
+
+#define init_new_context init_new_context
+extern int init_new_context(struct task_struct *task, struct mm_struct *mm);
+
+#define destroy_context destroy_context
+extern void destroy_context(struct mm_struct *mm);
+
+#include <asm-generic/mmu_context.h>
+
+#endif
diff --git a/arch/um/include/asm/msi.h b/arch/um/include/asm/msi.h
new file mode 100644
index 000000000..c8c6c381f
--- /dev/null
+++ b/arch/um/include/asm/msi.h
@@ -0,0 +1 @@
+#include <asm-generic/msi.h>
diff --git a/arch/um/include/asm/page.h b/arch/um/include/asm/page.h
new file mode 100644
index 000000000..e348ff489
--- /dev/null
+++ b/arch/um/include/asm/page.h
@@ -0,0 +1,98 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2000 - 2003 Jeff Dike (jdike@addtoit.com)
+ * Copyright 2003 PathScale, Inc.
+ */
+
+#ifndef __UM_PAGE_H
+#define __UM_PAGE_H
+
+#include <linux/const.h>
+
+#include <vdso/page.h>
+
+#ifndef __ASSEMBLER__
+
+struct page;
+
+#include <linux/pfn.h>
+#include <linux/types.h>
+#include <asm/vm-flags.h>
+
+/*
+ * These are used to make use of C type-checking..
+ */
+
+#define clear_page(page)	memset((void *)(page), 0, PAGE_SIZE)
+#define copy_page(to,from)	memcpy((void *)(to), (void *)(from), PAGE_SIZE)
+
+#define copy_user_page(to, from, vaddr, pg)	copy_page(to, from)
+
+typedef struct { unsigned long pte; } pte_t;
+typedef struct { unsigned long pgd; } pgd_t;
+
+#if CONFIG_PGTABLE_LEVELS > 2
+
+typedef struct { unsigned long pmd; } pmd_t;
+#define pmd_val(x)	((x).pmd)
+#define __pmd(x) ((pmd_t) { (x) } )
+
+#if CONFIG_PGTABLE_LEVELS > 3
+
+typedef struct { unsigned long pud; } pud_t;
+#define pud_val(x)	((x).pud)
+#define __pud(x) ((pud_t) { (x) } )
+
+#endif /* CONFIG_PGTABLE_LEVELS > 3 */
+#endif /* CONFIG_PGTABLE_LEVELS > 2 */
+
+#define pte_val(x)	((x).pte)
+
+#define pte_get_bits(p, bits) ((p).pte & (bits))
+#define pte_set_bits(p, bits) ((p).pte |= (bits))
+#define pte_clear_bits(p, bits) ((p).pte &= ~(bits))
+#define pte_copy(to, from) ((to).pte = (from).pte)
+#define pte_is_zero(p) (!((p).pte & ~_PAGE_NEEDSYNC))
+#define pte_set_val(p, phys, prot) (p).pte = (phys | pgprot_val(prot))
+
+typedef unsigned long phys_t;
+
+typedef struct { unsigned long pgprot; } pgprot_t;
+
+typedef struct page *pgtable_t;
+
+#define pgd_val(x)	((x).pgd)
+#define pgprot_val(x)	((x).pgprot)
+
+#define __pte(x) ((pte_t) { (x) } )
+#define __pgd(x) ((pgd_t) { (x) } )
+#define __pgprot(x)	((pgprot_t) { (x) } )
+
+extern unsigned long uml_physmem;
+
+#define PAGE_OFFSET (uml_physmem)
+#define KERNELBASE PAGE_OFFSET
+
+#define __va_space (8*1024*1024)
+
+#include <mem.h>
+
+/* Cast to unsigned long before casting to void * to avoid a warning from
+ * mmap_kmem about cutting a long long down to a void *.  Not sure that
+ * casting is the right thing, but 32-bit UML can't have 64-bit virtual
+ * addresses
+ */
+#define __pa(virt) uml_to_phys((void *) (unsigned long) (virt))
+#define __va(phys) uml_to_virt((unsigned long) (phys))
+
+#define phys_to_pfn(p) ((p) >> PAGE_SHIFT)
+#define pfn_to_phys(pfn) PFN_PHYS(pfn)
+
+#define virt_addr_valid(v) pfn_valid(phys_to_pfn(__pa(v)))
+
+#include <asm-generic/memory_model.h>
+#include <asm-generic/getorder.h>
+
+#endif	/* __ASSEMBLER__ */
+
+#endif	/* __UM_PAGE_H */
diff --git a/arch/um/include/asm/pci.h b/arch/um/include/asm/pci.h
new file mode 100644
index 000000000..238d2e7fa
--- /dev/null
+++ b/arch/um/include/asm/pci.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef __ASM_UM_PCI_H
+#define __ASM_UM_PCI_H
+#include <linux/types.h>
+#include <asm/io.h>
+
+/* Generic PCI */
+#include <asm-generic/pci.h>
+
+#ifdef CONFIG_PCI_MSI
+/*
+ * This is a bit of an annoying hack, and it assumes we only have
+ * the virt-pci (if anything). Which is true, but still.
+ */
+void *pci_root_bus_fwnode(struct pci_bus *bus);
+#define pci_root_bus_fwnode	pci_root_bus_fwnode
+#endif
+
+#endif  /* __ASM_UM_PCI_H */
diff --git a/arch/um/include/asm/pgalloc.h b/arch/um/include/asm/pgalloc.h
new file mode 100644
index 000000000..826ec44b5
--- /dev/null
+++ b/arch/um/include/asm/pgalloc.h
@@ -0,0 +1,45 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2000, 2001, 2002 Jeff Dike (jdike@karaya.com)
+ * Copyright 2003 PathScale, Inc.
+ * Derived from include/asm-i386/pgalloc.h and include/asm-i386/pgtable.h
+ */
+
+#ifndef __UM_PGALLOC_H
+#define __UM_PGALLOC_H
+
+#include <linux/mm.h>
+
+#include <asm-generic/pgalloc.h>
+
+#define pmd_populate_kernel(mm, pmd, pte) \
+	set_pmd(pmd, __pmd(_PAGE_TABLE + (unsigned long) __pa(pte)))
+
+#define pmd_populate(mm, pmd, pte) 				\
+	set_pmd(pmd, __pmd(_PAGE_TABLE +			\
+		((unsigned long long)page_to_pfn(pte) <<	\
+			(unsigned long long) PAGE_SHIFT)))
+
+/*
+ * Allocate and free page tables.
+ */
+extern pgd_t *pgd_alloc(struct mm_struct *);
+
+#define __pte_free_tlb(tlb, pte, address)	\
+	tlb_remove_ptdesc((tlb), page_ptdesc(pte))
+
+#if CONFIG_PGTABLE_LEVELS > 2
+
+#define __pmd_free_tlb(tlb, pmd, address)	\
+	tlb_remove_ptdesc((tlb), virt_to_ptdesc(pmd))
+
+#if CONFIG_PGTABLE_LEVELS > 3
+
+#define __pud_free_tlb(tlb, pud, address)	\
+	tlb_remove_ptdesc((tlb), virt_to_ptdesc(pud))
+
+#endif
+#endif
+
+#endif
+
diff --git a/arch/um/include/asm/pgtable-2level.h b/arch/um/include/asm/pgtable-2level.h
new file mode 100644
index 000000000..14ec16f92
--- /dev/null
+++ b/arch/um/include/asm/pgtable-2level.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2000, 2001, 2002 Jeff Dike (jdike@karaya.com)
+ * Copyright 2003 PathScale, Inc.
+ * Derived from include/asm-i386/pgtable.h
+ */
+
+#ifndef __UM_PGTABLE_2LEVEL_H
+#define __UM_PGTABLE_2LEVEL_H
+
+#include <asm-generic/pgtable-nopmd.h>
+
+/* PGDIR_SHIFT determines what a third-level page table entry can map */
+
+#define PGDIR_SHIFT	22
+#define PGDIR_SIZE	(1UL << PGDIR_SHIFT)
+#define PGDIR_MASK	(~(PGDIR_SIZE-1))
+
+/*
+ * entries per page directory level: the i386 is two-level, so
+ * we don't really have any PMD directory physically.
+ */
+#define PTRS_PER_PTE	1024
+#define USER_PTRS_PER_PGD ((TASK_SIZE + (PGDIR_SIZE - 1)) / PGDIR_SIZE)
+#define PTRS_PER_PGD	1024
+
+#define pte_ERROR(e) \
+        printk("%s:%d: bad pte %p(%08lx).\n", __FILE__, __LINE__, &(e), \
+	       pte_val(e))
+#define pgd_ERROR(e) \
+        printk("%s:%d: bad pgd %p(%08lx).\n", __FILE__, __LINE__, &(e), \
+	       pgd_val(e))
+
+static inline int pgd_needsync(pgd_t pgd)	{ return 0; }
+static inline void pgd_mkuptodate(pgd_t pgd)	{ }
+
+#define set_pmd(pmdptr, pmdval) (*(pmdptr) = (pmdval))
+
+#define pte_pfn(x) phys_to_pfn(pte_val(x))
+#define pfn_pmd(pfn, prot) __pmd(pfn_to_phys(pfn) | pgprot_val(prot))
+
+#endif
diff --git a/arch/um/include/asm/pgtable-4level.h b/arch/um/include/asm/pgtable-4level.h
new file mode 100644
index 000000000..7a271b7b8
--- /dev/null
+++ b/arch/um/include/asm/pgtable-4level.h
@@ -0,0 +1,110 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright 2003 PathScale Inc
+ * Derived from include/asm-i386/pgtable.h
+ */
+
+#ifndef __UM_PGTABLE_4LEVEL_H
+#define __UM_PGTABLE_4LEVEL_H
+
+#include <asm-generic/pgtable-nop4d.h>
+
+/* PGDIR_SHIFT determines what a fourth-level page table entry can map */
+
+#define PGDIR_SHIFT	39
+#define PGDIR_SIZE	(1UL << PGDIR_SHIFT)
+#define PGDIR_MASK	(~(PGDIR_SIZE-1))
+
+/* PUD_SHIFT determines the size of the area a third-level page table can
+ * map
+ */
+
+#define PUD_SHIFT	30
+#define PUD_SIZE	(1UL << PUD_SHIFT)
+#define PUD_MASK	(~(PUD_SIZE-1))
+
+/* PMD_SHIFT determines the size of the area a second-level page table can
+ * map
+ */
+
+#define PMD_SHIFT	21
+#define PMD_SIZE	(1UL << PMD_SHIFT)
+#define PMD_MASK	(~(PMD_SIZE-1))
+
+/*
+ * entries per page directory level
+ */
+
+#define PTRS_PER_PTE 512
+#define PTRS_PER_PMD 512
+#define PTRS_PER_PUD 512
+#define PTRS_PER_PGD 512
+
+#define USER_PTRS_PER_PGD ((TASK_SIZE + (PGDIR_SIZE - 1)) / PGDIR_SIZE)
+
+#define pte_ERROR(e) \
+        printk("%s:%d: bad pte %p(%016lx).\n", __FILE__, __LINE__, &(e), \
+	       pte_val(e))
+#define pmd_ERROR(e) \
+        printk("%s:%d: bad pmd %p(%016lx).\n", __FILE__, __LINE__, &(e), \
+	       pmd_val(e))
+#define pud_ERROR(e) \
+        printk("%s:%d: bad pud %p(%016lx).\n", __FILE__, __LINE__, &(e), \
+	       pud_val(e))
+#define pgd_ERROR(e) \
+        printk("%s:%d: bad pgd %p(%016lx).\n", __FILE__, __LINE__, &(e), \
+	       pgd_val(e))
+
+#define pud_none(x)	(!(pud_val(x) & ~_PAGE_NEEDSYNC))
+#define	pud_bad(x)	((pud_val(x) & (~PAGE_MASK & ~_PAGE_USER)) != _KERNPG_TABLE)
+#define pud_present(x)	(pud_val(x) & _PAGE_PRESENT)
+#define pud_populate(mm, pud, pmd) \
+	set_pud(pud, __pud(_PAGE_TABLE + __pa(pmd)))
+
+#define set_pud(pudptr, pudval) (*(pudptr) = (pudval))
+
+#define p4d_none(x)	(!(p4d_val(x) & ~_PAGE_NEEDSYNC))
+#define	p4d_bad(x)	((p4d_val(x) & (~PAGE_MASK & ~_PAGE_USER)) != _KERNPG_TABLE)
+#define p4d_present(x)	(p4d_val(x) & _PAGE_PRESENT)
+#define p4d_populate(mm, p4d, pud) \
+	set_p4d(p4d, __p4d(_PAGE_TABLE + __pa(pud)))
+
+#define set_p4d(p4dptr, p4dval) (*(p4dptr) = (p4dval))
+
+
+static inline int pgd_needsync(pgd_t pgd)
+{
+	return pgd_val(pgd) & _PAGE_NEEDSYNC;
+}
+
+static inline void pgd_mkuptodate(pgd_t pgd) { pgd_val(pgd) &= ~_PAGE_NEEDSYNC; }
+
+#define set_pmd(pmdptr, pmdval) (*(pmdptr) = (pmdval))
+
+static inline void pud_clear (pud_t *pud)
+{
+	set_pud(pud, __pud(_PAGE_NEEDSYNC));
+}
+
+static inline void p4d_clear (p4d_t *p4d)
+{
+	set_p4d(p4d, __p4d(_PAGE_NEEDSYNC));
+}
+
+#define pud_page(pud) phys_to_page(pud_val(pud) & PAGE_MASK)
+#define pud_pgtable(pud) ((pmd_t *) __va(pud_val(pud) & PAGE_MASK))
+
+#define p4d_page(p4d) phys_to_page(p4d_val(p4d) & PAGE_MASK)
+#define p4d_pgtable(p4d) ((pud_t *) __va(p4d_val(p4d) & PAGE_MASK))
+
+static inline unsigned long pte_pfn(pte_t pte)
+{
+	return phys_to_pfn(pte_val(pte));
+}
+
+static inline pmd_t pfn_pmd(unsigned long page_nr, pgprot_t pgprot)
+{
+	return __pmd((page_nr << PAGE_SHIFT) | pgprot_val(pgprot));
+}
+
+#endif
diff --git a/arch/um/include/asm/pgtable.h b/arch/um/include/asm/pgtable.h
new file mode 100644
index 000000000..88ea84343
--- /dev/null
+++ b/arch/um/include/asm/pgtable.h
@@ -0,0 +1,328 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Copyright 2003 PathScale, Inc.
+ * Derived from include/asm-i386/pgtable.h
+ */
+
+#ifndef __UM_PGTABLE_H
+#define __UM_PGTABLE_H
+
+#include <asm/page.h>
+#include <linux/mm_types.h>
+
+#define _PAGE_PRESENT	0x001
+#define _PAGE_NEEDSYNC	0x002
+#define _PAGE_RW	0x020
+#define _PAGE_USER	0x040
+#define _PAGE_ACCESSED	0x080
+#define _PAGE_DIRTY	0x100
+/* If _PAGE_PRESENT is clear, we use these: */
+#define _PAGE_PROTNONE	0x010	/* if the user mapped it with PROT_NONE;
+				   pte_present gives true */
+
+/* We borrow bit 10 to store the exclusive marker in swap PTEs. */
+#define _PAGE_SWP_EXCLUSIVE	0x400
+
+#if CONFIG_PGTABLE_LEVELS == 4
+#include <asm/pgtable-4level.h>
+#elif CONFIG_PGTABLE_LEVELS == 2
+#include <asm/pgtable-2level.h>
+#else
+#error "Unsupported number of page table levels"
+#endif
+
+extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
+
+/* Just any arbitrary offset to the start of the vmalloc VM area: the
+ * current 8MB value just means that there will be a 8MB "hole" after the
+ * physical memory until the kernel virtual memory starts.  That means that
+ * any out-of-bounds memory accesses will hopefully be caught.
+ * The vmalloc() routines leaves a hole of 4kB between each vmalloced
+ * area for the same reason. ;)
+ */
+
+#ifndef COMPILE_OFFSETS
+#include <as-layout.h> /* for high_physmem */
+#endif
+
+#define VMALLOC_OFFSET	(__va_space)
+#define VMALLOC_START	((high_physmem + VMALLOC_OFFSET) & ~(VMALLOC_OFFSET-1))
+#define VMALLOC_END	(TASK_SIZE-2*PAGE_SIZE)
+#define MODULES_VADDR	VMALLOC_START
+#define MODULES_END	VMALLOC_END
+
+#define _PAGE_TABLE	(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | _PAGE_ACCESSED | _PAGE_DIRTY)
+#define _KERNPG_TABLE	(_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | _PAGE_DIRTY)
+#define _PAGE_CHG_MASK	(PAGE_MASK | _PAGE_ACCESSED | _PAGE_DIRTY)
+#define __PAGE_KERNEL_EXEC                                              \
+	 (_PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY | _PAGE_ACCESSED)
+#define PAGE_NONE	__pgprot(_PAGE_PROTNONE | _PAGE_ACCESSED)
+#define PAGE_SHARED	__pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER | _PAGE_ACCESSED)
+#define PAGE_COPY	__pgprot(_PAGE_PRESENT | _PAGE_USER | _PAGE_ACCESSED)
+#define PAGE_READONLY	__pgprot(_PAGE_PRESENT | _PAGE_USER | _PAGE_ACCESSED)
+#define PAGE_KERNEL	__pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY | _PAGE_ACCESSED)
+#define PAGE_KERNEL_EXEC	__pgprot(__PAGE_KERNEL_EXEC)
+
+/*
+ * The i386 can't do page protection for execute, and considers that the same
+ * are read.
+ * Also, write permissions imply read permissions. This is the closest we can
+ * get..
+ */
+
+#define pte_clear(mm, addr, xp) pte_set_val(*(xp), (phys_t) 0, __pgprot(_PAGE_NEEDSYNC))
+
+#define pmd_none(x)	(!((unsigned long)pmd_val(x) & ~_PAGE_NEEDSYNC))
+#define	pmd_bad(x)	((pmd_val(x) & (~PAGE_MASK & ~_PAGE_USER)) != _KERNPG_TABLE)
+
+#define pmd_present(x)	(pmd_val(x) & _PAGE_PRESENT)
+#define pmd_clear(xp)	do { pmd_val(*(xp)) = _PAGE_NEEDSYNC; } while (0)
+
+#define pmd_needsync(x)   (pmd_val(x) & _PAGE_NEEDSYNC)
+#define pmd_mkuptodate(x) (pmd_val(x) &= ~_PAGE_NEEDSYNC)
+
+#define pud_needsync(x)   (pud_val(x) & _PAGE_NEEDSYNC)
+#define pud_mkuptodate(x) (pud_val(x) &= ~_PAGE_NEEDSYNC)
+
+#define p4d_needsync(x)   (p4d_val(x) & _PAGE_NEEDSYNC)
+#define p4d_mkuptodate(x) (p4d_val(x) &= ~_PAGE_NEEDSYNC)
+
+#define pmd_pfn(pmd) (pmd_val(pmd) >> PAGE_SHIFT)
+#define pmd_page(pmd) phys_to_page(pmd_val(pmd) & PAGE_MASK)
+
+#define pte_page(x) pfn_to_page(pte_pfn(x))
+
+#define pte_present(x)	pte_get_bits(x, (_PAGE_PRESENT | _PAGE_PROTNONE))
+
+/*
+ * =================================
+ * Flags checking section.
+ * =================================
+ */
+
+static inline int pte_none(pte_t pte)
+{
+	return pte_is_zero(pte);
+}
+
+/*
+ * The following only work if pte_present() is true.
+ * Undefined behaviour if not..
+ */
+static inline int pte_read(pte_t pte)
+{
+	return !pte_get_bits(pte, _PAGE_PROTNONE);
+}
+
+static inline int pte_exec(pte_t pte)
+{
+	return !pte_get_bits(pte, _PAGE_PROTNONE);
+}
+
+static inline int pte_write(pte_t pte)
+{
+	return((pte_get_bits(pte, _PAGE_RW)) &&
+	       !(pte_get_bits(pte, _PAGE_PROTNONE)));
+}
+
+static inline int pte_dirty(pte_t pte)
+{
+	return pte_get_bits(pte, _PAGE_DIRTY);
+}
+
+static inline int pte_young(pte_t pte)
+{
+	return pte_get_bits(pte, _PAGE_ACCESSED);
+}
+
+static inline int pte_needsync(pte_t pte)
+{
+	return pte_get_bits(pte, _PAGE_NEEDSYNC);
+}
+
+/*
+ * =================================
+ * Flags setting section.
+ * =================================
+ */
+
+static inline pte_t pte_mkclean(pte_t pte)
+{
+	pte_clear_bits(pte, _PAGE_DIRTY);
+	return(pte);
+}
+
+static inline pte_t pte_mkold(pte_t pte)
+{
+	pte_clear_bits(pte, _PAGE_ACCESSED);
+	return(pte);
+}
+
+static inline pte_t pte_wrprotect(pte_t pte)
+{
+	pte_clear_bits(pte, _PAGE_RW);
+	return pte;
+}
+
+static inline pte_t pte_mkread(pte_t pte)
+{
+	pte_set_bits(pte, _PAGE_USER);
+	return pte;
+}
+
+static inline pte_t pte_mkdirty(pte_t pte)
+{
+	pte_set_bits(pte, _PAGE_DIRTY);
+	return(pte);
+}
+
+static inline pte_t pte_mkyoung(pte_t pte)
+{
+	pte_set_bits(pte, _PAGE_ACCESSED);
+	return(pte);
+}
+
+static inline pte_t pte_mkwrite_novma(pte_t pte)
+{
+	pte_set_bits(pte, _PAGE_RW);
+	return pte;
+}
+
+static inline pte_t pte_mkuptodate(pte_t pte)
+{
+	pte_clear_bits(pte, _PAGE_NEEDSYNC);
+	return pte;
+}
+
+static inline pte_t pte_mkneedsync(pte_t pte)
+{
+	pte_set_bits(pte, _PAGE_NEEDSYNC);
+	return(pte);
+}
+
+static inline void set_pte(pte_t *pteptr, pte_t pteval)
+{
+	pte_copy(*pteptr, pteval);
+
+	/* If it's a swap entry, it needs to be marked _PAGE_NEEDSYNC so
+	 * update_pte_range knows to unmap it.
+	 */
+
+	*pteptr = pte_mkneedsync(*pteptr);
+}
+
+#define PFN_PTE_SHIFT		PAGE_SHIFT
+
+static inline void um_tlb_mark_sync(struct mm_struct *mm, unsigned long start,
+				    unsigned long end)
+{
+	guard(spinlock_irqsave)(&mm->context.sync_tlb_lock);
+
+	if (!mm->context.sync_tlb_range_to) {
+		mm->context.sync_tlb_range_from = start;
+		mm->context.sync_tlb_range_to = end;
+	} else {
+		if (start < mm->context.sync_tlb_range_from)
+			mm->context.sync_tlb_range_from = start;
+		if (end > mm->context.sync_tlb_range_to)
+			mm->context.sync_tlb_range_to = end;
+	}
+}
+
+#define set_ptes set_ptes
+static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
+			    pte_t *ptep, pte_t pte, int nr)
+{
+	/* Basically the default implementation */
+	size_t length = nr * PAGE_SIZE;
+
+	for (;;) {
+		set_pte(ptep, pte);
+		if (--nr == 0)
+			break;
+		ptep++;
+		pte = __pte(pte_val(pte) + (nr << PFN_PTE_SHIFT));
+	}
+
+	um_tlb_mark_sync(mm, addr, addr + length);
+}
+
+#define __HAVE_ARCH_PTE_SAME
+static inline int pte_same(pte_t pte_a, pte_t pte_b)
+{
+	return !((pte_val(pte_a) ^ pte_val(pte_b)) & ~_PAGE_NEEDSYNC);
+}
+
+#define __virt_to_page(virt) phys_to_page(__pa(virt))
+#define virt_to_page(addr) __virt_to_page((const unsigned long) addr)
+
+static inline pte_t pfn_pte(unsigned long pfn, pgprot_t pgprot)
+{
+	pte_t pte;
+
+	pte_set_val(pte, pfn_to_phys(pfn), pgprot);
+
+	return pte;
+}
+
+static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
+{
+	pte_set_val(pte, (pte_val(pte) & _PAGE_CHG_MASK), newprot);
+	return pte;
+}
+
+/*
+ * the pmd page can be thought of an array like this: pmd_t[PTRS_PER_PMD]
+ *
+ * this macro returns the index of the entry in the pmd page which would
+ * control the given virtual address
+ */
+#define pmd_page_vaddr(pmd) ((unsigned long) __va(pmd_val(pmd) & PAGE_MASK))
+
+struct mm_struct;
+extern pte_t *virt_to_pte(struct mm_struct *mm, unsigned long addr);
+
+#define update_mmu_cache(vma,address,ptep) do {} while (0)
+#define update_mmu_cache_range(vmf, vma, address, ptep, nr) do {} while (0)
+
+/*
+ * Encode/decode swap entries and swap PTEs. Swap PTEs are all PTEs that
+ * are !pte_none() && !pte_present().
+ *
+ * Format of swap PTEs:
+ *
+ *   3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
+ *   1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+ *   <--------------- offset ----------------> E < type -> 0 0 0 1 0
+ *
+ *   E is the exclusive marker that is not stored in swap entries.
+ *   _PAGE_NEEDSYNC (bit 1) is always set to 1 in set_pte().
+ */
+#define __swp_type(x)			(((x).val >> 5) & 0x1f)
+#define __swp_offset(x)			((x).val >> 11)
+
+#define __swp_entry(type, offset) \
+	((swp_entry_t) { (((type) & 0x1f) << 5) | ((offset) << 11) })
+#define __pte_to_swp_entry(pte) \
+	((swp_entry_t) { pte_val(pte_mkuptodate(pte)) })
+#define __swp_entry_to_pte(x)		((pte_t) { (x).val })
+
+static inline bool pte_swp_exclusive(pte_t pte)
+{
+	return pte_get_bits(pte, _PAGE_SWP_EXCLUSIVE);
+}
+
+static inline pte_t pte_swp_mkexclusive(pte_t pte)
+{
+	pte_set_bits(pte, _PAGE_SWP_EXCLUSIVE);
+	return pte;
+}
+
+static inline pte_t pte_swp_clear_exclusive(pte_t pte)
+{
+	pte_clear_bits(pte, _PAGE_SWP_EXCLUSIVE);
+	return pte;
+}
+
+#endif
diff --git a/arch/um/include/asm/processor-generic.h b/arch/um/include/asm/processor-generic.h
new file mode 100644
index 000000000..7854d51b6
--- /dev/null
+++ b/arch/um/include/asm/processor-generic.h
@@ -0,0 +1,88 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __UM_PROCESSOR_GENERIC_H
+#define __UM_PROCESSOR_GENERIC_H
+
+struct pt_regs;
+
+struct task_struct;
+
+#include <asm/ptrace.h>
+#include <sysdep/archsetjmp.h>
+
+#include <linux/prefetch.h>
+
+#include <asm/cpufeatures.h>
+
+struct mm_struct;
+
+struct thread_struct {
+	struct pt_regs *segv_regs;
+	struct task_struct *prev_sched;
+	struct arch_thread arch;
+	jmp_buf switch_buf;
+	struct {
+		struct {
+			int (*proc)(void *);
+			void *arg;
+		} thread;
+	} request;
+
+	void *segv_continue;
+
+	/* Contains variable sized FP registers */
+	struct pt_regs regs;
+};
+
+#define INIT_THREAD \
+{ \
+	.regs		   	= EMPTY_REGS,	\
+	.prev_sched		= NULL, \
+	.arch			= INIT_ARCH_THREAD, \
+	.request		= { } \
+}
+
+/*
+ * User space process size: 3GB (default).
+ */
+extern unsigned long task_size;
+
+#define TASK_SIZE (task_size)
+
+#undef STACK_TOP
+#undef STACK_TOP_MAX
+
+extern unsigned long stacksizelim;
+
+#define STACK_ROOM	(stacksizelim)
+#define STACK_TOP	(TASK_SIZE - 2 * PAGE_SIZE)
+#define STACK_TOP_MAX	STACK_TOP
+
+/* This decides where the kernel will search for a free chunk of vm
+ * space during mmap's.
+ */
+#define TASK_UNMAPPED_BASE	(0x40000000)
+
+extern void start_thread(struct pt_regs *regs, unsigned long entry, 
+			 unsigned long stack);
+
+struct cpuinfo_um {
+	unsigned long loops_per_jiffy;
+	int cache_alignment;
+	union {
+		__u32		x86_capability[NCAPINTS + NBUGINTS];
+		unsigned long	x86_capability_alignment;
+	};
+};
+
+extern struct cpuinfo_um boot_cpu_data;
+
+#define cache_line_size()	(boot_cpu_data.cache_alignment)
+
+#define KSTK_REG(tsk, reg) get_thread_reg(reg, &tsk->thread.switch_buf)
+extern unsigned long __get_wchan(struct task_struct *p);
+
+#endif
diff --git a/arch/um/include/asm/ptrace-generic.h b/arch/um/include/asm/ptrace-generic.h
new file mode 100644
index 000000000..86d74f9d3
--- /dev/null
+++ b/arch/um/include/asm/ptrace-generic.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __UM_PTRACE_GENERIC_H
+#define __UM_PTRACE_GENERIC_H
+
+#ifndef __ASSEMBLER__
+
+#include <sysdep/ptrace.h>
+
+struct pt_regs {
+	struct uml_pt_regs regs;
+};
+
+#define arch_has_single_step()	(1)
+
+#define EMPTY_REGS { .regs = EMPTY_UML_PT_REGS }
+
+#define PT_REGS_IP(r) UPT_IP(&(r)->regs)
+#define PT_REGS_SP(r) UPT_SP(&(r)->regs)
+
+#define PT_REGS_RESTART_SYSCALL(r) UPT_RESTART_SYSCALL(&(r)->regs)
+
+#define PT_REGS_SYSCALL_NR(r) UPT_SYSCALL_NR(&(r)->regs)
+
+#define instruction_pointer(regs) PT_REGS_IP(regs)
+
+#define PTRACE_OLDSETOPTIONS 21
+
+struct task_struct;
+
+extern long subarch_ptrace(struct task_struct *child, long request,
+	unsigned long addr, unsigned long data);
+extern unsigned long getreg(struct task_struct *child, int regno);
+extern int putreg(struct task_struct *child, int regno, unsigned long value);
+
+extern int poke_user(struct task_struct *child, long addr, long data);
+extern int peek_user(struct task_struct *child, long addr, long data);
+
+extern int arch_set_tls(struct task_struct *new, unsigned long tls);
+extern void clear_flushed_tls(struct task_struct *task);
+extern int syscall_trace_enter(struct pt_regs *regs);
+extern void syscall_trace_leave(struct pt_regs *regs);
+
+#endif
+
+#endif
diff --git a/arch/um/include/asm/sections.h b/arch/um/include/asm/sections.h
new file mode 100644
index 000000000..a3c1fb6ed
--- /dev/null
+++ b/arch/um/include/asm/sections.h
@@ -0,0 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UM_SECTIONS_H
+#define __UM_SECTIONS_H
+
+#include <asm-generic/sections.h>
+
+extern char __binary_start[];
+extern char __syscall_stub_start[], __syscall_stub_end[];
+
+#endif
diff --git a/arch/um/include/asm/setup.h b/arch/um/include/asm/setup.h
new file mode 100644
index 000000000..80ada899f
--- /dev/null
+++ b/arch/um/include/asm/setup.h
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef SETUP_H_INCLUDED
+#define SETUP_H_INCLUDED
+
+/* POSIX mandated with _POSIX_ARG_MAX that we can rely on 4096 chars in the
+ * command line, so this choice is ok.
+ */
+
+#define COMMAND_LINE_SIZE 4096
+
+#endif		/* SETUP_H_INCLUDED */
diff --git a/arch/um/include/asm/smp.h b/arch/um/include/asm/smp.h
new file mode 100644
index 000000000..be1743a6f
--- /dev/null
+++ b/arch/um/include/asm/smp.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UM_SMP_H
+#define __UM_SMP_H
+
+#if IS_ENABLED(CONFIG_SMP)
+
+#include <linux/cpumask.h>
+#include <shared/smp.h>
+
+#define raw_smp_processor_id() uml_curr_cpu()
+
+void arch_smp_send_reschedule(int cpu);
+
+void arch_send_call_function_single_ipi(int cpu);
+
+void arch_send_call_function_ipi_mask(const struct cpumask *mask);
+
+#endif /* CONFIG_SMP */
+
+#endif
diff --git a/arch/um/include/asm/stacktrace.h b/arch/um/include/asm/stacktrace.h
new file mode 100644
index 000000000..436b55952
--- /dev/null
+++ b/arch/um/include/asm/stacktrace.h
@@ -0,0 +1,43 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_UML_STACKTRACE_H
+#define _ASM_UML_STACKTRACE_H
+
+#include <linux/uaccess.h>
+#include <linux/ptrace.h>
+
+struct stack_frame {
+	struct stack_frame *next_frame;
+	unsigned long return_address;
+};
+
+struct stacktrace_ops {
+	void (*address)(void *data, unsigned long address, int reliable);
+};
+
+#ifdef CONFIG_FRAME_POINTER
+static inline unsigned long
+get_frame_pointer(struct task_struct *task, struct pt_regs *segv_regs)
+{
+	if (!task || task == current)
+		return segv_regs ? PT_REGS_BP(segv_regs) : current_bp();
+	return KSTK_EBP(task);
+}
+#else
+static inline unsigned long
+get_frame_pointer(struct task_struct *task, struct pt_regs *segv_regs)
+{
+	return 0;
+}
+#endif
+
+static inline unsigned long
+*get_stack_pointer(struct task_struct *task, struct pt_regs *segv_regs)
+{
+	if (!task || task == current)
+		return segv_regs ? (unsigned long *)PT_REGS_SP(segv_regs) : current_sp();
+	return (unsigned long *)KSTK_ESP(task);
+}
+
+void dump_trace(struct task_struct *tsk, const struct stacktrace_ops *ops, void *data);
+
+#endif /* _ASM_UML_STACKTRACE_H */
diff --git a/arch/um/include/asm/syscall-generic.h b/arch/um/include/asm/syscall-generic.h
new file mode 100644
index 000000000..bcd73bcfe
--- /dev/null
+++ b/arch/um/include/asm/syscall-generic.h
@@ -0,0 +1,86 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Access to user system call parameters and results
+ *
+ * See asm-generic/syscall.h for function descriptions.
+ *
+ * Copyright (C) 2015 Mickaël Salaün <mic@digikod.net>
+ */
+
+#ifndef __UM_SYSCALL_GENERIC_H
+#define __UM_SYSCALL_GENERIC_H
+
+#include <asm/ptrace.h>
+#include <linux/err.h>
+#include <linux/sched.h>
+#include <sysdep/ptrace.h>
+
+static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
+{
+
+	return PT_REGS_SYSCALL_NR(regs);
+}
+
+static inline void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
+{
+	PT_REGS_SYSCALL_NR(regs) = nr;
+}
+
+static inline void syscall_rollback(struct task_struct *task,
+				    struct pt_regs *regs)
+{
+	/* do nothing */
+}
+
+static inline long syscall_get_error(struct task_struct *task,
+				     struct pt_regs *regs)
+{
+	const long error = regs_return_value(regs);
+
+	return IS_ERR_VALUE(error) ? error : 0;
+}
+
+static inline long syscall_get_return_value(struct task_struct *task,
+					    struct pt_regs *regs)
+{
+	return regs_return_value(regs);
+}
+
+static inline void syscall_set_return_value(struct task_struct *task,
+					    struct pt_regs *regs,
+					    int error, long val)
+{
+	PT_REGS_SET_SYSCALL_RETURN(regs, (long) error ?: val);
+}
+
+static inline void syscall_get_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 unsigned long *args)
+{
+	const struct uml_pt_regs *r = &regs->regs;
+
+	*args++ = UPT_SYSCALL_ARG1(r);
+	*args++ = UPT_SYSCALL_ARG2(r);
+	*args++ = UPT_SYSCALL_ARG3(r);
+	*args++ = UPT_SYSCALL_ARG4(r);
+	*args++ = UPT_SYSCALL_ARG5(r);
+	*args   = UPT_SYSCALL_ARG6(r);
+}
+
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	struct uml_pt_regs *r = &regs->regs;
+
+	UPT_SYSCALL_ARG1(r) = *args++;
+	UPT_SYSCALL_ARG2(r) = *args++;
+	UPT_SYSCALL_ARG3(r) = *args++;
+	UPT_SYSCALL_ARG4(r) = *args++;
+	UPT_SYSCALL_ARG5(r) = *args++;
+	UPT_SYSCALL_ARG6(r) = *args;
+}
+
+/* See arch/x86/um/asm/syscall.h for syscall_get_arch() definition. */
+
+#endif	/* __UM_SYSCALL_GENERIC_H */
diff --git a/arch/um/include/asm/thread_info.h b/arch/um/include/asm/thread_info.h
new file mode 100644
index 000000000..7a6f4dc99
--- /dev/null
+++ b/arch/um/include/asm/thread_info.h
@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __UM_THREAD_INFO_H
+#define __UM_THREAD_INFO_H
+
+#define THREAD_SIZE_ORDER CONFIG_KERNEL_STACK_ORDER
+#define THREAD_SIZE ((1 << CONFIG_KERNEL_STACK_ORDER) * PAGE_SIZE)
+
+#ifndef __ASSEMBLER__
+
+#include <asm/types.h>
+#include <asm/page.h>
+#include <asm/segment.h>
+#include <sysdep/ptrace_user.h>
+
+struct thread_info {
+	unsigned long		flags;		/* low level flags */
+	__u32			cpu;		/* current CPU */
+	int			preempt_count;  /* 0 => preemptable,
+						   <0 => BUG */
+};
+
+#define INIT_THREAD_INFO(tsk)			\
+{						\
+	.flags =		0,		\
+	.cpu =		0,			\
+	.preempt_count = INIT_PREEMPT_COUNT,	\
+}
+
+#endif
+
+#define TIF_SYSCALL_TRACE	0	/* syscall trace active */
+#define TIF_SIGPENDING		1	/* signal pending */
+#define TIF_NEED_RESCHED	2	/* rescheduling necessary */
+#define TIF_NOTIFY_SIGNAL	3	/* signal notifications exist */
+#define TIF_RESTART_BLOCK	4
+#define TIF_MEMDIE		5	/* is terminating due to OOM killer */
+#define TIF_SYSCALL_AUDIT	6
+#define TIF_RESTORE_SIGMASK	7
+#define TIF_NOTIFY_RESUME	8
+#define TIF_SECCOMP		9	/* secure computing */
+#define TIF_SINGLESTEP		10	/* single stepping userspace */
+#define TIF_SYSCALL_TRACEPOINT	11	/* syscall tracepoint instrumentation */
+
+
+#define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
+#define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
+#define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
+#define _TIF_NOTIFY_SIGNAL	(1 << TIF_NOTIFY_SIGNAL)
+#define _TIF_MEMDIE		(1 << TIF_MEMDIE)
+#define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
+#define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
+#define _TIF_SECCOMP		(1 << TIF_SECCOMP)
+#define _TIF_SINGLESTEP		(1 << TIF_SINGLESTEP)
+
+#define _TIF_WORK_MASK		(_TIF_NEED_RESCHED | _TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL | \
+				 _TIF_NOTIFY_RESUME)
+
+#endif
diff --git a/arch/um/include/asm/timex.h b/arch/um/include/asm/timex.h
new file mode 100644
index 000000000..39e392ebc
--- /dev/null
+++ b/arch/um/include/asm/timex.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UM_TIMEX_H
+#define __UM_TIMEX_H
+
+/*
+ * Do not fall back to the host architecture header because latter likely
+ * includes facilities like cpu_feature_enabled() which are present only
+ * there. That would result in build breakages and/or efforts to "emulate"
+ * those facilities in UML.
+ */
+#include <asm-generic/timex.h>
+
+#endif
diff --git a/arch/um/include/asm/tlb.h b/arch/um/include/asm/tlb.h
new file mode 100644
index 000000000..0422467bd
--- /dev/null
+++ b/arch/um/include/asm/tlb.h
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UM_TLB_H
+#define __UM_TLB_H
+
+#include <linux/mm.h>
+
+#include <asm/tlbflush.h>
+#include <asm/cacheflush.h>
+#include <asm-generic/tlb.h>
+
+#endif
diff --git a/arch/um/include/asm/tlbflush.h b/arch/um/include/asm/tlbflush.h
new file mode 100644
index 000000000..13a300994
--- /dev/null
+++ b/arch/um/include/asm/tlbflush.h
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __UM_TLBFLUSH_H
+#define __UM_TLBFLUSH_H
+
+#include <linux/mm.h>
+
+/*
+ * In UML, we need to sync the TLB over by using mmap/munmap syscalls from
+ * the process handling the MM (which can be the kernel itself).
+ *
+ * To track updates, we can hook into set_ptes and flush_tlb_*. With set_ptes
+ * we catch all PTE transitions where memory that was unusable becomes usable.
+ * While with flush_tlb_* we can track any memory that becomes unusable and
+ * even if a higher layer of the page table was modified.
+ *
+ * So, we simply track updates using both methods and mark the memory area to
+ * be synced later on. The only special case is that flush_tlb_kern_* needs to
+ * be executed immediately as there is no good synchronization point in that
+ * case. In contrast, in the set_ptes case we can wait for the next kernel
+ * segfault before we do the synchornization.
+ *
+ *  - flush_tlb_all() flushes all processes TLBs
+ *  - flush_tlb_mm(mm) flushes the specified mm context TLB's
+ *  - flush_tlb_page(vma, vmaddr) flushes one page
+ *  - flush_tlb_range(vma, start, end) flushes a range of pages
+ *  - flush_tlb_kernel_range(start, end) flushes a range of kernel pages
+ */
+
+extern int um_tlb_sync(struct mm_struct *mm);
+
+extern void flush_tlb_all(void);
+extern void flush_tlb_mm(struct mm_struct *mm);
+
+static inline void flush_tlb_page(struct vm_area_struct *vma,
+				  unsigned long address)
+{
+	um_tlb_mark_sync(vma->vm_mm, address, address + PAGE_SIZE);
+}
+
+static inline void flush_tlb_range(struct vm_area_struct *vma,
+				   unsigned long start, unsigned long end)
+{
+	um_tlb_mark_sync(vma->vm_mm, start, end);
+}
+
+static inline void flush_tlb_kernel_range(unsigned long start,
+					  unsigned long end)
+{
+	um_tlb_mark_sync(&init_mm, start, end);
+
+	/* Kernel needs to be synced immediately */
+	um_tlb_sync(&init_mm);
+}
+
+#endif
diff --git a/arch/um/include/asm/uaccess.h b/arch/um/include/asm/uaccess.h
new file mode 100644
index 000000000..4417c8b1d
--- /dev/null
+++ b/arch/um/include/asm/uaccess.h
@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
+ * Copyright (C) 2015 Richard Weinberger (richard@nod.at)
+ */
+
+#ifndef __UM_UACCESS_H
+#define __UM_UACCESS_H
+
+#include <asm/elf.h>
+#include <linux/unaligned.h>
+#include <sysdep/faultinfo.h>
+
+#define __under_task_size(addr, size) \
+	(((unsigned long) (addr) < TASK_SIZE) && \
+	 (((unsigned long) (addr) + (size)) < TASK_SIZE))
+
+#define __addr_range_nowrap(addr, size) \
+	((unsigned long) (addr) <= ((unsigned long) (addr) + (size)))
+
+extern unsigned long raw_copy_from_user(void *to, const void __user *from, unsigned long n);
+extern unsigned long raw_copy_to_user(void __user *to, const void *from, unsigned long n);
+extern unsigned long __clear_user(void __user *mem, unsigned long len);
+static inline int __access_ok(const void __user *ptr, unsigned long size);
+
+/* Teach asm-generic/uaccess.h that we have C functions for these. */
+#define __access_ok __access_ok
+#define __clear_user __clear_user
+
+#define INLINE_COPY_USER
+
+#include <asm-generic/uaccess.h>
+
+static inline int __access_ok(const void __user *ptr, unsigned long size)
+{
+	unsigned long addr = (unsigned long)ptr;
+	return __addr_range_nowrap(addr, size) && __under_task_size(addr, size);
+}
+
+#define __get_kernel_nofault(dst, src, type, err_label)			\
+do {									\
+	int __faulted;							\
+									\
+	___backtrack_faulted(__faulted);				\
+	if (__faulted) {						\
+		*((type *)dst) = (type) 0;				\
+		goto err_label;						\
+	}								\
+	*((type *)dst) = get_unaligned((type *)(src));			\
+	barrier();							\
+	current->thread.segv_continue = NULL;				\
+} while (0)
+
+#define __put_kernel_nofault(dst, src, type, err_label)			\
+do {									\
+	int __faulted;							\
+									\
+	___backtrack_faulted(__faulted);				\
+	if (__faulted)							\
+		goto err_label;						\
+	put_unaligned(*((type *)src), (type *)(dst));			\
+	barrier();							\
+	current->thread.segv_continue = NULL;				\
+} while (0)
+
+#endif
diff --git a/arch/um/include/asm/unwind.h b/arch/um/include/asm/unwind.h
new file mode 100644
index 000000000..7ffa5437b
--- /dev/null
+++ b/arch/um/include/asm/unwind.h
@@ -0,0 +1,8 @@
+#ifndef _ASM_UML_UNWIND_H
+#define _ASM_UML_UNWIND_H
+
+static inline void
+unwind_module_init(struct module *mod, void *orc_ip, size_t orc_ip_size,
+		   void *orc, size_t orc_size) {}
+
+#endif /* _ASM_UML_UNWIND_H */
diff --git a/arch/um/include/asm/vmalloc.h b/arch/um/include/asm/vmalloc.h
new file mode 100644
index 000000000..9a7b9ed93
--- /dev/null
+++ b/arch/um/include/asm/vmalloc.h
@@ -0,0 +1,4 @@
+#ifndef _ASM_UM_VMALLOC_H
+#define _ASM_UM_VMALLOC_H
+
+#endif /* _ASM_UM_VMALLOC_H */
diff --git a/arch/um/include/asm/vmlinux.lds.h b/arch/um/include/asm/vmlinux.lds.h
new file mode 100644
index 000000000..149494ae7
--- /dev/null
+++ b/arch/um/include/asm/vmlinux.lds.h
@@ -0,0 +1,2 @@
+#include <asm/thread_info.h>
+#include <asm-generic/vmlinux.lds.h>
diff --git a/arch/um/include/linux/smp-internal.h b/arch/um/include/linux/smp-internal.h
new file mode 100644
index 000000000..1dbcbc23f
--- /dev/null
+++ b/arch/um/include/linux/smp-internal.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UM_SMP_INTERNAL_H
+#define __UM_SMP_INTERNAL_H
+
+#if IS_ENABLED(CONFIG_SMP)
+
+void prefill_possible_map(void);
+
+#else /* !CONFIG_SMP */
+
+static inline void prefill_possible_map(void) { }
+
+#endif /* CONFIG_SMP */
+
+extern char cpu_irqstacks[NR_CPUS][THREAD_SIZE] __aligned(THREAD_SIZE);
+
+#endif /* __UM_SMP_INTERNAL_H */
diff --git a/arch/um/include/linux/time-internal.h b/arch/um/include/linux/time-internal.h
new file mode 100644
index 000000000..c274eb5ad
--- /dev/null
+++ b/arch/um/include/linux/time-internal.h
@@ -0,0 +1,96 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2012 - 2014 Cisco Systems
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __TIMER_INTERNAL_H__
+#define __TIMER_INTERNAL_H__
+#include <linux/list.h>
+#include <asm/bug.h>
+#include <shared/timetravel.h>
+
+#define TIMER_MULTIPLIER 256
+#define TIMER_MIN_DELTA  500
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+struct time_travel_event {
+	unsigned long long time;
+	void (*fn)(struct time_travel_event *d);
+	struct list_head list;
+	bool pending, onstack;
+};
+
+void time_travel_sleep(void);
+
+static inline void
+time_travel_set_event_fn(struct time_travel_event *e,
+			 void (*fn)(struct time_travel_event *d))
+{
+	e->fn = fn;
+}
+
+void __time_travel_propagate_time(void);
+
+static inline void time_travel_propagate_time(void)
+{
+	if (time_travel_mode == TT_MODE_EXTERNAL)
+		__time_travel_propagate_time();
+}
+
+void __time_travel_wait_readable(int fd);
+
+static inline void time_travel_wait_readable(int fd)
+{
+	if (time_travel_mode == TT_MODE_EXTERNAL)
+		__time_travel_wait_readable(fd);
+}
+
+void time_travel_add_irq_event(struct time_travel_event *e);
+void time_travel_add_event_rel(struct time_travel_event *e,
+			       unsigned long long delay_ns);
+bool time_travel_del_event(struct time_travel_event *e);
+#else
+struct time_travel_event {
+};
+
+static inline void time_travel_sleep(void)
+{
+}
+
+/* this is a macro so the event/function need not exist */
+#define time_travel_set_event_fn(e, fn) do {} while (0)
+
+static inline void time_travel_propagate_time(void)
+{
+}
+
+static inline void time_travel_wait_readable(int fd)
+{
+}
+
+static inline void time_travel_add_irq_event(struct time_travel_event *e)
+{
+	WARN_ON(1);
+}
+
+/*
+ * not inlines so the data structure need not exist,
+ * cause linker failures
+ */
+extern void time_travel_not_configured(void);
+#define time_travel_add_event_rel(...) time_travel_not_configured()
+#define time_travel_del_event(...) time_travel_not_configured()
+#endif /* CONFIG_UML_TIME_TRAVEL_SUPPORT */
+
+extern unsigned long tt_extra_sched_jiffies;
+
+/*
+ * Without CONFIG_UML_TIME_TRAVEL_SUPPORT this is a linker error if used,
+ * which is intentional since we really shouldn't link it in that case.
+ */
+void time_travel_ndelay(unsigned long nsec);
+
+int um_setup_timer(void);
+
+#endif /* __TIMER_INTERNAL_H__ */
diff --git a/arch/um/include/linux/virtio-uml.h b/arch/um/include/linux/virtio-uml.h
new file mode 100644
index 000000000..2f652fa90
--- /dev/null
+++ b/arch/um/include/linux/virtio-uml.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2021 Intel Corporation
+ * Author: Johannes Berg <johannes@sipsolutions.net>
+ */
+
+#ifndef __VIRTIO_UML_H__
+#define __VIRTIO_UML_H__
+
+void virtio_uml_set_no_vq_suspend(struct virtio_device *vdev,
+				  bool no_vq_suspend);
+
+#endif /* __VIRTIO_UML_H__ */
diff --git a/arch/um/include/shared/arch.h b/arch/um/include/shared/arch.h
new file mode 100644
index 000000000..cc398a21a
--- /dev/null
+++ b/arch/um/include/shared/arch.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __ARCH_H__
+#define __ARCH_H__
+
+#include <sysdep/ptrace.h>
+
+extern void arch_check_bugs(void);
+extern int arch_fixup(unsigned long address, struct uml_pt_regs *regs);
+extern void arch_examine_signal(int sig, struct uml_pt_regs *regs);
+
+void mc_set_rip(void *_mc, void *target);
+
+#endif
diff --git a/arch/um/include/shared/as-layout.h b/arch/um/include/shared/as-layout.h
new file mode 100644
index 000000000..02ef258e3
--- /dev/null
+++ b/arch/um/include/shared/as-layout.h
@@ -0,0 +1,57 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __START_H__
+#define __START_H__
+
+#include <generated/asm-offsets.h>
+
+/*
+ * Stolen from linux/const.h, which can't be directly included since
+ * this is used in userspace code, which has no access to the kernel
+ * headers.  Changed to be suitable for adding casts to the start,
+ * rather than "UL" to the end.
+ */
+
+/* Some constant macros are used in both assembler and
+ * C code.  Therefore we cannot annotate them always with
+ * 'UL' and other type specifiers unilaterally.  We
+ * use the following macros to deal with this.
+ */
+#define STUB_START stub_start
+#define STUB_CODE STUB_START
+#define STUB_DATA (STUB_CODE + UM_KERN_PAGE_SIZE)
+#define STUB_DATA_PAGES 2
+#define STUB_SIZE ((1 + STUB_DATA_PAGES) * UM_KERN_PAGE_SIZE)
+#define STUB_END (STUB_START + STUB_SIZE)
+
+#ifndef __ASSEMBLER__
+
+#include <sysdep/ptrace.h>
+
+struct task_struct;
+extern struct task_struct *cpu_tasks[];
+
+extern unsigned long long physmem_size;
+
+extern unsigned long high_physmem;
+extern unsigned long uml_physmem;
+extern unsigned long uml_reserved;
+extern unsigned long end_vm;
+extern unsigned long start_vm;
+
+extern unsigned long brk_start;
+
+extern unsigned long stub_start;
+
+extern int linux_main(int argc, char **argv, char **envp);
+extern void uml_finishsetup(void);
+
+struct siginfo;
+extern void (*sig_info[])(int, struct siginfo *si, struct uml_pt_regs *, void *);
+
+#endif
+
+#endif
diff --git a/arch/um/include/shared/elf_user.h b/arch/um/include/shared/elf_user.h
new file mode 100644
index 000000000..fd461ee40
--- /dev/null
+++ b/arch/um/include/shared/elf_user.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2004 Fujitsu Siemens Computers GmbH
+ * Author: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
+ */
+
+#ifndef __ELF_USER_H__
+#define __ELF_USER_H__
+
+/* For compilation on a host that doesn't support AT_SYSINFO (Linux 2.4)  */
+
+#ifndef AT_SYSINFO
+#define AT_SYSINFO 32
+#endif
+#ifndef AT_SYSINFO_EHDR
+#define AT_SYSINFO_EHDR 33
+#endif
+
+#endif
diff --git a/arch/um/include/shared/frame_kern.h b/arch/um/include/shared/frame_kern.h
new file mode 100644
index 000000000..ed952ac66
--- /dev/null
+++ b/arch/um/include/shared/frame_kern.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
+ */
+
+#ifndef __FRAME_KERN_H_
+#define __FRAME_KERN_H_
+
+extern int setup_signal_stack_sc(unsigned long stack_top, struct ksignal *ksig,
+				 struct pt_regs *regs, sigset_t *mask);
+extern int setup_signal_stack_si(unsigned long stack_top, struct ksignal *ksig,
+				 struct pt_regs *regs, sigset_t *mask);
+
+#endif
+
diff --git a/arch/um/include/shared/init.h b/arch/um/include/shared/init.h
new file mode 100644
index 000000000..1a659e2e8
--- /dev/null
+++ b/arch/um/include/shared/init.h
@@ -0,0 +1,127 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_UML_INIT_H
+#define _LINUX_UML_INIT_H
+
+/* These macros are used to mark some functions or
+ * initialized data (doesn't apply to uninitialized data)
+ * as `initialization' functions. The kernel can take this
+ * as hint that the function is used only during the initialization
+ * phase and free up used memory resources after
+ *
+ * Usage:
+ * For functions:
+ *
+ * You should add __init immediately before the function name, like:
+ *
+ * static void __init initme(int x, int y)
+ * {
+ *    extern int z; z = x * y;
+ * }
+ *
+ * If the function has a prototype somewhere, you can also add
+ * __init between closing brace of the prototype and semicolon:
+ *
+ * extern int initialize_foobar_device(int, int, int) __init;
+ *
+ * For initialized data:
+ * You should insert __initdata between the variable name and equal
+ * sign followed by value, e.g.:
+ *
+ * static int init_variable __initdata = 0;
+ * static const char linux_logo[] __initconst = { 0x32, 0x36, ... };
+ *
+ * Don't forget to initialize data not at file scope, i.e. within a function,
+ * as gcc otherwise puts the data into the bss section and not into the init
+ * section.
+ *
+ * Also note, that this data cannot be "const".
+ */
+
+#ifndef _LINUX_INIT_H
+typedef int (*initcall_t)(void);
+typedef void (*exitcall_t)(void);
+
+#include <linux/compiler_types.h>
+
+/* These are for everybody (although not all archs will actually
+   discard it in modules) */
+#define __init		__section(".init.text")
+#define __initdata	__section(".init.data")
+#define __exitdata	__section(".exit.data")
+#define __exit_call	__used __section(".exitcall.exit")
+
+#ifdef MODULE
+#define __exit		__section(".exit.text")
+#else
+#define __exit		__used __section(".exit.text")
+#endif
+
+#endif
+
+#ifndef MODULE
+struct uml_param {
+        const char *str;
+        int (*setup_func)(char *, int *);
+};
+
+extern initcall_t __uml_postsetup_start, __uml_postsetup_end;
+extern const char *__uml_help_start, *__uml_help_end;
+#endif
+
+#define __uml_exitcall(fn)						\
+	static exitcall_t __uml_exitcall_##fn __uml_exit_call = fn
+
+extern struct uml_param __uml_setup_start, __uml_setup_end;
+
+#define __uml_postsetup(fn)						\
+	static initcall_t __uml_postsetup_##fn __uml_postsetup_call = fn
+
+#define __non_empty_string(dummyname,string)				\
+	struct __uml_non_empty_string_struct_##dummyname		\
+	{								\
+		char _string[sizeof(string)-2];				\
+	}
+
+#ifndef MODULE
+#define __uml_setup(str, fn, help...)					\
+	__non_empty_string(fn ##_setup, str);				\
+	__uml_help(fn, help);						\
+	static char __uml_setup_str_##fn[] __initdata = str;		\
+	static struct uml_param __uml_setup_##fn __uml_init_setup = { __uml_setup_str_##fn, fn }
+#else
+#define __uml_setup(str, fn, help...)					\
+
+#endif
+
+#define __uml_help(fn, help...)						\
+	__non_empty_string(fn ##__help, help);				\
+	static char __uml_help_str_##fn[] __initdata = help;		\
+	static const char *__uml_help_##fn __uml_setup_help = __uml_help_str_##fn
+
+/*
+ * Mark functions and data as being only used at initialization
+ * or exit time.
+ */
+#define __uml_init_setup	__used __section(".uml.setup.init")
+#define __uml_setup_help	__used __section(".uml.help.init")
+#define __uml_postsetup_call	__used __section(".uml.postsetup.init")
+#define __uml_exit_call		__used __section(".uml.exitcall.exit")
+
+#ifdef __UM_HOST__
+
+#define __define_initcall(level,fn) \
+	static initcall_t __initcall_##fn __used \
+	__attribute__((__section__(".initcall" level ".init"))) = fn
+
+/* Userspace initcalls shouldn't depend on anything in the kernel, so we'll
+ * make them run first.
+ */
+#define __initcall(fn) __define_initcall("1", fn)
+
+#define __exitcall(fn) static exitcall_t __exitcall_##fn __exit_call = fn
+
+#define __init_call	__used __section(".initcall.init")
+
+#endif
+
+#endif /* _LINUX_UML_INIT_H */
diff --git a/arch/um/include/shared/irq_kern.h b/arch/um/include/shared/irq_kern.h
new file mode 100644
index 000000000..44357fa6e
--- /dev/null
+++ b/arch/um/include/shared/irq_kern.h
@@ -0,0 +1,80 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2001, 2002 Jeff Dike (jdike@karaya.com)
+ */
+
+#ifndef __IRQ_KERN_H__
+#define __IRQ_KERN_H__
+
+#include <linux/interrupt.h>
+#include <linux/time-internal.h>
+#include <asm/ptrace.h>
+#include "irq_user.h"
+
+#define UM_IRQ_ALLOC	-1
+
+int um_request_irq(int irq, int fd, enum um_irq_type type,
+		   irq_handler_t handler, unsigned long irqflags,
+		   const char *devname, void *dev_id);
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+/**
+ * um_request_irq_tt - request an IRQ with timetravel handler
+ *
+ * @irq: the IRQ number, or %UM_IRQ_ALLOC
+ * @fd: The file descriptor to request an IRQ for
+ * @type: read or write
+ * @handler: the (generic style) IRQ handler
+ * @irqflags: Linux IRQ flags
+ * @devname: name for this to show
+ * @dev_id: data pointer to pass to the IRQ handler
+ * @timetravel_handler: the timetravel interrupt handler, invoked with the IRQ
+ *	number, fd, dev_id and time-travel event pointer.
+ *
+ * Returns: The interrupt number assigned or a negative error.
+ *
+ * Note that the timetravel handler is invoked only if the time_travel_mode is
+ * %TT_MODE_EXTERNAL, and then it is invoked even while the system is suspended!
+ * This function must call time_travel_add_irq_event() for the event passed with
+ * an appropriate delay, before sending an ACK on the socket it was invoked for.
+ *
+ * If this was called while the system is suspended, then adding the event will
+ * cause the system to resume.
+ *
+ * Since this function will almost certainly have to handle the FD's condition,
+ * a read will consume the message, and after that it is up to the code using
+ * it to pass such a message to the @handler in whichever way it can.
+ *
+ * If time_travel_mode is not %TT_MODE_EXTERNAL the @timetravel_handler will
+ * not be invoked at all and the @handler must handle the FD becoming
+ * readable (or writable) instead. Use um_irq_timetravel_handler_used() to
+ * distinguish these cases.
+ *
+ * See virtio_uml.c for an example.
+ */
+int um_request_irq_tt(int irq, int fd, enum um_irq_type type,
+		      irq_handler_t handler, unsigned long irqflags,
+		      const char *devname, void *dev_id,
+		      void (*timetravel_handler)(int, int, void *,
+						 struct time_travel_event *));
+#else
+static inline
+int um_request_irq_tt(int irq, int fd, enum um_irq_type type,
+		      irq_handler_t handler, unsigned long irqflags,
+		      const char *devname, void *dev_id,
+		      void (*timetravel_handler)(int, int, void *,
+						 struct time_travel_event *))
+{
+	return um_request_irq(irq, fd, type, handler, irqflags,
+			      devname, dev_id);
+}
+#endif
+
+static inline bool um_irq_timetravel_handler_used(void)
+{
+	return time_travel_mode == TT_MODE_EXTERNAL;
+}
+
+void um_free_irq(int irq, void *dev_id);
+void free_irqs(void);
+#endif
diff --git a/arch/um/include/shared/irq_user.h b/arch/um/include/shared/irq_user.h
new file mode 100644
index 000000000..746abc24a
--- /dev/null
+++ b/arch/um/include/shared/irq_user.h
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __IRQ_USER_H__
+#define __IRQ_USER_H__
+
+#include <sysdep/ptrace.h>
+
+enum um_irq_type {
+	IRQ_READ,
+	IRQ_WRITE,
+	NUM_IRQ_TYPES,
+};
+
+struct siginfo;
+extern void sigio_handler(int sig, struct siginfo *unused_si,
+			  struct uml_pt_regs *regs, void *mc);
+extern void sigchld_handler(int sig, struct siginfo *unused_si,
+			   struct uml_pt_regs *regs, void *mc);
+void sigio_run_timetravel_handlers(void);
+extern void free_irq_by_fd(int fd);
+extern void deactivate_fd(int fd, int irqnum);
+extern int deactivate_all_fds(void);
+
+#endif
diff --git a/arch/um/include/shared/kern.h b/arch/um/include/shared/kern.h
new file mode 100644
index 000000000..3a9c75a84
--- /dev/null
+++ b/arch/um/include/shared/kern.h
@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2000 Jeff Dike (jdike@karaya.com)
+ */
+
+#ifndef __KERN_H__
+#define __KERN_H__
+
+/* These are all user-mode things which are convenient to call directly
+ * from kernel code and for which writing a wrapper is too much of a pain.
+ * The regular include files can't be included because this file is included
+ * only into kernel code, and user-space includes conflict with kernel
+ * includes.
+ */
+
+extern int printf(const char *fmt, ...);
+extern void *sbrk(int increment);
+extern int pause(void);
+extern void exit(int);
+
+#endif
+
diff --git a/arch/um/include/shared/kern_util.h b/arch/um/include/shared/kern_util.h
new file mode 100644
index 000000000..9812efd14
--- /dev/null
+++ b/arch/um/include/shared/kern_util.h
@@ -0,0 +1,70 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __KERN_UTIL_H__
+#define __KERN_UTIL_H__
+
+#include <sysdep/ptrace.h>
+#include <sysdep/faultinfo.h>
+
+struct siginfo;
+
+extern int uml_exitcode;
+
+extern int kmalloc_ok;
+
+extern unsigned long alloc_stack(int order, int atomic);
+extern void free_stack(unsigned long stack, int order);
+
+struct pt_regs;
+extern void do_signal(struct pt_regs *regs);
+extern void interrupt_end(void);
+extern void relay_signal(int sig, struct siginfo *si, struct uml_pt_regs *regs,
+			 void *mc);
+
+extern unsigned long segv(struct faultinfo fi, unsigned long ip,
+			  int is_user, struct uml_pt_regs *regs,
+			  void *mc);
+extern int handle_page_fault(unsigned long address, unsigned long ip,
+			     int is_write, int is_user, int *code_out);
+
+extern unsigned int do_IRQ(int irq, struct uml_pt_regs *regs);
+extern void initial_thread_cb(void (*proc)(void *), void *arg);
+
+extern void timer_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs);
+
+extern void uml_pm_wake(void);
+
+extern int start_uml(void);
+
+extern void uml_cleanup(void);
+extern void do_uml_exitcalls(void);
+
+/*
+ * Are we disallowed to sleep? Used to choose between GFP_KERNEL and
+ * GFP_ATOMIC.
+ */
+extern int __uml_cant_sleep(void);
+extern int get_current_pid(void);
+extern int copy_from_user_proc(void *to, void *from, int size);
+extern char *uml_strdup(const char *string);
+int uml_need_resched(void);
+
+extern unsigned long to_irq_stack(unsigned long *mask_out);
+extern unsigned long from_irq_stack(int nested);
+
+extern int singlestepping(void);
+
+extern void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs,
+			 void *mc);
+extern void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs,
+		  void *mc);
+extern void fatal_sigsegv(void) __attribute__ ((noreturn));
+
+void um_idle_sleep(void);
+
+void kasan_map_memory(void *start, size_t len);
+
+#endif
diff --git a/arch/um/include/shared/longjmp.h b/arch/um/include/shared/longjmp.h
new file mode 100644
index 000000000..c53e43d98
--- /dev/null
+++ b/arch/um/include/shared/longjmp.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UML_LONGJMP_H
+#define __UML_LONGJMP_H
+
+#include <sysdep/archsetjmp.h>
+#include <os.h>
+
+extern int setjmp(jmp_buf);
+extern void longjmp(jmp_buf, int);
+
+#define UML_LONGJMP(buf, val) do { \
+	longjmp(*buf, val);	\
+} while(0)
+
+#define UML_SETJMP(buf) ({				\
+	int n, enable;					\
+	enable = um_get_signals();			\
+	n = setjmp(*buf);				\
+	if(n != 0)					\
+		um_set_signals_trace(enable);		\
+	n; })
+
+#endif
diff --git a/arch/um/include/shared/mem.h b/arch/um/include/shared/mem.h
new file mode 100644
index 000000000..98aacd544
--- /dev/null
+++ b/arch/um/include/shared/mem.h
@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __MEM_H__
+#define __MEM_H__
+
+extern int phys_mapping(unsigned long phys, unsigned long long *offset_out);
+
+extern unsigned long uml_physmem;
+static inline unsigned long uml_to_phys(void *virt)
+{
+	return(((unsigned long) virt) - uml_physmem);
+}
+
+static inline void *uml_to_virt(unsigned long phys)
+{
+	return((void *) uml_physmem + phys);
+}
+
+#endif
diff --git a/arch/um/include/shared/mem_user.h b/arch/um/include/shared/mem_user.h
new file mode 100644
index 000000000..8a5b72872
--- /dev/null
+++ b/arch/um/include/shared/mem_user.h
@@ -0,0 +1,42 @@
+/*
+ * arch/um/include/mem_user.h
+ *
+ * BRIEF MODULE DESCRIPTION
+ * user side memory interface for support IO memory inside user mode linux
+ *
+ * Copyright (C) 2001 RidgeRun, Inc.
+ * Author: RidgeRun, Inc.
+ *         Greg Lonnon glonnon@ridgerun.com or info@ridgerun.com
+ *
+ *  This program is free software; you can redistribute  it and/or modify it
+ *  under  the terms of  the GNU General  Public License as published by the
+ *  Free Software Foundation;  either version 2 of the  License, or (at your
+ *  option) any later version.
+ *
+ *  THIS  SOFTWARE  IS PROVIDED   ``AS  IS'' AND   ANY  EXPRESS OR IMPLIED
+ *  WARRANTIES,   INCLUDING, BUT NOT  LIMITED  TO, THE IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN
+ *  NO  EVENT  SHALL   THE AUTHOR  BE    LIABLE FOR ANY   DIRECT, INDIRECT,
+ *  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ *  NOT LIMITED   TO, PROCUREMENT OF  SUBSTITUTE GOODS  OR SERVICES; LOSS OF
+ *  USE, DATA,  OR PROFITS; OR  BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ *  ANY THEORY OF LIABILITY, WHETHER IN  CONTRACT, STRICT LIABILITY, OR TORT
+ *  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ *  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ *  You should have received a copy of the  GNU General Public License along
+ *  with this program; if not, write  to the Free Software Foundation, Inc.,
+ *  675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#ifndef _MEM_USER_H
+#define _MEM_USER_H
+
+#define ROUND_4M(n) ((((unsigned long) (n)) + (1 << 22)) & ~((1 << 22) - 1))
+
+extern void setup_physmem(unsigned long start, unsigned long usable,
+			  unsigned long len);
+extern void map_memory(unsigned long virt, unsigned long phys,
+		       unsigned long len, int r, int w, int x);
+
+#endif
diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
new file mode 100644
index 000000000..b26e94292
--- /dev/null
+++ b/arch/um/include/shared/os.h
@@ -0,0 +1,359 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
+ * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __OS_H__
+#define __OS_H__
+
+#include <irq_user.h>
+#include <longjmp.h>
+#include <mm_id.h>
+/* This is to get size_t */
+#ifndef __UM_HOST__
+#include <linux/types.h>
+#else
+#include <sys/types.h>
+#endif
+
+#define CATCH_EINTR(expr) while ((errno = 0, ((expr) < 0)) && (errno == EINTR))
+
+#define OS_TYPE_FILE 1
+#define OS_TYPE_DIR 2
+#define OS_TYPE_SYMLINK 3
+#define OS_TYPE_CHARDEV 4
+#define OS_TYPE_BLOCKDEV 5
+#define OS_TYPE_FIFO 6
+#define OS_TYPE_SOCK 7
+
+/* os_access() flags */
+#define OS_ACC_F_OK    0       /* Test for existence.  */
+#define OS_ACC_X_OK    1       /* Test for execute permission.  */
+#define OS_ACC_W_OK    2       /* Test for write permission.  */
+#define OS_ACC_R_OK    4       /* Test for read permission.  */
+#define OS_ACC_RW_OK   (OS_ACC_W_OK | OS_ACC_R_OK) /* Test for RW permission */
+
+#ifdef CONFIG_64BIT
+#define OS_LIB_PATH	"/usr/lib64/"
+#else
+#define OS_LIB_PATH	"/usr/lib/"
+#endif
+
+#define OS_SENDMSG_MAX_FDS 8
+
+/*
+ * types taken from stat_file() in hostfs_user.c
+ * (if they are wrong here, they are wrong there...).
+ */
+struct uml_stat {
+	int                ust_dev;        /* device */
+	unsigned long long ust_ino;        /* inode */
+	int                ust_mode;       /* protection */
+	int                ust_nlink;      /* number of hard links */
+	int                ust_uid;        /* user ID of owner */
+	int                ust_gid;        /* group ID of owner */
+	unsigned long long ust_size;       /* total size, in bytes */
+	int                ust_blksize;    /* blocksize for filesystem I/O */
+	unsigned long long ust_blocks;     /* number of blocks allocated */
+	unsigned long      ust_atime;      /* time of last access */
+	unsigned long      ust_mtime;      /* time of last modification */
+	unsigned long      ust_ctime;      /* time of last change */
+};
+
+struct openflags {
+	unsigned int r : 1;
+	unsigned int w : 1;
+	unsigned int s : 1;	/* O_SYNC */
+	unsigned int c : 1;	/* O_CREAT */
+	unsigned int t : 1;	/* O_TRUNC */
+	unsigned int a : 1;	/* O_APPEND */
+	unsigned int e : 1;	/* O_EXCL */
+	unsigned int cl : 1;    /* FD_CLOEXEC */
+};
+
+#define OPENFLAGS() ((struct openflags) { .r = 0, .w = 0, .s = 0, .c = 0, \
+					  .t = 0, .a = 0, .e = 0, .cl = 0 })
+
+static inline struct openflags of_read(struct openflags flags)
+{
+	flags.r = 1;
+	return flags;
+}
+
+static inline struct openflags of_write(struct openflags flags)
+{
+	flags.w = 1;
+	return flags;
+}
+
+static inline struct openflags of_rdwr(struct openflags flags)
+{
+	return of_read(of_write(flags));
+}
+
+static inline struct openflags of_set_rw(struct openflags flags, int r, int w)
+{
+	flags.r = r;
+	flags.w = w;
+	return flags;
+}
+
+static inline struct openflags of_sync(struct openflags flags)
+{
+	flags.s = 1;
+	return flags;
+}
+
+static inline struct openflags of_create(struct openflags flags)
+{
+	flags.c = 1;
+	return flags;
+}
+
+static inline struct openflags of_trunc(struct openflags flags)
+{
+	flags.t = 1;
+	return flags;
+}
+
+static inline struct openflags of_append(struct openflags flags)
+{
+	flags.a = 1;
+	return flags;
+}
+
+static inline struct openflags of_excl(struct openflags flags)
+{
+	flags.e = 1;
+	return flags;
+}
+
+static inline struct openflags of_cloexec(struct openflags flags)
+{
+	flags.cl = 1;
+	return flags;
+}
+
+/* file.c */
+extern int os_stat_file(const char *file_name, struct uml_stat *buf);
+extern int os_stat_fd(const int fd, struct uml_stat *buf);
+extern int os_access(const char *file, int mode);
+extern int os_set_exec_close(int fd);
+extern int os_ioctl_generic(int fd, unsigned int cmd, unsigned long arg);
+extern int os_get_ifname(int fd, char *namebuf);
+extern int os_mode_fd(int fd, int mode);
+
+extern int os_seek_file(int fd, unsigned long long offset);
+extern int os_open_file(const char *file, struct openflags flags, int mode);
+extern int os_read_file(int fd, void *buf, int len);
+extern int os_write_file(int fd, const void *buf, int count);
+extern int os_sync_file(int fd);
+extern int os_file_size(const char *file, unsigned long long *size_out);
+extern int os_pread_file(int fd, void *buf, int len, unsigned long long offset);
+extern int os_pwrite_file(int fd, const void *buf, int count, unsigned long long offset);
+extern int os_file_modtime(const char *file, long long *modtime);
+extern int os_pipe(int *fd, int stream, int close_on_exec);
+extern int os_set_fd_async(int fd);
+extern int os_clear_fd_async(int fd);
+extern int os_set_fd_block(int fd, int blocking);
+extern int os_accept_connection(int fd);
+extern int os_create_unix_socket(const char *file, int len, int close_on_exec);
+extern int os_shutdown_socket(int fd, int r, int w);
+extern int os_dup_file(int fd);
+extern void os_close_file(int fd);
+ssize_t os_rcv_fd_msg(int fd, int *fds, unsigned int n_fds,
+		      void *data, size_t data_len);
+extern int os_connect_socket(const char *name);
+extern int os_file_type(char *file);
+extern int os_file_mode(const char *file, struct openflags *mode_out);
+extern int os_lock_file(int fd, int excl);
+extern void os_flush_stdout(void);
+extern unsigned os_major(unsigned long long dev);
+extern unsigned os_minor(unsigned long long dev);
+extern unsigned long long os_makedev(unsigned major, unsigned minor);
+extern int os_falloc_punch(int fd, unsigned long long offset, int count);
+extern int os_falloc_zeroes(int fd, unsigned long long offset, int count);
+extern int os_eventfd(unsigned int initval, int flags);
+extern int os_sendmsg_fds(int fd, const void *buf, unsigned int len,
+			  const int *fds, unsigned int fds_num);
+int os_poll(unsigned int n, const int *fds);
+void *os_mmap_rw_shared(int fd, size_t size);
+void *os_mremap_rw_shared(void *old_addr, size_t old_size, size_t new_size);
+
+/* start_up.c */
+extern void os_early_checks(void);
+extern void os_check_bugs(void);
+extern void check_host_supports_tls(int *supports_tls, int *tls_min);
+extern void get_host_cpu_features(
+	void (*flags_helper_func)(char *line),
+	void (*cache_helper_func)(char *line));
+
+/* mem.c */
+extern int create_mem_file(unsigned long long len);
+
+/* tlb.c */
+extern void report_enomem(void);
+
+/* process.c */
+pid_t os_reap_child(void);
+extern void os_alarm_process(int pid);
+extern void os_kill_process(int pid, int reap_child);
+extern void os_kill_ptraced_process(int pid, int reap_child);
+
+extern int os_getpid(void);
+
+extern void init_new_thread_signals(void);
+
+extern int os_map_memory(void *virt, int fd, unsigned long long off,
+			 unsigned long len, int r, int w, int x);
+extern int os_protect_memory(void *addr, unsigned long len,
+			     int r, int w, int x);
+extern int os_unmap_memory(void *addr, int len);
+extern int os_drop_memory(void *addr, int length);
+extern int can_drop_memory(void);
+
+void os_set_pdeathsig(void);
+
+int os_futex_wait(void *uaddr, unsigned int val);
+int os_futex_wake(void *uaddr);
+
+/* execvp.c */
+extern int execvp_noalloc(char *buf, const char *file, char *const argv[]);
+/* helper.c */
+extern int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv);
+extern int run_helper_thread(int (*proc)(void *), void *arg,
+			     unsigned int flags, unsigned long *stack_out);
+extern int helper_wait(int pid);
+
+struct os_helper_thread;
+int os_run_helper_thread(struct os_helper_thread **td_out,
+			 void *(*routine)(void *), void *arg);
+void os_kill_helper_thread(struct os_helper_thread *td);
+void os_fix_helper_thread_signals(void);
+
+/* umid.c */
+extern int umid_file_name(char *name, char *buf, int len);
+extern int set_umid(char *name);
+extern char *get_umid(void);
+
+/* signal.c */
+extern void timer_set_signal_handler(void);
+extern void set_sigstack(void *sig_stack, int size);
+extern void set_handler(int sig);
+extern void send_sigio_to_self(void);
+extern int change_sig(int signal, int on);
+extern void block_signals(void);
+extern void unblock_signals(void);
+extern int um_get_signals(void);
+extern int um_set_signals(int enable);
+extern int um_set_signals_trace(int enable);
+extern void deliver_alarm(void);
+extern void register_pm_wake_signal(void);
+extern void block_signals_hard(void);
+extern void unblock_signals_hard(void);
+extern void mark_sigio_pending(void);
+
+/* util.c */
+extern void stack_protections(unsigned long address);
+extern int raw(int fd);
+extern void setup_machinename(char *machine_out);
+extern void setup_hostinfo(char *buf, int len);
+extern ssize_t os_getrandom(void *buf, size_t len, unsigned int flags);
+extern void os_dump_core(void) __attribute__ ((noreturn));
+extern void um_early_printk(const char *s, unsigned int n);
+extern void os_fix_helper_signals(void);
+extern void os_info(const char *fmt, ...)
+	__attribute__ ((format (printf, 1, 2)));
+extern void os_warn(const char *fmt, ...)
+	__attribute__ ((format (printf, 1, 2)));
+
+/* time.c */
+void os_idle_prepare(void);
+extern void os_idle_sleep(void);
+extern int os_timer_create(void);
+extern int os_timer_set_interval(int cpu, unsigned long long nsecs);
+extern int os_timer_one_shot(int cpu, unsigned long long nsecs);
+extern void os_timer_disable(int cpu);
+extern long long os_persistent_clock_emulation(void);
+extern long long os_nsecs(void);
+
+/* skas/mem.c */
+int syscall_stub_flush(struct mm_id *mm_idp);
+struct stub_syscall *syscall_stub_alloc(struct mm_id *mm_idp);
+void syscall_stub_dump_error(struct mm_id *mm_idp);
+
+int map(struct mm_id *mm_idp, unsigned long virt,
+	unsigned long len, int prot, int phys_fd,
+	unsigned long long offset);
+int unmap(struct mm_id *mm_idp, unsigned long addr, unsigned long len);
+
+/* skas/process.c */
+extern int is_skas_winch(int pid, int fd, void *data);
+extern int start_userspace(struct mm_id *mm_id);
+extern void userspace(struct uml_pt_regs *regs);
+extern void new_thread(void *stack, jmp_buf *buf, void (*handler)(void));
+extern void switch_threads(jmp_buf *me, jmp_buf *you);
+extern int start_idle_thread(void *stack, jmp_buf *switch_buf);
+extern void initial_thread_cb_skas(void (*proc)(void *),
+				 void *arg);
+extern void halt_skas(void);
+extern void reboot_skas(void);
+
+/* irq.c */
+extern int os_waiting_for_events_epoll(void);
+extern void *os_epoll_get_data_pointer(int index);
+extern int os_epoll_triggered(int index, int events);
+extern int os_event_mask(enum um_irq_type irq_type);
+extern int os_setup_epoll(void);
+extern int os_add_epoll_fd(int events, int fd, void *data);
+extern int os_mod_epoll_fd(int events, int fd, void *data);
+extern int os_del_epoll_fd(int fd);
+extern void os_set_ioignore(void);
+extern void os_close_epoll_fd(void);
+extern void um_irqs_suspend(void);
+extern void um_irqs_resume(void);
+
+/* sigio.c */
+extern int add_sigio_fd(int fd);
+extern int ignore_sigio_fd(int fd);
+extern void maybe_sigio_broken(int fd);
+extern void sigio_broken(void);
+/*
+ * unlocked versions for IRQ controller code.
+ *
+ * This is safe because it's used at suspend/resume and nothing
+ * else is running.
+ */
+extern int __add_sigio_fd(int fd);
+extern int __ignore_sigio_fd(int fd);
+
+/* tty.c */
+extern int get_pty(void);
+
+long syscall(long number, ...);
+
+/* irqflags tracing */
+extern void block_signals_trace(void);
+extern void unblock_signals_trace(void);
+extern void um_trace_signals_on(void);
+extern void um_trace_signals_off(void);
+
+/* time-travel */
+extern void deliver_time_travel_irqs(void);
+
+/* smp.c */
+#if IS_ENABLED(CONFIG_SMP)
+void os_init_smp(void);
+int os_start_cpu_thread(int cpu);
+void os_start_secondary(void *arg, jmp_buf *switch_buf);
+int os_send_ipi(int cpu, int vector);
+void os_local_ipi_enable(void);
+void os_local_ipi_disable(void);
+#else /* !CONFIG_SMP */
+static inline void os_local_ipi_enable(void) { }
+static inline void os_local_ipi_disable(void) { }
+#endif /* CONFIG_SMP */
+
+#endif
diff --git a/arch/um/include/shared/ptrace_user.h b/arch/um/include/shared/ptrace_user.h
new file mode 100644
index 000000000..8a705d8f9
--- /dev/null
+++ b/arch/um/include/shared/ptrace_user.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __PTRACE_USER_H__
+#define __PTRACE_USER_H__
+
+#include <sys/ptrace.h>
+#include <sysdep/ptrace_user.h>
+
+extern int ptrace_getregs(long pid, unsigned long *regs_out);
+extern int ptrace_setregs(long pid, unsigned long *regs_in);
+
+#endif
diff --git a/arch/um/include/shared/registers.h b/arch/um/include/shared/registers.h
new file mode 100644
index 000000000..7d81b2339
--- /dev/null
+++ b/arch/um/include/shared/registers.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2004 PathScale, Inc
+ */
+
+#ifndef __REGISTERS_H
+#define __REGISTERS_H
+
+#include <sysdep/ptrace.h>
+
+extern int init_pid_registers(int pid);
+extern void get_safe_registers(unsigned long *regs, unsigned long *fp_regs);
+extern int get_fp_registers(int pid, unsigned long *regs);
+extern int put_fp_registers(int pid, unsigned long *regs);
+
+#endif
diff --git a/arch/um/include/shared/sigio.h b/arch/um/include/shared/sigio.h
new file mode 100644
index 000000000..c6c2edce1
--- /dev/null
+++ b/arch/um/include/shared/sigio.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
+ */
+
+#ifndef __SIGIO_H__
+#define __SIGIO_H__
+
+extern void sigio_lock(void);
+extern void sigio_unlock(void);
+
+#endif
diff --git a/arch/um/include/shared/skas/mm_id.h b/arch/um/include/shared/skas/mm_id.h
new file mode 100644
index 000000000..18c062143
--- /dev/null
+++ b/arch/um/include/shared/skas/mm_id.h
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2005 Jeff Dike (jdike@karaya.com)
+ */
+
+#ifndef __MM_ID_H
+#define __MM_ID_H
+
+#include <linux/compiler_types.h>
+
+#define STUB_MAX_FDS 4
+
+struct mm_id {
+	int pid;
+	unsigned long stack;
+	int syscall_data_len;
+
+	/* Only used with SECCOMP mode */
+	int sock;
+	int syscall_fd_num;
+	int syscall_fd_map[STUB_MAX_FDS];
+};
+
+struct mutex *__get_turnstile(struct mm_id *mm_id);
+void enter_turnstile(struct mm_id *mm_id) __acquires(__get_turnstile(mm_id));
+void exit_turnstile(struct mm_id *mm_id) __releases(__get_turnstile(mm_id));
+
+void notify_mm_kill(int pid);
+
+#endif
diff --git a/arch/um/include/shared/skas/skas.h b/arch/um/include/shared/skas/skas.h
new file mode 100644
index 000000000..2237ffede
--- /dev/null
+++ b/arch/um/include/shared/skas/skas.h
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __SKAS_H
+#define __SKAS_H
+
+#include <sysdep/ptrace.h>
+
+extern int using_seccomp;
+
+extern void new_thread_handler(void);
+extern void handle_syscall(struct uml_pt_regs *regs);
+extern unsigned long current_stub_stack(void);
+extern struct mm_id *current_mm_id(void);
+extern void current_mm_sync(void);
+void initial_jmpbuf_lock(void);
+void initial_jmpbuf_unlock(void);
+
+#endif
diff --git a/arch/um/include/shared/skas/stub-data.h b/arch/um/include/shared/skas/stub-data.h
new file mode 100644
index 000000000..27db38e95
--- /dev/null
+++ b/arch/um/include/shared/skas/stub-data.h
@@ -0,0 +1,76 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+
+ * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
+ * Copyright (C) 2005 Jeff Dike (jdike@karaya.com)
+ */
+
+#ifndef __STUB_DATA_H
+#define __STUB_DATA_H
+
+#include <linux/compiler_types.h>
+#include <as-layout.h>
+#include <sysdep/tls.h>
+#include <sysdep/stub-data.h>
+#include <mm_id.h>
+
+#define FUTEX_IN_CHILD 0
+#define FUTEX_IN_KERN 1
+
+struct stub_init_data {
+	int seccomp;
+
+	unsigned long stub_start;
+
+	int stub_code_fd;
+	unsigned long stub_code_offset;
+	int stub_data_fd;
+	unsigned long stub_data_offset;
+
+	unsigned long signal_handler;
+	unsigned long signal_restorer;
+};
+
+#define STUB_NEXT_SYSCALL(s) \
+	((struct stub_syscall *) (((unsigned long) s) + (s)->cmd_len))
+
+enum stub_syscall_type {
+	STUB_SYSCALL_UNSET = 0,
+	STUB_SYSCALL_MMAP,
+	STUB_SYSCALL_MUNMAP,
+};
+
+struct stub_syscall {
+	struct {
+		unsigned long addr;
+		unsigned long length;
+		unsigned long offset;
+		int fd;
+		int prot;
+	} mem;
+
+	enum stub_syscall_type syscall;
+};
+
+struct stub_data {
+	long err;
+
+	int syscall_data_len;
+	/* 128 leaves enough room for additional fields in the struct */
+	struct stub_syscall syscall_data[(UM_KERN_PAGE_SIZE - 128) / sizeof(struct stub_syscall)] __aligned(16);
+
+	/* data shared with signal handler (only used in seccomp mode) */
+	short restart_wait;
+	unsigned int futex;
+	int signal;
+	unsigned short si_offset;
+	unsigned short mctx_offset;
+
+	/* seccomp architecture specific state restore */
+	struct stub_data_arch arch_data;
+
+	/* Stack for our signal handlers and for calling into . */
+	unsigned char sigstack[UM_KERN_PAGE_SIZE] __aligned(UM_KERN_PAGE_SIZE);
+};
+
+#endif
diff --git a/arch/um/include/shared/smp.h b/arch/um/include/shared/smp.h
new file mode 100644
index 000000000..06e3faa95
--- /dev/null
+++ b/arch/um/include/shared/smp.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UM_SHARED_SMP_H
+#define __UM_SHARED_SMP_H
+
+#if IS_ENABLED(CONFIG_SMP)
+
+extern int uml_ncpus;
+
+int uml_curr_cpu(void);
+void uml_start_secondary(void *opaque);
+void uml_ipi_handler(int vector);
+
+#else /* !CONFIG_SMP */
+
+#define uml_ncpus 1
+#define uml_curr_cpu() 0
+
+#endif /* CONFIG_SMP */
+
+#endif /* __UM_SHARED_SMP_H */
diff --git a/arch/um/include/shared/timetravel.h b/arch/um/include/shared/timetravel.h
new file mode 100644
index 000000000..7c2b277b7
--- /dev/null
+++ b/arch/um/include/shared/timetravel.h
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2019-2021 Intel Corporation
+ */
+#ifndef _UM_TIME_TRAVEL_H_
+#define _UM_TIME_TRAVEL_H_
+
+enum time_travel_mode {
+	TT_MODE_OFF,
+	TT_MODE_BASIC,
+	TT_MODE_INFCPU,
+	TT_MODE_EXTERNAL,
+};
+
+#if IS_ENABLED(CONFIG_UML_TIME_TRAVEL_SUPPORT)
+extern enum time_travel_mode time_travel_mode;
+extern int time_travel_should_print_bc_msg;
+#else
+#define time_travel_mode TT_MODE_OFF
+#define time_travel_should_print_bc_msg 0
+#endif /* CONFIG_UML_TIME_TRAVEL_SUPPORT */
+
+void _time_travel_print_bc_msg(void);
+static inline void time_travel_print_bc_msg(void)
+{
+	if (time_travel_should_print_bc_msg)
+		_time_travel_print_bc_msg();
+}
+
+#endif /* _UM_TIME_TRAVEL_H_ */
diff --git a/arch/um/include/shared/um_malloc.h b/arch/um/include/shared/um_malloc.h
new file mode 100644
index 000000000..815dd03e8
--- /dev/null
+++ b/arch/um/include/shared/um_malloc.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2005 Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
+ */
+
+#ifndef __UM_MALLOC_H__
+#define __UM_MALLOC_H__
+
+#include <generated/asm-offsets.h>
+
+extern void *uml_kmalloc(int size, int flags);
+extern void kfree(const void *ptr);
+
+extern void *vmalloc_noprof(unsigned long size);
+#define vmalloc(...)		vmalloc_noprof(__VA_ARGS__)
+extern void vfree(const void *ptr);
+
+#endif /* __UM_MALLOC_H__ */
+
+
diff --git a/arch/um/include/shared/user.h b/arch/um/include/shared/user.h
new file mode 100644
index 000000000..139eb78a4
--- /dev/null
+++ b/arch/um/include/shared/user.h
@@ -0,0 +1,68 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#ifndef __USER_H__
+#define __USER_H__
+
+#include <generated/asm-offsets.h>
+
+/*
+ * The usual definition - copied here because the kernel provides its own,
+ * fancier, type-safe, definition.  Using that one would require
+ * copying too much infrastructure for my taste, so userspace files
+ * get less checking than kernel files.
+ */
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
+/* This is to get size_t and NULL */
+#ifndef __UM_HOST__
+#include <linux/types.h>
+#else
+#include <stddef.h>
+#include <sys/types.h>
+#endif
+
+extern void panic(const char *fmt, ...)
+	__attribute__ ((format (printf, 1, 2)));
+
+/* Requires preincluding include/linux/kern_levels.h */
+#define UM_KERN_EMERG	KERN_EMERG
+#define UM_KERN_ALERT	KERN_ALERT
+#define UM_KERN_CRIT	KERN_CRIT
+#define UM_KERN_ERR	KERN_ERR
+#define UM_KERN_WARNING	KERN_WARNING
+#define UM_KERN_NOTICE	KERN_NOTICE
+#define UM_KERN_INFO	KERN_INFO
+#define UM_KERN_DEBUG	KERN_DEBUG
+#define UM_KERN_CONT	KERN_CONT
+
+#if IS_ENABLED(CONFIG_PRINTK)
+#define printk(...) _printk(__VA_ARGS__)
+extern int _printk(const char *fmt, ...)
+	__attribute__ ((format (printf, 1, 2)));
+extern void print_hex_dump(const char *level, const char *prefix_str,
+			   int prefix_type, int rowsize, int groupsize,
+			   const void *buf, size_t len, _Bool ascii);
+#else
+static inline int printk(const char *fmt, ...)
+{
+	return 0;
+}
+static inline void print_hex_dump(const char *level, const char *prefix_str,
+				  int prefix_type, int rowsize, int groupsize,
+				  const void *buf, size_t len, _Bool ascii)
+{
+}
+#endif
+
+extern int in_aton(char *str);
+extern size_t strlcat(char *, const char *, size_t);
+extern size_t sized_strscpy(char *, const char *, size_t);
+#define strscpy(dst, src)	sized_strscpy(dst, src, sizeof(dst))
+
+/* Copied from linux/compiler-gcc.h since we can't include it directly */
+#define barrier() __asm__ __volatile__("": : :"memory")
+
+#endif
diff --git a/arch/um/include/uapi/asm/Kbuild b/arch/um/include/uapi/asm/Kbuild
new file mode 100644
index 000000000..f66554cd5
--- /dev/null
+++ b/arch/um/include/uapi/asm/Kbuild
@@ -0,0 +1 @@
+# SPDX-License-Identifier: GPL-2.0
diff --git a/arch/um/kernel/Makefile b/arch/um/kernel/Makefile
new file mode 100644
index 000000000..be60bc451
--- /dev/null
+++ b/arch/um/kernel/Makefile
@@ -0,0 +1,65 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux,intel}.com)
+#
+
+# Don't instrument UML-specific code; without this, we may crash when
+# accessing the instrumentation buffer for the first time from the
+# kernel.
+KCOV_INSTRUMENT                := n
+
+CPPFLAGS_vmlinux.lds := -DSTART=$(LDS_START)		\
+                        -DELF_ARCH=$(LDS_ELF_ARCH)	\
+                        -DELF_FORMAT=$(LDS_ELF_FORMAT)	\
+			$(LDS_EXTRA)
+always-$(KBUILD_BUILTIN) := vmlinux.lds
+
+obj-y = config.o exec.o exitcode.o irq.o ksyms.o mem.o \
+	physmem.o process.o ptrace.o reboot.o sigio.o \
+	signal.o sysrq.o time.o tlb.o trap.o \
+	um_arch.o umid.o kmsg_dump.o capflags.o skas/
+obj-y += load_file.o
+
+obj-$(CONFIG_BLK_DEV_INITRD) += initrd.o
+obj-$(CONFIG_GPROF)	+= gprof_syms.o
+obj-$(CONFIG_OF) += dtb.o
+obj-$(CONFIG_EARLY_PRINTK) += early_printk.o
+obj-$(CONFIG_STACKTRACE) += stacktrace.o
+obj-$(CONFIG_SMP) += smp.o
+
+USER_OBJS := config.o
+
+include $(srctree)/arch/um/scripts/Makefile.rules
+
+targets := config.c config.tmp capflags.c
+
+# Be careful with the below Sed code - sed is pitfall-rich!
+# We use sed to lower build requirements, for "embedded" builders for instance.
+
+$(obj)/config.tmp: $(objtree)/.config FORCE
+	$(call if_changed,quote1)
+
+quiet_cmd_quote1 = QUOTE   $@
+      cmd_quote1 = sed -e 's/"/\\"/g' -e 's/^/"/' -e 's/$$/\\n",/' \
+		   $< > $@
+
+$(obj)/config.c: $(src)/config.c.in $(obj)/config.tmp FORCE
+	$(call if_changed,quote2)
+
+quiet_cmd_mkcapflags = MKCAP   $@
+      cmd_mkcapflags = $(CONFIG_SHELL) $(src)/../../x86/kernel/cpu/mkcapflags.sh $@ $^
+
+cpufeature = $(src)/../../x86/include/asm/cpufeatures.h
+vmxfeature = $(src)/../../x86/include/asm/vmxfeatures.h
+
+$(obj)/capflags.c: $(cpufeature) $(vmxfeature) $(src)/../../x86/kernel/cpu/mkcapflags.sh FORCE
+	$(call if_changed,mkcapflags)
+
+quiet_cmd_quote2 = QUOTE   $@
+      cmd_quote2 = sed -e '/CONFIG/{'          \
+		  -e 's/"CONFIG"//'            \
+		  -e 'r $(obj)/config.tmp'     \
+		  -e 'a \'                     \
+		  -e '""'                      \
+		  -e '}'                       \
+		  $< > $@
diff --git a/arch/um/kernel/asm-offsets.c b/arch/um/kernel/asm-offsets.c
new file mode 100644
index 000000000..d620b6f6d
--- /dev/null
+++ b/arch/um/kernel/asm-offsets.c
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#define COMPILE_OFFSETS
+#include <linux/stddef.h>
+#include <linux/sched.h>
+#include <linux/elf.h>
+#include <linux/crypto.h>
+#include <linux/kbuild.h>
+#include <linux/audit.h>
+#include <linux/fs.h>
+#include <asm/mman.h>
+#include <asm/seccomp.h>
+#include <asm/extable.h>
+
+/* workaround for a warning with -Wmissing-prototypes */
+void foo(void);
+
+void foo(void)
+{
+	DEFINE(KERNEL_MADV_REMOVE, MADV_REMOVE);
+
+	DEFINE(UM_KERN_PAGE_SIZE, PAGE_SIZE);
+	DEFINE(UM_KERN_PAGE_MASK, PAGE_MASK);
+	DEFINE(UM_KERN_PAGE_SHIFT, PAGE_SHIFT);
+
+	DEFINE(UM_GFP_KERNEL, GFP_KERNEL);
+	DEFINE(UM_GFP_ATOMIC, GFP_ATOMIC);
+
+	DEFINE(UM_THREAD_SIZE, THREAD_SIZE);
+
+	DEFINE(UM_NSEC_PER_SEC, NSEC_PER_SEC);
+	DEFINE(UM_NSEC_PER_USEC, NSEC_PER_USEC);
+
+	DEFINE(UM_KERN_GDT_ENTRY_TLS_ENTRIES, GDT_ENTRY_TLS_ENTRIES);
+
+	DEFINE(UM_SECCOMP_ARCH_NATIVE, SECCOMP_ARCH_NATIVE);
+
+	DEFINE(HOSTFS_ATTR_MODE, ATTR_MODE);
+	DEFINE(HOSTFS_ATTR_UID, ATTR_UID);
+	DEFINE(HOSTFS_ATTR_GID, ATTR_GID);
+	DEFINE(HOSTFS_ATTR_SIZE, ATTR_SIZE);
+	DEFINE(HOSTFS_ATTR_ATIME, ATTR_ATIME);
+	DEFINE(HOSTFS_ATTR_MTIME, ATTR_MTIME);
+	DEFINE(HOSTFS_ATTR_CTIME, ATTR_CTIME);
+	DEFINE(HOSTFS_ATTR_ATIME_SET, ATTR_ATIME_SET);
+	DEFINE(HOSTFS_ATTR_MTIME_SET, ATTR_MTIME_SET);
+
+	DEFINE(ALT_INSTR_SIZE, sizeof(struct alt_instr));
+	DEFINE(EXTABLE_SIZE,   sizeof(struct exception_table_entry));
+}
diff --git a/arch/um/kernel/config.c.in b/arch/um/kernel/config.c.in
new file mode 100644
index 000000000..3ece3c3b3
--- /dev/null
+++ b/arch/um/kernel/config.c.in
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 Jeff Dike (jdike@karaya.com)
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <init.h>
+
+static __initdata const char *config[] = {
+"CONFIG"
+};
+
+static int __init print_config(char *line, int *add)
+{
+	int i;
+	for (i = 0; i < sizeof(config)/sizeof(config[0]); i++)
+		printf("%s", config[i]);
+	exit(0);
+}
+
+__uml_setup("--showconfig", print_config,
+"--showconfig\n"
+"    Prints the config file that this UML binary was generated from.\n\n"
+);
+
diff --git a/arch/um/kernel/dtb.c b/arch/um/kernel/dtb.c
new file mode 100644
index 000000000..47cd3d869
--- /dev/null
+++ b/arch/um/kernel/dtb.c
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/init.h>
+#include <linux/of_fdt.h>
+#include <linux/printk.h>
+#include <linux/memblock.h>
+#include <init.h>
+
+#include "um_arch.h"
+
+static char *dtb __initdata;
+
+void uml_dtb_init(void)
+{
+	long long size;
+	void *area;
+
+	area = uml_load_file(dtb, &size);
+	if (area) {
+		if (!early_init_dt_scan(area, __pa(area))) {
+			pr_err("invalid DTB %s\n", dtb);
+			memblock_free(area, size);
+			return;
+		}
+
+		early_init_fdt_scan_reserved_mem();
+	}
+
+	unflatten_device_tree();
+}
+
+static int __init uml_dtb_setup(char *line, int *add)
+{
+	*add = 0;
+	dtb = line;
+	return 0;
+}
+
+__uml_setup("dtb=", uml_dtb_setup,
+"dtb=<file>\n"
+"    Boot the kernel with the devicetree blob from the specified file.\n\n"
+);
diff --git a/arch/um/kernel/dyn.lds.S b/arch/um/kernel/dyn.lds.S
new file mode 100644
index 000000000..ad3cefeff
--- /dev/null
+++ b/arch/um/kernel/dyn.lds.S
@@ -0,0 +1,182 @@
+#include <asm/vmlinux.lds.h>
+#include <asm/page.h>
+
+OUTPUT_FORMAT(ELF_FORMAT)
+OUTPUT_ARCH(ELF_ARCH)
+ENTRY(_start)
+jiffies = jiffies_64;
+
+VERSION {
+  {
+    local: *;
+  };
+}
+
+SECTIONS
+{
+  PROVIDE (__executable_start = START);
+  . = START + SIZEOF_HEADERS;
+  .interp         : { *(.interp) }
+  __binary_start = .;
+  . = ALIGN(4096);		/* Init code and data */
+  _text = .;
+  INIT_TEXT_SECTION(PAGE_SIZE)
+
+  . = ALIGN(PAGE_SIZE);
+
+  /* Read-only sections, merged into text segment: */
+  .hash           : { *(.hash) }
+  .gnu.hash       : { *(.gnu.hash) }
+  .dynsym         : { *(.dynsym) }
+  .dynstr         : { *(.dynstr) }
+  .gnu.version    : { *(.gnu.version) }
+  .gnu.version_d  : { *(.gnu.version_d) }
+  .gnu.version_r  : { *(.gnu.version_r) }
+  .rel.init       : { *(.rel.init) }
+  .rela.init      : { *(.rela.init) }
+  .rel.text       : { *(.rel.text .rel.text.* .rel.gnu.linkonce.t.*) }
+  .rela.text      : { *(.rela.text .rela.text.* .rela.gnu.linkonce.t.*) }
+  .rel.fini       : { *(.rel.fini) }
+  .rela.fini      : { *(.rela.fini) }
+  .rel.rodata     : { *(.rel.rodata .rel.rodata.* .rel.gnu.linkonce.r.*) }
+  .rela.rodata    : { *(.rela.rodata .rela.rodata.* .rela.gnu.linkonce.r.*) }
+  .rel.data       : { *(.rel.data .rel.data.* .rel.gnu.linkonce.d.*) }
+  .rela.data      : { *(.rela.data .rela.data.* .rela.gnu.linkonce.d.*) }
+  .rel.tdata	  : { *(.rel.tdata .rel.tdata.* .rel.gnu.linkonce.td.*) }
+  .rela.tdata	  : { *(.rela.tdata .rela.tdata.* .rela.gnu.linkonce.td.*) }
+  .rel.tbss	  : { *(.rel.tbss .rel.tbss.* .rel.gnu.linkonce.tb.*) }
+  .rela.tbss	  : { *(.rela.tbss .rela.tbss.* .rela.gnu.linkonce.tb.*) }
+  .rel.ctors      : { *(.rel.ctors) }
+  .rela.ctors     : { *(.rela.ctors) }
+  .rel.dtors      : { *(.rel.dtors) }
+  .rela.dtors     : { *(.rela.dtors) }
+  .rel.got        : { *(.rel.got) }
+  .rela.got       : { *(.rela.got) }
+  .rel.bss        : { *(.rel.bss .rel.bss.* .rel.gnu.linkonce.b.*) }
+  .rela.bss       : { *(.rela.bss .rela.bss.* .rela.gnu.linkonce.b.*) }
+  .rel.plt : {
+	*(.rel.plt)
+	PROVIDE_HIDDEN(__rel_iplt_start = .);
+	*(.rel.iplt)
+	PROVIDE_HIDDEN(__rel_iplt_end = .);
+  }
+  .rela.plt : {
+	*(.rela.plt)
+	PROVIDE_HIDDEN(__rela_iplt_start = .);
+	*(.rela.iplt)
+	PROVIDE_HIDDEN(__rela_iplt_end = .);
+  }
+  .init           : {
+    KEEP (*(.init))
+  } =0x90909090
+  .plt            : { *(.plt) }
+  .text           : {
+    _stext = .;
+    TEXT_TEXT
+    SCHED_TEXT
+    LOCK_TEXT
+    IRQENTRY_TEXT
+    SOFTIRQENTRY_TEXT
+    *(.fixup)
+    *(.stub .text.* .gnu.linkonce.t.*)
+    /* .gnu.warning sections are handled specially by elf32.em.  */
+    *(.gnu.warning)
+
+    . = ALIGN(PAGE_SIZE);
+  } =0x90909090
+  . = ALIGN(PAGE_SIZE);
+  .syscall_stub : {
+	__syscall_stub_start = .;
+	*(.__syscall_stub*)
+	__syscall_stub_end = .;
+  }
+  .fini           : {
+    KEEP (*(.fini))
+  } =0x90909090
+
+  .kstrtab : { *(.kstrtab) }
+
+  #include <asm/common.lds.S>
+
+  __init_begin = .;
+  init.data : { INIT_DATA }
+  __init_end = .;
+
+  /* Ensure the __preinit_array_start label is properly aligned.  We
+     could instead move the label definition inside the section, but
+     the linker would then create the section even if it turns out to
+     be empty, which isn't pretty.  */
+  . = ALIGN(32 / 8);
+  .preinit_array     : { *(.preinit_array) }
+  .init_array     : {
+    *(.kasan_init)
+    *(.init_array.*)
+    *(.init_array)
+  }
+  .fini_array     : { *(.fini_array) }
+  .data           : {
+    INIT_TASK_DATA(KERNEL_STACK_SIZE)
+    DATA_DATA
+    *(.data.* .gnu.linkonce.d.*)
+    SORT(CONSTRUCTORS)
+  }
+  .data1          : { *(.data1) }
+  .tdata	  : { *(.tdata .tdata.* .gnu.linkonce.td.*) }
+  .tbss		  : { *(.tbss .tbss.* .gnu.linkonce.tb.*) *(.tcommon) }
+  .eh_frame       : { KEEP (*(.eh_frame)) }
+  .gcc_except_table   : { *(.gcc_except_table) }
+  .dynamic        : { *(.dynamic) }
+  .ctors          : {
+    /* gcc uses crtbegin.o to find the start of
+       the constructors, so we make sure it is
+       first.  Because this is a wildcard, it
+       doesn't matter if the user does not
+       actually link against crtbegin.o; the
+       linker won't look for a file to match a
+       wildcard.  The wildcard also means that it
+       doesn't matter which directory crtbegin.o
+       is in.  */
+    KEEP (*crtbegin.o(.ctors))
+    /* We don't want to include the .ctor section from
+       from the crtend.o file until after the sorted ctors.
+       The .ctor section from the crtend file contains the
+       end of ctors marker and it must be last */
+    KEEP (*(EXCLUDE_FILE (*crtend.o ) .ctors))
+    KEEP (*(SORT(.ctors.*)))
+    KEEP (*(.ctors))
+  }
+  .dtors          : {
+    KEEP (*crtbegin.o(.dtors))
+    KEEP (*(EXCLUDE_FILE (*crtend.o ) .dtors))
+    KEEP (*(SORT(.dtors.*)))
+    KEEP (*(.dtors))
+  }
+  .jcr            : { KEEP (*(.jcr)) }
+  .got            : { *(.got.plt) *(.got) }
+  _edata = .;
+  PROVIDE (edata = .);
+  .bss            : {
+   __bss_start = .;
+   *(.dynbss)
+   *(.bss .bss.* .gnu.linkonce.b.*)
+   *(COMMON)
+   /* Align here to ensure that the .bss section occupies space up to
+      _end.  Align after .bss to ensure correct alignment even if the
+      .bss section disappears because there are no input sections.  */
+   . = ALIGN(32 / 8);
+  . = ALIGN(32 / 8);
+  }
+   __bss_stop = .;
+  _end = .;
+  PROVIDE (end = .);
+
+  STABS_DEBUG
+  DWARF_DEBUG
+  MODINFO
+  ELF_DETAILS
+
+  DISCARDS
+}
+
+ASSERT(__syscall_stub_end - __syscall_stub_start <= PAGE_SIZE,
+       "STUB code must not be larger than one page");
diff --git a/arch/um/kernel/early_printk.c b/arch/um/kernel/early_printk.c
new file mode 100644
index 000000000..c350c2331
--- /dev/null
+++ b/arch/um/kernel/early_printk.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2011 Richard Weinberger <richrd@nod.at>
+ */
+
+#include <linux/kernel.h>
+#include <linux/console.h>
+#include <linux/init.h>
+#include <os.h>
+
+static void early_console_write(struct console *con, const char *s, unsigned int n)
+{
+	um_early_printk(s, n);
+}
+
+static struct console early_console_dev = {
+	.name = "earlycon",
+	.write = early_console_write,
+	.flags = CON_BOOT,
+	.index = -1,
+};
+
+static int __init setup_early_printk(char *buf)
+{
+	if (!early_console) {
+		early_console = &early_console_dev;
+		register_console(&early_console_dev);
+	}
+	return 0;
+}
+
+early_param("earlyprintk", setup_early_printk);
diff --git a/arch/um/kernel/exec.c b/arch/um/kernel/exec.c
new file mode 100644
index 000000000..13812fa97
--- /dev/null
+++ b/arch/um/kernel/exec.c
@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/stddef.h>
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/ptrace.h>
+#include <linux/sched/mm.h>
+#include <linux/sched/task.h>
+#include <linux/sched/task_stack.h>
+#include <linux/slab.h>
+#include <asm/current.h>
+#include <asm/processor.h>
+#include <linux/uaccess.h>
+#include <as-layout.h>
+#include <mem_user.h>
+#include <registers.h>
+#include <skas.h>
+#include <os.h>
+
+void flush_thread(void)
+{
+	arch_flush_thread(&current->thread.arch);
+
+	get_safe_registers(current_pt_regs()->regs.gp,
+			   current_pt_regs()->regs.fp);
+}
+
+void start_thread(struct pt_regs *regs, unsigned long eip, unsigned long esp)
+{
+	PT_REGS_IP(regs) = eip;
+	PT_REGS_SP(regs) = esp;
+	clear_thread_flag(TIF_SINGLESTEP);
+}
+EXPORT_SYMBOL(start_thread);
diff --git a/arch/um/kernel/exitcode.c b/arch/um/kernel/exitcode.c
new file mode 100644
index 000000000..43edc2aa5
--- /dev/null
+++ b/arch/um/kernel/exitcode.c
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/ctype.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/types.h>
+#include <linux/uaccess.h>
+
+/*
+ * If read and write race, the read will still atomically read a valid
+ * value.
+ */
+int uml_exitcode = 0;
+
+static int exitcode_proc_show(struct seq_file *m, void *v)
+{
+	int val;
+
+	/*
+	 * Save uml_exitcode in a local so that we don't need to guarantee
+	 * that sprintf accesses it atomically.
+	 */
+	val = uml_exitcode;
+	seq_printf(m, "%d\n", val);
+	return 0;
+}
+
+static int exitcode_proc_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, exitcode_proc_show, NULL);
+}
+
+static ssize_t exitcode_proc_write(struct file *file,
+		const char __user *buffer, size_t count, loff_t *pos)
+{
+	char *end, buf[sizeof("nnnnn\0")];
+	size_t size;
+	int tmp;
+
+	size = min(count, sizeof(buf));
+	if (copy_from_user(buf, buffer, size))
+		return -EFAULT;
+
+	tmp = simple_strtol(buf, &end, 0);
+	if ((*end != '\0') && !isspace(*end))
+		return -EINVAL;
+
+	uml_exitcode = tmp;
+	return count;
+}
+
+static const struct proc_ops exitcode_proc_ops = {
+	.proc_open	= exitcode_proc_open,
+	.proc_read	= seq_read,
+	.proc_lseek	= seq_lseek,
+	.proc_release	= single_release,
+	.proc_write	= exitcode_proc_write,
+};
+
+static int make_proc_exitcode(void)
+{
+	struct proc_dir_entry *ent;
+
+	ent = proc_create("exitcode", 0600, NULL, &exitcode_proc_ops);
+	if (ent == NULL) {
+		printk(KERN_WARNING "make_proc_exitcode : Failed to register "
+		       "/proc/exitcode\n");
+		return 0;
+	}
+	return 0;
+}
+
+__initcall(make_proc_exitcode);
diff --git a/arch/um/kernel/gprof_syms.c b/arch/um/kernel/gprof_syms.c
new file mode 100644
index 000000000..84d536908
--- /dev/null
+++ b/arch/um/kernel/gprof_syms.c
@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0
+/* 
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/module.h>
+
+extern void mcount(void);
+EXPORT_SYMBOL(mcount);
diff --git a/arch/um/kernel/initrd.c b/arch/um/kernel/initrd.c
new file mode 100644
index 000000000..99dba8274
--- /dev/null
+++ b/arch/um/kernel/initrd.c
@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/init.h>
+#include <linux/memblock.h>
+#include <linux/initrd.h>
+#include <asm/types.h>
+#include <init.h>
+#include <os.h>
+
+#include "um_arch.h"
+
+/* Changed by uml_initrd_setup, which is a setup */
+static char *initrd __initdata = NULL;
+
+int __init read_initrd(void)
+{
+	unsigned long long size;
+	void *area;
+
+	if (!initrd)
+		return 0;
+
+	area = uml_load_file(initrd, &size);
+	if (!area)
+		return 0;
+
+	initrd_start = (unsigned long) area;
+	initrd_end = initrd_start + size;
+	return 0;
+}
+
+static int __init uml_initrd_setup(char *line, int *add)
+{
+	*add = 0;
+	initrd = line;
+	return 0;
+}
+
+__uml_setup("initrd=", uml_initrd_setup,
+"initrd=<initrd image>\n"
+"    This is used to boot UML from an initrd image.  The argument is the\n"
+"    name of the file containing the image.\n\n"
+);
diff --git a/arch/um/kernel/irq.c b/arch/um/kernel/irq.c
new file mode 100644
index 000000000..ddfd6e9bd
--- /dev/null
+++ b/arch/um/kernel/irq.c
@@ -0,0 +1,728 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2017 - Cambridge Greys Ltd
+ * Copyright (C) 2011 - 2014 Cisco Systems Inc
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Derived (i.e. mostly copied) from arch/i386/kernel/irq.c:
+ *	Copyright (C) 1992, 1998 Linus Torvalds, Ingo Molnar
+ */
+
+#include <linux/cpumask.h>
+#include <linux/hardirq.h>
+#include <linux/interrupt.h>
+#include <linux/kernel_stat.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/seq_file.h>
+#include <linux/slab.h>
+#include <as-layout.h>
+#include <kern_util.h>
+#include <os.h>
+#include <irq_user.h>
+#include <irq_kern.h>
+#include <linux/time-internal.h>
+
+DEFINE_PER_CPU_SHARED_ALIGNED(irq_cpustat_t, irq_stat);
+
+#define irq_stats(x)		(&per_cpu(irq_stat, x))
+
+/* When epoll triggers we do not know why it did so
+ * we can also have different IRQs for read and write.
+ * This is why we keep a small irq_reg array for each fd -
+ * one entry per IRQ type
+ */
+struct irq_reg {
+	void *id;
+	int irq;
+	/* it's cheaper to store this than to query it */
+	int events;
+	bool active;
+	bool pending;
+	bool wakeup;
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+	bool pending_event;
+	void (*timetravel_handler)(int, int, void *,
+				   struct time_travel_event *);
+	struct time_travel_event event;
+#endif
+};
+
+struct irq_entry {
+	struct list_head list;
+	int fd;
+	struct irq_reg reg[NUM_IRQ_TYPES];
+	bool suspended;
+	bool sigio_workaround;
+};
+
+static DEFINE_RAW_SPINLOCK(irq_lock);
+static LIST_HEAD(active_fds);
+static DECLARE_BITMAP(irqs_allocated, UM_LAST_SIGNAL_IRQ);
+static bool irqs_suspended;
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+static bool irqs_pending;
+#endif
+
+static void irq_io_loop(struct irq_reg *irq, struct uml_pt_regs *regs)
+{
+/*
+ * irq->active guards against reentry
+ * irq->pending accumulates pending requests
+ * if pending is raised the irq_handler is re-run
+ * until pending is cleared
+ */
+	if (irq->active) {
+		irq->active = false;
+
+		do {
+			irq->pending = false;
+			do_IRQ(irq->irq, regs);
+		} while (irq->pending);
+
+		irq->active = true;
+	} else {
+		irq->pending = true;
+	}
+}
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+static void irq_event_handler(struct time_travel_event *ev)
+{
+	struct irq_reg *reg = container_of(ev, struct irq_reg, event);
+
+	/* do nothing if suspended; just cause a wakeup and mark as pending */
+	if (irqs_suspended) {
+		irqs_pending = true;
+		reg->pending_event = true;
+		return;
+	}
+
+	generic_handle_irq(reg->irq);
+}
+
+static bool irq_do_timetravel_handler(struct irq_entry *entry,
+				      enum um_irq_type t)
+{
+	struct irq_reg *reg = &entry->reg[t];
+
+	if (!reg->timetravel_handler)
+		return false;
+
+	/*
+	 * Handle all messages - we might get multiple even while
+	 * interrupts are already suspended, due to suspend order
+	 * etc. Note that time_travel_add_irq_event() will not add
+	 * an event twice, if it's pending already "first wins".
+	 */
+	reg->timetravel_handler(reg->irq, entry->fd, reg->id, &reg->event);
+
+	if (!reg->event.pending)
+		return false;
+
+	return true;
+}
+
+static void irq_do_pending_events(bool timetravel_handlers_only)
+{
+	struct irq_entry *entry;
+
+	if (!irqs_pending || timetravel_handlers_only)
+		return;
+
+	irqs_pending = false;
+
+	list_for_each_entry(entry, &active_fds, list) {
+		enum um_irq_type t;
+
+		for (t = 0; t < NUM_IRQ_TYPES; t++) {
+			struct irq_reg *reg = &entry->reg[t];
+
+			/*
+			 * Any timetravel_handler was invoked already, just
+			 * directly run the IRQ.
+			 */
+			if (reg->pending_event) {
+				irq_enter();
+				generic_handle_irq(reg->irq);
+				irq_exit();
+				reg->pending_event = false;
+			}
+		}
+	}
+}
+#else
+static bool irq_do_timetravel_handler(struct irq_entry *entry,
+				      enum um_irq_type t)
+{
+	return false;
+}
+
+static void irq_do_pending_events(bool timetravel_handlers_only)
+{
+}
+#endif
+
+static void sigio_reg_handler(int idx, struct irq_entry *entry, enum um_irq_type t,
+			      struct uml_pt_regs *regs,
+			      bool timetravel_handlers_only)
+{
+	struct irq_reg *reg = &entry->reg[t];
+
+	if (!reg->events)
+		return;
+
+	if (os_epoll_triggered(idx, reg->events) <= 0)
+		return;
+
+	if (irq_do_timetravel_handler(entry, t))
+		return;
+
+	/*
+	 * If we're called to only run time-travel handlers then don't
+	 * actually proceed but mark sigio as pending (if applicable).
+	 * For suspend/resume, timetravel_handlers_only may be true
+	 * despite time-travel not being configured and used.
+	 */
+	if (timetravel_handlers_only) {
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+		reg->pending_event = true;
+		irqs_pending = true;
+		mark_sigio_pending();
+#endif
+		return;
+	}
+
+	irq_io_loop(reg, regs);
+}
+
+static void _sigio_handler(struct uml_pt_regs *regs,
+			   bool timetravel_handlers_only)
+{
+	struct irq_entry *irq_entry;
+	int n, i;
+
+	if (timetravel_handlers_only && !um_irq_timetravel_handler_used())
+		return;
+
+	/* Flush out pending events that were ignored due to time-travel. */
+	if (!irqs_suspended)
+		irq_do_pending_events(timetravel_handlers_only);
+
+	while (1) {
+		/* This is now lockless - epoll keeps back-referencesto the irqs
+		 * which have trigger it so there is no need to walk the irq
+		 * list and lock it every time. We avoid locking by turning off
+		 * IO for a specific fd by executing os_del_epoll_fd(fd) before
+		 * we do any changes to the actual data structures
+		 */
+		n = os_waiting_for_events_epoll();
+
+		if (n <= 0) {
+			if (n == -EINTR)
+				continue;
+			else
+				break;
+		}
+
+		for (i = 0; i < n ; i++) {
+			enum um_irq_type t;
+
+			irq_entry = os_epoll_get_data_pointer(i);
+
+			for (t = 0; t < NUM_IRQ_TYPES; t++)
+				sigio_reg_handler(i, irq_entry, t, regs,
+						  timetravel_handlers_only);
+		}
+	}
+
+	if (!timetravel_handlers_only)
+		free_irqs();
+}
+
+void sigio_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs,
+		   void *mc)
+{
+	preempt_disable();
+	_sigio_handler(regs, irqs_suspended);
+	preempt_enable();
+}
+
+static struct irq_entry *get_irq_entry_by_fd(int fd)
+{
+	struct irq_entry *walk;
+
+	lockdep_assert_held(&irq_lock);
+
+	list_for_each_entry(walk, &active_fds, list) {
+		if (walk->fd == fd)
+			return walk;
+	}
+
+	return NULL;
+}
+
+static void remove_irq_entry(struct irq_entry *to_free, bool remove)
+{
+	if (!to_free)
+		return;
+
+	if (remove)
+		os_del_epoll_fd(to_free->fd);
+	list_del(&to_free->list);
+}
+
+static bool update_irq_entry(struct irq_entry *entry)
+{
+	enum um_irq_type i;
+	int events = 0;
+
+	for (i = 0; i < NUM_IRQ_TYPES; i++)
+		events |= entry->reg[i].events;
+
+	if (events) {
+		/* will modify (instead of add) if needed */
+		os_add_epoll_fd(events, entry->fd, entry);
+		return true;
+	}
+
+	os_del_epoll_fd(entry->fd);
+	return false;
+}
+
+static struct irq_entry *update_or_remove_irq_entry(struct irq_entry *entry)
+{
+	if (update_irq_entry(entry))
+		return NULL;
+	remove_irq_entry(entry, false);
+	return entry;
+}
+
+static int activate_fd(int irq, int fd, enum um_irq_type type, void *dev_id,
+		       void (*timetravel_handler)(int, int, void *,
+						  struct time_travel_event *))
+{
+	struct irq_entry *irq_entry, *to_free = NULL;
+	int err, events = os_event_mask(type);
+	unsigned long flags;
+
+	err = os_set_fd_async(fd);
+	if (err < 0)
+		goto out;
+
+	raw_spin_lock_irqsave(&irq_lock, flags);
+	irq_entry = get_irq_entry_by_fd(fd);
+	if (irq_entry) {
+already:
+		/* cannot register the same FD twice with the same type */
+		if (WARN_ON(irq_entry->reg[type].events)) {
+			err = -EALREADY;
+			goto out_unlock;
+		}
+
+		/* temporarily disable to avoid IRQ-side locking */
+		os_del_epoll_fd(fd);
+	} else {
+		struct irq_entry *new;
+
+		/* don't restore interrupts */
+		raw_spin_unlock(&irq_lock);
+		new = kzalloc_obj(*irq_entry, GFP_ATOMIC);
+		if (!new) {
+			local_irq_restore(flags);
+			return -ENOMEM;
+		}
+		raw_spin_lock(&irq_lock);
+		irq_entry = get_irq_entry_by_fd(fd);
+		if (irq_entry) {
+			to_free = new;
+			goto already;
+		}
+		irq_entry = new;
+		irq_entry->fd = fd;
+		list_add_tail(&irq_entry->list, &active_fds);
+		maybe_sigio_broken(fd);
+	}
+
+	irq_entry->reg[type].id = dev_id;
+	irq_entry->reg[type].irq = irq;
+	irq_entry->reg[type].active = true;
+	irq_entry->reg[type].events = events;
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+	if (um_irq_timetravel_handler_used()) {
+		irq_entry->reg[type].timetravel_handler = timetravel_handler;
+		irq_entry->reg[type].event.fn = irq_event_handler;
+	}
+#endif
+
+	WARN_ON(!update_irq_entry(irq_entry));
+	err = 0;
+out_unlock:
+	raw_spin_unlock_irqrestore(&irq_lock, flags);
+out:
+	kfree(to_free);
+	return err;
+}
+
+/*
+ * Remove the entry or entries for a specific FD, if you
+ * don't want to remove all the possible entries then use
+ * um_free_irq() or deactivate_fd() instead.
+ */
+void free_irq_by_fd(int fd)
+{
+	struct irq_entry *to_free;
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&irq_lock, flags);
+	to_free = get_irq_entry_by_fd(fd);
+	remove_irq_entry(to_free, true);
+	raw_spin_unlock_irqrestore(&irq_lock, flags);
+	kfree(to_free);
+}
+EXPORT_SYMBOL(free_irq_by_fd);
+
+static void free_irq_by_irq_and_dev(unsigned int irq, void *dev)
+{
+	struct irq_entry *entry, *to_free = NULL;
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&irq_lock, flags);
+	list_for_each_entry(entry, &active_fds, list) {
+		enum um_irq_type i;
+
+		for (i = 0; i < NUM_IRQ_TYPES; i++) {
+			struct irq_reg *reg = &entry->reg[i];
+
+			if (!reg->events)
+				continue;
+			if (reg->irq != irq)
+				continue;
+			if (reg->id != dev)
+				continue;
+
+			os_del_epoll_fd(entry->fd);
+			reg->events = 0;
+			to_free = update_or_remove_irq_entry(entry);
+			goto out;
+		}
+	}
+out:
+	raw_spin_unlock_irqrestore(&irq_lock, flags);
+	kfree(to_free);
+}
+
+void deactivate_fd(int fd, int irqnum)
+{
+	struct irq_entry *entry;
+	unsigned long flags;
+	enum um_irq_type i;
+
+	os_del_epoll_fd(fd);
+
+	raw_spin_lock_irqsave(&irq_lock, flags);
+	entry = get_irq_entry_by_fd(fd);
+	if (!entry)
+		goto out;
+
+	for (i = 0; i < NUM_IRQ_TYPES; i++) {
+		if (!entry->reg[i].events)
+			continue;
+		if (entry->reg[i].irq == irqnum)
+			entry->reg[i].events = 0;
+	}
+
+	entry = update_or_remove_irq_entry(entry);
+out:
+	raw_spin_unlock_irqrestore(&irq_lock, flags);
+	kfree(entry);
+
+	ignore_sigio_fd(fd);
+}
+EXPORT_SYMBOL(deactivate_fd);
+
+/*
+ * Called just before shutdown in order to provide a clean exec
+ * environment in case the system is rebooting.  No locking because
+ * that would cause a pointless shutdown hang if something hadn't
+ * released the lock.
+ */
+int deactivate_all_fds(void)
+{
+	struct irq_entry *entry;
+
+	/* Stop IO. The IRQ loop has no lock so this is our
+	 * only way of making sure we are safe to dispose
+	 * of all IRQ handlers
+	 */
+	os_set_ioignore();
+
+	/* we can no longer call kfree() here so just deactivate */
+	list_for_each_entry(entry, &active_fds, list)
+		os_del_epoll_fd(entry->fd);
+	os_close_epoll_fd();
+	return 0;
+}
+
+/*
+ * do_IRQ handles all normal device IRQs (the special
+ * SMP cross-CPU interrupts have their own specific
+ * handlers).
+ */
+unsigned int do_IRQ(int irq, struct uml_pt_regs *regs)
+{
+	struct pt_regs *old_regs = set_irq_regs((struct pt_regs *)regs);
+	irq_enter();
+	generic_handle_irq(irq);
+	irq_exit();
+	set_irq_regs(old_regs);
+	return 1;
+}
+
+void um_free_irq(int irq, void *dev)
+{
+	if (WARN(irq < 0 || irq > UM_LAST_SIGNAL_IRQ,
+		 "freeing invalid irq %d", irq))
+		return;
+
+	free_irq_by_irq_and_dev(irq, dev);
+	free_irq(irq, dev);
+	clear_bit(irq, irqs_allocated);
+}
+EXPORT_SYMBOL(um_free_irq);
+
+static int
+_um_request_irq(int irq, int fd, enum um_irq_type type,
+		irq_handler_t handler, unsigned long irqflags,
+		const char *devname, void *dev_id,
+		void (*timetravel_handler)(int, int, void *,
+					   struct time_travel_event *))
+{
+	int err;
+
+	if (irq == UM_IRQ_ALLOC) {
+		int i;
+
+		for (i = UM_FIRST_DYN_IRQ; i < NR_IRQS; i++) {
+			if (!test_and_set_bit(i, irqs_allocated)) {
+				irq = i;
+				break;
+			}
+		}
+	}
+
+	if (irq < 0)
+		return -ENOSPC;
+
+	if (fd != -1) {
+		err = activate_fd(irq, fd, type, dev_id, timetravel_handler);
+		if (err)
+			goto error;
+	}
+
+	err = request_irq(irq, handler, irqflags, devname, dev_id);
+	if (err < 0)
+		goto error;
+
+	return irq;
+error:
+	clear_bit(irq, irqs_allocated);
+	return err;
+}
+
+int um_request_irq(int irq, int fd, enum um_irq_type type,
+		   irq_handler_t handler, unsigned long irqflags,
+		   const char *devname, void *dev_id)
+{
+	return _um_request_irq(irq, fd, type, handler, irqflags,
+			       devname, dev_id, NULL);
+}
+EXPORT_SYMBOL(um_request_irq);
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+int um_request_irq_tt(int irq, int fd, enum um_irq_type type,
+		      irq_handler_t handler, unsigned long irqflags,
+		      const char *devname, void *dev_id,
+		      void (*timetravel_handler)(int, int, void *,
+						 struct time_travel_event *))
+{
+	return _um_request_irq(irq, fd, type, handler, irqflags,
+			       devname, dev_id, timetravel_handler);
+}
+EXPORT_SYMBOL(um_request_irq_tt);
+
+void sigio_run_timetravel_handlers(void)
+{
+	_sigio_handler(NULL, true);
+}
+#endif
+
+#ifdef CONFIG_PM_SLEEP
+void um_irqs_suspend(void)
+{
+	struct irq_entry *entry;
+	unsigned long flags;
+
+	irqs_suspended = true;
+
+	raw_spin_lock_irqsave(&irq_lock, flags);
+	list_for_each_entry(entry, &active_fds, list) {
+		enum um_irq_type t;
+		bool clear = true;
+
+		for (t = 0; t < NUM_IRQ_TYPES; t++) {
+			if (!entry->reg[t].events)
+				continue;
+
+			/*
+			 * For the SIGIO_WRITE_IRQ, which is used to handle the
+			 * SIGIO workaround thread, we need special handling:
+			 * enable wake for it itself, but below we tell it about
+			 * any FDs that should be suspended.
+			 */
+			if (entry->reg[t].wakeup ||
+			    entry->reg[t].irq == SIGIO_WRITE_IRQ
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+			    || entry->reg[t].timetravel_handler
+#endif
+			    ) {
+				clear = false;
+				break;
+			}
+		}
+
+		if (clear) {
+			entry->suspended = true;
+			os_clear_fd_async(entry->fd);
+			entry->sigio_workaround =
+				!__ignore_sigio_fd(entry->fd);
+		}
+	}
+	raw_spin_unlock_irqrestore(&irq_lock, flags);
+}
+
+void um_irqs_resume(void)
+{
+	struct irq_entry *entry;
+	unsigned long flags;
+
+
+	raw_spin_lock_irqsave(&irq_lock, flags);
+	list_for_each_entry(entry, &active_fds, list) {
+		if (entry->suspended) {
+			int err = os_set_fd_async(entry->fd);
+
+			WARN(err < 0, "os_set_fd_async returned %d\n", err);
+			entry->suspended = false;
+
+			if (entry->sigio_workaround) {
+				err = __add_sigio_fd(entry->fd);
+				WARN(err < 0, "add_sigio_returned %d\n", err);
+			}
+		}
+	}
+	raw_spin_unlock_irqrestore(&irq_lock, flags);
+
+	irqs_suspended = false;
+	send_sigio_to_self();
+}
+
+static int normal_irq_set_wake(struct irq_data *d, unsigned int on)
+{
+	struct irq_entry *entry;
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&irq_lock, flags);
+	list_for_each_entry(entry, &active_fds, list) {
+		enum um_irq_type t;
+
+		for (t = 0; t < NUM_IRQ_TYPES; t++) {
+			if (!entry->reg[t].events)
+				continue;
+
+			if (entry->reg[t].irq != d->irq)
+				continue;
+			entry->reg[t].wakeup = on;
+			goto unlock;
+		}
+	}
+unlock:
+	raw_spin_unlock_irqrestore(&irq_lock, flags);
+	return 0;
+}
+#else
+#define normal_irq_set_wake NULL
+#endif
+
+/*
+ * irq_chip must define at least enable/disable and ack when
+ * the edge handler is used.
+ */
+static void dummy(struct irq_data *d)
+{
+}
+
+/* This is used for everything other than the timer. */
+static struct irq_chip normal_irq_type = {
+	.name = "SIGIO",
+	.irq_disable = dummy,
+	.irq_enable = dummy,
+	.irq_ack = dummy,
+	.irq_mask = dummy,
+	.irq_unmask = dummy,
+	.irq_set_wake = normal_irq_set_wake,
+};
+
+static struct irq_chip alarm_irq_type = {
+	.name = "SIGALRM",
+	.irq_disable = dummy,
+	.irq_enable = dummy,
+	.irq_ack = dummy,
+	.irq_mask = dummy,
+	.irq_unmask = dummy,
+};
+
+void __init init_IRQ(void)
+{
+	int i;
+
+	irq_set_chip_and_handler(TIMER_IRQ, &alarm_irq_type, handle_percpu_irq);
+
+	for (i = 1; i < UM_LAST_SIGNAL_IRQ; i++)
+		irq_set_chip_and_handler(i, &normal_irq_type, handle_edge_irq);
+	/* Initialize EPOLL Loop */
+	os_setup_epoll();
+}
+
+int __init arch_probe_nr_irqs(void)
+{
+	return NR_IRQS;
+}
+
+void sigchld_handler(int sig, struct siginfo *unused_si,
+		     struct uml_pt_regs *regs, void *mc)
+{
+	do_IRQ(SIGCHLD_IRQ, regs);
+}
+
+/*
+ * /proc/interrupts printing for arch specific interrupts
+ */
+int arch_show_interrupts(struct seq_file *p, int prec)
+{
+#if IS_ENABLED(CONFIG_SMP)
+	int cpu;
+
+	seq_printf(p, "%*s: ", prec, "RES");
+	for_each_online_cpu(cpu)
+		seq_printf(p, "%10u ", irq_stats(cpu)->irq_resched_count);
+	seq_puts(p, " Rescheduling interrupts\n");
+
+	seq_printf(p, "%*s: ", prec, "CAL");
+	for_each_online_cpu(cpu)
+		seq_printf(p, "%10u ", irq_stats(cpu)->irq_call_count);
+	seq_puts(p, " Function call interrupts\n");
+#endif
+
+	return 0;
+}
diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
new file mode 100644
index 000000000..fc0f543d1
--- /dev/null
+++ b/arch/um/kernel/kmsg_dump.c
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kmsg_dump.h>
+#include <linux/spinlock.h>
+#include <linux/console.h>
+#include <linux/string.h>
+#include <shared/init.h>
+#include <shared/kern.h>
+#include <os.h>
+
+static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
+				struct kmsg_dump_detail *detail)
+{
+	static struct kmsg_dump_iter iter;
+	static DEFINE_SPINLOCK(lock);
+	static char line[1024];
+	struct console *con;
+	unsigned long flags;
+	size_t len = 0;
+	int cookie;
+
+	/*
+	 * If no consoles are available to output crash information, dump
+	 * the kmsg buffer to stdout.
+	 */
+
+	cookie = console_srcu_read_lock();
+	for_each_console_srcu(con) {
+		/*
+		 * The ttynull console and disabled consoles are ignored
+		 * since they cannot output. All other consoles are
+		 * expected to output the crash information.
+		 */
+		if (strcmp(con->name, "ttynull") != 0 &&
+		    console_is_usable(con, console_srcu_read_flags(con), true)) {
+			break;
+		}
+	}
+	console_srcu_read_unlock(cookie);
+	if (con)
+		return;
+
+	if (!spin_trylock_irqsave(&lock, flags))
+		return;
+
+	kmsg_dump_rewind(&iter);
+
+	printf("kmsg_dump:\n");
+	while (kmsg_dump_get_line(&iter, true, line, sizeof(line), &len)) {
+		line[len] = '\0';
+		printf("%s", line);
+	}
+
+	spin_unlock_irqrestore(&lock, flags);
+}
+
+static struct kmsg_dumper kmsg_dumper = {
+	.dump = kmsg_dumper_stdout
+};
+
+static int __init kmsg_dumper_stdout_init(void)
+{
+	return kmsg_dump_register(&kmsg_dumper);
+}
+
+__uml_postsetup(kmsg_dumper_stdout_init);
diff --git a/arch/um/kernel/ksyms.c b/arch/um/kernel/ksyms.c
new file mode 100644
index 000000000..96314c31e
--- /dev/null
+++ b/arch/um/kernel/ksyms.c
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0
+/* 
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/module.h>
+#include <os.h>
+
+EXPORT_SYMBOL(um_get_signals);
+EXPORT_SYMBOL(um_set_signals);
+
+EXPORT_SYMBOL(os_stat_fd);
+EXPORT_SYMBOL(os_stat_file);
+EXPORT_SYMBOL(os_access);
+EXPORT_SYMBOL(os_set_exec_close);
+EXPORT_SYMBOL(os_getpid);
+EXPORT_SYMBOL(os_open_file);
+EXPORT_SYMBOL(os_read_file);
+EXPORT_SYMBOL(os_write_file);
+EXPORT_SYMBOL(os_seek_file);
+EXPORT_SYMBOL(os_lock_file);
+EXPORT_SYMBOL(os_ioctl_generic);
+EXPORT_SYMBOL(os_pipe);
+EXPORT_SYMBOL(os_file_type);
+EXPORT_SYMBOL(os_file_mode);
+EXPORT_SYMBOL(os_file_size);
+EXPORT_SYMBOL(os_flush_stdout);
+EXPORT_SYMBOL(os_close_file);
+EXPORT_SYMBOL(os_set_fd_async);
+EXPORT_SYMBOL(os_set_fd_block);
+EXPORT_SYMBOL(helper_wait);
+EXPORT_SYMBOL(os_shutdown_socket);
+EXPORT_SYMBOL(os_create_unix_socket);
+EXPORT_SYMBOL(os_connect_socket);
+EXPORT_SYMBOL(os_accept_connection);
+EXPORT_SYMBOL(os_rcv_fd_msg);
+EXPORT_SYMBOL(run_helper);
+EXPORT_SYMBOL(os_major);
+EXPORT_SYMBOL(os_minor);
+EXPORT_SYMBOL(os_makedev);
+EXPORT_SYMBOL(os_eventfd);
+EXPORT_SYMBOL(os_sendmsg_fds);
+
+EXPORT_SYMBOL(add_sigio_fd);
+EXPORT_SYMBOL(ignore_sigio_fd);
+EXPORT_SYMBOL(sigio_broken);
+
+EXPORT_SYMBOL(syscall);
diff --git a/arch/um/kernel/load_file.c b/arch/um/kernel/load_file.c
new file mode 100644
index 000000000..cb9d178ab
--- /dev/null
+++ b/arch/um/kernel/load_file.c
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+#include <linux/memblock.h>
+#include <os.h>
+
+#include "um_arch.h"
+
+static int __init __uml_load_file(const char *filename, void *buf, int size)
+{
+	int fd, n;
+
+	fd = os_open_file(filename, of_read(OPENFLAGS()), 0);
+	if (fd < 0) {
+		printk(KERN_ERR "Opening '%s' failed - err = %d\n", filename,
+		       -fd);
+		return -1;
+	}
+	n = os_read_file(fd, buf, size);
+	if (n != size) {
+		printk(KERN_ERR "Read of %d bytes from '%s' failed, "
+		       "err = %d\n", size,
+		       filename, -n);
+		return -1;
+	}
+
+	os_close_file(fd);
+	return 0;
+}
+
+void *uml_load_file(const char *filename, unsigned long long *size)
+{
+	void *area;
+	int err;
+
+	*size = 0;
+
+	if (!filename)
+		return NULL;
+
+	err = os_file_size(filename, size);
+	if (err)
+		return NULL;
+
+	if (*size == 0) {
+		printk(KERN_ERR "\"%s\" is empty\n", filename);
+		return NULL;
+	}
+
+	area = memblock_alloc_or_panic(*size, SMP_CACHE_BYTES);
+
+	if (__uml_load_file(filename, area, *size)) {
+		memblock_free(area, *size);
+		return NULL;
+	}
+
+	return area;
+}
diff --git a/arch/um/kernel/mem.c b/arch/um/kernel/mem.c
new file mode 100644
index 000000000..1eef0e42e
--- /dev/null
+++ b/arch/um/kernel/mem.c
@@ -0,0 +1,139 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/stddef.h>
+#include <linux/module.h>
+#include <linux/memblock.h>
+#include <linux/mm.h>
+#include <linux/swap.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <asm/sections.h>
+#include <asm/page.h>
+#include <asm/pgalloc.h>
+#include <as-layout.h>
+#include <init.h>
+#include <kern.h>
+#include <kern_util.h>
+#include <mem_user.h>
+#include <os.h>
+#include <um_malloc.h>
+#include <linux/sched/task.h>
+#include <linux/kasan.h>
+
+#ifdef CONFIG_KASAN
+void __init kasan_init(void)
+{
+	/*
+	 * kasan_map_memory will map all of the required address space and
+	 * the host machine will allocate physical memory as necessary.
+	 */
+	kasan_map_memory((void *)KASAN_SHADOW_START, KASAN_SHADOW_SIZE);
+	init_task.kasan_depth = 0;
+	/*
+	 * Since kasan_init() is called before main(),
+	 * KASAN is initialized but the enablement is deferred after
+	 * jump_label_init(). See arch_mm_preinit().
+	 */
+}
+
+static void (*kasan_init_ptr)(void)
+__section(".kasan_init") __used
+= kasan_init;
+#endif
+
+/*
+ * Initialized during boot, and readonly for initializing page tables
+ * afterwards
+ */
+pgd_t swapper_pg_dir[PTRS_PER_PGD];
+
+/* Initialized at boot time, and readonly after that */
+int kmalloc_ok = 0;
+
+/* Used during early boot */
+static unsigned long brk_end;
+
+void __init arch_mm_preinit(void)
+{
+	/* Safe to call after jump_label_init(). Enables KASAN. */
+	kasan_init_generic();
+
+	/* Map in the area just after the brk now that kmalloc is about
+	 * to be turned on.
+	 */
+	brk_end = PAGE_ALIGN((unsigned long) sbrk(0));
+	map_memory(brk_end, __pa(brk_end), uml_reserved - brk_end, 1, 1, 0);
+	memblock_free((void *)brk_end, uml_reserved - brk_end);
+	uml_reserved = brk_end;
+	min_low_pfn = PFN_UP(__pa(uml_reserved));
+	max_pfn = max_low_pfn;
+}
+
+void __init mem_init(void)
+{
+	kmalloc_ok = 1;
+}
+
+void __init arch_zone_limits_init(unsigned long *max_zone_pfns)
+{
+	max_zone_pfns[ZONE_NORMAL] = high_physmem >> PAGE_SHIFT;
+}
+
+/*
+ * This can't do anything because nothing in the kernel image can be freed
+ * since it's not in kernel physical memory.
+ */
+
+void free_initmem(void)
+{
+}
+
+/* Allocate and free page tables. */
+
+pgd_t *pgd_alloc(struct mm_struct *mm)
+{
+	pgd_t *pgd = __pgd_alloc(mm, 0);
+
+	if (pgd)
+		memcpy(pgd + USER_PTRS_PER_PGD,
+		       swapper_pg_dir + USER_PTRS_PER_PGD,
+		       (PTRS_PER_PGD - USER_PTRS_PER_PGD) * sizeof(pgd_t));
+
+	return pgd;
+}
+
+void *uml_kmalloc(int size, int flags)
+{
+	return kmalloc(size, flags);
+}
+
+static const pgprot_t protection_map[16] = {
+	[VM_NONE]					= PAGE_NONE,
+	[VM_READ]					= PAGE_READONLY,
+	[VM_WRITE]					= PAGE_COPY,
+	[VM_WRITE | VM_READ]				= PAGE_COPY,
+	[VM_EXEC]					= PAGE_READONLY,
+	[VM_EXEC | VM_READ]				= PAGE_READONLY,
+	[VM_EXEC | VM_WRITE]				= PAGE_COPY,
+	[VM_EXEC | VM_WRITE | VM_READ]			= PAGE_COPY,
+	[VM_SHARED]					= PAGE_NONE,
+	[VM_SHARED | VM_READ]				= PAGE_READONLY,
+	[VM_SHARED | VM_WRITE]				= PAGE_SHARED,
+	[VM_SHARED | VM_WRITE | VM_READ]		= PAGE_SHARED,
+	[VM_SHARED | VM_EXEC]				= PAGE_READONLY,
+	[VM_SHARED | VM_EXEC | VM_READ]			= PAGE_READONLY,
+	[VM_SHARED | VM_EXEC | VM_WRITE]		= PAGE_SHARED,
+	[VM_SHARED | VM_EXEC | VM_WRITE | VM_READ]	= PAGE_SHARED
+};
+DECLARE_VM_GET_PAGE_PROT
+
+void mark_rodata_ro(void)
+{
+	unsigned long rodata_start = PFN_ALIGN(__start_rodata);
+	unsigned long rodata_end = PFN_ALIGN(__end_rodata);
+
+	os_protect_memory((void *)rodata_start, rodata_end - rodata_start, 1, 0, 0);
+}
diff --git a/arch/um/kernel/physmem.c b/arch/um/kernel/physmem.c
new file mode 100644
index 000000000..ae6ca373c
--- /dev/null
+++ b/arch/um/kernel/physmem.c
@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/module.h>
+#include <linux/memblock.h>
+#include <linux/mm.h>
+#include <linux/pfn.h>
+#include <asm/page.h>
+#include <asm/sections.h>
+#include <as-layout.h>
+#include <init.h>
+#include <kern.h>
+#include <kern_util.h>
+#include <mem_user.h>
+#include <os.h>
+
+static int physmem_fd = -1;
+
+/* Changed during early boot */
+unsigned long high_physmem;
+EXPORT_SYMBOL(high_physmem);
+
+void map_memory(unsigned long virt, unsigned long phys, unsigned long len,
+		int r, int w, int x)
+{
+	__u64 offset;
+	int fd, err;
+
+	fd = phys_mapping(phys, &offset);
+	err = os_map_memory((void *) virt, fd, offset, len, r, w, x);
+	if (err) {
+		if (err == -ENOMEM)
+			printk(KERN_ERR "try increasing the host's "
+			       "/proc/sys/vm/max_map_count to <physical "
+			       "memory size>/4096\n");
+		panic("map_memory(0x%lx, %d, 0x%llx, %ld, %d, %d, %d) failed, "
+		      "err = %d\n", virt, fd, offset, len, r, w, x, err);
+	}
+}
+
+/**
+ * setup_physmem() - Setup physical memory for UML
+ * @start:	Start address of the physical kernel memory,
+ *		i.e start address of the executable image.
+ * @reserve_end:	end address of the physical kernel memory.
+ * @len:	Length of total physical memory that should be mapped/made
+ *		available, in bytes.
+ *
+ * Creates an unlinked temporary file of size (len) and memory maps
+ * it on the last executable image address (uml_reserved).
+ *
+ * The offset is needed as the length of the total physical memory
+ * (len) includes the size of the memory used be the executable image,
+ * but the mapped-to address is the last address of the executable image
+ * (uml_reserved == end address of executable image).
+ *
+ * The memory mapped memory of the temporary file is used as backing memory
+ * of all user space processes/kernel tasks.
+ */
+void __init setup_physmem(unsigned long start, unsigned long reserve_end,
+			  unsigned long len)
+{
+	unsigned long reserve = reserve_end - start;
+	unsigned long map_size = len - reserve;
+	int err;
+
+	if (len <= reserve) {
+		os_warn("Too few physical memory! Needed=%lu, given=%lu\n",
+			reserve, len);
+		exit(1);
+	}
+
+	physmem_fd = create_mem_file(len);
+
+	err = os_map_memory((void *) reserve_end, physmem_fd, reserve,
+			    map_size, 1, 1, 1);
+	if (err < 0) {
+		os_warn("setup_physmem - mapping %lu bytes of memory at 0x%p "
+			"failed - errno = %d\n", map_size,
+			(void *) reserve_end, err);
+		exit(1);
+	}
+
+	/*
+	 * Special kludge - This page will be mapped in to userspace processes
+	 * from physmem_fd, so it needs to be written out there.
+	 */
+	os_seek_file(physmem_fd, __pa(__syscall_stub_start));
+	os_write_file(physmem_fd, __syscall_stub_start, PAGE_SIZE);
+
+	memblock_add(__pa(start), len);
+	memblock_reserve(__pa(start), reserve);
+
+	min_low_pfn = PFN_UP(__pa(reserve_end));
+	max_low_pfn = min_low_pfn + (map_size >> PAGE_SHIFT);
+}
+
+int phys_mapping(unsigned long phys, unsigned long long *offset_out)
+{
+	int fd = -1;
+
+	if (phys < physmem_size) {
+		fd = physmem_fd;
+		*offset_out = phys;
+	}
+
+	return fd;
+}
+EXPORT_SYMBOL(phys_mapping);
+
+static int __init uml_mem_setup(char *line, int *add)
+{
+	char *retptr;
+
+	*add = 0;
+	physmem_size = memparse(line,&retptr);
+	return 0;
+}
+__uml_setup("mem=", uml_mem_setup,
+"mem=<Amount of desired ram>\n"
+"    This controls how much \"physical\" memory the kernel allocates\n"
+"    for the system. The size is specified as a number followed by\n"
+"    one of 'k', 'K', 'm', 'M', which have the obvious meanings.\n"
+"    This is not related to the amount of memory in the host.  It can\n"
+"    be more, and the excess, if it's ever used, will just be swapped out.\n"
+"	Example: mem=64M\n\n"
+);
diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
new file mode 100644
index 000000000..63b38a3f7
--- /dev/null
+++ b/arch/um/kernel/process.c
@@ -0,0 +1,309 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
+ * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Copyright 2003 PathScale, Inc.
+ */
+
+#include <linux/stddef.h>
+#include <linux/err.h>
+#include <linux/hardirq.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/personality.h>
+#include <linux/proc_fs.h>
+#include <linux/ptrace.h>
+#include <linux/random.h>
+#include <linux/cpu.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/sched/debug.h>
+#include <linux/sched/task.h>
+#include <linux/sched/task_stack.h>
+#include <linux/seq_file.h>
+#include <linux/tick.h>
+#include <linux/threads.h>
+#include <linux/resume_user_mode.h>
+#include <asm/current.h>
+#include <asm/mmu_context.h>
+#include <asm/switch_to.h>
+#include <asm/exec.h>
+#include <linux/uaccess.h>
+#include <as-layout.h>
+#include <kern_util.h>
+#include <os.h>
+#include <skas.h>
+#include <registers.h>
+#include <linux/time-internal.h>
+#include <linux/elfcore.h>
+
+/*
+ * This is a per-cpu array.  A processor only modifies its entry and it only
+ * cares about its entry, so it's OK if another processor is modifying its
+ * entry.
+ */
+struct task_struct *cpu_tasks[NR_CPUS] = {
+	[0 ... NR_CPUS - 1] = &init_task,
+};
+EXPORT_SYMBOL(cpu_tasks);
+
+void free_stack(unsigned long stack, int order)
+{
+	free_pages(stack, order);
+}
+
+unsigned long alloc_stack(int order, int atomic)
+{
+	unsigned long page;
+	gfp_t flags = GFP_KERNEL;
+
+	if (atomic)
+		flags = GFP_ATOMIC;
+	page = __get_free_pages(flags, order);
+
+	return page;
+}
+
+static inline void set_current(struct task_struct *task)
+{
+	cpu_tasks[task_thread_info(task)->cpu] = task;
+}
+
+struct task_struct *__switch_to(struct task_struct *from, struct task_struct *to)
+{
+	to->thread.prev_sched = from;
+	set_current(to);
+
+	switch_threads(&from->thread.switch_buf, &to->thread.switch_buf);
+	arch_switch_to(current);
+
+	return current->thread.prev_sched;
+}
+
+void interrupt_end(void)
+{
+	struct pt_regs *regs = &current->thread.regs;
+	unsigned long thread_flags;
+
+	thread_flags = read_thread_flags();
+	while (thread_flags & _TIF_WORK_MASK) {
+		if (thread_flags & _TIF_NEED_RESCHED)
+			schedule();
+		if (thread_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
+			do_signal(regs);
+		if (thread_flags & _TIF_NOTIFY_RESUME)
+			resume_user_mode_work(regs);
+		thread_flags = read_thread_flags();
+	}
+}
+
+int get_current_pid(void)
+{
+	return task_pid_nr(current);
+}
+
+/*
+ * This is called magically, by its address being stuffed in a jmp_buf
+ * and being longjmp-d to.
+ */
+void new_thread_handler(void)
+{
+	int (*fn)(void *);
+	void *arg;
+
+	if (current->thread.prev_sched != NULL)
+		schedule_tail(current->thread.prev_sched);
+	current->thread.prev_sched = NULL;
+
+	fn = current->thread.request.thread.proc;
+	arg = current->thread.request.thread.arg;
+
+	/*
+	 * callback returns only if the kernel thread execs a process
+	 */
+	fn(arg);
+	userspace(&current->thread.regs.regs);
+}
+
+/* Called magically, see new_thread_handler above */
+static void fork_handler(void)
+{
+	schedule_tail(current->thread.prev_sched);
+
+	/*
+	 * XXX: if interrupt_end() calls schedule, this call to
+	 * arch_switch_to isn't needed. We could want to apply this to
+	 * improve performance. -bb
+	 */
+	arch_switch_to(current);
+
+	current->thread.prev_sched = NULL;
+
+	userspace(&current->thread.regs.regs);
+}
+
+int copy_thread(struct task_struct * p, const struct kernel_clone_args *args)
+{
+	u64 clone_flags = args->flags;
+	unsigned long sp = args->stack;
+	unsigned long tls = args->tls;
+	void (*handler)(void);
+	int ret = 0;
+
+	p->thread = (struct thread_struct) INIT_THREAD;
+
+	if (!args->fn) {
+	  	memcpy(&p->thread.regs.regs, current_pt_regs(),
+		       sizeof(p->thread.regs.regs));
+		PT_REGS_SET_SYSCALL_RETURN(&p->thread.regs, 0);
+		if (sp != 0)
+			REGS_SP(p->thread.regs.regs.gp) = sp;
+
+		handler = fork_handler;
+
+		arch_copy_thread(&current->thread.arch, &p->thread.arch);
+	} else {
+		get_safe_registers(p->thread.regs.regs.gp, p->thread.regs.regs.fp);
+		p->thread.request.thread.proc = args->fn;
+		p->thread.request.thread.arg = args->fn_arg;
+		handler = new_thread_handler;
+	}
+
+	new_thread(task_stack_page(p), &p->thread.switch_buf, handler);
+
+	if (!args->fn) {
+		clear_flushed_tls(p);
+
+		/*
+		 * Set a new TLS for the child thread?
+		 */
+		if (clone_flags & CLONE_SETTLS)
+			ret = arch_set_tls(p, tls);
+	}
+
+	return ret;
+}
+
+void initial_thread_cb(void (*proc)(void *), void *arg)
+{
+	initial_thread_cb_skas(proc, arg);
+}
+
+int arch_dup_task_struct(struct task_struct *dst,
+			 struct task_struct *src)
+{
+	/* init_task is not dynamically sized (missing FPU state) */
+	if (unlikely(src == &init_task)) {
+		memcpy(dst, src, sizeof(init_task));
+		memset((void *)dst + sizeof(init_task), 0,
+		       arch_task_struct_size - sizeof(init_task));
+	} else {
+		memcpy(dst, src, arch_task_struct_size);
+	}
+
+	return 0;
+}
+
+void um_idle_sleep(void)
+{
+	if (time_travel_mode != TT_MODE_OFF)
+		time_travel_sleep();
+	else
+		os_idle_sleep();
+}
+
+void arch_cpu_idle(void)
+{
+	um_idle_sleep();
+}
+
+void arch_cpu_idle_prepare(void)
+{
+	os_idle_prepare();
+}
+
+int __uml_cant_sleep(void) {
+	return in_atomic() || irqs_disabled() || in_interrupt();
+	/* Is in_interrupt() really needed? */
+}
+
+int uml_need_resched(void)
+{
+	return need_resched();
+}
+
+extern exitcall_t __uml_exitcall_begin, __uml_exitcall_end;
+
+void do_uml_exitcalls(void)
+{
+	exitcall_t *call;
+
+	call = &__uml_exitcall_end;
+	while (--call >= &__uml_exitcall_begin)
+		(*call)();
+}
+
+char *uml_strdup(const char *string)
+{
+	return kstrdup(string, GFP_KERNEL);
+}
+EXPORT_SYMBOL(uml_strdup);
+
+int copy_from_user_proc(void *to, void __user *from, int size)
+{
+	return copy_from_user(to, from, size);
+}
+
+int singlestepping(void)
+{
+	return test_thread_flag(TIF_SINGLESTEP);
+}
+
+/*
+ * Only x86 and x86_64 have an arch_align_stack().
+ * All other arches have "#define arch_align_stack(x) (x)"
+ * in their asm/exec.h
+ * As this is included in UML from asm-um/system-generic.h,
+ * we can use it to behave as the subarch does.
+ */
+#ifndef arch_align_stack
+unsigned long arch_align_stack(unsigned long sp)
+{
+	if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
+		sp -= get_random_u32_below(8192);
+	return sp & ~0xf;
+}
+#endif
+
+unsigned long __get_wchan(struct task_struct *p)
+{
+	unsigned long stack_page, sp, ip;
+	bool seen_sched = 0;
+
+	stack_page = (unsigned long) task_stack_page(p);
+	/* Bail if the process has no kernel stack for some reason */
+	if (stack_page == 0)
+		return 0;
+
+	sp = p->thread.switch_buf->JB_SP;
+	/*
+	 * Bail if the stack pointer is below the bottom of the kernel
+	 * stack for some reason
+	 */
+	if (sp < stack_page)
+		return 0;
+
+	while (sp < stack_page + THREAD_SIZE) {
+		ip = *((unsigned long *) sp);
+		if (in_sched_functions(ip))
+			/* Ignore everything until we're above the scheduler */
+			seen_sched = 1;
+		else if (kernel_text_address(ip) && seen_sched)
+			return ip;
+
+		sp += sizeof(unsigned long);
+	}
+
+	return 0;
+}
diff --git a/arch/um/kernel/ptrace.c b/arch/um/kernel/ptrace.c
new file mode 100644
index 000000000..7da0a5223
--- /dev/null
+++ b/arch/um/kernel/ptrace.c
@@ -0,0 +1,161 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/audit.h>
+#include <linux/ptrace.h>
+#include <linux/sched.h>
+#include <linux/uaccess.h>
+#include <asm/ptrace-abi.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/syscalls.h>
+
+void user_enable_single_step(struct task_struct *child)
+{
+	set_tsk_thread_flag(child, TIF_SINGLESTEP);
+
+#ifdef SUBARCH_SET_SINGLESTEPPING
+	SUBARCH_SET_SINGLESTEPPING(child, 1);
+#endif
+}
+
+void user_disable_single_step(struct task_struct *child)
+{
+	clear_tsk_thread_flag(child, TIF_SINGLESTEP);
+
+#ifdef SUBARCH_SET_SINGLESTEPPING
+	SUBARCH_SET_SINGLESTEPPING(child, 0);
+#endif
+}
+
+/*
+ * Called by kernel/ptrace.c when detaching..
+ */
+void ptrace_disable(struct task_struct *child)
+{
+	user_disable_single_step(child);
+}
+
+long arch_ptrace(struct task_struct *child, long request,
+		 unsigned long addr, unsigned long data)
+{
+	int i, ret;
+	unsigned long __user *p = (void __user *)data;
+	void __user *vp = p;
+
+	switch (request) {
+	/* read the word at location addr in the USER area. */
+	case PTRACE_PEEKUSR:
+		ret = peek_user(child, addr, data);
+		break;
+
+	/* write the word at location addr in the USER area */
+	case PTRACE_POKEUSR:
+		ret = poke_user(child, addr, data);
+		break;
+
+	case PTRACE_SYSEMU:
+	case PTRACE_SYSEMU_SINGLESTEP:
+		ret = -EIO;
+		break;
+
+#ifdef PTRACE_GETREGS
+	case PTRACE_GETREGS: { /* Get all gp regs from the child. */
+		if (!access_ok(p, MAX_REG_OFFSET)) {
+			ret = -EIO;
+			break;
+		}
+		for ( i = 0; i < MAX_REG_OFFSET; i += sizeof(long) ) {
+			__put_user(getreg(child, i), p);
+			p++;
+		}
+		ret = 0;
+		break;
+	}
+#endif
+#ifdef PTRACE_SETREGS
+	case PTRACE_SETREGS: { /* Set all gp regs in the child. */
+		unsigned long tmp = 0;
+		if (!access_ok(p, MAX_REG_OFFSET)) {
+			ret = -EIO;
+			break;
+		}
+		for ( i = 0; i < MAX_REG_OFFSET; i += sizeof(long) ) {
+			__get_user(tmp, p);
+			putreg(child, i, tmp);
+			p++;
+		}
+		ret = 0;
+		break;
+	}
+#endif
+	case PTRACE_GET_THREAD_AREA:
+		ret = ptrace_get_thread_area(child, addr, vp);
+		break;
+
+	case PTRACE_SET_THREAD_AREA:
+		ret = ptrace_set_thread_area(child, addr, vp);
+		break;
+
+	default:
+		ret = ptrace_request(child, request, addr, data);
+		if (ret == -EIO)
+			ret = subarch_ptrace(child, request, addr, data);
+		break;
+	}
+
+	return ret;
+}
+
+static void send_sigtrap(struct uml_pt_regs *regs, int error_code)
+{
+	/* Send us the fake SIGTRAP */
+	force_sig_fault(SIGTRAP, TRAP_BRKPT,
+			/* User-mode eip? */
+			UPT_IS_USER(regs) ? (void __user *) UPT_IP(regs) : NULL);
+}
+
+/*
+ * XXX Check TIF_SINGLESTEP for singlestepping check and
+ * PT_PTRACED vs TIF_SYSCALL_TRACE for syscall tracing check
+ */
+int syscall_trace_enter(struct pt_regs *regs)
+{
+	audit_syscall_entry(UPT_SYSCALL_NR(&regs->regs),
+			    UPT_SYSCALL_ARG1(&regs->regs),
+			    UPT_SYSCALL_ARG2(&regs->regs),
+			    UPT_SYSCALL_ARG3(&regs->regs),
+			    UPT_SYSCALL_ARG4(&regs->regs));
+
+	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
+		trace_sys_enter(regs, UPT_SYSCALL_NR(&regs->regs));
+
+	if (!test_thread_flag(TIF_SYSCALL_TRACE))
+		return 0;
+
+	return !ptrace_report_syscall_permit_entry(regs);
+}
+
+void syscall_trace_leave(struct pt_regs *regs)
+{
+	int ptraced = current->ptrace;
+
+	audit_syscall_exit(regs);
+
+	/* Fake a debug trap */
+	if (test_thread_flag(TIF_SINGLESTEP))
+		send_sigtrap(&regs->regs, 0);
+
+	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
+		trace_sys_exit(regs, PT_REGS_SYSCALL_RET(regs));
+
+	if (!test_thread_flag(TIF_SYSCALL_TRACE))
+		return;
+
+	ptrace_report_syscall_exit(regs, 0);
+	/* force do_signal() --> is_syscall() */
+	if (ptraced & PT_PTRACED)
+		set_thread_flag(TIF_SIGPENDING);
+}
diff --git a/arch/um/kernel/reboot.c b/arch/um/kernel/reboot.c
new file mode 100644
index 000000000..680bce4bd
--- /dev/null
+++ b/arch/um/kernel/reboot.c
@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: GPL-2.0
+/* 
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/sched/signal.h>
+#include <linux/sched/task.h>
+#include <linux/sched/mm.h>
+#include <linux/spinlock.h>
+#include <linux/slab.h>
+#include <linux/oom.h>
+#include <linux/reboot.h>
+#include <kern_util.h>
+#include <os.h>
+#include <skas.h>
+
+void (*pm_power_off)(void);
+EXPORT_SYMBOL(pm_power_off);
+
+static void kill_off_processes(void)
+{
+	struct task_struct *p;
+	int pid;
+
+	read_lock(&tasklist_lock);
+	for_each_process(p) {
+		struct task_struct *t;
+
+		t = find_lock_task_mm(p);
+		if (!t)
+			continue;
+		pid = t->mm->context.id.pid;
+		task_unlock(t);
+		os_kill_ptraced_process(pid, 1);
+	}
+	read_unlock(&tasklist_lock);
+}
+
+void uml_cleanup(void)
+{
+	kmalloc_ok = 0;
+	do_uml_exitcalls();
+	kill_off_processes();
+}
+
+void machine_restart(char * __unused)
+{
+	uml_cleanup();
+	reboot_skas();
+}
+
+void machine_power_off(void)
+{
+	uml_cleanup();
+	halt_skas();
+}
+
+void machine_halt(void)
+{
+	machine_power_off();
+}
+
+static int sys_power_off_handler(struct sys_off_data *data)
+{
+	machine_power_off();
+	return 0;
+}
+
+static int register_power_off(void)
+{
+	register_sys_off_handler(SYS_OFF_MODE_POWER_OFF,
+				 SYS_OFF_PRIO_DEFAULT,
+				 sys_power_off_handler, NULL);
+	return 0;
+}
+__initcall(register_power_off);
diff --git a/arch/um/kernel/sigio.c b/arch/um/kernel/sigio.c
new file mode 100644
index 000000000..4fc047420
--- /dev/null
+++ b/arch/um/kernel/sigio.c
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
+ */
+
+#include <linux/interrupt.h>
+#include <irq_kern.h>
+#include <os.h>
+#include <sigio.h>
+
+/* These are called from os-Linux/sigio.c to protect its pollfds arrays. */
+static DEFINE_MUTEX(sigio_mutex);
+
+void sigio_lock(void)
+{
+	mutex_lock(&sigio_mutex);
+}
+
+void sigio_unlock(void)
+{
+	mutex_unlock(&sigio_mutex);
+}
diff --git a/arch/um/kernel/signal.c b/arch/um/kernel/signal.c
new file mode 100644
index 000000000..a56b44522
--- /dev/null
+++ b/arch/um/kernel/signal.c
@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/module.h>
+#include <linux/ptrace.h>
+#include <linux/sched.h>
+#include <linux/ftrace.h>
+#include <asm/siginfo.h>
+#include <asm/signal.h>
+#include <asm/unistd.h>
+#include <frame_kern.h>
+#include <kern_util.h>
+#include <os.h>
+
+EXPORT_SYMBOL(block_signals);
+EXPORT_SYMBOL(unblock_signals);
+
+void block_signals_trace(void)
+{
+	block_signals();
+	if (current_thread_info())
+		trace_hardirqs_off();
+}
+
+void unblock_signals_trace(void)
+{
+	if (current_thread_info())
+		trace_hardirqs_on();
+	unblock_signals();
+}
+
+void um_trace_signals_on(void)
+{
+	if (current_thread_info())
+		trace_hardirqs_on();
+}
+
+void um_trace_signals_off(void)
+{
+	if (current_thread_info())
+		trace_hardirqs_off();
+}
+
+/*
+ * OK, we're invoking a handler
+ */
+static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
+{
+	sigset_t *oldset = sigmask_to_save();
+	int singlestep = 0;
+	unsigned long sp;
+	int err;
+
+	if (test_thread_flag(TIF_SINGLESTEP) && (current->ptrace & PT_PTRACED))
+		singlestep = 1;
+
+	/* Did we come from a system call? */
+	if (PT_REGS_SYSCALL_NR(regs) >= 0) {
+		/* If so, check system call restarting.. */
+		switch (PT_REGS_SYSCALL_RET(regs)) {
+		case -ERESTART_RESTARTBLOCK:
+		case -ERESTARTNOHAND:
+			PT_REGS_SYSCALL_RET(regs) = -EINTR;
+			break;
+
+		case -ERESTARTSYS:
+			if (!(ksig->ka.sa.sa_flags & SA_RESTART)) {
+				PT_REGS_SYSCALL_RET(regs) = -EINTR;
+				break;
+			}
+			fallthrough;
+		case -ERESTARTNOINTR:
+			PT_REGS_RESTART_SYSCALL(regs);
+			PT_REGS_ORIG_SYSCALL(regs) = PT_REGS_SYSCALL_NR(regs);
+			break;
+		}
+	}
+
+	sp = PT_REGS_SP(regs);
+	if ((ksig->ka.sa.sa_flags & SA_ONSTACK) && (sas_ss_flags(sp) == 0))
+		sp = current->sas_ss_sp + current->sas_ss_size;
+
+#ifdef CONFIG_ARCH_HAS_SC_SIGNALS
+	if (!(ksig->ka.sa.sa_flags & SA_SIGINFO))
+		err = setup_signal_stack_sc(sp, ksig, regs, oldset);
+	else
+#endif
+		err = setup_signal_stack_si(sp, ksig, regs, oldset);
+
+	signal_setup_done(err, ksig, singlestep);
+}
+
+void do_signal(struct pt_regs *regs)
+{
+	struct ksignal ksig;
+	int handled_sig = 0;
+
+	while (get_signal(&ksig)) {
+		handled_sig = 1;
+		/* Whee!  Actually deliver the signal.  */
+		handle_signal(&ksig, regs);
+	}
+
+	/* Did we come from a system call? */
+	if (!handled_sig && (PT_REGS_SYSCALL_NR(regs) >= 0)) {
+		/* Restart the system call - no handlers present */
+		switch (PT_REGS_SYSCALL_RET(regs)) {
+		case -ERESTARTNOHAND:
+		case -ERESTARTSYS:
+		case -ERESTARTNOINTR:
+			PT_REGS_ORIG_SYSCALL(regs) = PT_REGS_SYSCALL_NR(regs);
+			PT_REGS_RESTART_SYSCALL(regs);
+			break;
+		case -ERESTART_RESTARTBLOCK:
+			PT_REGS_ORIG_SYSCALL(regs) = __NR_restart_syscall;
+			PT_REGS_RESTART_SYSCALL(regs);
+			break;
+		}
+	}
+
+	/*
+	 * if there's no signal to deliver, we just put the saved sigmask
+	 * back
+	 */
+	if (!handled_sig)
+		restore_saved_sigmask();
+}
diff --git a/arch/um/kernel/skas/.gitignore b/arch/um/kernel/skas/.gitignore
new file mode 100644
index 000000000..c3409ced0
--- /dev/null
+++ b/arch/um/kernel/skas/.gitignore
@@ -0,0 +1,2 @@
+stub_exe
+stub_exe.dbg
diff --git a/arch/um/kernel/skas/Makefile b/arch/um/kernel/skas/Makefile
new file mode 100644
index 000000000..3384be426
--- /dev/null
+++ b/arch/um/kernel/skas/Makefile
@@ -0,0 +1,50 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+#
+
+obj-y := stub.o mmu.o process.o syscall.o uaccess.o \
+	 stub_exe_embed.o
+
+# Stub executable
+
+stub_exe_objs-y := stub_exe.o
+
+stub_exe_objs := $(foreach F,$(stub_exe_objs-y),$(obj)/$F)
+
+# Object file containing the ELF executable
+$(obj)/stub_exe_embed.o: $(src)/stub_exe_embed.S $(obj)/stub_exe
+
+$(obj)/stub_exe.dbg: $(stub_exe_objs) FORCE
+	$(call if_changed,stub_exe)
+
+$(obj)/stub_exe: OBJCOPYFLAGS := -S
+$(obj)/stub_exe: $(obj)/stub_exe.dbg FORCE
+	$(call if_changed,objcopy)
+
+quiet_cmd_stub_exe = STUB_EXE $@
+      cmd_stub_exe = $(CC) -nostdlib -o $@ \
+			   $(filter-out $(UM_GPROF_OPT) $(UM_GCOV_OPT),$(KBUILD_CFLAGS)) $(STUB_EXE_LDFLAGS) \
+			   $(filter %.o,$^)
+
+STUB_EXE_LDFLAGS = -Wl,-n -static
+
+targets += stub_exe.dbg stub_exe $(stub_exe_objs-y)
+
+# end
+
+# stub.o is in the stub, so it can't be built with profiling
+# GCC hardened also auto-enables -fpic, but we need %ebx so it can't work ->
+# disable it
+
+CFLAGS_stub.o := $(CFLAGS_NO_HARDENING)
+CFLAGS_stub_exe.o := $(CFLAGS_NO_HARDENING)
+
+# Clang will call memset() from __builtin_alloca() when stack variable
+# initialization is enabled, which is used in stub_exe.c.
+CFLAGS_stub_exe.o += $(call cc-option, -ftrivial-auto-var-init=uninitialized)
+
+UNPROFILE_OBJS := stub.o stub_exe.o
+KCOV_INSTRUMENT := n
+
+include $(srctree)/arch/um/scripts/Makefile.rules
diff --git a/arch/um/kernel/skas/mmu.c b/arch/um/kernel/skas/mmu.c
new file mode 100644
index 000000000..b50170960
--- /dev/null
+++ b/arch/um/kernel/skas/mmu.c
@@ -0,0 +1,165 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/mm.h>
+#include <linux/sched/signal.h>
+#include <linux/slab.h>
+
+#include <shared/irq_kern.h>
+#include <asm/pgalloc.h>
+#include <asm/sections.h>
+#include <asm/mmu_context.h>
+#include <as-layout.h>
+#include <os.h>
+#include <skas.h>
+#include <stub-data.h>
+
+/* Ensure the stub_data struct covers the allocated area */
+static_assert(sizeof(struct stub_data) == STUB_DATA_PAGES * UM_KERN_PAGE_SIZE);
+
+static spinlock_t mm_list_lock;
+static struct list_head mm_list;
+
+struct mutex *__get_turnstile(struct mm_id *mm_id)
+{
+	struct mm_context *ctx = container_of(mm_id, struct mm_context, id);
+
+	return &ctx->turnstile;
+}
+
+void enter_turnstile(struct mm_id *mm_id)
+{
+	mutex_lock(__get_turnstile(mm_id));
+}
+
+void exit_turnstile(struct mm_id *mm_id)
+{
+	mutex_unlock(__get_turnstile(mm_id));
+}
+
+int init_new_context(struct task_struct *task, struct mm_struct *mm)
+{
+	struct mm_id *new_id = &mm->context.id;
+	unsigned long stack = 0;
+	int ret = -ENOMEM;
+
+	mutex_init(&mm->context.turnstile);
+	spin_lock_init(&mm->context.sync_tlb_lock);
+
+	stack = __get_free_pages(GFP_KERNEL | __GFP_ZERO, ilog2(STUB_DATA_PAGES));
+	if (stack == 0)
+		goto out;
+
+	new_id->stack = stack;
+	new_id->syscall_data_len = 0;
+	new_id->syscall_fd_num = 0;
+
+	scoped_guard(spinlock_irqsave, &mm_list_lock) {
+		/* Insert into list, used for lookups when the child dies */
+		list_add(&mm->context.list, &mm_list);
+	}
+
+	ret = start_userspace(new_id);
+	if (ret < 0)
+		goto out_free;
+
+	/* Ensure the new MM is clean and nothing unwanted is mapped */
+	unmap(new_id, 0, STUB_START);
+
+	return 0;
+
+ out_free:
+	free_pages(new_id->stack, ilog2(STUB_DATA_PAGES));
+ out:
+	return ret;
+}
+
+void destroy_context(struct mm_struct *mm)
+{
+	struct mm_context *mmu = &mm->context;
+
+	/*
+	 * If init_new_context wasn't called, this will be
+	 * zero, resulting in a kill(0), which will result in the
+	 * whole UML suddenly dying.  Also, cover negative and
+	 * 1 cases, since they shouldn't happen either.
+	 *
+	 * Negative cases happen if the child died unexpectedly.
+	 */
+	if (mmu->id.pid >= 0 && mmu->id.pid < 2) {
+		printk(KERN_ERR "corrupt mm_context - pid = %d\n",
+		       mmu->id.pid);
+		return;
+	}
+
+	scoped_guard(spinlock_irqsave, &mm_list_lock)
+		list_del(&mm->context.list);
+
+	if (mmu->id.pid > 0) {
+		os_kill_ptraced_process(mmu->id.pid, 1);
+		mmu->id.pid = -1;
+	}
+
+	if (using_seccomp && mmu->id.sock)
+		os_close_file(mmu->id.sock);
+
+	free_pages(mmu->id.stack, ilog2(STUB_DATA_PAGES));
+}
+
+static irqreturn_t mm_sigchld_irq(int irq, void* dev)
+{
+	struct mm_context *mm_context;
+	pid_t pid;
+
+	guard(spinlock)(&mm_list_lock);
+
+	while ((pid = os_reap_child()) > 0) {
+		/*
+		* A child died, check if we have an MM with the PID. This is
+		* only relevant in SECCOMP mode (as ptrace will fail anyway).
+		*
+		* See wait_stub_done_seccomp for more details.
+		*/
+		list_for_each_entry(mm_context, &mm_list, list) {
+			if (mm_context->id.pid == pid) {
+				struct stub_data *stub_data;
+				printk("Unexpectedly lost MM child! Affected tasks will segfault.");
+
+				/* Marks the MM as dead */
+				mm_context->id.pid = -1;
+
+				stub_data = (void *)mm_context->id.stack;
+				stub_data->futex = FUTEX_IN_KERN;
+#if IS_ENABLED(CONFIG_SMP)
+				os_futex_wake(&stub_data->futex);
+#endif
+
+				/*
+				 * NOTE: Currently executing syscalls by
+				 * affected tasks may finish normally.
+				 */
+				break;
+			}
+		}
+	}
+
+	return IRQ_HANDLED;
+}
+
+static int __init init_child_tracking(void)
+{
+	int err;
+
+	spin_lock_init(&mm_list_lock);
+	INIT_LIST_HEAD(&mm_list);
+
+	err = request_irq(SIGCHLD_IRQ, mm_sigchld_irq, 0, "SIGCHLD", NULL);
+	if (err < 0)
+		panic("Failed to register SIGCHLD IRQ: %d", err);
+
+	return 0;
+}
+early_initcall(init_child_tracking)
diff --git a/arch/um/kernel/skas/process.c b/arch/um/kernel/skas/process.c
new file mode 100644
index 000000000..4a7673b02
--- /dev/null
+++ b/arch/um/kernel/skas/process.c
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/init.h>
+#include <linux/sched/mm.h>
+#include <linux/sched/task_stack.h>
+#include <linux/sched/task.h>
+#include <linux/smp-internal.h>
+
+#include <asm/tlbflush.h>
+
+#include <as-layout.h>
+#include <kern.h>
+#include <os.h>
+#include <skas.h>
+#include <kern_util.h>
+
+extern void start_kernel(void);
+
+static int __init start_kernel_proc(void *unused)
+{
+	block_signals_trace();
+
+	start_kernel();
+	return 0;
+}
+
+char cpu_irqstacks[NR_CPUS][THREAD_SIZE] __aligned(THREAD_SIZE);
+
+int __init start_uml(void)
+{
+	stack_protections((unsigned long) &cpu_irqstacks[0]);
+	set_sigstack(cpu_irqstacks[0], THREAD_SIZE);
+
+	init_new_thread_signals();
+
+	init_task.thread.request.thread.proc = start_kernel_proc;
+	init_task.thread.request.thread.arg = NULL;
+	return start_idle_thread(task_stack_page(&init_task),
+				 &init_task.thread.switch_buf);
+}
+
+unsigned long current_stub_stack(void)
+{
+	if (current->mm == NULL)
+		return 0;
+
+	return current->mm->context.id.stack;
+}
+
+struct mm_id *current_mm_id(void)
+{
+	if (current->mm == NULL)
+		return NULL;
+
+	return &current->mm->context.id;
+}
+
+void current_mm_sync(void)
+{
+	if (current->mm == NULL)
+		return;
+
+	um_tlb_sync(current->mm);
+}
+
+static DEFINE_SPINLOCK(initial_jmpbuf_spinlock);
+
+void initial_jmpbuf_lock(void)
+{
+	spin_lock_irq(&initial_jmpbuf_spinlock);
+}
+
+void initial_jmpbuf_unlock(void)
+{
+	spin_unlock_irq(&initial_jmpbuf_spinlock);
+}
diff --git a/arch/um/kernel/skas/stub.c b/arch/um/kernel/skas/stub.c
new file mode 100644
index 000000000..e09216a20
--- /dev/null
+++ b/arch/um/kernel/skas/stub.c
@@ -0,0 +1,181 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2021 Benjamin Berg <benjamin@sipsolutions.net>
+ */
+
+#include <sysdep/stub.h>
+
+#include <linux/futex.h>
+#include <sys/socket.h>
+#include <errno.h>
+
+/*
+ * Known security issues
+ *
+ * Userspace can jump to this address to execute *any* syscall that is
+ * permitted by the stub. As we will return afterwards, it can do
+ * whatever it likes, including:
+ * - Tricking the kernel into handing out the memory FD
+ * - Using this memory FD to read/write all physical memory
+ * - Running in parallel to the kernel processing a syscall
+ *   (possibly creating data races?)
+ * - Blocking e.g. SIGALRM to avoid time based scheduling
+ *
+ * To avoid this, the permitted location for each syscall needs to be
+ * checked for in the SECCOMP filter (which is reasonably simple). Also,
+ * more care will need to go into considerations how the code might be
+ * tricked by using a prepared stack (or even modifying the stack from
+ * another thread in case SMP support is added).
+ *
+ * As for the SIGALRM, the best counter measure will be to check in the
+ * kernel that the process is reporting back the SIGALRM in a timely
+ * fashion.
+ */
+static __always_inline int syscall_handler(int fd_map[STUB_MAX_FDS])
+{
+	struct stub_data *d = get_stub_data();
+	int i;
+	unsigned long res;
+	int fd;
+
+	for (i = 0; i < d->syscall_data_len; i++) {
+		struct stub_syscall *sc = &d->syscall_data[i];
+
+		switch (sc->syscall) {
+		case STUB_SYSCALL_MMAP:
+			if (fd_map)
+				fd = fd_map[sc->mem.fd];
+			else
+				fd = sc->mem.fd;
+
+			res = stub_syscall6(STUB_MMAP_NR,
+					    sc->mem.addr, sc->mem.length,
+					    sc->mem.prot,
+					    MAP_SHARED | MAP_FIXED,
+					    fd, sc->mem.offset);
+			if (res != sc->mem.addr) {
+				d->err = res;
+				d->syscall_data_len = i;
+				return -1;
+			}
+			break;
+		case STUB_SYSCALL_MUNMAP:
+			res = stub_syscall2(__NR_munmap,
+					    sc->mem.addr, sc->mem.length);
+			if (res) {
+				d->err = res;
+				d->syscall_data_len = i;
+				return -1;
+			}
+			break;
+		default:
+			d->err = -95; /* EOPNOTSUPP */
+			d->syscall_data_len = i;
+			return -1;
+		}
+	}
+
+	d->err = 0;
+	d->syscall_data_len = 0;
+
+	return 0;
+}
+
+void __section(".__syscall_stub")
+stub_syscall_handler(void)
+{
+	syscall_handler(NULL);
+
+	trap_myself();
+}
+
+void __section(".__syscall_stub")
+stub_signal_interrupt(int sig, siginfo_t *info, void *p)
+{
+	struct stub_data *d = get_stub_data();
+	char rcv_data;
+	union {
+		char data[CMSG_SPACE(sizeof(int) * STUB_MAX_FDS)];
+		struct cmsghdr align;
+	} ctrl = {};
+	struct iovec iov = {
+		.iov_base = &rcv_data,
+		.iov_len = 1,
+	};
+	struct msghdr msghdr = {
+		.msg_iov = &iov,
+		.msg_iovlen = 1,
+		.msg_control = &ctrl,
+		.msg_controllen = sizeof(ctrl),
+	};
+	ucontext_t *uc = p;
+	struct cmsghdr *fd_msg;
+	int *fd_map;
+	int num_fds;
+	long res;
+
+	d->signal = sig;
+	d->si_offset = (unsigned long)info - (unsigned long)&d->sigstack[0];
+	d->mctx_offset = (unsigned long)&uc->uc_mcontext - (unsigned long)&d->sigstack[0];
+
+restart_wait:
+	d->futex = FUTEX_IN_KERN;
+	do {
+		res = stub_syscall3(__NR_futex, (unsigned long)&d->futex,
+				    FUTEX_WAKE, 1);
+	} while (res == -EINTR);
+
+	do {
+		res = stub_syscall4(__NR_futex, (unsigned long)&d->futex,
+				    FUTEX_WAIT, FUTEX_IN_KERN, 0);
+	} while (res == -EINTR || d->futex == FUTEX_IN_KERN);
+
+	if (res < 0 && res != -EAGAIN)
+		stub_syscall1(__NR_exit_group, 1);
+
+	if (d->syscall_data_len) {
+		/* Read passed FDs (if any) */
+		do {
+			res = stub_syscall3(__NR_recvmsg, 0, (unsigned long)&msghdr, 0);
+		} while (res == -EINTR);
+
+		/* We should never have a receive error (other than -EAGAIN) */
+		if (res < 0 && res != -EAGAIN)
+			stub_syscall1(__NR_exit_group, 1);
+
+		/* Receive the FDs */
+		num_fds = 0;
+		fd_msg = msghdr.msg_control;
+		fd_map = (void *)CMSG_DATA(fd_msg);
+		if (res == iov.iov_len && msghdr.msg_controllen > sizeof(struct cmsghdr))
+			num_fds = (fd_msg->cmsg_len - CMSG_LEN(0)) / sizeof(int);
+
+		/* Try running queued syscalls. */
+		res = syscall_handler(fd_map);
+
+		while (num_fds)
+			stub_syscall2(__NR_close, fd_map[--num_fds], 0);
+	} else {
+		res = 0;
+	}
+
+	if (res < 0 || d->restart_wait) {
+		/* Report SIGSYS if we restart. */
+		d->signal = SIGSYS;
+		d->restart_wait = 0;
+
+		goto restart_wait;
+	}
+
+	/* Restore arch dependent state that is not part of the mcontext */
+	stub_seccomp_restore_state(&d->arch_data);
+
+	/* Return so that the host modified mcontext is restored. */
+}
+
+void __section(".__syscall_stub")
+stub_signal_restorer(void)
+{
+	/* We must not have anything on the stack when doing rt_sigreturn */
+	stub_syscall0(__NR_rt_sigreturn);
+}
diff --git a/arch/um/kernel/skas/stub_exe.c b/arch/um/kernel/skas/stub_exe.c
new file mode 100644
index 000000000..cbafaa684
--- /dev/null
+++ b/arch/um/kernel/skas/stub_exe.c
@@ -0,0 +1,230 @@
+#include <sys/ptrace.h>
+#include <sys/prctl.h>
+#include <sys/fcntl.h>
+#include <asm/unistd.h>
+#include <sysdep/stub.h>
+#include <stub-data.h>
+#include <linux/filter.h>
+#include <linux/seccomp.h>
+#include <generated/asm-offsets.h>
+
+void _start(void);
+
+noinline static void real_init(void)
+{
+	struct stub_init_data init_data;
+	unsigned long res;
+	struct {
+		void  *ss_sp;
+		int    ss_flags;
+		size_t ss_size;
+	} stack = {
+		.ss_size = STUB_DATA_PAGES * UM_KERN_PAGE_SIZE,
+	};
+	struct {
+		void *sa_handler_;
+		unsigned long sa_flags;
+		void *sa_restorer;
+		unsigned long long sa_mask;
+	} sa = {
+		/* Need to set SA_RESTORER (but the handler never returns) */
+		.sa_flags = SA_ONSTACK | SA_NODEFER | SA_SIGINFO | 0x04000000,
+	};
+
+	/* set a nice name */
+	stub_syscall2(__NR_prctl, PR_SET_NAME, (unsigned long)"uml-userspace");
+
+	/* Make sure this process dies if the kernel dies */
+	stub_syscall2(__NR_prctl, PR_SET_PDEATHSIG, SIGKILL);
+
+	/* Needed in SECCOMP mode (and safe to do anyway) */
+	stub_syscall5(__NR_prctl, PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
+
+	/* read information from STDIN and close it */
+	res = stub_syscall3(__NR_read, 0,
+			    (unsigned long)&init_data, sizeof(init_data));
+	if (res != sizeof(init_data))
+		stub_syscall1(__NR_exit, 10);
+
+	/* In SECCOMP mode, FD 0 is a socket and is later used for FD passing */
+	if (!init_data.seccomp)
+		stub_syscall1(__NR_close, 0);
+	else
+		stub_syscall3(__NR_fcntl, 0, F_SETFL, O_NONBLOCK);
+
+	/* map stub code + data */
+	res = stub_syscall6(STUB_MMAP_NR,
+			    init_data.stub_start, UM_KERN_PAGE_SIZE,
+			    PROT_READ | PROT_EXEC, MAP_FIXED | MAP_SHARED,
+			    init_data.stub_code_fd, init_data.stub_code_offset);
+	if (res != init_data.stub_start)
+		stub_syscall1(__NR_exit, 11);
+
+	res = stub_syscall6(STUB_MMAP_NR,
+			    init_data.stub_start + UM_KERN_PAGE_SIZE,
+			    STUB_DATA_PAGES * UM_KERN_PAGE_SIZE,
+			    PROT_READ | PROT_WRITE, MAP_FIXED | MAP_SHARED,
+			    init_data.stub_data_fd, init_data.stub_data_offset);
+	if (res != init_data.stub_start + UM_KERN_PAGE_SIZE)
+		stub_syscall1(__NR_exit, 12);
+
+	/* In SECCOMP mode, we only need the signalling FD from now on */
+	if (init_data.seccomp) {
+		res = stub_syscall3(__NR_close_range, 1, ~0U, 0);
+		if (res != 0)
+			stub_syscall1(__NR_exit, 13);
+	}
+
+	/* setup signal stack inside stub data */
+	stack.ss_sp = (void *)init_data.stub_start + UM_KERN_PAGE_SIZE;
+	stub_syscall2(__NR_sigaltstack, (unsigned long)&stack, 0);
+
+	/* register signal handlers */
+	sa.sa_handler_ = (void *) init_data.signal_handler;
+	sa.sa_restorer = (void *) init_data.signal_restorer;
+	if (!init_data.seccomp) {
+		/* In ptrace mode, the SIGSEGV handler never returns */
+		sa.sa_mask = 0;
+
+		res = stub_syscall4(__NR_rt_sigaction, SIGSEGV,
+				    (unsigned long)&sa, 0, sizeof(sa.sa_mask));
+		if (res != 0)
+			stub_syscall1(__NR_exit, 14);
+	} else {
+		/* SECCOMP mode uses rt_sigreturn, need to mask all signals */
+		sa.sa_mask = ~0ULL;
+
+		res = stub_syscall4(__NR_rt_sigaction, SIGSEGV,
+				    (unsigned long)&sa, 0, sizeof(sa.sa_mask));
+		if (res != 0)
+			stub_syscall1(__NR_exit, 15);
+
+		res = stub_syscall4(__NR_rt_sigaction, SIGSYS,
+				    (unsigned long)&sa, 0, sizeof(sa.sa_mask));
+		if (res != 0)
+			stub_syscall1(__NR_exit, 16);
+
+		res = stub_syscall4(__NR_rt_sigaction, SIGALRM,
+				    (unsigned long)&sa, 0, sizeof(sa.sa_mask));
+		if (res != 0)
+			stub_syscall1(__NR_exit, 17);
+
+		res = stub_syscall4(__NR_rt_sigaction, SIGTRAP,
+				    (unsigned long)&sa, 0, sizeof(sa.sa_mask));
+		if (res != 0)
+			stub_syscall1(__NR_exit, 18);
+
+		res = stub_syscall4(__NR_rt_sigaction, SIGILL,
+				    (unsigned long)&sa, 0, sizeof(sa.sa_mask));
+		if (res != 0)
+			stub_syscall1(__NR_exit, 19);
+
+		res = stub_syscall4(__NR_rt_sigaction, SIGFPE,
+				    (unsigned long)&sa, 0, sizeof(sa.sa_mask));
+		if (res != 0)
+			stub_syscall1(__NR_exit, 20);
+	}
+
+	/*
+	 * If in seccomp mode, install the SECCOMP filter and trigger a syscall.
+	 * Otherwise set PTRACE_TRACEME and do a SIGSTOP.
+	 */
+	if (init_data.seccomp) {
+		struct sock_filter filter[] = {
+#if __BITS_PER_LONG > 32
+			/* [0] Load upper 32bit of instruction pointer from seccomp_data */
+			BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
+				 (offsetof(struct seccomp_data, instruction_pointer) + 4)),
+
+			/* [1] Jump forward 3 instructions if the upper address is not identical */
+			BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, (init_data.stub_start) >> 32, 0, 3),
+#endif
+			/* [2] Load lower 32bit of instruction pointer from seccomp_data */
+			BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
+				 (offsetof(struct seccomp_data, instruction_pointer))),
+
+			/* [3] Mask out lower bits */
+			BPF_STMT(BPF_ALU | BPF_AND | BPF_K, 0xfffff000),
+
+			/* [4] Jump to [6] if the lower bits are not on the expected page */
+			BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, (init_data.stub_start) & 0xfffff000, 1, 0),
+
+			/* [5] Trap call, allow */
+			BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_TRAP),
+
+			/* [6,7] Check architecture */
+			BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
+				 offsetof(struct seccomp_data, arch)),
+			BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K,
+				 UM_SECCOMP_ARCH_NATIVE, 1, 0),
+
+			/* [8] Kill (for architecture check) */
+			BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_KILL_PROCESS),
+
+			/* [9] Load syscall number */
+			BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
+				 offsetof(struct seccomp_data, nr)),
+
+			/* [10-16] Check against permitted syscalls */
+			BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_futex,
+				 7, 0),
+			BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K,__NR_recvmsg,
+				 6, 0),
+			BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K,__NR_close,
+				 5, 0),
+			BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, STUB_MMAP_NR,
+				 4, 0),
+			BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_munmap,
+				 3, 0),
+#ifdef __i386__
+			BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_set_thread_area,
+				 2, 0),
+#else
+			BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_arch_prctl,
+				 2, 0),
+#endif
+			BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_rt_sigreturn,
+				 1, 0),
+
+			/* [17] Not one of the permitted syscalls */
+			BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_KILL_PROCESS),
+
+			/* [18] Permitted call for the stub */
+			BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
+		};
+		struct sock_fprog prog = {
+			.len = sizeof(filter) / sizeof(filter[0]),
+			.filter = filter,
+		};
+
+		if (stub_syscall3(__NR_seccomp, SECCOMP_SET_MODE_FILTER,
+				  SECCOMP_FILTER_FLAG_TSYNC,
+				  (unsigned long)&prog) != 0)
+			stub_syscall1(__NR_exit, 21);
+
+		/* Fall through, the exit syscall will cause SIGSYS */
+	} else {
+		stub_syscall4(__NR_ptrace, PTRACE_TRACEME, 0, 0, 0);
+
+		stub_syscall2(__NR_kill, stub_syscall0(__NR_getpid), SIGSTOP);
+	}
+
+	stub_syscall1(__NR_exit, 30);
+
+	__builtin_unreachable();
+}
+
+__attribute__((naked)) void _start(void)
+{
+	/*
+	 * Since the stack after exec() starts at the top-most address,
+	 * but that's exactly where we also want to map the stub data
+	 * and code, this must:
+	 *  - push the stack by 1 code and STUB_DATA_PAGES data pages
+	 *  - call real_init()
+	 * This way, real_init() can use the stack normally, while the
+	 * original stack further down (higher address) will become
+	 * inaccessible after the mmap() calls above.
+	 */
+	stub_start(real_init);
+}
diff --git a/arch/um/kernel/skas/stub_exe_embed.S b/arch/um/kernel/skas/stub_exe_embed.S
new file mode 100644
index 000000000..6d8914fbe
--- /dev/null
+++ b/arch/um/kernel/skas/stub_exe_embed.S
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/init.h>
+#include <linux/linkage.h>
+
+__INITDATA
+
+SYM_DATA_START(stub_exe_start)
+	.incbin "arch/um/kernel/skas/stub_exe"
+SYM_DATA_END_LABEL(stub_exe_start, SYM_L_GLOBAL, stub_exe_end)
+
+__FINIT
diff --git a/arch/um/kernel/skas/syscall.c b/arch/um/kernel/skas/syscall.c
new file mode 100644
index 000000000..bc117733e
--- /dev/null
+++ b/arch/um/kernel/skas/syscall.c
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/kernel.h>
+#include <linux/ptrace.h>
+#include <linux/seccomp.h>
+#include <kern_util.h>
+#include <sysdep/ptrace.h>
+#include <sysdep/ptrace_user.h>
+#include <linux/time-internal.h>
+#include <asm/syscall.h>
+#include <asm/unistd.h>
+#include <asm/delay.h>
+
+void handle_syscall(struct uml_pt_regs *r)
+{
+	struct pt_regs *regs = container_of(r, struct pt_regs, regs);
+	int syscall;
+
+	/* Initialize the syscall number and default return value. */
+	UPT_SYSCALL_NR(r) = PT_SYSCALL_NR(r->gp);
+	PT_REGS_SET_SYSCALL_RETURN(regs, -ENOSYS);
+
+	if (syscall_trace_enter(regs))
+		goto out;
+
+	/* Do the seccomp check after ptrace; failures should be fast. */
+	if (!seccomp_permit_syscall())
+		goto out;
+
+	syscall = UPT_SYSCALL_NR(r);
+
+	/*
+	 * If no time passes, then sched_yield may not actually yield, causing
+	 * broken spinlock implementations in userspace (ASAN) to hang for long
+	 * periods of time.
+	 */
+	if ((time_travel_mode == TT_MODE_INFCPU ||
+	     time_travel_mode == TT_MODE_EXTERNAL) &&
+	    syscall == __NR_sched_yield)
+		tt_extra_sched_jiffies += 1;
+
+	if (syscall >= 0 && syscall < __NR_syscalls) {
+		unsigned long ret;
+
+		ret = (*sys_call_table[syscall])(UPT_SYSCALL_ARG1(&regs->regs),
+						 UPT_SYSCALL_ARG2(&regs->regs),
+						 UPT_SYSCALL_ARG3(&regs->regs),
+						 UPT_SYSCALL_ARG4(&regs->regs),
+						 UPT_SYSCALL_ARG5(&regs->regs),
+						 UPT_SYSCALL_ARG6(&regs->regs));
+
+		PT_REGS_SET_SYSCALL_RETURN(regs, ret);
+
+		/*
+		 * An error value here can be some form of -ERESTARTSYS
+		 * and then we'd just loop. Make any error syscalls take
+		 * some time, so that it won't just loop if something is
+		 * not ready, and hopefully other things will make some
+		 * progress.
+		 */
+		if (IS_ERR_VALUE(ret) &&
+		    (time_travel_mode == TT_MODE_INFCPU ||
+		     time_travel_mode == TT_MODE_EXTERNAL)) {
+			um_udelay(1);
+			schedule();
+		}
+	}
+
+out:
+	syscall_trace_leave(regs);
+}
diff --git a/arch/um/kernel/skas/uaccess.c b/arch/um/kernel/skas/uaccess.c
new file mode 100644
index 000000000..caef1deef
--- /dev/null
+++ b/arch/um/kernel/skas/uaccess.c
@@ -0,0 +1,368 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/err.h>
+#include <linux/highmem.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <asm/current.h>
+#include <asm/page.h>
+#include <kern_util.h>
+#include <asm/futex.h>
+#include <os.h>
+
+pte_t *virt_to_pte(struct mm_struct *mm, unsigned long addr)
+{
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+
+	if (mm == NULL)
+		return NULL;
+
+	pgd = pgd_offset(mm, addr);
+	if (!pgd_present(*pgd))
+		return NULL;
+
+	p4d = p4d_offset(pgd, addr);
+	if (!p4d_present(*p4d))
+		return NULL;
+
+	pud = pud_offset(p4d, addr);
+	if (!pud_present(*pud))
+		return NULL;
+
+	pmd = pmd_offset(pud, addr);
+	if (!pmd_present(*pmd))
+		return NULL;
+
+	return pte_offset_kernel(pmd, addr);
+}
+
+static pte_t *maybe_map(unsigned long virt, int is_write)
+{
+	pte_t *pte = virt_to_pte(current->mm, virt);
+	int err, dummy_code;
+
+	if ((pte == NULL) || !pte_present(*pte) ||
+	    (is_write && !pte_write(*pte))) {
+		err = handle_page_fault(virt, 0, is_write, 1, &dummy_code);
+		if (err)
+			return NULL;
+		pte = virt_to_pte(current->mm, virt);
+	}
+	if (!pte_present(*pte))
+		pte = NULL;
+
+	return pte;
+}
+
+static int do_op_one_page(unsigned long addr, int len, int is_write,
+		 int (*op)(unsigned long addr, int len, void *arg), void *arg)
+{
+	struct page *page;
+	pte_t *pte;
+	int n;
+
+	pte = maybe_map(addr, is_write);
+	if (pte == NULL)
+		return -1;
+
+	page = pte_page(*pte);
+#ifdef CONFIG_64BIT
+	pagefault_disable();
+	addr = (unsigned long) page_address(page) +
+		(addr & ~PAGE_MASK);
+#else
+	addr = (unsigned long) kmap_atomic(page) +
+		(addr & ~PAGE_MASK);
+#endif
+	n = (*op)(addr, len, arg);
+
+#ifdef CONFIG_64BIT
+	pagefault_enable();
+#else
+	kunmap_atomic((void *)addr);
+#endif
+
+	return n;
+}
+
+static long buffer_op(unsigned long addr, int len, int is_write,
+		      int (*op)(unsigned long, int, void *), void *arg)
+{
+	long size, remain, n;
+
+	size = min(PAGE_ALIGN(addr) - addr, (unsigned long) len);
+	remain = len;
+
+	n = do_op_one_page(addr, size, is_write, op, arg);
+	if (n != 0) {
+		remain = (n < 0 ? remain : 0);
+		goto out;
+	}
+
+	addr += size;
+	remain -= size;
+	if (remain == 0)
+		goto out;
+
+	while (addr < ((addr + remain) & PAGE_MASK)) {
+		n = do_op_one_page(addr, PAGE_SIZE, is_write, op, arg);
+		if (n != 0) {
+			remain = (n < 0 ? remain : 0);
+			goto out;
+		}
+
+		addr += PAGE_SIZE;
+		remain -= PAGE_SIZE;
+	}
+	if (remain == 0)
+		goto out;
+
+	n = do_op_one_page(addr, remain, is_write, op, arg);
+	if (n != 0) {
+		remain = (n < 0 ? remain : 0);
+		goto out;
+	}
+
+	return 0;
+ out:
+	return remain;
+}
+
+static int copy_chunk_from_user(unsigned long from, int len, void *arg)
+{
+	unsigned long *to_ptr = arg, to = *to_ptr;
+
+	memcpy((void *) to, (void *) from, len);
+	*to_ptr += len;
+	return 0;
+}
+
+unsigned long raw_copy_from_user(void *to, const void __user *from, unsigned long n)
+{
+	return buffer_op((unsigned long) from, n, 0, copy_chunk_from_user, &to);
+}
+EXPORT_SYMBOL(raw_copy_from_user);
+
+static int copy_chunk_to_user(unsigned long to, int len, void *arg)
+{
+	unsigned long *from_ptr = arg, from = *from_ptr;
+
+	memcpy((void *) to, (void *) from, len);
+	*from_ptr += len;
+	return 0;
+}
+
+unsigned long raw_copy_to_user(void __user *to, const void *from, unsigned long n)
+{
+	return buffer_op((unsigned long) to, n, 1, copy_chunk_to_user, &from);
+}
+EXPORT_SYMBOL(raw_copy_to_user);
+
+static int strncpy_chunk_from_user(unsigned long from, int len, void *arg)
+{
+	char **to_ptr = arg, *to = *to_ptr;
+	int n;
+
+	n = strnlen((void *) from, len);
+	memcpy_and_pad(to, len, (void *) from, n, 0);
+	*to_ptr += n;
+
+	if (n < len)
+	        return 1;
+	return 0;
+}
+
+long strncpy_from_user(char *dst, const char __user *src, long count)
+{
+	long n;
+	char *ptr = dst;
+
+	if (!access_ok(src, 1))
+		return -EFAULT;
+	n = buffer_op((unsigned long) src, count, 0, strncpy_chunk_from_user,
+		      &ptr);
+	if (n != 0)
+		return -EFAULT;
+	return strnlen(dst, count);
+}
+EXPORT_SYMBOL(strncpy_from_user);
+
+static int clear_chunk(unsigned long addr, int len, void *unused)
+{
+	memset((void *) addr, 0, len);
+	return 0;
+}
+
+unsigned long __clear_user(void __user *mem, unsigned long len)
+{
+	return buffer_op((unsigned long) mem, len, 1, clear_chunk, NULL);
+}
+EXPORT_SYMBOL(__clear_user);
+
+static int strnlen_chunk(unsigned long str, int len, void *arg)
+{
+	int *len_ptr = arg, n;
+
+	n = strnlen((void *) str, len);
+	*len_ptr += n;
+
+	if (n < len)
+		return 1;
+	return 0;
+}
+
+long strnlen_user(const char __user *str, long len)
+{
+	int count = 0, n;
+
+	if (!access_ok(str, 1))
+		return -EFAULT;
+	n = buffer_op((unsigned long) str, len, 0, strnlen_chunk, &count);
+	if (n == 0)
+		return count + 1;
+	return 0;
+}
+EXPORT_SYMBOL(strnlen_user);
+
+/**
+ * arch_futex_atomic_op_inuser() - Atomic arithmetic operation with constant
+ *			  argument and comparison of the previous
+ *			  futex value with another constant.
+ *
+ * @op:		operation to execute
+ * @oparg:	argument to operation
+ * @oval:	old value at uaddr
+ * @uaddr:	pointer to user space address
+ *
+ * Return:
+ * 0 - On success
+ * -EFAULT - User access resulted in a page fault
+ * -EAGAIN - Atomic operation was unable to complete due to contention
+ * -ENOSYS - Operation not supported
+ */
+
+int arch_futex_atomic_op_inuser(int op, u32 oparg, int *oval, u32 __user *uaddr)
+{
+	int oldval, ret;
+	struct page *page;
+	unsigned long addr = (unsigned long) uaddr;
+	pte_t *pte;
+
+	ret = -EFAULT;
+	if (!access_ok(uaddr, sizeof(*uaddr)))
+		return -EFAULT;
+	preempt_disable();
+	pte = maybe_map(addr, 1);
+	if (pte == NULL)
+		goto out_inuser;
+
+	page = pte_page(*pte);
+#ifdef CONFIG_64BIT
+	pagefault_disable();
+	addr = (unsigned long) page_address(page) +
+			(((unsigned long) addr) & ~PAGE_MASK);
+#else
+	addr = (unsigned long) kmap_atomic(page) +
+		((unsigned long) addr & ~PAGE_MASK);
+#endif
+	uaddr = (u32 *) addr;
+	oldval = *uaddr;
+
+	ret = 0;
+
+	switch (op) {
+	case FUTEX_OP_SET:
+		*uaddr = oparg;
+		break;
+	case FUTEX_OP_ADD:
+		*uaddr += oparg;
+		break;
+	case FUTEX_OP_OR:
+		*uaddr |= oparg;
+		break;
+	case FUTEX_OP_ANDN:
+		*uaddr &= ~oparg;
+		break;
+	case FUTEX_OP_XOR:
+		*uaddr ^= oparg;
+		break;
+	default:
+		ret = -ENOSYS;
+	}
+#ifdef CONFIG_64BIT
+	pagefault_enable();
+#else
+	kunmap_atomic((void *)addr);
+#endif
+
+out_inuser:
+	preempt_enable();
+
+	if (ret == 0)
+		*oval = oldval;
+
+	return ret;
+}
+EXPORT_SYMBOL(arch_futex_atomic_op_inuser);
+
+/**
+ * futex_atomic_cmpxchg_inatomic() - Compare and exchange the content of the
+ *				uaddr with newval if the current value is
+ *				oldval.
+ * @uval:	pointer to store content of @uaddr
+ * @uaddr:	pointer to user space address
+ * @oldval:	old value
+ * @newval:	new value to store to @uaddr
+ *
+ * Return:
+ * 0 - On success
+ * -EFAULT - User access resulted in a page fault
+ * -EAGAIN - Atomic operation was unable to complete due to contention
+ */
+
+int futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
+			      u32 oldval, u32 newval)
+{
+	struct page *page;
+	pte_t *pte;
+	int ret = -EFAULT;
+
+	if (!access_ok(uaddr, sizeof(*uaddr)))
+		return -EFAULT;
+
+	preempt_disable();
+	pte = maybe_map((unsigned long) uaddr, 1);
+	if (pte == NULL)
+		goto out_inatomic;
+
+	page = pte_page(*pte);
+#ifdef CONFIG_64BIT
+	pagefault_disable();
+	uaddr = page_address(page) + (((unsigned long) uaddr) & ~PAGE_MASK);
+#else
+	uaddr = kmap_atomic(page) + ((unsigned long) uaddr & ~PAGE_MASK);
+#endif
+
+	*uval = *uaddr;
+
+	ret = cmpxchg(uaddr, oldval, newval);
+
+#ifdef CONFIG_64BIT
+	pagefault_enable();
+#else
+	kunmap_atomic(uaddr);
+#endif
+	ret = 0;
+
+out_inatomic:
+	preempt_enable();
+	return ret;
+}
+EXPORT_SYMBOL(futex_atomic_cmpxchg_inatomic);
diff --git a/arch/um/kernel/smp.c b/arch/um/kernel/smp.c
new file mode 100644
index 000000000..f1e52b734
--- /dev/null
+++ b/arch/um/kernel/smp.c
@@ -0,0 +1,242 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2025 Ant Group
+ * Author: Tiwei Bie <tiwei.btw@antgroup.com>
+ *
+ * Based on the previous implementation in TT mode
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/sched.h>
+#include <linux/sched/task.h>
+#include <linux/sched/task_stack.h>
+#include <linux/module.h>
+#include <linux/processor.h>
+#include <linux/threads.h>
+#include <linux/cpu.h>
+#include <linux/hardirq.h>
+#include <linux/smp.h>
+#include <linux/smp-internal.h>
+#include <init.h>
+#include <kern.h>
+#include <os.h>
+#include <smp.h>
+
+enum {
+	UML_IPI_RES = 0,
+	UML_IPI_CALL_SINGLE,
+	UML_IPI_CALL,
+	UML_IPI_STOP,
+};
+
+void arch_smp_send_reschedule(int cpu)
+{
+	os_send_ipi(cpu, UML_IPI_RES);
+}
+
+void arch_send_call_function_single_ipi(int cpu)
+{
+	os_send_ipi(cpu, UML_IPI_CALL_SINGLE);
+}
+
+void arch_send_call_function_ipi_mask(const struct cpumask *mask)
+{
+	int cpu;
+
+	for_each_cpu(cpu, mask)
+		os_send_ipi(cpu, UML_IPI_CALL);
+}
+
+void smp_send_stop(void)
+{
+	int cpu, me = smp_processor_id();
+
+	for_each_online_cpu(cpu) {
+		if (cpu == me)
+			continue;
+		os_send_ipi(cpu, UML_IPI_STOP);
+	}
+}
+
+static void ipi_handler(int vector, struct uml_pt_regs *regs)
+{
+	struct pt_regs *old_regs = set_irq_regs((struct pt_regs *)regs);
+	int cpu = raw_smp_processor_id();
+
+	irq_enter();
+
+	if (current->mm)
+		os_alarm_process(current->mm->context.id.pid);
+
+	switch (vector) {
+	case UML_IPI_RES:
+		inc_irq_stat(irq_resched_count);
+		scheduler_ipi();
+		break;
+
+	case UML_IPI_CALL_SINGLE:
+		inc_irq_stat(irq_call_count);
+		generic_smp_call_function_single_interrupt();
+		break;
+
+	case UML_IPI_CALL:
+		inc_irq_stat(irq_call_count);
+		generic_smp_call_function_interrupt();
+		break;
+
+	case UML_IPI_STOP:
+		set_cpu_online(cpu, false);
+		while (1)
+			pause();
+		break;
+
+	default:
+		pr_err("CPU#%d received unknown IPI (vector=%d)!\n", cpu, vector);
+		break;
+	}
+
+	irq_exit();
+	set_irq_regs(old_regs);
+}
+
+void uml_ipi_handler(int vector)
+{
+	struct uml_pt_regs r = { .is_user = 0 };
+
+	preempt_disable();
+	ipi_handler(vector, &r);
+	preempt_enable();
+}
+
+/* AP states used only during CPU startup */
+enum {
+	UML_CPU_PAUSED = 0,
+	UML_CPU_RUNNING,
+};
+
+static int cpu_states[NR_CPUS];
+
+static int start_secondary(void *unused)
+{
+	int err, cpu = raw_smp_processor_id();
+
+	notify_cpu_starting(cpu);
+	set_cpu_online(cpu, true);
+
+	err = um_setup_timer();
+	if (err)
+		panic("CPU#%d failed to setup timer, err = %d", cpu, err);
+
+	local_irq_enable();
+
+	cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
+
+	return 0;
+}
+
+void uml_start_secondary(void *opaque)
+{
+	int cpu = raw_smp_processor_id();
+	struct mm_struct *mm = &init_mm;
+	struct task_struct *idle;
+
+	stack_protections((unsigned long) &cpu_irqstacks[cpu]);
+	set_sigstack(&cpu_irqstacks[cpu], THREAD_SIZE);
+
+	set_cpu_present(cpu, true);
+	os_futex_wait(&cpu_states[cpu], UML_CPU_PAUSED);
+
+	smp_rmb(); /* paired with smp_wmb() in __cpu_up() */
+
+	idle = cpu_tasks[cpu];
+	idle->thread_info.cpu = cpu;
+
+	mmgrab(mm);
+	idle->active_mm = mm;
+
+	idle->thread.request.thread.proc = start_secondary;
+	idle->thread.request.thread.arg = NULL;
+
+	new_thread(task_stack_page(idle), &idle->thread.switch_buf,
+		   new_thread_handler);
+	os_start_secondary(opaque, &idle->thread.switch_buf);
+}
+
+void __init smp_prepare_cpus(unsigned int max_cpus)
+{
+	int err, cpu, me = smp_processor_id();
+	unsigned long deadline;
+
+	os_init_smp();
+
+	for_each_possible_cpu(cpu) {
+		if (cpu == me)
+			continue;
+
+		pr_debug("Booting processor %d...\n", cpu);
+		err = os_start_cpu_thread(cpu);
+		if (err) {
+			pr_crit("CPU#%d failed to start cpu thread, err = %d",
+				cpu, err);
+			continue;
+		}
+
+		deadline = jiffies + msecs_to_jiffies(1000);
+		spin_until_cond(cpu_present(cpu) ||
+				time_is_before_jiffies(deadline));
+
+		if (!cpu_present(cpu))
+			pr_crit("CPU#%d failed to boot\n", cpu);
+	}
+}
+
+int __cpu_up(unsigned int cpu, struct task_struct *tidle)
+{
+	cpu_tasks[cpu] = tidle;
+	smp_wmb(); /* paired with smp_rmb() in uml_start_secondary() */
+	cpu_states[cpu] = UML_CPU_RUNNING;
+	os_futex_wake(&cpu_states[cpu]);
+	spin_until_cond(cpu_online(cpu));
+
+	return 0;
+}
+
+void __init smp_cpus_done(unsigned int max_cpus)
+{
+}
+
+/* Set in uml_ncpus_setup */
+int uml_ncpus = 1;
+
+void __init prefill_possible_map(void)
+{
+	int cpu;
+
+	for (cpu = 0; cpu < uml_ncpus; cpu++)
+		set_cpu_possible(cpu, true);
+	for (; cpu < NR_CPUS; cpu++)
+		set_cpu_possible(cpu, false);
+}
+
+static int __init uml_ncpus_setup(char *line, int *add)
+{
+	*add = 0;
+
+	if (kstrtoint(line, 10, &uml_ncpus)) {
+		os_warn("%s: Couldn't parse '%s'\n", __func__, line);
+		return -1;
+	}
+
+	uml_ncpus = clamp(uml_ncpus, 1, NR_CPUS);
+
+	return 0;
+}
+
+__uml_setup("ncpus=", uml_ncpus_setup,
+"ncpus=<# of desired CPUs>\n"
+"    This tells UML how many virtual processors to start. The maximum\n"
+"    number of supported virtual processors can be obtained by querying\n"
+"    the CONFIG_NR_CPUS option using --showconfig.\n\n"
+);
+
+EXPORT_SYMBOL(uml_curr_cpu);
diff --git a/arch/um/kernel/stacktrace.c b/arch/um/kernel/stacktrace.c
new file mode 100644
index 000000000..fd3b61b3d
--- /dev/null
+++ b/arch/um/kernel/stacktrace.c
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Copyright (C) 2013 Richard Weinberger <richard@nod.at>
+ * Copyright (C) 2014 Google Inc., Author: Daniel Walter <dwalter@google.com>
+ */
+
+#include <linux/kallsyms.h>
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/stacktrace.h>
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <asm/stacktrace.h>
+
+void dump_trace(struct task_struct *tsk,
+		const struct stacktrace_ops *ops,
+		void *data)
+{
+	int reliable = 0;
+	unsigned long *sp, bp, addr;
+	struct pt_regs *segv_regs = tsk->thread.segv_regs;
+	struct stack_frame *frame;
+
+	bp = get_frame_pointer(tsk, segv_regs);
+	sp = get_stack_pointer(tsk, segv_regs);
+
+	frame = (struct stack_frame *)bp;
+	while (((long) sp & (THREAD_SIZE-1)) != 0) {
+		addr = READ_ONCE_NOCHECK(*sp);
+		if (__kernel_text_address(addr)) {
+			reliable = 0;
+			if ((unsigned long) sp == bp + sizeof(long)) {
+				frame = frame ? frame->next_frame : NULL;
+				bp = (unsigned long)frame;
+				reliable = 1;
+			}
+			ops->address(data, addr, reliable);
+		}
+		sp++;
+	}
+}
+
+static void save_addr(void *data, unsigned long address, int reliable)
+{
+	struct stack_trace *trace = data;
+
+	if (!reliable)
+		return;
+	if (trace->nr_entries >= trace->max_entries)
+		return;
+
+	trace->entries[trace->nr_entries++] = address;
+}
+
+static const struct stacktrace_ops dump_ops = {
+	.address = save_addr
+};
+
+static void __save_stack_trace(struct task_struct *tsk, struct stack_trace *trace)
+{
+	dump_trace(tsk, &dump_ops, trace);
+}
+
+void save_stack_trace(struct stack_trace *trace)
+{
+	__save_stack_trace(current, trace);
+}
+EXPORT_SYMBOL_GPL(save_stack_trace);
+
+void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
+{
+	__save_stack_trace(tsk, trace);
+}
+EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
diff --git a/arch/um/kernel/sysrq.c b/arch/um/kernel/sysrq.c
new file mode 100644
index 000000000..13ee56666
--- /dev/null
+++ b/arch/um/kernel/sysrq.c
@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Copyright (C) 2013 Richard Weinberger <richrd@nod.at>
+ */
+
+#include <linux/kallsyms.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/sched/debug.h>
+#include <linux/sched/task_stack.h>
+
+#include <asm/stacktrace.h>
+#include <os.h>
+
+static void _print_addr(void *data, unsigned long address, int reliable)
+{
+	const char *loglvl = data;
+
+	printk("%s [<%08lx>] %s%pS\n", loglvl, address, reliable ? "" : "? ",
+		(void *)address);
+}
+
+static const struct stacktrace_ops stackops = {
+	.address = _print_addr
+};
+
+void show_stack(struct task_struct *task, unsigned long *stack,
+		       const char *loglvl)
+{
+	struct pt_regs *segv_regs = current->thread.segv_regs;
+	int i;
+
+	if (!stack)
+		stack = get_stack_pointer(task, segv_regs);
+
+	printk("%sStack:\n", loglvl);
+	for (i = 0; i < 3 * STACKSLOTS_PER_LINE; i++) {
+		if (kstack_end(stack))
+			break;
+		if (i && ((i % STACKSLOTS_PER_LINE) == 0))
+			pr_cont("\n");
+		pr_cont(" %08lx", READ_ONCE_NOCHECK(*stack));
+		stack++;
+	}
+
+	printk("%sCall Trace:\n", loglvl);
+	dump_trace(task ?: current, &stackops, (void *)loglvl);
+}
diff --git a/arch/um/kernel/time.c b/arch/um/kernel/time.c
new file mode 100644
index 000000000..b344a36b4
--- /dev/null
+++ b/arch/um/kernel/time.c
@@ -0,0 +1,1092 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
+ * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
+ * Copyright (C) 2012-2014 Cisco Systems
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Copyright (C) 2019 Intel Corporation
+ */
+
+#include <linux/clockchips.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/jiffies.h>
+#include <linux/mm.h>
+#include <linux/sched.h>
+#include <linux/spinlock.h>
+#include <linux/threads.h>
+#include <asm/irq.h>
+#include <asm/param.h>
+#include <kern_util.h>
+#include <os.h>
+#include <linux/delay.h>
+#include <linux/time-internal.h>
+#include <linux/um_timetravel.h>
+#include <shared/init.h>
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+#include <linux/sched/clock.h>
+
+enum time_travel_mode time_travel_mode;
+EXPORT_SYMBOL_GPL(time_travel_mode);
+
+static bool time_travel_start_set;
+static unsigned long long time_travel_start;
+static unsigned long long time_travel_time;
+static unsigned long long time_travel_shm_offset;
+static LIST_HEAD(time_travel_events);
+static LIST_HEAD(time_travel_irqs);
+static unsigned long long time_travel_timer_interval;
+static unsigned long long time_travel_next_event;
+static struct time_travel_event time_travel_timer_event;
+static int time_travel_ext_fd = -1;
+static unsigned int time_travel_ext_waiting;
+static bool time_travel_ext_prev_request_valid;
+static unsigned long long time_travel_ext_prev_request;
+static unsigned long long *time_travel_ext_free_until;
+static unsigned long long _time_travel_ext_free_until;
+static u16 time_travel_shm_id;
+static struct um_timetravel_schedshm *time_travel_shm;
+static union um_timetravel_schedshm_client *time_travel_shm_client;
+
+unsigned long tt_extra_sched_jiffies;
+
+notrace unsigned long long sched_clock(void)
+{
+	return (unsigned long long)(jiffies - INITIAL_JIFFIES +
+				    tt_extra_sched_jiffies)
+					* (NSEC_PER_SEC / HZ);
+}
+
+static void time_travel_set_time(unsigned long long ns)
+{
+	if (unlikely(ns < time_travel_time))
+		panic("time-travel: time goes backwards %lld -> %lld\n",
+		      time_travel_time, ns);
+	else if (unlikely(ns >= S64_MAX))
+		panic("The system was going to sleep forever, aborting");
+
+	time_travel_time = ns;
+}
+
+enum time_travel_message_handling {
+	TTMH_IDLE,
+	TTMH_POLL,
+	TTMH_READ,
+	TTMH_READ_START_ACK,
+};
+
+static u64 bc_message;
+int time_travel_should_print_bc_msg;
+
+void _time_travel_print_bc_msg(void)
+{
+	time_travel_should_print_bc_msg = 0;
+	printk(KERN_INFO "time-travel: received broadcast 0x%llx\n", bc_message);
+}
+
+static void time_travel_setup_shm(int fd, u16 id)
+{
+	u32 len;
+
+	time_travel_shm = os_mmap_rw_shared(fd, sizeof(*time_travel_shm));
+
+	if (!time_travel_shm)
+		goto out;
+
+	len = time_travel_shm->len;
+
+	if (time_travel_shm->version != UM_TIMETRAVEL_SCHEDSHM_VERSION ||
+	    len < struct_size(time_travel_shm, clients, id + 1)) {
+		os_unmap_memory(time_travel_shm, sizeof(*time_travel_shm));
+		time_travel_shm = NULL;
+		goto out;
+	}
+
+	time_travel_shm = os_mremap_rw_shared(time_travel_shm,
+					      sizeof(*time_travel_shm),
+					      len);
+	if (!time_travel_shm)
+		goto out;
+
+	time_travel_shm_offset = time_travel_shm->current_time;
+	time_travel_shm_client = &time_travel_shm->clients[id];
+	time_travel_shm_client->capa |= UM_TIMETRAVEL_SCHEDSHM_CAP_TIME_SHARE;
+	time_travel_shm_id = id;
+	/* always look at that free_until from now on */
+	time_travel_ext_free_until = &time_travel_shm->free_until;
+out:
+	os_close_file(fd);
+}
+
+static void time_travel_handle_message(struct um_timetravel_msg *msg,
+				       enum time_travel_message_handling mode)
+{
+	struct um_timetravel_msg resp = {
+		.op = UM_TIMETRAVEL_ACK,
+	};
+	int ret;
+
+	/*
+	 * We can't unlock here, but interrupt signals with a timetravel_handler
+	 * (see um_request_irq_tt) get to the timetravel_handler anyway.
+	 */
+	if (mode != TTMH_READ) {
+		BUG_ON(mode == TTMH_IDLE && !irqs_disabled());
+
+		while (os_poll(1, &time_travel_ext_fd) != 0) {
+			/* nothing */
+		}
+	}
+
+	if (unlikely(mode == TTMH_READ_START_ACK)) {
+		int fd[UM_TIMETRAVEL_SHARED_MAX_FDS];
+
+		ret = os_rcv_fd_msg(time_travel_ext_fd, fd,
+				    ARRAY_SIZE(fd), msg, sizeof(*msg));
+		if (ret == sizeof(*msg)) {
+			time_travel_setup_shm(fd[UM_TIMETRAVEL_SHARED_MEMFD],
+					      msg->time & UM_TIMETRAVEL_START_ACK_ID);
+			/* we don't use the logging for now */
+			os_close_file(fd[UM_TIMETRAVEL_SHARED_LOGFD]);
+		}
+	} else {
+		ret = os_read_file(time_travel_ext_fd, msg, sizeof(*msg));
+	}
+
+	if (ret == 0)
+		panic("time-travel external link is broken\n");
+	if (ret != sizeof(*msg))
+		panic("invalid time-travel message - %d bytes\n", ret);
+
+	switch (msg->op) {
+	default:
+		WARN_ONCE(1, "time-travel: unexpected message %lld\n",
+			  (unsigned long long)msg->op);
+		break;
+	case UM_TIMETRAVEL_ACK:
+		return;
+	case UM_TIMETRAVEL_RUN:
+		time_travel_set_time(msg->time);
+		if (time_travel_shm) {
+			/* no request right now since we're running */
+			time_travel_shm_client->flags &=
+				~UM_TIMETRAVEL_SCHEDSHM_FLAGS_REQ_RUN;
+			/* no ack for shared memory RUN */
+			return;
+		}
+		break;
+	case UM_TIMETRAVEL_FREE_UNTIL:
+		/* not supposed to get this with shm, but ignore it */
+		if (time_travel_shm)
+			break;
+		time_travel_ext_free_until = &_time_travel_ext_free_until;
+		_time_travel_ext_free_until = msg->time;
+		break;
+	case UM_TIMETRAVEL_BROADCAST:
+		bc_message = msg->time;
+		time_travel_should_print_bc_msg = 1;
+		break;
+	}
+
+	resp.seq = msg->seq;
+	os_write_file(time_travel_ext_fd, &resp, sizeof(resp));
+}
+
+static u64 time_travel_ext_req(u32 op, u64 time)
+{
+	static int seq;
+	int mseq = ++seq;
+	struct um_timetravel_msg msg = {
+		.op = op,
+		.time = time,
+		.seq = mseq,
+	};
+
+	/*
+	 * We need to block even the timetravel handlers of SIGIO here and
+	 * only restore their use when we got the ACK - otherwise we may
+	 * (will) get interrupted by that, try to queue the IRQ for future
+	 * processing and thus send another request while we're still waiting
+	 * for an ACK, but the peer doesn't know we got interrupted and will
+	 * send the ACKs in the same order as the message, but we'd need to
+	 * see them in the opposite order ...
+	 *
+	 * This wouldn't matter *too* much, but some ACKs carry the
+	 * current time (for UM_TIMETRAVEL_GET) and getting another
+	 * ACK without a time would confuse us a lot!
+	 *
+	 * The sequence number assignment that happens here lets us
+	 * debug such message handling issues more easily.
+	 */
+	block_signals_hard();
+	os_write_file(time_travel_ext_fd, &msg, sizeof(msg));
+
+	/* no ACK expected for WAIT in shared memory mode */
+	if (msg.op == UM_TIMETRAVEL_WAIT && time_travel_shm)
+		goto done;
+
+	while (msg.op != UM_TIMETRAVEL_ACK)
+		time_travel_handle_message(&msg,
+					   op == UM_TIMETRAVEL_START ?
+						TTMH_READ_START_ACK :
+						TTMH_READ);
+
+	if (msg.seq != mseq)
+		panic("time-travel: ACK message has different seqno! op=%d, seq=%d != %d time=%lld\n",
+		      msg.op, msg.seq, mseq, msg.time);
+
+	if (op == UM_TIMETRAVEL_GET)
+		time_travel_set_time(msg.time);
+done:
+	unblock_signals_hard();
+
+	return msg.time;
+}
+
+void __time_travel_wait_readable(int fd)
+{
+	int fds[2] = { fd, time_travel_ext_fd };
+	int ret;
+
+	if (time_travel_mode != TT_MODE_EXTERNAL)
+		return;
+
+	while ((ret = os_poll(2, fds))) {
+		struct um_timetravel_msg msg;
+
+		if (ret == 1)
+			time_travel_handle_message(&msg, TTMH_READ);
+	}
+}
+EXPORT_SYMBOL_GPL(__time_travel_wait_readable);
+
+static void time_travel_ext_update_request(unsigned long long time)
+{
+	if (time_travel_mode != TT_MODE_EXTERNAL)
+		return;
+
+	/* asked for exactly this time previously */
+	if (time_travel_ext_prev_request_valid &&
+	    time == time_travel_ext_prev_request)
+		return;
+
+	/*
+	 * if we're running and are allowed to run past the request
+	 * then we don't need to update it either
+	 *
+	 * Note for shm we ignore FREE_UNTIL messages and leave the pointer
+	 * to shared memory, and for non-shm the offset is 0.
+	 */
+	if (!time_travel_ext_waiting && time_travel_ext_free_until &&
+	    time < (*time_travel_ext_free_until - time_travel_shm_offset))
+		return;
+
+	time_travel_ext_prev_request = time;
+	time_travel_ext_prev_request_valid = true;
+
+	if (time_travel_shm) {
+		union um_timetravel_schedshm_client *running;
+
+		running = &time_travel_shm->clients[time_travel_shm->running_id];
+
+		if (running->capa & UM_TIMETRAVEL_SCHEDSHM_CAP_TIME_SHARE) {
+			time_travel_shm_client->flags |=
+				UM_TIMETRAVEL_SCHEDSHM_FLAGS_REQ_RUN;
+			time += time_travel_shm_offset;
+			time_travel_shm_client->req_time = time;
+			if (time < time_travel_shm->free_until)
+				time_travel_shm->free_until = time;
+			return;
+		}
+	}
+
+	time_travel_ext_req(UM_TIMETRAVEL_REQUEST, time);
+}
+
+void __time_travel_propagate_time(void)
+{
+	static unsigned long long last_propagated;
+
+	if (time_travel_shm) {
+		if (time_travel_shm->running_id != time_travel_shm_id)
+			panic("time-travel: setting time while not running\n");
+		time_travel_shm->current_time = time_travel_time +
+						time_travel_shm_offset;
+		return;
+	}
+
+	if (last_propagated == time_travel_time)
+		return;
+
+	time_travel_ext_req(UM_TIMETRAVEL_UPDATE, time_travel_time);
+	last_propagated = time_travel_time;
+}
+EXPORT_SYMBOL_GPL(__time_travel_propagate_time);
+
+/* returns true if we must do a wait to the simtime device */
+static bool time_travel_ext_request(unsigned long long time)
+{
+	/*
+	 * If we received an external sync point ("free until") then we
+	 * don't have to request/wait for anything until then, unless
+	 * we're already waiting.
+	 *
+	 * Note for shm we ignore FREE_UNTIL messages and leave the pointer
+	 * to shared memory, and for non-shm the offset is 0.
+	 */
+	if (!time_travel_ext_waiting && time_travel_ext_free_until &&
+	    time < (*time_travel_ext_free_until - time_travel_shm_offset))
+		return false;
+
+	time_travel_ext_update_request(time);
+	return true;
+}
+
+static void time_travel_ext_wait(bool idle)
+{
+	struct um_timetravel_msg msg = {
+		.op = UM_TIMETRAVEL_ACK,
+	};
+
+	time_travel_ext_prev_request_valid = false;
+	if (!time_travel_shm)
+		time_travel_ext_free_until = NULL;
+	time_travel_ext_waiting++;
+
+	time_travel_ext_req(UM_TIMETRAVEL_WAIT, -1);
+
+	/*
+	 * Here we are deep in the idle loop, so we have to break out of the
+	 * kernel abstraction in a sense and implement this in terms of the
+	 * UML system waiting on the VQ interrupt while sleeping, when we get
+	 * the signal it'll call time_travel_ext_vq_notify_done() completing the
+	 * call.
+	 */
+	while (msg.op != UM_TIMETRAVEL_RUN)
+		time_travel_handle_message(&msg, idle ? TTMH_IDLE : TTMH_POLL);
+
+	time_travel_ext_waiting--;
+
+	/* we might request more stuff while polling - reset when we run */
+	time_travel_ext_prev_request_valid = false;
+}
+
+static void time_travel_ext_get_time(void)
+{
+	if (time_travel_shm)
+		time_travel_set_time(time_travel_shm->current_time -
+				     time_travel_shm_offset);
+	else
+		time_travel_ext_req(UM_TIMETRAVEL_GET, -1);
+}
+
+static void __time_travel_update_time(unsigned long long ns, bool idle)
+{
+	if (time_travel_mode == TT_MODE_EXTERNAL && time_travel_ext_request(ns))
+		time_travel_ext_wait(idle);
+	else
+		time_travel_set_time(ns);
+}
+
+static struct time_travel_event *time_travel_first_event(void)
+{
+	return list_first_entry_or_null(&time_travel_events,
+					struct time_travel_event,
+					list);
+}
+
+static void __time_travel_add_event(struct time_travel_event *e,
+				    unsigned long long time)
+{
+	struct time_travel_event *tmp;
+	bool inserted = false;
+	unsigned long flags;
+
+	if (e->pending)
+		return;
+
+	e->pending = true;
+	e->time = time;
+
+	local_irq_save(flags);
+	list_for_each_entry(tmp, &time_travel_events, list) {
+		/*
+		 * Add the new entry before one with higher time,
+		 * or if they're equal and both on stack, because
+		 * in that case we need to unwind the stack in the
+		 * right order, and the later event (timer sleep
+		 * or such) must be dequeued first.
+		 */
+		if ((tmp->time > e->time) ||
+		    (tmp->time == e->time && tmp->onstack && e->onstack)) {
+			list_add_tail(&e->list, &tmp->list);
+			inserted = true;
+			break;
+		}
+	}
+
+	if (!inserted)
+		list_add_tail(&e->list, &time_travel_events);
+
+	tmp = time_travel_first_event();
+	time_travel_ext_update_request(tmp->time);
+	time_travel_next_event = tmp->time;
+	local_irq_restore(flags);
+}
+
+static void time_travel_add_event(struct time_travel_event *e,
+				  unsigned long long time)
+{
+	if (WARN_ON(!e->fn))
+		return;
+
+	__time_travel_add_event(e, time);
+}
+
+void time_travel_add_event_rel(struct time_travel_event *e,
+			       unsigned long long delay_ns)
+{
+	time_travel_add_event(e, time_travel_time + delay_ns);
+}
+
+static void time_travel_periodic_timer(struct time_travel_event *e)
+{
+	time_travel_add_event(&time_travel_timer_event,
+			      time_travel_time + time_travel_timer_interval);
+
+	/* clock tick; decrease extra jiffies by keeping sched_clock constant */
+	if (tt_extra_sched_jiffies > 0)
+		tt_extra_sched_jiffies -= 1;
+
+	deliver_alarm();
+}
+
+void deliver_time_travel_irqs(void)
+{
+	struct time_travel_event *e;
+	unsigned long flags;
+
+	/*
+	 * Don't do anything for most cases. Note that because here we have
+	 * to disable IRQs (and re-enable later) we'll actually recurse at
+	 * the end of the function, so this is strictly necessary.
+	 */
+	if (likely(list_empty(&time_travel_irqs)))
+		return;
+
+	local_irq_save(flags);
+	irq_enter();
+	while ((e = list_first_entry_or_null(&time_travel_irqs,
+					     struct time_travel_event,
+					     list))) {
+		list_del(&e->list);
+		e->pending = false;
+		e->fn(e);
+	}
+	irq_exit();
+	local_irq_restore(flags);
+}
+
+static void time_travel_deliver_event(struct time_travel_event *e)
+{
+	if (e == &time_travel_timer_event) {
+		/*
+		 * deliver_alarm() does the irq_enter/irq_exit
+		 * by itself, so must handle it specially here
+		 */
+		e->fn(e);
+	} else if (irqs_disabled()) {
+		list_add_tail(&e->list, &time_travel_irqs);
+		/*
+		 * set pending again, it was set to false when the
+		 * event was deleted from the original list, but
+		 * now it's still pending until we deliver the IRQ.
+		 */
+		e->pending = true;
+	} else {
+		unsigned long flags;
+
+		local_irq_save(flags);
+		irq_enter();
+		e->fn(e);
+		irq_exit();
+		local_irq_restore(flags);
+	}
+}
+
+bool time_travel_del_event(struct time_travel_event *e)
+{
+	unsigned long flags;
+
+	if (!e->pending)
+		return false;
+	local_irq_save(flags);
+	list_del(&e->list);
+	e->pending = false;
+	local_irq_restore(flags);
+	return true;
+}
+
+static void time_travel_update_time(unsigned long long next, bool idle)
+{
+	struct time_travel_event ne = {
+		.onstack = true,
+	};
+	struct time_travel_event *e;
+	bool finished = idle;
+
+	/* add it without a handler - we deal with that specifically below */
+	__time_travel_add_event(&ne, next);
+
+	do {
+		e = time_travel_first_event();
+
+		BUG_ON(!e);
+		__time_travel_update_time(e->time, idle);
+
+		/* new events may have been inserted while we were waiting */
+		if (e == time_travel_first_event()) {
+			BUG_ON(!time_travel_del_event(e));
+			BUG_ON(time_travel_time != e->time);
+
+			if (e == &ne) {
+				finished = true;
+			} else {
+				if (e->onstack)
+					panic("On-stack event dequeued outside of the stack! time=%lld, event time=%lld, event=%pS\n",
+					      time_travel_time, e->time, e);
+				time_travel_deliver_event(e);
+			}
+		}
+
+		e = time_travel_first_event();
+		if (e)
+			time_travel_ext_update_request(e->time);
+	} while (ne.pending && !finished);
+
+	time_travel_del_event(&ne);
+}
+
+static void time_travel_update_time_rel(unsigned long long offs)
+{
+	unsigned long flags;
+
+	/*
+	 * Disable interrupts before calculating the new time so
+	 * that a real timer interrupt (signal) can't happen at
+	 * a bad time e.g. after we read time_travel_time but
+	 * before we've completed updating the time.
+	 */
+	local_irq_save(flags);
+	time_travel_update_time(time_travel_time + offs, false);
+	local_irq_restore(flags);
+}
+
+void time_travel_ndelay(unsigned long nsec)
+{
+	/*
+	 * Not strictly needed to use _rel() version since this is
+	 * only used in INFCPU/EXT modes, but it doesn't hurt and
+	 * is more readable too.
+	 */
+	time_travel_update_time_rel(nsec);
+}
+EXPORT_SYMBOL(time_travel_ndelay);
+
+void time_travel_add_irq_event(struct time_travel_event *e)
+{
+	BUG_ON(time_travel_mode != TT_MODE_EXTERNAL);
+
+	time_travel_ext_get_time();
+	/*
+	 * We could model interrupt latency here, for now just
+	 * don't have any latency at all and request the exact
+	 * same time (again) to run the interrupt...
+	 */
+	time_travel_add_event(e, time_travel_time);
+}
+EXPORT_SYMBOL_GPL(time_travel_add_irq_event);
+
+static void time_travel_oneshot_timer(struct time_travel_event *e)
+{
+	/* clock tick; decrease extra jiffies by keeping sched_clock constant */
+	if (tt_extra_sched_jiffies > 0)
+		tt_extra_sched_jiffies -= 1;
+
+	deliver_alarm();
+}
+
+void time_travel_sleep(void)
+{
+	/*
+	 * Wait "forever" (using S64_MAX because there are some potential
+	 * wrapping issues, especially with the current TT_MODE_EXTERNAL
+	 * controller application.
+	 */
+	unsigned long long next = S64_MAX;
+	int cpu = raw_smp_processor_id();
+
+	if (time_travel_mode == TT_MODE_BASIC)
+		os_timer_disable(cpu);
+
+	time_travel_update_time(next, true);
+
+	if (time_travel_mode == TT_MODE_BASIC &&
+	    time_travel_timer_event.pending) {
+		if (time_travel_timer_event.fn == time_travel_periodic_timer) {
+			/*
+			 * This is somewhat wrong - we should get the first
+			 * one sooner like the os_timer_one_shot() below...
+			 */
+			os_timer_set_interval(cpu, time_travel_timer_interval);
+		} else {
+			os_timer_one_shot(cpu, time_travel_timer_event.time - next);
+		}
+	}
+}
+
+static void time_travel_handle_real_alarm(void)
+{
+	time_travel_set_time(time_travel_next_event);
+
+	time_travel_del_event(&time_travel_timer_event);
+
+	if (time_travel_timer_event.fn == time_travel_periodic_timer)
+		time_travel_add_event(&time_travel_timer_event,
+				      time_travel_time +
+				      time_travel_timer_interval);
+}
+
+static void time_travel_set_interval(unsigned long long interval)
+{
+	time_travel_timer_interval = interval;
+}
+
+static int time_travel_connect_external(const char *socket)
+{
+	const char *sep;
+	unsigned long long id = (unsigned long long)-1;
+	int rc;
+
+	if ((sep = strchr(socket, ':'))) {
+		char buf[25] = {};
+		if (sep - socket > sizeof(buf) - 1)
+			goto invalid_number;
+
+		memcpy(buf, socket, sep - socket);
+		if (kstrtoull(buf, 0, &id)) {
+invalid_number:
+			panic("time-travel: invalid external ID in string '%s'\n",
+			      socket);
+			return -EINVAL;
+		}
+
+		socket = sep + 1;
+	}
+
+	rc = os_connect_socket(socket);
+	if (rc < 0) {
+		panic("time-travel: failed to connect to external socket %s\n",
+		      socket);
+		return rc;
+	}
+
+	time_travel_ext_fd = rc;
+
+	time_travel_ext_req(UM_TIMETRAVEL_START, id);
+
+	return 1;
+}
+
+static void time_travel_set_start(void)
+{
+	if (time_travel_start_set)
+		return;
+
+	switch (time_travel_mode) {
+	case TT_MODE_EXTERNAL:
+		time_travel_start = time_travel_ext_req(UM_TIMETRAVEL_GET_TOD, -1);
+		/* controller gave us the *current* time, so adjust by that */
+		time_travel_ext_get_time();
+		time_travel_start -= time_travel_time;
+		break;
+	case TT_MODE_INFCPU:
+	case TT_MODE_BASIC:
+		if (!time_travel_start_set)
+			time_travel_start = os_persistent_clock_emulation();
+		break;
+	case TT_MODE_OFF:
+		/* we just read the host clock with os_persistent_clock_emulation() */
+		break;
+	}
+
+	time_travel_start_set = true;
+}
+#else /* CONFIG_UML_TIME_TRAVEL_SUPPORT */
+#define time_travel_start_set 0
+#define time_travel_start 0
+#define time_travel_time 0
+#define time_travel_ext_waiting 0
+
+static inline void time_travel_update_time(unsigned long long ns, bool idle)
+{
+}
+
+static inline void time_travel_update_time_rel(unsigned long long offs)
+{
+}
+
+static inline void time_travel_handle_real_alarm(void)
+{
+}
+
+static void time_travel_set_interval(unsigned long long interval)
+{
+}
+
+static inline void time_travel_set_start(void)
+{
+}
+
+/* fail link if this actually gets used */
+extern u64 time_travel_ext_req(u32 op, u64 time);
+
+/* these are empty macros so the struct/fn need not exist */
+#define time_travel_add_event(e, time) do { } while (0)
+/* externally not usable - redefine here so we can */
+#undef time_travel_del_event
+#define time_travel_del_event(e) do { } while (0)
+#endif
+
+static struct clock_event_device timer_clockevent[NR_CPUS];
+
+void timer_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
+{
+	unsigned long flags;
+
+	/*
+	 * In basic time-travel mode we still get real interrupts
+	 * (signals) but since we don't read time from the OS, we
+	 * must update the simulated time here to the expiry when
+	 * we get a signal.
+	 * This is not the case in inf-cpu mode, since there we
+	 * never get any real signals from the OS.
+	 */
+	if (time_travel_mode == TT_MODE_BASIC)
+		time_travel_handle_real_alarm();
+
+	local_irq_save(flags);
+	do_IRQ(TIMER_IRQ, regs);
+	local_irq_restore(flags);
+}
+
+static int itimer_shutdown(struct clock_event_device *evt)
+{
+	int cpu = evt - &timer_clockevent[0];
+
+	if (time_travel_mode != TT_MODE_OFF)
+		time_travel_del_event(&time_travel_timer_event);
+
+	if (time_travel_mode != TT_MODE_INFCPU &&
+	    time_travel_mode != TT_MODE_EXTERNAL)
+		os_timer_disable(cpu);
+
+	return 0;
+}
+
+static int itimer_set_periodic(struct clock_event_device *evt)
+{
+	unsigned long long interval = NSEC_PER_SEC / HZ;
+	int cpu = evt - &timer_clockevent[0];
+
+	if (time_travel_mode != TT_MODE_OFF) {
+		time_travel_del_event(&time_travel_timer_event);
+		time_travel_set_event_fn(&time_travel_timer_event,
+					 time_travel_periodic_timer);
+		time_travel_set_interval(interval);
+		time_travel_add_event(&time_travel_timer_event,
+				      time_travel_time + interval);
+	}
+
+	if (time_travel_mode != TT_MODE_INFCPU &&
+	    time_travel_mode != TT_MODE_EXTERNAL)
+		os_timer_set_interval(cpu, interval);
+
+	return 0;
+}
+
+static int itimer_next_event(unsigned long delta,
+			     struct clock_event_device *evt)
+{
+	delta += 1;
+
+	if (time_travel_mode != TT_MODE_OFF) {
+		time_travel_del_event(&time_travel_timer_event);
+		time_travel_set_event_fn(&time_travel_timer_event,
+					 time_travel_oneshot_timer);
+		time_travel_add_event(&time_travel_timer_event,
+				      time_travel_time + delta);
+	}
+
+	if (time_travel_mode != TT_MODE_INFCPU &&
+	    time_travel_mode != TT_MODE_EXTERNAL)
+		return os_timer_one_shot(raw_smp_processor_id(), delta);
+
+	return 0;
+}
+
+static int itimer_one_shot(struct clock_event_device *evt)
+{
+	return itimer_next_event(0, evt);
+}
+
+static struct clock_event_device _timer_clockevent = {
+	.name			= "posix-timer",
+	.rating			= 250,
+	.features		= CLOCK_EVT_FEAT_PERIODIC |
+				  CLOCK_EVT_FEAT_ONESHOT,
+	.set_state_shutdown	= itimer_shutdown,
+	.set_state_periodic	= itimer_set_periodic,
+	.set_state_oneshot	= itimer_one_shot,
+	.set_next_event		= itimer_next_event,
+	.shift			= 0,
+	.max_delta_ns		= 0xffffffff,
+	.max_delta_ticks	= 0xffffffff,
+	.min_delta_ns		= TIMER_MIN_DELTA,
+	.min_delta_ticks	= TIMER_MIN_DELTA, // microsecond resolution should be enough for anyone, same as 640K RAM
+	.irq			= 0,
+	.mult			= 1,
+};
+
+static irqreturn_t um_timer(int irq, void *dev)
+{
+	int cpu = raw_smp_processor_id();
+	struct clock_event_device *evt = &timer_clockevent[cpu];
+
+	/*
+	 * Interrupt the (possibly) running userspace process, technically this
+	 * should only happen if userspace is currently executing.
+	 * With infinite CPU time-travel, we can only get here when userspace
+	 * is not executing. Do not notify there and avoid spurious scheduling.
+	 */
+	if (time_travel_mode != TT_MODE_INFCPU &&
+	    time_travel_mode != TT_MODE_EXTERNAL &&
+	    get_current()->mm)
+		os_alarm_process(get_current()->mm->context.id.pid);
+
+	evt->event_handler(evt);
+
+	return IRQ_HANDLED;
+}
+
+static u64 timer_read(struct clocksource *cs)
+{
+	if (time_travel_mode != TT_MODE_OFF) {
+		/*
+		 * We make reading the timer cost a bit so that we don't get
+		 * stuck in loops that expect time to move more than the
+		 * exact requested sleep amount, e.g. python's socket server,
+		 * see https://bugs.python.org/issue37026.
+		 *
+		 * However, don't do that when we're in interrupt or such as
+		 * then we might recurse into our own processing, and get to
+		 * even more waiting, and that's not good - it messes up the
+		 * "what do I do next" and onstack event we use to know when
+		 * to return from time_travel_update_time().
+		 */
+		if (!irqs_disabled() && !in_interrupt() && !in_softirq() &&
+		    !time_travel_ext_waiting)
+			time_travel_update_time_rel(TIMER_MULTIPLIER);
+		return time_travel_time / TIMER_MULTIPLIER;
+	}
+
+	return os_nsecs() / TIMER_MULTIPLIER;
+}
+
+static struct clocksource timer_clocksource = {
+	.name		= "timer",
+	.rating		= 300,
+	.read		= timer_read,
+	.mask		= CLOCKSOURCE_MASK(64),
+	.flags		= CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
+int um_setup_timer(void)
+{
+	int cpu = raw_smp_processor_id();
+	struct clock_event_device *evt = &timer_clockevent[cpu];
+	int err;
+
+	err = os_timer_create();
+	if (err)
+		return err;
+
+	memcpy(evt, &_timer_clockevent, sizeof(*evt));
+	evt->cpumask = cpumask_of(cpu);
+	clockevents_register_device(evt);
+
+	return 0;
+}
+
+static void __init um_timer_init(void)
+{
+	int err;
+
+	err = request_irq(TIMER_IRQ, um_timer, IRQF_TIMER, "hr timer", NULL);
+	if (err != 0)
+		printk(KERN_ERR "register_timer : request_irq failed - "
+		       "errno = %d\n", -err);
+
+	err = um_setup_timer();
+	if (err) {
+		printk(KERN_ERR "creation of timer failed - errno = %d\n", -err);
+		return;
+	}
+
+	err = clocksource_register_hz(&timer_clocksource, NSEC_PER_SEC/TIMER_MULTIPLIER);
+	if (err) {
+		printk(KERN_ERR "clocksource_register_hz returned %d\n", err);
+		return;
+	}
+}
+
+void read_persistent_clock64(struct timespec64 *ts)
+{
+	long long nsecs;
+
+	time_travel_set_start();
+
+	if (time_travel_mode != TT_MODE_OFF)
+		nsecs = time_travel_start + time_travel_time;
+	else
+		nsecs = os_persistent_clock_emulation();
+
+	set_normalized_timespec64(ts, nsecs / NSEC_PER_SEC,
+				  nsecs % NSEC_PER_SEC);
+}
+
+void __init time_init(void)
+{
+	timer_set_signal_handler();
+	late_time_init = um_timer_init;
+}
+
+#ifdef CONFIG_UML_TIME_TRAVEL_SUPPORT
+unsigned long calibrate_delay_is_known(void)
+{
+	if (time_travel_mode == TT_MODE_INFCPU ||
+	    time_travel_mode == TT_MODE_EXTERNAL)
+		return 1;
+	return 0;
+}
+
+static int setup_time_travel(char *str)
+{
+	if (strcmp(str, "=inf-cpu") == 0) {
+		time_travel_mode = TT_MODE_INFCPU;
+		_timer_clockevent.name = "time-travel-timer-infcpu";
+		timer_clocksource.name = "time-travel-clock";
+		return 1;
+	}
+
+	if (strncmp(str, "=ext:", 5) == 0) {
+		time_travel_mode = TT_MODE_EXTERNAL;
+		_timer_clockevent.name = "time-travel-timer-external";
+		timer_clocksource.name = "time-travel-clock-external";
+		return time_travel_connect_external(str + 5);
+	}
+
+	if (!*str) {
+		time_travel_mode = TT_MODE_BASIC;
+		_timer_clockevent.name = "time-travel-timer";
+		timer_clocksource.name = "time-travel-clock";
+		return 1;
+	}
+
+	return -EINVAL;
+}
+
+__setup("time-travel", setup_time_travel);
+__uml_help(setup_time_travel,
+"time-travel\n"
+"    This option just enables basic time travel mode, in which the clock/timers\n"
+"    inside the UML instance skip forward when there's nothing to do, rather than\n"
+"    waiting for real time to elapse. However, instance CPU speed is limited by\n"
+"    the real CPU speed, so e.g. a 10ms timer will always fire after ~10ms wall\n"
+"    clock (but quicker when there's nothing to do).\n"
+"\n"
+"time-travel=inf-cpu\n"
+"    This enables time travel mode with infinite processing power, in which there\n"
+"    are no wall clock timers, and any CPU processing happens - as seen from the\n"
+"    guest - instantly. This can be useful for accurate simulation regardless of\n"
+"    debug overhead, physical CPU speed, etc. but is somewhat dangerous as it can\n"
+"    easily lead to getting stuck (e.g. if anything in the system busy loops).\n"
+"\n"
+"time-travel=ext:[ID:]/path/to/socket\n"
+"    This enables time travel mode similar to =inf-cpu, except the system will\n"
+"    use the given socket to coordinate with a central scheduler, in order to\n"
+"    have more than one system simultaneously be on simulated time. The virtio\n"
+"    driver code in UML knows about this so you can also simulate networks and\n"
+"    devices using it, assuming the device has the right capabilities.\n"
+"    The optional ID is a 64-bit integer that's sent to the central scheduler.\n\n");
+
+static int setup_time_travel_start(char *str)
+{
+	int err;
+
+	err = kstrtoull(str, 0, &time_travel_start);
+	if (err)
+		return err;
+
+	time_travel_start_set = 1;
+	return 1;
+}
+
+__setup("time-travel-start=", setup_time_travel_start);
+__uml_help(setup_time_travel_start,
+"time-travel-start=<nanoseconds>\n"
+"    Configure the UML instance's wall clock to start at this value rather than\n"
+"    the host's wall clock at the time of UML boot.\n\n");
+
+static struct kobject *bc_time_kobject;
+
+static ssize_t bc_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf)
+{
+	return sprintf(buf, "0x%llx", bc_message);
+}
+
+static ssize_t bc_store(struct kobject *kobj, struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	int ret;
+	u64 user_bc_message;
+
+	ret = kstrtou64(buf, 0, &user_bc_message);
+	if (ret)
+		return ret;
+
+	bc_message = user_bc_message;
+
+	time_travel_ext_req(UM_TIMETRAVEL_BROADCAST, bc_message);
+	pr_info("um: time: sent broadcast message: 0x%llx\n", bc_message);
+	return count;
+}
+
+static struct kobj_attribute bc_attribute = __ATTR(bc-message, 0660, bc_show, bc_store);
+
+static int __init um_bc_start(void)
+{
+	if (time_travel_mode != TT_MODE_EXTERNAL)
+		return 0;
+
+	bc_time_kobject = kobject_create_and_add("um-ext-time", kernel_kobj);
+	if (!bc_time_kobject)
+		return 0;
+
+	if (sysfs_create_file(bc_time_kobject, &bc_attribute.attr))
+		pr_debug("failed to create the bc file in /sys/kernel/um_time");
+
+	return 0;
+}
+late_initcall(um_bc_start);
+#endif
diff --git a/arch/um/kernel/tlb.c b/arch/um/kernel/tlb.c
new file mode 100644
index 000000000..1f175716b
--- /dev/null
+++ b/arch/um/kernel/tlb.c
@@ -0,0 +1,225 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/sched/signal.h>
+
+#include <asm/tlbflush.h>
+#include <asm/mmu_context.h>
+#include <as-layout.h>
+#include <mem_user.h>
+#include <os.h>
+#include <skas.h>
+#include <kern_util.h>
+
+struct vm_ops {
+	struct mm_id *mm_idp;
+
+	int (*mmap)(struct mm_id *mm_idp,
+		    unsigned long virt, unsigned long len, int prot,
+		    int phys_fd, unsigned long long offset);
+	int (*unmap)(struct mm_id *mm_idp,
+		     unsigned long virt, unsigned long len);
+};
+
+static int kern_map(struct mm_id *mm_idp,
+		    unsigned long virt, unsigned long len, int prot,
+		    int phys_fd, unsigned long long offset)
+{
+	return os_map_memory((void *)virt, phys_fd, offset, len,
+			     prot & UM_PROT_READ, prot & UM_PROT_WRITE,
+			     prot & UM_PROT_EXEC);
+}
+
+static int kern_unmap(struct mm_id *mm_idp,
+		      unsigned long virt, unsigned long len)
+{
+	return os_unmap_memory((void *)virt, len);
+}
+
+void report_enomem(void)
+{
+	printk(KERN_ERR "UML ran out of memory on the host side! "
+			"This can happen due to a memory limitation or "
+			"vm.max_map_count has been reached.\n");
+}
+
+static inline int update_pte_range(pmd_t *pmd, unsigned long addr,
+				   unsigned long end,
+				   struct vm_ops *ops)
+{
+	pte_t *pte;
+	int ret = 0;
+
+	pte = pte_offset_kernel(pmd, addr);
+	do {
+		if (!pte_needsync(*pte))
+			continue;
+
+		if (pte_present(*pte)) {
+			__u64 offset;
+			unsigned long phys = pte_val(*pte) & PAGE_MASK;
+			int fd = phys_mapping(phys, &offset);
+			int r, w, x, prot;
+
+			r = pte_read(*pte);
+			w = pte_write(*pte);
+			x = pte_exec(*pte);
+			if (!pte_young(*pte)) {
+				r = 0;
+				w = 0;
+			} else if (!pte_dirty(*pte))
+				w = 0;
+
+			prot = (r ? UM_PROT_READ : 0) |
+			       (w ? UM_PROT_WRITE : 0) |
+			       (x ? UM_PROT_EXEC : 0);
+
+			ret = ops->mmap(ops->mm_idp, addr, PAGE_SIZE,
+					prot, fd, offset);
+		} else
+			ret = ops->unmap(ops->mm_idp, addr, PAGE_SIZE);
+
+		*pte = pte_mkuptodate(*pte);
+	} while (pte++, addr += PAGE_SIZE, ((addr < end) && !ret));
+	return ret;
+}
+
+static inline int update_pmd_range(pud_t *pud, unsigned long addr,
+				   unsigned long end,
+				   struct vm_ops *ops)
+{
+	pmd_t *pmd;
+	unsigned long next;
+	int ret = 0;
+
+	pmd = pmd_offset(pud, addr);
+	do {
+		next = pmd_addr_end(addr, end);
+		if (!pmd_present(*pmd)) {
+			if (pmd_needsync(*pmd)) {
+				ret = ops->unmap(ops->mm_idp, addr,
+						 next - addr);
+				pmd_mkuptodate(*pmd);
+			}
+		}
+		else ret = update_pte_range(pmd, addr, next, ops);
+	} while (pmd++, addr = next, ((addr < end) && !ret));
+	return ret;
+}
+
+static inline int update_pud_range(p4d_t *p4d, unsigned long addr,
+				   unsigned long end,
+				   struct vm_ops *ops)
+{
+	pud_t *pud;
+	unsigned long next;
+	int ret = 0;
+
+	pud = pud_offset(p4d, addr);
+	do {
+		next = pud_addr_end(addr, end);
+		if (!pud_present(*pud)) {
+			if (pud_needsync(*pud)) {
+				ret = ops->unmap(ops->mm_idp, addr,
+						 next - addr);
+				pud_mkuptodate(*pud);
+			}
+		}
+		else ret = update_pmd_range(pud, addr, next, ops);
+	} while (pud++, addr = next, ((addr < end) && !ret));
+	return ret;
+}
+
+static inline int update_p4d_range(pgd_t *pgd, unsigned long addr,
+				   unsigned long end,
+				   struct vm_ops *ops)
+{
+	p4d_t *p4d;
+	unsigned long next;
+	int ret = 0;
+
+	p4d = p4d_offset(pgd, addr);
+	do {
+		next = p4d_addr_end(addr, end);
+		if (!p4d_present(*p4d)) {
+			if (p4d_needsync(*p4d)) {
+				ret = ops->unmap(ops->mm_idp, addr,
+						 next - addr);
+				p4d_mkuptodate(*p4d);
+			}
+		} else
+			ret = update_pud_range(p4d, addr, next, ops);
+	} while (p4d++, addr = next, ((addr < end) && !ret));
+	return ret;
+}
+
+int um_tlb_sync(struct mm_struct *mm)
+{
+	pgd_t *pgd;
+	struct vm_ops ops;
+	unsigned long addr, next;
+	int ret = 0;
+
+	guard(spinlock_irqsave)(&mm->page_table_lock);
+	guard(spinlock_irqsave)(&mm->context.sync_tlb_lock);
+
+	if (mm->context.sync_tlb_range_to == 0)
+		return 0;
+
+	ops.mm_idp = &mm->context.id;
+	if (mm == &init_mm) {
+		ops.mmap = kern_map;
+		ops.unmap = kern_unmap;
+	} else {
+		ops.mmap = map;
+		ops.unmap = unmap;
+	}
+
+	addr = mm->context.sync_tlb_range_from;
+	pgd = pgd_offset(mm, addr);
+	do {
+		next = pgd_addr_end(addr, mm->context.sync_tlb_range_to);
+		if (!pgd_present(*pgd)) {
+			if (pgd_needsync(*pgd)) {
+				ret = ops.unmap(ops.mm_idp, addr,
+						next - addr);
+				pgd_mkuptodate(*pgd);
+			}
+		} else
+			ret = update_p4d_range(pgd, addr, next, &ops);
+	} while (pgd++, addr = next,
+		 ((addr < mm->context.sync_tlb_range_to) && !ret));
+
+	if (ret == -ENOMEM)
+		report_enomem();
+
+	mm->context.sync_tlb_range_from = 0;
+	mm->context.sync_tlb_range_to = 0;
+
+	return ret;
+}
+
+void flush_tlb_all(void)
+{
+	/*
+	 * Don't bother flushing if this address space is about to be
+	 * destroyed.
+	 */
+	if (atomic_read(&current->mm->mm_users) == 0)
+		return;
+
+	flush_tlb_mm(current->mm);
+}
+
+void flush_tlb_mm(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+	VMA_ITERATOR(vmi, mm, 0);
+
+	for_each_vma(vmi, vma)
+		um_tlb_mark_sync(mm, vma->vm_start, vma->vm_end);
+}
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
new file mode 100644
index 000000000..177615820
--- /dev/null
+++ b/arch/um/kernel/trap.c
@@ -0,0 +1,430 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/mm.h>
+#include <linux/sched/signal.h>
+#include <linux/hardirq.h>
+#include <linux/module.h>
+#include <linux/uaccess.h>
+#include <linux/sched/debug.h>
+#include <asm/current.h>
+#include <asm/tlbflush.h>
+#include <arch.h>
+#include <as-layout.h>
+#include <kern_util.h>
+#include <os.h>
+#include <skas.h>
+
+/*
+ * NOTE: UML does not have exception tables. As such, this is almost a copy
+ * of the code in mm/memory.c, only adjusting the logic to simply check whether
+ * we are coming from the kernel instead of doing an additional lookup in the
+ * exception table.
+ * We can do this simplification because we never get here if the exception was
+ * fixable.
+ */
+static inline bool get_mmap_lock_carefully(struct mm_struct *mm, bool is_user)
+{
+	if (likely(mmap_read_trylock(mm)))
+		return true;
+
+	if (!is_user)
+		return false;
+
+	return !mmap_read_lock_killable(mm);
+}
+
+static inline bool mmap_upgrade_trylock(struct mm_struct *mm)
+{
+	/*
+	 * We don't have this operation yet.
+	 *
+	 * It should be easy enough to do: it's basically a
+	 *    atomic_long_try_cmpxchg_acquire()
+	 * from RWSEM_READER_BIAS -> RWSEM_WRITER_LOCKED, but
+	 * it also needs the proper lockdep magic etc.
+	 */
+	return false;
+}
+
+static inline bool upgrade_mmap_lock_carefully(struct mm_struct *mm, bool is_user)
+{
+	mmap_read_unlock(mm);
+	if (!is_user)
+		return false;
+
+	return !mmap_write_lock_killable(mm);
+}
+
+/*
+ * Helper for page fault handling.
+ *
+ * This is kind of equivalend to "mmap_read_lock()" followed
+ * by "find_extend_vma()", except it's a lot more careful about
+ * the locking (and will drop the lock on failure).
+ *
+ * For example, if we have a kernel bug that causes a page
+ * fault, we don't want to just use mmap_read_lock() to get
+ * the mm lock, because that would deadlock if the bug were
+ * to happen while we're holding the mm lock for writing.
+ *
+ * So this checks the exception tables on kernel faults in
+ * order to only do this all for instructions that are actually
+ * expected to fault.
+ *
+ * We can also actually take the mm lock for writing if we
+ * need to extend the vma, which helps the VM layer a lot.
+ */
+static struct vm_area_struct *
+um_lock_mm_and_find_vma(struct mm_struct *mm,
+			unsigned long addr, bool is_user)
+{
+	struct vm_area_struct *vma;
+
+	if (!get_mmap_lock_carefully(mm, is_user))
+		return NULL;
+
+	vma = find_vma(mm, addr);
+	if (likely(vma && (vma->vm_start <= addr)))
+		return vma;
+
+	/*
+	 * Well, dang. We might still be successful, but only
+	 * if we can extend a vma to do so.
+	 */
+	if (!vma || !(vma->vm_flags & VM_GROWSDOWN)) {
+		mmap_read_unlock(mm);
+		return NULL;
+	}
+
+	/*
+	 * We can try to upgrade the mmap lock atomically,
+	 * in which case we can continue to use the vma
+	 * we already looked up.
+	 *
+	 * Otherwise we'll have to drop the mmap lock and
+	 * re-take it, and also look up the vma again,
+	 * re-checking it.
+	 */
+	if (!mmap_upgrade_trylock(mm)) {
+		if (!upgrade_mmap_lock_carefully(mm, is_user))
+			return NULL;
+
+		vma = find_vma(mm, addr);
+		if (!vma)
+			goto fail;
+		if (vma->vm_start <= addr)
+			goto success;
+		if (!(vma->vm_flags & VM_GROWSDOWN))
+			goto fail;
+	}
+
+	if (expand_stack_locked(vma, addr))
+		goto fail;
+
+success:
+	mmap_write_downgrade(mm);
+	return vma;
+
+fail:
+	mmap_write_unlock(mm);
+	return NULL;
+}
+
+/*
+ * Note this is constrained to return 0, -EFAULT, -EACCES, -ENOMEM by
+ * segv().
+ */
+int handle_page_fault(unsigned long address, unsigned long ip,
+		      int is_write, int is_user, int *code_out)
+{
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma;
+	pmd_t *pmd;
+	pte_t *pte;
+	int err = -EFAULT;
+	unsigned int flags = FAULT_FLAG_DEFAULT;
+
+	*code_out = SEGV_MAPERR;
+
+	/*
+	 * If the fault was with pagefaults disabled, don't take the fault, just
+	 * fail.
+	 */
+	if (faulthandler_disabled())
+		goto out_nosemaphore;
+
+	if (is_user)
+		flags |= FAULT_FLAG_USER;
+retry:
+	vma = um_lock_mm_and_find_vma(mm, address, is_user);
+	if (!vma)
+		goto out_nosemaphore;
+
+	*code_out = SEGV_ACCERR;
+	if (is_write) {
+		if (!(vma->vm_flags & VM_WRITE))
+			goto out;
+		flags |= FAULT_FLAG_WRITE;
+	} else {
+		/* Don't require VM_READ|VM_EXEC for write faults! */
+		if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
+			goto out;
+	}
+
+	do {
+		vm_fault_t fault;
+
+		fault = handle_mm_fault(vma, address, flags, NULL);
+
+		if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+			goto out_nosemaphore;
+
+		/* The fault is fully completed (including releasing mmap lock) */
+		if (fault & VM_FAULT_COMPLETED)
+			return 0;
+
+		if (unlikely(fault & VM_FAULT_ERROR)) {
+			if (fault & VM_FAULT_OOM) {
+				goto out_of_memory;
+			} else if (fault & VM_FAULT_SIGSEGV) {
+				goto out;
+			} else if (fault & VM_FAULT_SIGBUS) {
+				err = -EACCES;
+				goto out;
+			}
+			BUG();
+		}
+		if (fault & VM_FAULT_RETRY) {
+			flags |= FAULT_FLAG_TRIED;
+
+			goto retry;
+		}
+
+		pmd = pmd_off(mm, address);
+		pte = pte_offset_kernel(pmd, address);
+	} while (!pte_present(*pte));
+	err = 0;
+	/*
+	 * The below warning was added in place of
+	 *	pte_mkyoung(); if (is_write) pte_mkdirty();
+	 * If it's triggered, we'd see normally a hang here (a clean pte is
+	 * marked read-only to emulate the dirty bit).
+	 * However, the generic code can mark a PTE writable but clean on a
+	 * concurrent read fault, triggering this harmlessly. So comment it out.
+	 */
+#if 0
+	WARN_ON(!pte_young(*pte) || (is_write && !pte_dirty(*pte)));
+#endif
+
+out:
+	mmap_read_unlock(mm);
+out_nosemaphore:
+	return err;
+
+out_of_memory:
+	/*
+	 * We ran out of memory, call the OOM killer, and return the userspace
+	 * (which will retry the fault, or kill us if we got oom-killed).
+	 */
+	mmap_read_unlock(mm);
+	if (!is_user)
+		goto out_nosemaphore;
+	pagefault_out_of_memory();
+	return 0;
+}
+
+static void show_segv_info(struct uml_pt_regs *regs)
+{
+	struct task_struct *tsk = current;
+	struct faultinfo *fi = UPT_FAULTINFO(regs);
+
+	if (!unhandled_signal(tsk, SIGSEGV))
+		return;
+
+	if (!printk_ratelimit())
+		return;
+
+	printk("%s%s[%d]: segfault at %lx ip %px sp %px error %x",
+		task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
+		tsk->comm, task_pid_nr(tsk), FAULT_ADDRESS(*fi),
+		(void *)UPT_IP(regs), (void *)UPT_SP(regs),
+		fi->error_code);
+
+	print_vma_addr(KERN_CONT " in ", UPT_IP(regs));
+	printk(KERN_CONT "\n");
+}
+
+static void bad_segv(struct faultinfo fi, unsigned long ip)
+{
+	current->thread.arch.faultinfo = fi;
+	force_sig_fault(SIGSEGV, SEGV_ACCERR, (void __user *) FAULT_ADDRESS(fi));
+}
+
+void fatal_sigsegv(void)
+{
+	force_fatal_sig(SIGSEGV);
+	do_signal(&current->thread.regs);
+	/*
+	 * This is to tell gcc that we're not returning - do_signal
+	 * can, in general, return, but in this case, it's not, since
+	 * we just got a fatal SIGSEGV queued.
+	 */
+	os_dump_core();
+}
+
+/**
+ * segv_handler() - the SIGSEGV handler
+ * @sig:	the signal number
+ * @unused_si:	the signal info struct; unused in this handler
+ * @regs:	the ptrace register information
+ * @mc:		the mcontext of the signal
+ *
+ * The handler first extracts the faultinfo from the UML ptrace regs struct.
+ * If the userfault did not happen in an UML userspace process, bad_segv is called.
+ * Otherwise the signal did happen in a cloned userspace process, handle it.
+ */
+void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs,
+		  void *mc)
+{
+	struct faultinfo * fi = UPT_FAULTINFO(regs);
+
+	if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) {
+		show_segv_info(regs);
+		bad_segv(*fi, UPT_IP(regs));
+		return;
+	}
+	segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs, mc);
+}
+
+/*
+ * We give a *copy* of the faultinfo in the regs to segv.
+ * This must be done, since nesting SEGVs could overwrite
+ * the info in the regs. A pointer to the info then would
+ * give us bad data!
+ */
+unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
+		   struct uml_pt_regs *regs, void *mc)
+{
+	int si_code;
+	int err;
+	int is_write = FAULT_WRITE(fi);
+	unsigned long address = FAULT_ADDRESS(fi);
+
+	if (!is_user && regs)
+		current->thread.segv_regs = container_of(regs, struct pt_regs, regs);
+
+	if (!is_user && address >= start_vm && address < end_vm) {
+		/*
+		 * Kernel has pending updates from set_ptes that were not
+		 * flushed yet. Syncing them should fix the pagefault (if not
+		 * we'll get here again and panic).
+		 */
+		err = um_tlb_sync(&init_mm);
+		if (err == -ENOMEM)
+			report_enomem();
+		if (err)
+			panic("Failed to sync kernel TLBs: %d", err);
+		goto out;
+	}
+	else if (current->pagefault_disabled) {
+		if (!mc) {
+			show_regs(container_of(regs, struct pt_regs, regs));
+			panic("Segfault with pagefaults disabled but no mcontext");
+		}
+		if (!current->thread.segv_continue) {
+			show_regs(container_of(regs, struct pt_regs, regs));
+			panic("Segfault without recovery target");
+		}
+		mc_set_rip(mc, current->thread.segv_continue);
+		current->thread.segv_continue = NULL;
+		goto out;
+	}
+	else if (current->mm == NULL) {
+		show_regs(container_of(regs, struct pt_regs, regs));
+		panic("Segfault with no mm");
+	}
+	else if (!is_user && address > PAGE_SIZE && address < TASK_SIZE) {
+		show_regs(container_of(regs, struct pt_regs, regs));
+		panic("Kernel tried to access user memory at addr 0x%lx, ip 0x%lx",
+		       address, ip);
+	}
+
+	if (SEGV_IS_FIXABLE(&fi))
+		err = handle_page_fault(address, ip, is_write, is_user,
+					&si_code);
+	else {
+		err = -EFAULT;
+		/*
+		 * A thread accessed NULL, we get a fault, but CR2 is invalid.
+		 * This code is used in __do_copy_from_user() of TT mode.
+		 * XXX tt mode is gone, so maybe this isn't needed any more
+		 */
+		address = 0;
+	}
+
+	if (!err)
+		goto out;
+	else if (!is_user && arch_fixup(ip, regs))
+		goto out;
+
+	if (!is_user) {
+		show_regs(container_of(regs, struct pt_regs, regs));
+		panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
+		      address, ip);
+	}
+
+	show_segv_info(regs);
+
+	if (err == -EACCES) {
+		current->thread.arch.faultinfo = fi;
+		force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
+	} else {
+		BUG_ON(err != -EFAULT);
+		current->thread.arch.faultinfo = fi;
+		force_sig_fault(SIGSEGV, si_code, (void __user *) address);
+	}
+
+out:
+	if (regs)
+		current->thread.segv_regs = NULL;
+
+	return 0;
+}
+
+void relay_signal(int sig, struct siginfo *si, struct uml_pt_regs *regs,
+		  void *mc)
+{
+	int code, err;
+	if (!UPT_IS_USER(regs)) {
+		if (sig == SIGBUS)
+			printk(KERN_ERR "Bus error - the host /dev/shm or /tmp "
+			       "mount likely just ran out of space\n");
+		panic("Kernel mode signal %d", sig);
+	}
+
+	arch_examine_signal(sig, regs);
+
+	/* Is the signal layout for the signal known?
+	 * Signal data must be scrubbed to prevent information leaks.
+	 */
+	code = si->si_code;
+	err = si->si_errno;
+	if ((err == 0) && (siginfo_layout(sig, code) == SIL_FAULT)) {
+		struct faultinfo *fi = UPT_FAULTINFO(regs);
+		current->thread.arch.faultinfo = *fi;
+		force_sig_fault(sig, code, (void __user *)FAULT_ADDRESS(*fi));
+	} else {
+		printk(KERN_ERR "Attempted to relay unknown signal %d (si_code = %d) with errno %d\n",
+		       sig, code, err);
+		force_sig(sig);
+	}
+}
+
+void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs,
+	   void *mc)
+{
+	do_IRQ(WINCH_IRQ, regs);
+}
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
new file mode 100644
index 000000000..e4ee69396
--- /dev/null
+++ b/arch/um/kernel/um_arch.c
@@ -0,0 +1,539 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <linux/cpu.h>
+#include <linux/delay.h>
+#include <linux/init.h>
+#include <linux/mm.h>
+#include <linux/ctype.h>
+#include <linux/module.h>
+#include <linux/panic_notifier.h>
+#include <linux/seq_file.h>
+#include <linux/string.h>
+#include <linux/string_choices.h>
+#include <linux/utsname.h>
+#include <linux/sched.h>
+#include <linux/sched/task.h>
+#include <linux/kmsg_dump.h>
+#include <linux/suspend.h>
+#include <linux/random.h>
+#include <linux/smp-internal.h>
+
+#include <asm/processor.h>
+#include <asm/cpufeature.h>
+#include <asm/sections.h>
+#include <asm/setup.h>
+#include <asm/text-patching.h>
+#include <as-layout.h>
+#include <arch.h>
+#include <init.h>
+#include <kern.h>
+#include <kern_util.h>
+#include <mem_user.h>
+#include <os.h>
+
+#include "um_arch.h"
+
+#define DEFAULT_COMMAND_LINE_ROOT "root=98:0"
+#define DEFAULT_COMMAND_LINE_CONSOLE "console=tty0"
+
+/* Changed in add_arg and setup_arch, which run before SMP is started */
+static char __initdata command_line[COMMAND_LINE_SIZE] = { 0 };
+
+static void __init add_arg(char *arg)
+{
+	if (strlen(command_line) + strlen(arg) + 1 > COMMAND_LINE_SIZE) {
+		os_warn("add_arg: Too many command line arguments!\n");
+		exit(1);
+	}
+	if (strlen(command_line) > 0)
+		strcat(command_line, " ");
+	strcat(command_line, arg);
+}
+
+/*
+ * These fields are initialized at boot time and not changed.
+ */
+struct cpuinfo_um boot_cpu_data = {
+	.loops_per_jiffy	= 0,
+	.cache_alignment	= L1_CACHE_BYTES,
+	.x86_capability		= { 0 }
+};
+
+EXPORT_SYMBOL(boot_cpu_data);
+
+
+/* Changed in setup_arch, which is called in early boot */
+static char host_info[(__NEW_UTS_LEN + 1) * 5];
+
+static int show_cpuinfo(struct seq_file *m, void *v)
+{
+	int i = 0;
+
+#if IS_ENABLED(CONFIG_SMP)
+	i = (uintptr_t) v - 1;
+	if (!cpu_online(i))
+		return 0;
+#endif
+
+	seq_printf(m, "processor\t: %d\n", i);
+	seq_printf(m, "vendor_id\t: User Mode Linux\n");
+	seq_printf(m, "model name\t: UML\n");
+	seq_printf(m, "mode\t\t: skas\n");
+	seq_printf(m, "host\t\t: %s\n", host_info);
+	seq_printf(m, "fpu\t\t: %s\n", str_yes_no(cpu_has(&boot_cpu_data, X86_FEATURE_FPU)));
+	seq_printf(m, "flags\t\t:");
+	for (i = 0; i < 32*NCAPINTS; i++)
+		if (cpu_has(&boot_cpu_data, i) && (x86_cap_flags[i] != NULL))
+			seq_printf(m, " %s", x86_cap_flags[i]);
+	seq_printf(m, "\n");
+	seq_printf(m, "cache_alignment\t: %d\n", boot_cpu_data.cache_alignment);
+	seq_printf(m, "bogomips\t: %lu.%02lu\n",
+		   loops_per_jiffy/(500000/HZ),
+		   (loops_per_jiffy/(5000/HZ)) % 100);
+
+	return 0;
+}
+
+static void *c_start(struct seq_file *m, loff_t *pos)
+{
+	if (*pos < nr_cpu_ids)
+		return (void *)(uintptr_t)(*pos + 1);
+	return NULL;
+}
+
+static void *c_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	++*pos;
+	return c_start(m, pos);
+}
+
+static void c_stop(struct seq_file *m, void *v)
+{
+}
+
+const struct seq_operations cpuinfo_op = {
+	.start	= c_start,
+	.next	= c_next,
+	.stop	= c_stop,
+	.show	= show_cpuinfo,
+};
+
+/* Set in linux_main */
+unsigned long uml_physmem;
+EXPORT_SYMBOL(uml_physmem);
+
+unsigned long uml_reserved; /* Also modified in mem_init */
+unsigned long start_vm;
+unsigned long end_vm;
+
+/* Set in early boot */
+static int have_root __initdata;
+static int have_console __initdata;
+
+/* Set in uml_mem_setup and modified in linux_main */
+unsigned long long physmem_size = 64 * 1024 * 1024;
+EXPORT_SYMBOL(physmem_size);
+
+static const char *usage_string =
+"User Mode Linux v%s\n"
+"	available at http://user-mode-linux.sourceforge.net/\n\n";
+
+static int __init uml_version_setup(char *line, int *add)
+{
+	/* Explicitly use printf() to show version in stdout */
+	printf("%s\n", init_utsname()->release);
+	exit(0);
+
+	return 0;
+}
+
+__uml_setup("--version", uml_version_setup,
+"--version\n"
+"    Prints the version number of the kernel.\n\n"
+);
+
+static int __init uml_root_setup(char *line, int *add)
+{
+	have_root = 1;
+	return 0;
+}
+
+__uml_setup("root=", uml_root_setup,
+"root=<file containing the root fs>\n"
+"    This is actually used by the generic kernel in exactly the same\n"
+"    way as in any other kernel. If you configure a number of block\n"
+"    devices and want to boot off something other than ubd0, you \n"
+"    would use something like:\n"
+"        root=/dev/ubd5\n\n"
+);
+
+static int __init uml_console_setup(char *line, int *add)
+{
+	have_console = 1;
+	return 0;
+}
+
+__uml_setup("console=", uml_console_setup,
+"console=<preferred console>\n"
+"    Specify the preferred console output driver\n\n"
+);
+
+static int __init Usage(char *line, int *add)
+{
+	const char **p;
+
+	printf(usage_string, init_utsname()->release);
+	p = &__uml_help_start;
+	/* Explicitly use printf() to show help in stdout */
+	while (p < &__uml_help_end) {
+		printf("%s", *p);
+		p++;
+	}
+	exit(0);
+	return 0;
+}
+
+__uml_setup("--help", Usage,
+"--help\n"
+"    Prints this message.\n\n"
+);
+
+static void __init uml_checksetup(char *line, int *add)
+{
+	struct uml_param *p;
+
+	p = &__uml_setup_start;
+	while (p < &__uml_setup_end) {
+		size_t n;
+
+		n = strlen(p->str);
+		if (!strncmp(line, p->str, n) && p->setup_func(line + n, add))
+			return;
+		p++;
+	}
+}
+
+static void __init uml_postsetup(void)
+{
+	initcall_t *p;
+
+	p = &__uml_postsetup_start;
+	while (p < &__uml_postsetup_end) {
+		(*p)();
+		p++;
+	}
+	return;
+}
+
+static int panic_exit(struct notifier_block *self, unsigned long unused1,
+		      void *unused2)
+{
+	kmsg_dump(KMSG_DUMP_PANIC);
+	bust_spinlocks(1);
+	bust_spinlocks(0);
+	uml_exitcode = 1;
+	os_dump_core();
+
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block panic_exit_notifier = {
+	.notifier_call	= panic_exit,
+	.priority	= INT_MAX - 1, /* run as 2nd notifier, won't return */
+};
+
+void uml_finishsetup(void)
+{
+	atomic_notifier_chain_register(&panic_notifier_list,
+				       &panic_exit_notifier);
+
+	uml_postsetup();
+
+	new_thread_handler();
+}
+
+/* Set during early boot */
+unsigned long stub_start;
+unsigned long task_size;
+EXPORT_SYMBOL(task_size);
+
+unsigned long brk_start;
+
+#define MIN_VMALLOC (32 * 1024 * 1024)
+
+static void __init parse_host_cpu_flags(char *line)
+{
+	int i;
+	for (i = 0; i < 32*NCAPINTS; i++) {
+		if ((x86_cap_flags[i] != NULL) && strstr(line, x86_cap_flags[i]))
+			set_cpu_cap(&boot_cpu_data, i);
+	}
+}
+
+static void __init parse_cache_line(char *line)
+{
+	long res;
+	char *to_parse = strstr(line, ":");
+	if (to_parse) {
+		to_parse++;
+		while (*to_parse != 0 && isspace(*to_parse)) {
+			to_parse++;
+		}
+		if (kstrtoul(to_parse, 10, &res) == 0 && is_power_of_2(res))
+			boot_cpu_data.cache_alignment = res;
+		else
+			boot_cpu_data.cache_alignment = L1_CACHE_BYTES;
+	}
+}
+
+static unsigned long __init get_top_address(char **envp)
+{
+	unsigned long top_addr = (unsigned long) &top_addr;
+	int i;
+
+	/* The earliest variable should be after the program name in ELF */
+	for (i = 0; envp[i]; i++) {
+		if ((unsigned long) envp[i] > top_addr)
+			top_addr = (unsigned long) envp[i];
+	}
+
+	return PAGE_ALIGN(top_addr + 1);
+}
+
+int __init linux_main(int argc, char **argv, char **envp)
+{
+	unsigned long avail, diff;
+	unsigned long virtmem_size, max_physmem;
+	unsigned long host_task_size;
+	unsigned long stack;
+	unsigned int i;
+	int add;
+
+	for (i = 1; i < argc; i++) {
+		if ((i == 1) && (argv[i][0] == ' '))
+			continue;
+		add = 1;
+		uml_checksetup(argv[i], &add);
+		if (add)
+			add_arg(argv[i]);
+	}
+	if (have_root == 0)
+		add_arg(DEFAULT_COMMAND_LINE_ROOT);
+
+	if (have_console == 0)
+		add_arg(DEFAULT_COMMAND_LINE_CONSOLE);
+
+	host_task_size = get_top_address(envp);
+	/* reserve a few pages for the stubs */
+	stub_start = host_task_size - STUB_SIZE;
+	host_task_size = stub_start;
+
+	/* Limit TASK_SIZE to what is addressable by the page table */
+	task_size = host_task_size;
+	if (task_size > (unsigned long long) PTRS_PER_PGD * PGDIR_SIZE)
+		task_size = PTRS_PER_PGD * PGDIR_SIZE;
+
+	/*
+	 * TASK_SIZE needs to be PGDIR_SIZE aligned or else exit_mmap craps
+	 * out
+	 */
+	task_size = task_size & PGDIR_MASK;
+
+	/* OS sanity checks that need to happen before the kernel runs */
+	os_early_checks();
+
+	get_host_cpu_features(parse_host_cpu_flags, parse_cache_line);
+
+	brk_start = (unsigned long) sbrk(0);
+
+	/*
+	 * Increase physical memory size for exec-shield users
+	 * so they actually get what they asked for. This should
+	 * add zero for non-exec shield users
+	 */
+	diff = PAGE_ALIGN(brk_start) - PAGE_ALIGN((unsigned long) &_end);
+	if (diff > 1024 * 1024) {
+		os_info("Adding %ld bytes to physical memory to account for "
+			"exec-shield gap\n", diff);
+		physmem_size += diff;
+	}
+
+	uml_physmem = (unsigned long) __binary_start & PAGE_MASK;
+
+	/* Reserve up to 4M after the current brk */
+	uml_reserved = ROUND_4M(brk_start) + (1 << 22);
+
+	setup_machinename(init_utsname()->machine);
+
+	physmem_size = PAGE_ALIGN(physmem_size);
+	max_physmem = TASK_SIZE - uml_physmem - MIN_VMALLOC;
+	if (physmem_size > max_physmem) {
+		physmem_size = max_physmem;
+		os_info("Physical memory size shrunk to %llu bytes\n",
+			physmem_size);
+	}
+
+	high_physmem = uml_physmem + physmem_size;
+
+	start_vm = VMALLOC_START;
+
+	virtmem_size = physmem_size;
+	stack = (unsigned long) argv;
+	stack &= ~(1024 * 1024 - 1);
+	avail = stack - start_vm;
+	if (physmem_size > avail)
+		virtmem_size = avail;
+	end_vm = start_vm + virtmem_size;
+
+	if (virtmem_size < physmem_size)
+		os_info("Kernel virtual memory size shrunk to %lu bytes\n",
+			virtmem_size);
+
+	arch_task_struct_size = sizeof(struct task_struct) + host_fp_size;
+
+	os_flush_stdout();
+
+	return start_uml();
+}
+
+int __init __weak read_initrd(void)
+{
+	return 0;
+}
+
+void __init setup_arch(char **cmdline_p)
+{
+	u8 rng_seed[32];
+
+	stack_protections((unsigned long) init_task.stack);
+	setup_physmem(uml_physmem, uml_reserved, physmem_size);
+	uml_dtb_init();
+	read_initrd();
+
+	strscpy(boot_command_line, command_line, COMMAND_LINE_SIZE);
+	*cmdline_p = command_line;
+	setup_hostinfo(host_info, sizeof host_info);
+	prefill_possible_map();
+
+	if (os_getrandom(rng_seed, sizeof(rng_seed), 0) == sizeof(rng_seed)) {
+		add_bootloader_randomness(rng_seed, sizeof(rng_seed));
+		memzero_explicit(rng_seed, sizeof(rng_seed));
+	}
+}
+
+void __init arch_cpu_finalize_init(void)
+{
+	arch_check_bugs();
+	os_check_bugs();
+}
+
+void apply_seal_endbr(s32 *start, s32 *end)
+{
+}
+
+void apply_retpolines(s32 *start, s32 *end)
+{
+}
+
+void apply_returns(s32 *start, s32 *end)
+{
+}
+
+void apply_fineibt(s32 *start_retpoline, s32 *end_retpoline,
+		   s32 *start_cfi, s32 *end_cfi)
+{
+}
+
+void apply_alternatives(struct alt_instr *start, struct alt_instr *end)
+{
+}
+
+void *text_poke(void *addr, const void *opcode, size_t len)
+{
+	/*
+	 * In UML, the only reference to this function is in
+	 * apply_relocate_add(), which shouldn't ever actually call this
+	 * because UML doesn't have live patching.
+	 */
+	WARN_ON(1);
+
+	return memcpy(addr, opcode, len);
+}
+
+void *text_poke_copy(void *addr, const void *opcode, size_t len)
+{
+	return text_poke(addr, opcode, len);
+}
+
+void smp_text_poke_sync_each_cpu(void)
+{
+}
+
+void uml_pm_wake(void)
+{
+	pm_system_wakeup();
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int um_suspend_valid(suspend_state_t state)
+{
+	return state == PM_SUSPEND_MEM;
+}
+
+static int um_suspend_prepare(void)
+{
+	um_irqs_suspend();
+	return 0;
+}
+
+static int um_suspend_enter(suspend_state_t state)
+{
+	if (WARN_ON(state != PM_SUSPEND_MEM))
+		return -EINVAL;
+
+	/*
+	 * This is identical to the idle sleep, but we've just
+	 * (during suspend) turned off all interrupt sources
+	 * except for the ones we want, so now we can only wake
+	 * up on something we actually want to wake up on. All
+	 * timing has also been suspended.
+	 */
+	um_idle_sleep();
+	return 0;
+}
+
+static void um_suspend_finish(void)
+{
+	um_irqs_resume();
+}
+
+const struct platform_suspend_ops um_suspend_ops = {
+	.valid = um_suspend_valid,
+	.prepare = um_suspend_prepare,
+	.enter = um_suspend_enter,
+	.finish = um_suspend_finish,
+};
+
+static int init_pm_wake_signal(void)
+{
+	/*
+	 * In external time-travel mode we can't use signals to wake up
+	 * since that would mess with the scheduling. We'll have to do
+	 * some additional work to support wakeup on virtio devices or
+	 * similar, perhaps implementing a fake RTC controller that can
+	 * trigger wakeup (and request the appropriate scheduling from
+	 * the external scheduler when going to suspend.)
+	 */
+	if (time_travel_mode != TT_MODE_EXTERNAL)
+		register_pm_wake_signal();
+
+	suspend_set_ops(&um_suspend_ops);
+
+	return 0;
+}
+
+late_initcall(init_pm_wake_signal);
+#endif
diff --git a/arch/um/kernel/um_arch.h b/arch/um/kernel/um_arch.h
new file mode 100644
index 000000000..46e731ab9
--- /dev/null
+++ b/arch/um/kernel/um_arch.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef __UML_ARCH_H__
+#define __UML_ARCH_H__
+
+extern void * __init uml_load_file(const char *filename, unsigned long long *size);
+
+#ifdef CONFIG_OF
+extern void __init uml_dtb_init(void);
+#else
+static inline void uml_dtb_init(void) { }
+#endif
+
+extern int __init read_initrd(void);
+
+#endif
diff --git a/arch/um/kernel/umid.c b/arch/um/kernel/umid.c
new file mode 100644
index 000000000..72bc60ade
--- /dev/null
+++ b/arch/um/kernel/umid.c
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <asm/errno.h>
+#include <init.h>
+#include <kern.h>
+#include <os.h>
+
+/* Changed by set_umid_arg */
+static int umid_inited;
+
+static int __init set_umid_arg(char *name, int *add)
+{
+	int err;
+
+	if (umid_inited) {
+		os_warn("umid already set\n");
+		return 0;
+	}
+
+	*add = 0;
+	err = set_umid(name);
+	if (err == -EEXIST)
+		os_warn("umid '%s' already in use\n", name);
+	else if (!err)
+		umid_inited = 1;
+
+	return 0;
+}
+
+__uml_setup("umid=", set_umid_arg,
+"umid=<name>\n"
+"    This is used to assign a unique identity to this UML machine and\n"
+"    is used for naming the pid file and management console socket.\n\n"
+);
+
diff --git a/arch/um/kernel/uml.lds.S b/arch/um/kernel/uml.lds.S
new file mode 100644
index 000000000..30aa24348
--- /dev/null
+++ b/arch/um/kernel/uml.lds.S
@@ -0,0 +1,120 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <asm/vmlinux.lds.h>
+#include <asm/page.h>
+
+OUTPUT_FORMAT(ELF_FORMAT)
+OUTPUT_ARCH(ELF_ARCH)
+ENTRY(_start)
+jiffies = jiffies_64;
+
+VERSION {
+  {
+    local: *;
+  };
+}
+
+SECTIONS
+{
+  /* This must contain the right address - not quite the default ELF one.*/
+  PROVIDE (__executable_start = START);
+  /* Static binaries stick stuff here, like the sigreturn trampoline,
+   * invisibly to objdump.  So, just make __binary_start equal to the very
+   * beginning of the executable, and if there are unmapped pages after this,
+   * they are forever unusable.
+   */
+  __binary_start = START;
+
+  . = START + SIZEOF_HEADERS;
+  . = ALIGN(PAGE_SIZE);
+
+  _text = .;
+  INIT_TEXT_SECTION(0)
+
+  .text      :
+  {
+    _stext = .;
+    TEXT_TEXT
+    SCHED_TEXT
+    LOCK_TEXT
+    IRQENTRY_TEXT
+    SOFTIRQENTRY_TEXT
+    *(.fixup)
+    /* .gnu.warning sections are handled specially by elf32.em.  */
+    *(.gnu.warning)
+    *(.gnu.linkonce.t*)
+  }
+
+  . = ALIGN(PAGE_SIZE);
+  .syscall_stub : {
+	__syscall_stub_start = .;
+	*(.__syscall_stub*)
+	__syscall_stub_end = .;
+  }
+
+  /*
+   * These are needed even in a static link, even if they wind up being empty.
+   * Newer glibc needs these __rel{,a}_iplt_{start,end} symbols.
+   */
+  .rel.plt : {
+	*(.rel.plt)
+	PROVIDE_HIDDEN(__rel_iplt_start = .);
+	*(.rel.iplt)
+	PROVIDE_HIDDEN(__rel_iplt_end = .);
+  }
+  .rela.plt : {
+	*(.rela.plt)
+	PROVIDE_HIDDEN(__rela_iplt_start = .);
+	*(.rela.iplt)
+	PROVIDE_HIDDEN(__rela_iplt_end = .);
+  }
+
+  #include <asm/common.lds.S>
+
+  __init_begin = .;
+  init.data : { INIT_DATA }
+  __init_end = .;
+
+  .data    :
+  {
+    INIT_TASK_DATA(KERNEL_STACK_SIZE)
+    DATA_DATA
+    *(.gnu.linkonce.d*)
+    CONSTRUCTORS
+  }
+  .data1   : { *(.data1) }
+  .ctors         :
+  {
+    *(.ctors)
+  }
+  .dtors         :
+  {
+    *(.dtors)
+  }
+
+  .got           : { *(.got.plt) *(.got) }
+  .eh_frame       : { KEEP (*(.eh_frame)) }
+  .dynamic       : { *(.dynamic) }
+  .tdata	  : { *(.tdata .tdata.* .gnu.linkonce.td.*) }
+  .tbss		  : { *(.tbss .tbss.* .gnu.linkonce.tb.*) *(.tcommon) }
+  /* We want the small data sections together, so single-instruction offsets
+     can access them all, and initialized data all before uninitialized, so
+     we can shorten the on-disk segment size.  */
+  .sdata     : { *(.sdata) }
+  _edata  =  .;
+  PROVIDE (edata = .);
+  . = ALIGN(PAGE_SIZE);
+  __bss_start = .;
+  PROVIDE(_bss_start = .);
+  SBSS(0)
+  BSS(0)
+   __bss_stop = .;
+  _end = .;
+  PROVIDE (end = .);
+
+  STABS_DEBUG
+  DWARF_DEBUG
+  MODINFO
+  ELF_DETAILS
+
+  DISCARDS
+}
diff --git a/arch/um/kernel/vmlinux.lds.S b/arch/um/kernel/vmlinux.lds.S
new file mode 100644
index 000000000..53d719c04
--- /dev/null
+++ b/arch/um/kernel/vmlinux.lds.S
@@ -0,0 +1,8 @@
+#define RUNTIME_DISCARD_EXIT
+KERNEL_STACK_SIZE = 4096 * (1 << CONFIG_KERNEL_STACK_ORDER);
+
+#ifdef CONFIG_LD_SCRIPT_STATIC
+#include "uml.lds.S"
+#else
+#include "dyn.lds.S"
+#endif
diff --git a/arch/um/os-Linux/Makefile b/arch/um/os-Linux/Makefile
new file mode 100644
index 000000000..f8d672d57
--- /dev/null
+++ b/arch/um/os-Linux/Makefile
@@ -0,0 +1,23 @@
+# SPDX-License-Identifier: GPL-2.0
+# 
+# Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+#
+
+# Don't instrument UML-specific code
+KCOV_INSTRUMENT                := n
+
+obj-y = elf_aux.o execvp.o file.o helper.o irq.o main.o mem.o process.o \
+	registers.o sigio.o signal.o start_up.o time.o tty.o \
+	umid.o user_syms.o util.o skas/
+
+CFLAGS_signal.o += -Wframe-larger-than=4096
+
+CFLAGS_main.o += -Wno-frame-larger-than
+
+obj-$(CONFIG_SMP) += smp.o
+
+USER_OBJS := $(user-objs-y) elf_aux.o execvp.o file.o helper.o irq.o \
+	main.o mem.o process.o registers.o sigio.o signal.o start_up.o time.o \
+	tty.o umid.o util.o smp.o
+
+include $(srctree)/arch/um/scripts/Makefile.rules
diff --git a/arch/um/os-Linux/elf_aux.c b/arch/um/os-Linux/elf_aux.c
new file mode 100644
index 000000000..72f416edf
--- /dev/null
+++ b/arch/um/os-Linux/elf_aux.c
@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  arch/um/kernel/elf_aux.c
+ *
+ *  Scan the ELF auxiliary vector provided by the host to extract
+ *  information about vsyscall-page, etc.
+ *
+ *  Copyright (C) 2004 Fujitsu Siemens Computers GmbH
+ *  Author: Bodo Stroesser (bodo.stroesser@fujitsu-siemens.com)
+ */
+#include <elf.h>
+#include <stddef.h>
+#include <init.h>
+#include <elf_user.h>
+#include <mem_user.h>
+#include "internal.h"
+#include <linux/swab.h>
+
+#if __BITS_PER_LONG == 64
+typedef Elf64_auxv_t elf_auxv_t;
+#else
+typedef Elf32_auxv_t elf_auxv_t;
+#endif
+
+/* These are initialized very early in boot and never changed */
+char * elf_aux_platform;
+long elf_aux_hwcap;
+
+__init void scan_elf_aux( char **envp)
+{
+	elf_auxv_t * auxv;
+
+	while ( *envp++ != NULL) ;
+
+	for ( auxv = (elf_auxv_t *)envp; auxv->a_type != AT_NULL; auxv++) {
+		switch ( auxv->a_type ) {
+			case AT_HWCAP:
+				elf_aux_hwcap = auxv->a_un.a_val;
+				break;
+			case AT_PLATFORM:
+                                /* elf.h removed the pointer elements from
+                                 * a_un, so we have to use a_val, which is
+                                 * all that's left.
+                                 */
+				elf_aux_platform =
+					(char *) (long) auxv->a_un.a_val;
+				break;
+		}
+	}
+}
diff --git a/arch/um/os-Linux/execvp.c b/arch/um/os-Linux/execvp.c
new file mode 100644
index 000000000..c09a5fd5e
--- /dev/null
+++ b/arch/um/os-Linux/execvp.c
@@ -0,0 +1,150 @@
+/* Copyright (C) 2006 by Paolo Giarrusso - modified from glibc' execvp.c.
+   Original copyright notice follows:
+
+   Copyright (C) 1991,92,1995-99,2002,2004 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+#include <unistd.h>
+
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <limits.h>
+
+#ifndef TEST
+#include <um_malloc.h>
+#else
+#include <stdio.h>
+#define um_kmalloc malloc
+#endif
+#include <os.h>
+
+/* Execute FILE, searching in the `PATH' environment variable if it contains
+   no slashes, with arguments ARGV and environment from `environ'.  */
+int execvp_noalloc(char *buf, const char *file, char *const argv[])
+{
+	if (*file == '\0') {
+		return -ENOENT;
+	}
+
+	if (strchr (file, '/') != NULL) {
+		/* Don't search when it contains a slash.  */
+		execv(file, argv);
+	} else {
+		int got_eacces;
+		size_t len, pathlen;
+		char *name, *p;
+		char *path = getenv("PATH");
+		if (path == NULL)
+			path = ":/bin:/usr/bin";
+
+		len = strlen(file) + 1;
+		pathlen = strlen(path);
+		/* Copy the file name at the top.  */
+		name = memcpy(buf + pathlen + 1, file, len);
+		/* And add the slash.  */
+		*--name = '/';
+
+		got_eacces = 0;
+		p = path;
+		do {
+			char *startp;
+
+			path = p;
+			//Let's avoid this GNU extension.
+			//p = strchrnul (path, ':');
+			p = strchr(path, ':');
+			if (!p)
+				p = strchr(path, '\0');
+
+			if (p == path)
+				/* Two adjacent colons, or a colon at the beginning or the end
+				   of `PATH' means to search the current directory.  */
+				startp = name + 1;
+			else
+				startp = memcpy(name - (p - path), path, p - path);
+
+			/* Try to execute this name.  If it works, execv will not return.  */
+			execv(startp, argv);
+
+			/*
+			if (errno == ENOEXEC) {
+			}
+			*/
+
+			switch (errno) {
+				case EACCES:
+					/* Record the we got a `Permission denied' error.  If we end
+					   up finding no executable we can use, we want to diagnose
+					   that we did find one but were denied access.  */
+					got_eacces = 1;
+					break;
+				case ENOENT:
+				case ESTALE:
+				case ENOTDIR:
+					/* Those errors indicate the file is missing or not executable
+					   by us, in which case we want to just try the next path
+					   directory.  */
+				case ENODEV:
+				case ETIMEDOUT:
+					/* Some strange filesystems like AFS return even
+					   stranger error numbers.  They cannot reasonably mean
+					   anything else so ignore those, too.  */
+				case ENOEXEC:
+					/* We won't go searching for the shell
+					 * if it is not executable - the Linux
+					 * kernel already handles this enough,
+					 * for us. */
+					break;
+
+				default:
+					/* Some other error means we found an executable file, but
+					   something went wrong executing it; return the error to our
+					   caller.  */
+					return -errno;
+			}
+		} while (*p++ != '\0');
+
+		/* We tried every element and none of them worked.  */
+		if (got_eacces)
+			/* At least one failure was due to permissions, so report that
+			   error.  */
+			return -EACCES;
+	}
+
+	/* Return the error from the last attempt (probably ENOENT).  */
+	return -errno;
+}
+#ifdef TEST
+int main(int argc, char**argv)
+{
+	char buf[PATH_MAX];
+	int ret;
+	argc--;
+	if (!argc) {
+		os_warn("Not enough arguments\n");
+		return 1;
+	}
+	argv++;
+	if (ret = execvp_noalloc(buf, argv[0], argv)) {
+		errno = -ret;
+		perror("execvp_noalloc");
+	}
+	return 0;
+}
+#endif
diff --git a/arch/um/os-Linux/file.c b/arch/um/os-Linux/file.c
new file mode 100644
index 000000000..21f0e50fb
--- /dev/null
+++ b/arch/um/os-Linux/file.c
@@ -0,0 +1,726 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <linux/falloc.h>
+#include <sys/ioctl.h>
+#include <sys/mount.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/sysmacros.h>
+#include <sys/un.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/eventfd.h>
+#include <poll.h>
+#include <os.h>
+
+static void copy_stat(struct uml_stat *dst, const struct stat64 *src)
+{
+	*dst = ((struct uml_stat) {
+		.ust_dev     = src->st_dev,     /* device */
+		.ust_ino     = src->st_ino,     /* inode */
+		.ust_mode    = src->st_mode,    /* protection */
+		.ust_nlink   = src->st_nlink,   /* number of hard links */
+		.ust_uid     = src->st_uid,     /* user ID of owner */
+		.ust_gid     = src->st_gid,     /* group ID of owner */
+		.ust_size    = src->st_size,    /* total size, in bytes */
+		.ust_blksize = src->st_blksize, /* blocksize for filesys I/O */
+		.ust_blocks  = src->st_blocks,  /* number of blocks allocated */
+		.ust_atime   = src->st_atime,   /* time of last access */
+		.ust_mtime   = src->st_mtime,   /* time of last modification */
+		.ust_ctime   = src->st_ctime,   /* time of last change */
+	});
+}
+
+int os_stat_fd(const int fd, struct uml_stat *ubuf)
+{
+	struct stat64 sbuf;
+	int err;
+
+	CATCH_EINTR(err = fstat64(fd, &sbuf));
+	if (err < 0)
+		return -errno;
+
+	if (ubuf != NULL)
+		copy_stat(ubuf, &sbuf);
+	return err;
+}
+
+int os_stat_file(const char *file_name, struct uml_stat *ubuf)
+{
+	struct stat64 sbuf;
+	int err;
+
+	CATCH_EINTR(err = stat64(file_name, &sbuf));
+	if (err < 0)
+		return -errno;
+
+	if (ubuf != NULL)
+		copy_stat(ubuf, &sbuf);
+	return err;
+}
+
+int os_access(const char *file, int mode)
+{
+	int amode, err;
+
+	amode = (mode & OS_ACC_R_OK ? R_OK : 0) |
+		(mode & OS_ACC_W_OK ? W_OK : 0) |
+		(mode & OS_ACC_X_OK ? X_OK : 0) |
+		(mode & OS_ACC_F_OK ? F_OK : 0);
+
+	err = access(file, amode);
+	if (err < 0)
+		return -errno;
+
+	return 0;
+}
+
+/* FIXME? required only by hostaudio (because it passes ioctls verbatim) */
+int os_ioctl_generic(int fd, unsigned int cmd, unsigned long arg)
+{
+	int err;
+
+	err = ioctl(fd, cmd, arg);
+	if (err < 0)
+		return -errno;
+
+	return err;
+}
+
+/* FIXME: ensure namebuf in os_get_if_name is big enough */
+int os_get_ifname(int fd, char* namebuf)
+{
+	if (ioctl(fd, SIOCGIFNAME, namebuf) < 0)
+		return -errno;
+
+	return 0;
+}
+
+int os_mode_fd(int fd, int mode)
+{
+	int err;
+
+	CATCH_EINTR(err = fchmod(fd, mode));
+	if (err < 0)
+		return -errno;
+
+	return 0;
+}
+
+int os_file_type(char *file)
+{
+	struct uml_stat buf;
+	int err;
+
+	err = os_stat_file(file, &buf);
+	if (err < 0)
+		return err;
+
+	if (S_ISDIR(buf.ust_mode))
+		return OS_TYPE_DIR;
+	else if (S_ISLNK(buf.ust_mode))
+		return OS_TYPE_SYMLINK;
+	else if (S_ISCHR(buf.ust_mode))
+		return OS_TYPE_CHARDEV;
+	else if (S_ISBLK(buf.ust_mode))
+		return OS_TYPE_BLOCKDEV;
+	else if (S_ISFIFO(buf.ust_mode))
+		return OS_TYPE_FIFO;
+	else if (S_ISSOCK(buf.ust_mode))
+		return OS_TYPE_SOCK;
+	else return OS_TYPE_FILE;
+}
+
+int os_file_mode(const char *file, struct openflags *mode_out)
+{
+	int err;
+
+	*mode_out = OPENFLAGS();
+
+	err = access(file, W_OK);
+	if (err && (errno != EACCES))
+		return -errno;
+	else if (!err)
+		*mode_out = of_write(*mode_out);
+
+	err = access(file, R_OK);
+	if (err && (errno != EACCES))
+		return -errno;
+	else if (!err)
+		*mode_out = of_read(*mode_out);
+
+	return err;
+}
+
+int os_open_file(const char *file, struct openflags flags, int mode)
+{
+	int fd, err, f = 0;
+
+	if (flags.r && flags.w)
+		f = O_RDWR;
+	else if (flags.r)
+		f = O_RDONLY;
+	else if (flags.w)
+		f = O_WRONLY;
+	else f = 0;
+
+	if (flags.s)
+		f |= O_SYNC;
+	if (flags.c)
+		f |= O_CREAT;
+	if (flags.t)
+		f |= O_TRUNC;
+	if (flags.e)
+		f |= O_EXCL;
+	if (flags.a)
+		f |= O_APPEND;
+
+	fd = open64(file, f, mode);
+	if (fd < 0)
+		return -errno;
+
+	if (flags.cl && fcntl(fd, F_SETFD, 1)) {
+		err = -errno;
+		close(fd);
+		return err;
+	}
+
+	return fd;
+}
+
+int os_connect_socket(const char *name)
+{
+	struct sockaddr_un sock;
+	int fd, err;
+
+	sock.sun_family = AF_UNIX;
+	snprintf(sock.sun_path, sizeof(sock.sun_path), "%s", name);
+
+	fd = socket(AF_UNIX, SOCK_STREAM, 0);
+	if (fd < 0) {
+		err = -errno;
+		goto out;
+	}
+
+	err = connect(fd, (struct sockaddr *) &sock, sizeof(sock));
+	if (err) {
+		err = -errno;
+		goto out_close;
+	}
+
+	return fd;
+
+out_close:
+	close(fd);
+out:
+	return err;
+}
+
+int os_dup_file(int fd)
+{
+	int new_fd = dup(fd);
+
+	if (new_fd < 0)
+		return -errno;
+
+	return new_fd;
+}
+
+void os_close_file(int fd)
+{
+	close(fd);
+}
+
+int os_seek_file(int fd, unsigned long long offset)
+{
+	unsigned long long actual;
+
+	actual = lseek64(fd, offset, SEEK_SET);
+	if (actual != offset)
+		return -errno;
+	return 0;
+}
+
+int os_read_file(int fd, void *buf, int len)
+{
+	int n = read(fd, buf, len);
+
+	if (n < 0)
+		return -errno;
+	return n;
+}
+
+int os_pread_file(int fd, void *buf, int len, unsigned long long offset)
+{
+	int n = pread(fd, buf, len, offset);
+
+	if (n < 0)
+		return -errno;
+	return n;
+}
+
+int os_write_file(int fd, const void *buf, int len)
+{
+	int n = write(fd, (void *) buf, len);
+
+	if (n < 0)
+		return -errno;
+	return n;
+}
+
+int os_sync_file(int fd)
+{
+	int n = fdatasync(fd);
+
+	if (n < 0)
+		return -errno;
+	return n;
+}
+
+int os_pwrite_file(int fd, const void *buf, int len, unsigned long long offset)
+{
+	int n = pwrite(fd, (void *) buf, len, offset);
+
+	if (n < 0)
+		return -errno;
+	return n;
+}
+
+
+int os_file_size(const char *file, unsigned long long *size_out)
+{
+	struct uml_stat buf;
+	int err;
+
+	err = os_stat_file(file, &buf);
+	if (err < 0) {
+		printk(UM_KERN_ERR "Couldn't stat \"%s\" : err = %d\n", file,
+		       -err);
+		return err;
+	}
+
+	if (S_ISBLK(buf.ust_mode)) {
+		int fd;
+		long blocks;
+
+		fd = open(file, O_RDONLY, 0);
+		if (fd < 0) {
+			err = -errno;
+			printk(UM_KERN_ERR "Couldn't open \"%s\", "
+			       "errno = %d\n", file, errno);
+			return err;
+		}
+		if (ioctl(fd, BLKGETSIZE, &blocks) < 0) {
+			err = -errno;
+			printk(UM_KERN_ERR "Couldn't get the block size of "
+			       "\"%s\", errno = %d\n", file, errno);
+			close(fd);
+			return err;
+		}
+		*size_out = ((long long) blocks) * 512;
+		close(fd);
+	}
+	else *size_out = buf.ust_size;
+
+	return 0;
+}
+
+int os_file_modtime(const char *file, long long *modtime)
+{
+	struct uml_stat buf;
+	int err;
+
+	err = os_stat_file(file, &buf);
+	if (err < 0) {
+		printk(UM_KERN_ERR "Couldn't stat \"%s\" : err = %d\n", file,
+		       -err);
+		return err;
+	}
+
+	*modtime = buf.ust_mtime;
+	return 0;
+}
+
+int os_set_exec_close(int fd)
+{
+	int err;
+
+	CATCH_EINTR(err = fcntl(fd, F_SETFD, FD_CLOEXEC));
+
+	if (err < 0)
+		return -errno;
+	return err;
+}
+
+int os_pipe(int *fds, int stream, int close_on_exec)
+{
+	int err, type = stream ? SOCK_STREAM : SOCK_DGRAM;
+
+	err = socketpair(AF_UNIX, type, 0, fds);
+	if (err < 0)
+		return -errno;
+
+	if (!close_on_exec)
+		return 0;
+
+	err = os_set_exec_close(fds[0]);
+	if (err < 0)
+		goto error;
+
+	err = os_set_exec_close(fds[1]);
+	if (err < 0)
+		goto error;
+
+	return 0;
+
+ error:
+	printk(UM_KERN_ERR "os_pipe : Setting FD_CLOEXEC failed, err = %d\n",
+	       -err);
+	close(fds[1]);
+	close(fds[0]);
+	return err;
+}
+
+int os_set_fd_async(int fd)
+{
+	int err, flags;
+
+	flags = fcntl(fd, F_GETFL);
+	if (flags < 0)
+		return -errno;
+
+	flags |= O_ASYNC | O_NONBLOCK;
+	if (fcntl(fd, F_SETFL, flags) < 0) {
+		err = -errno;
+		printk(UM_KERN_ERR "os_set_fd_async : failed to set O_ASYNC "
+		       "and O_NONBLOCK on fd # %d, errno = %d\n", fd, errno);
+		return err;
+	}
+
+	if ((fcntl(fd, F_SETSIG, SIGIO) < 0) ||
+	    (fcntl(fd, F_SETOWN, os_getpid()) < 0)) {
+		err = -errno;
+		printk(UM_KERN_ERR "os_set_fd_async : Failed to fcntl F_SETOWN "
+		       "(or F_SETSIG) fd %d, errno = %d\n", fd, errno);
+		return err;
+	}
+
+	return 0;
+}
+
+int os_clear_fd_async(int fd)
+{
+	int flags;
+
+	flags = fcntl(fd, F_GETFL);
+	if (flags < 0)
+		return -errno;
+
+	flags &= ~(O_ASYNC | O_NONBLOCK);
+	if (fcntl(fd, F_SETFL, flags) < 0)
+		return -errno;
+	return 0;
+}
+
+int os_set_fd_block(int fd, int blocking)
+{
+	int flags;
+
+	flags = fcntl(fd, F_GETFL);
+	if (flags < 0)
+		return -errno;
+
+	if (blocking)
+		flags &= ~O_NONBLOCK;
+	else
+		flags |= O_NONBLOCK;
+
+	if (fcntl(fd, F_SETFL, flags) < 0)
+		return -errno;
+
+	return 0;
+}
+
+int os_accept_connection(int fd)
+{
+	int new;
+
+	new = accept(fd, NULL, 0);
+	if (new < 0)
+		return -errno;
+	return new;
+}
+
+#ifndef SHUT_RD
+#define SHUT_RD 0
+#endif
+
+#ifndef SHUT_WR
+#define SHUT_WR 1
+#endif
+
+#ifndef SHUT_RDWR
+#define SHUT_RDWR 2
+#endif
+
+int os_shutdown_socket(int fd, int r, int w)
+{
+	int what, err;
+
+	if (r && w)
+		what = SHUT_RDWR;
+	else if (r)
+		what = SHUT_RD;
+	else if (w)
+		what = SHUT_WR;
+	else
+		return -EINVAL;
+
+	err = shutdown(fd, what);
+	if (err < 0)
+		return -errno;
+	return 0;
+}
+
+/**
+ * os_rcv_fd_msg - receive message with (optional) FDs
+ * @fd: the FD to receive from
+ * @fds: the array for FDs to write to
+ * @n_fds: number of FDs to receive (@fds array size)
+ * @data: the message buffer
+ * @data_len: the size of the message to receive
+ *
+ * Receive a message with FDs.
+ *
+ * Returns: the size of the received message, or an error code
+ */
+ssize_t os_rcv_fd_msg(int fd, int *fds, unsigned int n_fds,
+		      void *data, size_t data_len)
+{
+#define MAX_RCV_FDS	2
+	char buf[CMSG_SPACE(sizeof(*fds) * MAX_RCV_FDS)];
+	struct cmsghdr *cmsg;
+	struct iovec iov = {
+		.iov_base = data,
+		.iov_len = data_len,
+	};
+	struct msghdr msg = {
+		.msg_iov = &iov,
+		.msg_iovlen = 1,
+		.msg_control = buf,
+		.msg_controllen = CMSG_SPACE(sizeof(*fds) * n_fds),
+	};
+	int n;
+
+	if (n_fds > MAX_RCV_FDS)
+		return -EINVAL;
+
+	n = recvmsg(fd, &msg, 0);
+	if (n < 0)
+		return -errno;
+
+	cmsg = CMSG_FIRSTHDR(&msg);
+	if (!cmsg ||
+	    cmsg->cmsg_level != SOL_SOCKET ||
+	    cmsg->cmsg_type != SCM_RIGHTS)
+		return n;
+
+	memcpy(fds, CMSG_DATA(cmsg), cmsg->cmsg_len - CMSG_LEN(0));
+	return n;
+}
+
+int os_create_unix_socket(const char *file, int len, int close_on_exec)
+{
+	struct sockaddr_un addr;
+	int sock, err;
+
+	sock = socket(PF_UNIX, SOCK_DGRAM, 0);
+	if (sock < 0)
+		return -errno;
+
+	if (close_on_exec) {
+		err = os_set_exec_close(sock);
+		if (err < 0)
+			printk(UM_KERN_ERR "create_unix_socket : "
+			       "close_on_exec failed, err = %d", -err);
+	}
+
+	addr.sun_family = AF_UNIX;
+
+	snprintf(addr.sun_path, len, "%s", file);
+
+	err = bind(sock, (struct sockaddr *) &addr, sizeof(addr));
+	if (err < 0)
+		return -errno;
+
+	return sock;
+}
+
+void os_flush_stdout(void)
+{
+	fflush(stdout);
+}
+
+int os_lock_file(int fd, int excl)
+{
+	int type = excl ? F_WRLCK : F_RDLCK;
+	struct flock lock = ((struct flock) { .l_type	= type,
+					      .l_whence	= SEEK_SET,
+					      .l_start	= 0,
+					      .l_len	= 0 } );
+	int err, save;
+
+	err = fcntl(fd, F_SETLK, &lock);
+	if (!err)
+		goto out;
+
+	save = -errno;
+	err = fcntl(fd, F_GETLK, &lock);
+	if (err) {
+		err = -errno;
+		goto out;
+	}
+
+	printk(UM_KERN_ERR "F_SETLK failed, file already locked by pid %d\n",
+	       lock.l_pid);
+	err = save;
+ out:
+	return err;
+}
+
+unsigned os_major(unsigned long long dev)
+{
+	return major(dev);
+}
+
+unsigned os_minor(unsigned long long dev)
+{
+	return minor(dev);
+}
+
+unsigned long long os_makedev(unsigned major, unsigned minor)
+{
+	return makedev(major, minor);
+}
+
+int os_falloc_punch(int fd, unsigned long long offset, int len)
+{
+	int n = fallocate(fd, FALLOC_FL_PUNCH_HOLE|FALLOC_FL_KEEP_SIZE, offset, len);
+
+	if (n < 0)
+		return -errno;
+	return n;
+}
+
+int os_falloc_zeroes(int fd, unsigned long long offset, int len)
+{
+	int n = fallocate(fd, FALLOC_FL_ZERO_RANGE|FALLOC_FL_KEEP_SIZE, offset, len);
+
+	if (n < 0)
+		return -errno;
+	return n;
+}
+
+int os_eventfd(unsigned int initval, int flags)
+{
+	int fd = eventfd(initval, flags);
+
+	if (fd < 0)
+		return -errno;
+	return fd;
+}
+
+int os_sendmsg_fds(int fd, const void *buf, unsigned int len, const int *fds,
+		   unsigned int fds_num)
+{
+	struct iovec iov = {
+		.iov_base = (void *) buf,
+		.iov_len = len,
+	};
+	union {
+		char control[CMSG_SPACE(sizeof(*fds) * OS_SENDMSG_MAX_FDS)];
+		struct cmsghdr align;
+	} u;
+	unsigned int fds_size = sizeof(*fds) * fds_num;
+	struct msghdr msg = {
+		.msg_iov = &iov,
+		.msg_iovlen = 1,
+		.msg_control = u.control,
+		.msg_controllen = CMSG_SPACE(fds_size),
+	};
+	struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msg);
+	int err;
+
+	if (fds_num > OS_SENDMSG_MAX_FDS)
+		return -EINVAL;
+	memset(u.control, 0, sizeof(u.control));
+	cmsg->cmsg_level = SOL_SOCKET;
+	cmsg->cmsg_type = SCM_RIGHTS;
+	cmsg->cmsg_len = CMSG_LEN(fds_size);
+	memcpy(CMSG_DATA(cmsg), fds, fds_size);
+	err = sendmsg(fd, &msg, 0);
+
+	if (err < 0)
+		return -errno;
+	return err;
+}
+
+int os_poll(unsigned int n, const int *fds)
+{
+	/* currently need 2 FDs at most so avoid dynamic allocation */
+	struct pollfd pollfds[2] = {};
+	unsigned int i;
+	int ret;
+
+	if (n > ARRAY_SIZE(pollfds))
+		return -EINVAL;
+
+	for (i = 0; i < n; i++) {
+		pollfds[i].fd = fds[i];
+		pollfds[i].events = POLLIN;
+	}
+
+	ret = poll(pollfds, n, -1);
+	if (ret < 0)
+		return -errno;
+
+	/* Return the index of the available FD */
+	for (i = 0; i < n; i++) {
+		if (pollfds[i].revents)
+			return i;
+	}
+
+	return -EIO;
+}
+
+void *os_mmap_rw_shared(int fd, size_t size)
+{
+	void *res = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+
+	if (res == MAP_FAILED)
+		return NULL;
+
+	return res;
+}
+
+void *os_mremap_rw_shared(void *old_addr, size_t old_size, size_t new_size)
+{
+	void *res;
+
+	res = mremap(old_addr, old_size, new_size, MREMAP_MAYMOVE, NULL);
+
+	if (res == MAP_FAILED)
+		return NULL;
+
+	return res;
+}
diff --git a/arch/um/os-Linux/helper.c b/arch/um/os-Linux/helper.c
new file mode 100644
index 000000000..89c2ad2a4
--- /dev/null
+++ b/arch/um/os-Linux/helper.c
@@ -0,0 +1,236 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sched.h>
+#include <pthread.h>
+#include <linux/limits.h>
+#include <sys/socket.h>
+#include <sys/wait.h>
+#include <kern_util.h>
+#include <os.h>
+#include <um_malloc.h>
+
+struct helper_data {
+	void (*pre_exec)(void*);
+	void *pre_data;
+	char **argv;
+	int fd;
+	char *buf;
+};
+
+static int helper_child(void *arg)
+{
+	struct helper_data *data = arg;
+	char **argv = data->argv;
+	int err, ret;
+
+	if (data->pre_exec != NULL)
+		(*data->pre_exec)(data->pre_data);
+	err = execvp_noalloc(data->buf, argv[0], argv);
+
+	/* If the exec succeeds, we don't get here */
+	CATCH_EINTR(ret = write(data->fd, &err, sizeof(err)));
+
+	return 0;
+}
+
+/* Returns either the pid of the child process we run or -E* on failure. */
+int run_helper(void (*pre_exec)(void *), void *pre_data, char **argv)
+{
+	struct helper_data data;
+	unsigned long stack, sp;
+	int pid, fds[2], ret, n;
+
+	stack = alloc_stack(0, __uml_cant_sleep());
+	if (stack == 0)
+		return -ENOMEM;
+
+	ret = socketpair(AF_UNIX, SOCK_STREAM, 0, fds);
+	if (ret < 0) {
+		ret = -errno;
+		printk(UM_KERN_ERR "run_helper : pipe failed, errno = %d\n",
+		       errno);
+		goto out_free;
+	}
+
+	ret = os_set_exec_close(fds[1]);
+	if (ret < 0) {
+		printk(UM_KERN_ERR "run_helper : setting FD_CLOEXEC failed, "
+		       "ret = %d\n", -ret);
+		goto out_close;
+	}
+
+	sp = stack + UM_KERN_PAGE_SIZE;
+	data.pre_exec = pre_exec;
+	data.pre_data = pre_data;
+	data.argv = argv;
+	data.fd = fds[1];
+	data.buf = __uml_cant_sleep() ? uml_kmalloc(PATH_MAX, UM_GFP_ATOMIC) :
+					uml_kmalloc(PATH_MAX, UM_GFP_KERNEL);
+	pid = clone(helper_child, (void *) sp, CLONE_VM, &data);
+	if (pid < 0) {
+		ret = -errno;
+		printk(UM_KERN_ERR "run_helper : clone failed, errno = %d\n",
+		       errno);
+		goto out_free2;
+	}
+
+	close(fds[1]);
+	fds[1] = -1;
+
+	/*
+	 * Read the errno value from the child, if the exec failed, or get 0 if
+	 * the exec succeeded because the pipe fd was set as close-on-exec.
+	 */
+	n = read(fds[0], &ret, sizeof(ret));
+	if (n == 0) {
+		ret = pid;
+	} else {
+		if (n < 0) {
+			n = -errno;
+			printk(UM_KERN_ERR "run_helper : read on pipe failed, "
+			       "ret = %d\n", -n);
+			ret = n;
+		}
+		CATCH_EINTR(waitpid(pid, NULL, __WALL));
+	}
+
+	if (ret < 0)
+		printk(UM_KERN_ERR "run_helper : failed to exec %s on host: %s\n",
+		       argv[0], strerror(-ret));
+
+out_free2:
+	kfree(data.buf);
+out_close:
+	if (fds[1] != -1)
+		close(fds[1]);
+	close(fds[0]);
+out_free:
+	free_stack(stack, 0);
+	return ret;
+}
+
+int run_helper_thread(int (*proc)(void *), void *arg, unsigned int flags,
+		      unsigned long *stack_out)
+{
+	unsigned long stack, sp;
+	int pid, status, err;
+
+	/* To share memory space, use os_run_helper_thread() instead. */
+	if (flags & CLONE_VM)
+		return -EINVAL;
+
+	stack = alloc_stack(0, __uml_cant_sleep());
+	if (stack == 0)
+		return -ENOMEM;
+
+	sp = stack + UM_KERN_PAGE_SIZE;
+	pid = clone(proc, (void *) sp, flags, arg);
+	if (pid < 0) {
+		err = -errno;
+		printk(UM_KERN_ERR "run_helper_thread : clone failed, "
+		       "errno = %d\n", errno);
+		return err;
+	}
+	if (stack_out == NULL) {
+		CATCH_EINTR(pid = waitpid(pid, &status, __WALL));
+		if (pid < 0) {
+			err = -errno;
+			printk(UM_KERN_ERR "run_helper_thread - wait failed, "
+			       "errno = %d\n", errno);
+			pid = err;
+		}
+		if (!WIFEXITED(status) || (WEXITSTATUS(status) != 0))
+			printk(UM_KERN_ERR "run_helper_thread - thread "
+			       "returned status 0x%x\n", status);
+		free_stack(stack, 0);
+	} else
+		*stack_out = stack;
+	return pid;
+}
+
+int helper_wait(int pid)
+{
+	int ret, status;
+	int wflags = __WALL;
+
+	CATCH_EINTR(ret = waitpid(pid, &status, wflags));
+	if (ret < 0) {
+		printk(UM_KERN_ERR "helper_wait : waitpid process %d failed, "
+		       "errno = %d\n", pid, errno);
+		return -errno;
+	} else if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
+		printk(UM_KERN_ERR "helper_wait : process %d exited with "
+		       "status 0x%x\n", pid, status);
+		return -ECHILD;
+	} else
+		return 0;
+}
+
+struct os_helper_thread {
+	pthread_t handle;
+};
+
+int os_run_helper_thread(struct os_helper_thread **td_out,
+			 void *(*routine)(void *), void *arg)
+{
+	struct os_helper_thread *td;
+	sigset_t sigset, oset;
+	int err, flags;
+
+	flags = __uml_cant_sleep() ? UM_GFP_ATOMIC : UM_GFP_KERNEL;
+	td = uml_kmalloc(sizeof(*td), flags);
+	if (!td)
+		return -ENOMEM;
+
+	sigfillset(&sigset);
+	if (sigprocmask(SIG_SETMASK, &sigset, &oset) < 0) {
+		err = -errno;
+		kfree(td);
+		return err;
+	}
+
+	err = pthread_create(&td->handle, NULL, routine, arg);
+
+	if (sigprocmask(SIG_SETMASK, &oset, NULL) < 0)
+		panic("Failed to restore the signal mask: %d", errno);
+
+	if (err != 0)
+		kfree(td);
+	else
+		*td_out = td;
+
+	return -err;
+}
+
+void os_kill_helper_thread(struct os_helper_thread *td)
+{
+	pthread_cancel(td->handle);
+	pthread_join(td->handle, NULL);
+	kfree(td);
+}
+
+void os_fix_helper_thread_signals(void)
+{
+	sigset_t sigset;
+
+	sigemptyset(&sigset);
+
+	sigaddset(&sigset, SIGWINCH);
+	sigaddset(&sigset, SIGPIPE);
+	sigaddset(&sigset, SIGPROF);
+	sigaddset(&sigset, SIGINT);
+	sigaddset(&sigset, SIGTERM);
+	sigaddset(&sigset, SIGCHLD);
+	sigaddset(&sigset, SIGALRM);
+	sigaddset(&sigset, SIGIO);
+	sigaddset(&sigset, SIGUSR1);
+
+	pthread_sigmask(SIG_SETMASK, &sigset, NULL);
+}
diff --git a/arch/um/os-Linux/internal.h b/arch/um/os-Linux/internal.h
new file mode 100644
index 000000000..bac9fcc8c
--- /dev/null
+++ b/arch/um/os-Linux/internal.h
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __UM_OS_LINUX_INTERNAL_H
+#define __UM_OS_LINUX_INTERNAL_H
+
+#include <mm_id.h>
+#include <stub-data.h>
+#include <signal.h>
+
+/*
+ * elf_aux.c
+ */
+void scan_elf_aux(char **envp);
+
+/*
+ * mem.c
+ */
+void check_tmpexec(void);
+
+/*
+ * signal.c
+ */
+extern __thread int signals_enabled;
+int timer_alarm_pending(void);
+
+/*
+ * skas/process.c
+ */
+void wait_stub_done(int pid);
+void wait_stub_done_seccomp(struct mm_id *mm_idp, int running, int wait_sigsys);
+
+/*
+ * smp.c
+ */
+#define IPI_SIGNAL	SIGRTMIN
+
+#endif /* __UM_OS_LINUX_INTERNAL_H */
diff --git a/arch/um/os-Linux/irq.c b/arch/um/os-Linux/irq.c
new file mode 100644
index 000000000..cf7e49c08
--- /dev/null
+++ b/arch/um/os-Linux/irq.c
@@ -0,0 +1,145 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2017 - Cambridge Greys Ltd
+ * Copyright (C) 2011 - 2014 Cisco Systems Inc
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stdlib.h>
+#include <errno.h>
+#include <sys/epoll.h>
+#include <signal.h>
+#include <string.h>
+#include <irq_user.h>
+#include <os.h>
+#include <um_malloc.h>
+
+/* Epoll support */
+
+static int epollfd = -1;
+
+#define MAX_EPOLL_EVENTS 64
+
+static struct epoll_event epoll_events[MAX_EPOLL_EVENTS];
+
+/* Helper to return an Epoll data pointer from an epoll event structure.
+ * We need to keep this one on the userspace side to keep includes separate
+ */
+
+void *os_epoll_get_data_pointer(int index)
+{
+	return epoll_events[index].data.ptr;
+}
+
+/* Helper to compare events versus the events in the epoll structure.
+ * Same as above - needs to be on the userspace side
+ */
+
+
+int os_epoll_triggered(int index, int events)
+{
+	return epoll_events[index].events & events;
+}
+/* Helper to set the event mask.
+ * The event mask is opaque to the kernel side, because it does not have
+ * access to the right includes/defines for EPOLL constants.
+ */
+
+int os_event_mask(enum um_irq_type irq_type)
+{
+	if (irq_type == IRQ_READ)
+		return EPOLLIN | EPOLLPRI | EPOLLERR | EPOLLHUP | EPOLLRDHUP;
+	if (irq_type == IRQ_WRITE)
+		return EPOLLOUT;
+	return 0;
+}
+
+/*
+ * Initial Epoll Setup
+ */
+int os_setup_epoll(void)
+{
+	epollfd = epoll_create(MAX_EPOLL_EVENTS);
+	return epollfd;
+}
+
+/*
+ * Helper to run the actual epoll_wait
+ */
+int os_waiting_for_events_epoll(void)
+{
+	int n, err;
+
+	n = epoll_wait(epollfd,
+		(struct epoll_event *) &epoll_events, MAX_EPOLL_EVENTS, 0);
+	if (n < 0) {
+		err = -errno;
+		if (errno != EINTR)
+			printk(
+				UM_KERN_ERR "os_waiting_for_events:"
+				" epoll returned %d, error = %s\n", n,
+				strerror(errno)
+			);
+		return err;
+	}
+	return n;
+}
+
+
+/*
+ * Helper to add a fd to epoll
+ */
+int os_add_epoll_fd(int events, int fd, void *data)
+{
+	struct epoll_event event;
+	int result;
+
+	event.data.ptr = data;
+	event.events = events | EPOLLET;
+	result = epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &event);
+	if ((result) && (errno == EEXIST))
+		result = os_mod_epoll_fd(events, fd, data);
+	if (result)
+		printk("epollctl add err fd %d, %s\n", fd, strerror(errno));
+	return result;
+}
+
+/*
+ * Helper to mod the fd event mask and/or data backreference
+ */
+int os_mod_epoll_fd(int events, int fd, void *data)
+{
+	struct epoll_event event;
+	int result;
+
+	event.data.ptr = data;
+	event.events = events;
+	result = epoll_ctl(epollfd, EPOLL_CTL_MOD, fd, &event);
+	if (result)
+		printk(UM_KERN_ERR
+			"epollctl mod err fd %d, %s\n", fd, strerror(errno));
+	return result;
+}
+
+/*
+ * Helper to delete the epoll fd
+ */
+int os_del_epoll_fd(int fd)
+{
+	struct epoll_event event;
+	/* This is quiet as we use this as IO ON/OFF - so it is often
+	 * invoked on a non-existent fd
+	 */
+	return epoll_ctl(epollfd, EPOLL_CTL_DEL, fd, &event);
+}
+
+void os_set_ioignore(void)
+{
+	signal(SIGIO, SIG_IGN);
+}
+
+void os_close_epoll_fd(void)
+{
+	/* Needed so we do not leak an fd when rebooting */
+	os_close_file(epollfd);
+}
diff --git a/arch/um/os-Linux/main.c b/arch/um/os-Linux/main.c
new file mode 100644
index 000000000..7e114862a
--- /dev/null
+++ b/arch/um/os-Linux/main.c
@@ -0,0 +1,265 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <signal.h>
+#include <string.h>
+#include <sys/resource.h>
+#include <sys/personality.h>
+#include <as-layout.h>
+#include <init.h>
+#include <kern_util.h>
+#include <os.h>
+#include <um_malloc.h>
+#include "internal.h"
+
+#define STACKSIZE (8 * 1024 * 1024)
+
+static void __init set_stklim(void)
+{
+	struct rlimit lim;
+
+	if (getrlimit(RLIMIT_STACK, &lim) < 0) {
+		perror("getrlimit");
+		exit(1);
+	}
+	if ((lim.rlim_cur == RLIM_INFINITY) || (lim.rlim_cur > STACKSIZE)) {
+		lim.rlim_cur = STACKSIZE;
+		if (setrlimit(RLIMIT_STACK, &lim) < 0) {
+			perror("setrlimit");
+			exit(1);
+		}
+	}
+}
+
+static void last_ditch_exit(int sig)
+{
+	uml_cleanup();
+	exit(1);
+}
+
+static void __init install_fatal_handler(int sig)
+{
+	struct sigaction action;
+
+	/* All signals are enabled in this handler ... */
+	sigemptyset(&action.sa_mask);
+
+	/*
+	 * ... including the signal being handled, plus we want the
+	 * handler reset to the default behavior, so that if an exit
+	 * handler is hanging for some reason, the UML will just die
+	 * after this signal is sent a second time.
+	 */
+	action.sa_flags = SA_RESETHAND | SA_NODEFER;
+	action.sa_restorer = NULL;
+	action.sa_handler = last_ditch_exit;
+	if (sigaction(sig, &action, NULL) < 0) {
+		os_warn("failed to install handler for signal %d "
+			"- errno = %d\n", sig, errno);
+		exit(1);
+	}
+}
+
+#define UML_LIB_PATH	":" OS_LIB_PATH "/uml"
+
+static void __init setup_env_path(void)
+{
+	char *new_path = NULL;
+	char *old_path = NULL;
+	int path_len = 0;
+
+	old_path = getenv("PATH");
+	/*
+	 * if no PATH variable is set or it has an empty value
+	 * just use the default + /usr/lib/uml
+	 */
+	if (!old_path || (path_len = strlen(old_path)) == 0) {
+		if (putenv("PATH=:/bin:/usr/bin/" UML_LIB_PATH))
+			perror("couldn't putenv");
+		return;
+	}
+
+	/* append /usr/lib/uml to the existing path */
+	path_len += strlen("PATH=" UML_LIB_PATH) + 1;
+	new_path = malloc(path_len);
+	if (!new_path) {
+		perror("couldn't malloc to set a new PATH");
+		return;
+	}
+	snprintf(new_path, path_len, "PATH=%s" UML_LIB_PATH, old_path);
+	if (putenv(new_path)) {
+		perror("couldn't putenv to set a new PATH");
+		free(new_path);
+	}
+}
+
+int __init main(int argc, char **argv, char **envp)
+{
+	char **new_argv;
+	int ret, i, err;
+
+	/* Disable randomization and re-exec if it was changed successfully */
+	ret = personality(PER_LINUX | ADDR_NO_RANDOMIZE);
+	if (ret >= 0 && (ret & (PER_LINUX | ADDR_NO_RANDOMIZE)) !=
+			 (PER_LINUX | ADDR_NO_RANDOMIZE)) {
+		char buf[4096] = {};
+		ssize_t ret;
+
+		ret = readlink("/proc/self/exe", buf, sizeof(buf));
+		if (ret < 0 || ret >= sizeof(buf)) {
+			perror("readlink failure");
+			exit(1);
+		}
+		execve(buf, argv, envp);
+	}
+
+	set_stklim();
+
+	setup_env_path();
+
+	setsid();
+
+	new_argv = malloc((argc + 1) * sizeof(char *));
+	if (new_argv == NULL) {
+		perror("Mallocing argv");
+		exit(1);
+	}
+	for (i = 0; i < argc; i++) {
+		new_argv[i] = strdup(argv[i]);
+		if (new_argv[i] == NULL) {
+			perror("Mallocing an arg");
+			exit(1);
+		}
+	}
+	new_argv[argc] = NULL;
+
+	/*
+	 * Allow these signals to bring down a UML if all other
+	 * methods of control fail.
+	 */
+	install_fatal_handler(SIGINT);
+	install_fatal_handler(SIGTERM);
+
+	scan_elf_aux(envp);
+
+	change_sig(SIGPIPE, 0);
+	ret = linux_main(argc, argv, envp);
+
+	/*
+	 * Disable SIGPROF - I have no idea why libc doesn't do this or turn
+	 * off the profiling time, but UML dies with a SIGPROF just before
+	 * exiting when profiling is active.
+	 */
+	change_sig(SIGPROF, 0);
+
+	/*
+	 * This signal stuff used to be in the reboot case.  However,
+	 * sometimes a timer signal can come in when we're halting (reproducably
+	 * when writing out gcov information, presumably because that takes
+	 * some time) and cause a segfault.
+	 */
+
+	/* stop timers and set timer signal to be ignored */
+	os_timer_disable(0);
+
+	/* disable SIGIO for the fds and set SIGIO to be ignored */
+	err = deactivate_all_fds();
+	if (err)
+		os_warn("deactivate_all_fds failed, errno = %d\n", -err);
+
+	/*
+	 * Let any pending signals fire now.  This ensures
+	 * that they won't be delivered after the exec, when
+	 * they are definitely not expected.
+	 */
+	unblock_signals();
+
+	os_info("\n");
+	/* Reboot */
+	if (ret) {
+		execvp(new_argv[0], new_argv);
+		perror("Failed to exec kernel");
+		ret = 1;
+	}
+	return uml_exitcode;
+}
+
+extern void *__real_malloc(int);
+extern void __real_free(void *);
+
+/* workaround for -Wmissing-prototypes warnings */
+void *__wrap_malloc(int size);
+void *__wrap_calloc(int n, int size);
+void __wrap_free(void *ptr);
+
+void *__wrap_malloc(int size)
+{
+	void *ret;
+
+	if (!kmalloc_ok)
+		return __real_malloc(size);
+	else if (size <= UM_KERN_PAGE_SIZE)
+		/* finding contiguous pages can be hard*/
+		ret = uml_kmalloc(size, UM_GFP_KERNEL);
+	else ret = vmalloc(size);
+
+	/*
+	 * glibc people insist that if malloc fails, errno should be
+	 * set by malloc as well. So we do.
+	 */
+	if (ret == NULL)
+		errno = ENOMEM;
+
+	return ret;
+}
+
+void *__wrap_calloc(int n, int size)
+{
+	void *ptr = __wrap_malloc(n * size);
+
+	if (ptr == NULL)
+		return NULL;
+	memset(ptr, 0, n * size);
+	return ptr;
+}
+
+void __wrap_free(void *ptr)
+{
+	unsigned long addr = (unsigned long) ptr;
+
+	/*
+	 * We need to know how the allocation happened, so it can be correctly
+	 * freed.  This is done by seeing what region of memory the pointer is
+	 * in -
+	 * 	physical memory - kmalloc/kfree
+	 *	kernel virtual memory - vmalloc/vfree
+	 * 	anywhere else - malloc/free
+	 * If kmalloc is not yet possible, then either high_physmem and/or
+	 * end_vm are still 0 (as at startup), in which case we call free, or
+	 * we have set them, but anyway addr has not been allocated from those
+	 * areas. So, in both cases __real_free is called.
+	 *
+	 * CAN_KMALLOC is checked because it would be bad to free a buffer
+	 * with kmalloc/vmalloc after they have been turned off during
+	 * shutdown.
+	 * XXX: However, we sometimes shutdown CAN_KMALLOC temporarily, so
+	 * there is a possibility for memory leaks.
+	 */
+
+	if ((addr >= uml_physmem) && (addr < high_physmem)) {
+		if (kmalloc_ok)
+			kfree(ptr);
+	}
+	else if ((addr >= start_vm) && (addr < end_vm)) {
+		if (kmalloc_ok)
+			vfree(ptr);
+	}
+	else __real_free(ptr);
+}
diff --git a/arch/um/os-Linux/mem.c b/arch/um/os-Linux/mem.c
new file mode 100644
index 000000000..72f302f4d
--- /dev/null
+++ b/arch/um/os-Linux/mem.c
@@ -0,0 +1,246 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stdio.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <sys/vfs.h>
+#include <linux/magic.h>
+#include <init.h>
+#include <kern_util.h>
+#include <os.h>
+#include "internal.h"
+
+/*
+ * kasan_map_memory - maps memory from @start with a size of @len.
+ * The allocated memory is filled with zeroes upon success.
+ * @start: the start address of the memory to be mapped
+ * @len: the length of the memory to be mapped
+ *
+ * This function is used to map shadow memory for KASAN in uml
+ */
+void kasan_map_memory(void *start, size_t len)
+{
+	if (mmap(start,
+		 len,
+		 PROT_READ|PROT_WRITE,
+		 MAP_FIXED|MAP_ANONYMOUS|MAP_PRIVATE|MAP_NORESERVE,
+		 -1,
+		 0) == MAP_FAILED) {
+		os_info("Couldn't allocate shadow memory: %s\n.",
+			strerror(errno));
+		exit(1);
+	}
+
+	if (madvise(start, len, MADV_DONTDUMP)) {
+		os_info("Couldn't set MAD_DONTDUMP on shadow memory: %s\n.",
+			strerror(errno));
+		exit(1);
+	}
+
+	if (madvise(start, len, MADV_DONTFORK)) {
+		os_info("Couldn't set MADV_DONTFORK on shadow memory: %s\n.",
+			strerror(errno));
+		exit(1);
+	}
+}
+
+/* Set by make_tempfile() during early boot. */
+char *tempdir = NULL;
+
+/* Check if dir is on tmpfs. Return 0 if yes, -1 if no or error. */
+static int __init check_tmpfs(const char *dir)
+{
+	struct statfs st;
+
+	os_info("Checking if %s is on tmpfs...", dir);
+	if (statfs(dir, &st) < 0) {
+		os_info("%s\n", strerror(errno));
+	} else if (st.f_type != TMPFS_MAGIC) {
+		os_info("no\n");
+	} else {
+		os_info("OK\n");
+		return 0;
+	}
+	return -1;
+}
+
+/*
+ * Choose the tempdir to use. We want something on tmpfs so that our memory is
+ * not subject to the host's vm.dirty_ratio. If a tempdir is specified in the
+ * environment, we use that even if it's not on tmpfs, but we warn the user.
+ * Otherwise, we try common tmpfs locations, and if no tmpfs directory is found
+ * then we fall back to /tmp.
+ */
+static char * __init choose_tempdir(void)
+{
+	static const char * const vars[] = {
+		"TMPDIR",
+		"TMP",
+		"TEMP",
+		NULL
+	};
+	static const char fallback_dir[] = "/tmp";
+	static const char * const tmpfs_dirs[] = {
+		"/dev/shm",
+		fallback_dir,
+		NULL
+	};
+	int i;
+	const char *dir;
+
+	os_info("Checking environment variables for a tempdir...");
+	for (i = 0; vars[i]; i++) {
+		dir = getenv(vars[i]);
+		if ((dir != NULL) && (*dir != '\0')) {
+			os_info("%s\n", dir);
+			if (check_tmpfs(dir) >= 0)
+				goto done;
+			else
+				goto warn;
+		}
+	}
+	os_info("none found\n");
+
+	for (i = 0; tmpfs_dirs[i]; i++) {
+		dir = tmpfs_dirs[i];
+		if (check_tmpfs(dir) >= 0)
+			goto done;
+	}
+
+	dir = fallback_dir;
+warn:
+	os_warn("Warning: tempdir %s is not on tmpfs\n", dir);
+done:
+	/* Make a copy since getenv results may not remain valid forever. */
+	return strdup(dir);
+}
+
+/*
+ * Create an unlinked tempfile in a suitable tempdir. template must be the
+ * basename part of the template with a leading '/'.
+ */
+static int __init make_tempfile(const char *template)
+{
+	char *tempname;
+	int fd;
+
+	if (tempdir == NULL) {
+		tempdir = choose_tempdir();
+		if (tempdir == NULL) {
+			os_warn("Failed to choose tempdir: %s\n",
+				strerror(errno));
+			return -1;
+		}
+	}
+
+#ifdef O_TMPFILE
+	fd = open(tempdir, O_CLOEXEC | O_RDWR | O_EXCL | O_TMPFILE, 0700);
+	/*
+	 * If the running system does not support O_TMPFILE flag then retry
+	 * without it.
+	 */
+	if (fd != -1 || (errno != EINVAL && errno != EISDIR &&
+			errno != EOPNOTSUPP))
+		return fd;
+#endif
+
+	tempname = malloc(strlen(tempdir) + strlen(template) + 1);
+	if (tempname == NULL)
+		return -1;
+
+	strcpy(tempname, tempdir);
+	strcat(tempname, template);
+	fd = mkstemp(tempname);
+	if (fd < 0) {
+		os_warn("open - cannot create %s: %s\n", tempname,
+			strerror(errno));
+		goto out;
+	}
+	if (unlink(tempname) < 0) {
+		perror("unlink");
+		goto close;
+	}
+	free(tempname);
+	return fd;
+close:
+	close(fd);
+out:
+	free(tempname);
+	return -1;
+}
+
+#define TEMPNAME_TEMPLATE "/vm_file-XXXXXX"
+
+static int __init create_tmp_file(unsigned long long len)
+{
+	int fd, err;
+	char zero;
+
+	fd = make_tempfile(TEMPNAME_TEMPLATE);
+	if (fd < 0)
+		exit(1);
+
+	/*
+	 * Seek to len - 1 because writing a character there will
+	 * increase the file size by one byte, to the desired length.
+	 */
+	if (lseek64(fd, len - 1, SEEK_SET) < 0) {
+		perror("lseek64");
+		exit(1);
+	}
+
+	zero = 0;
+
+	err = write(fd, &zero, 1);
+	if (err != 1) {
+		perror("write");
+		exit(1);
+	}
+
+	return fd;
+}
+
+int __init create_mem_file(unsigned long long len)
+{
+	int err, fd;
+
+	fd = create_tmp_file(len);
+
+	err = os_set_exec_close(fd);
+	if (err < 0) {
+		errno = -err;
+		perror("exec_close");
+	}
+	return fd;
+}
+
+void __init check_tmpexec(void)
+{
+	void *addr;
+	int err, fd = create_tmp_file(UM_KERN_PAGE_SIZE);
+
+	addr = mmap(NULL, UM_KERN_PAGE_SIZE,
+		    PROT_READ | PROT_WRITE | PROT_EXEC, MAP_PRIVATE, fd, 0);
+	os_info("Checking PROT_EXEC mmap in %s...", tempdir);
+	if (addr == MAP_FAILED) {
+		err = errno;
+		os_warn("%s\n", strerror(err));
+		close(fd);
+		if (err == EPERM)
+			os_warn("%s must be not mounted noexec\n", tempdir);
+		exit(1);
+	}
+	os_info("OK\n");
+	munmap(addr, UM_KERN_PAGE_SIZE);
+
+	close(fd);
+}
diff --git a/arch/um/os-Linux/process.c b/arch/um/os-Linux/process.c
new file mode 100644
index 000000000..3a2a84ab9
--- /dev/null
+++ b/arch/um/os-Linux/process.c
@@ -0,0 +1,211 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <signal.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <linux/futex.h>
+#include <sys/mman.h>
+#include <sys/ptrace.h>
+#include <sys/prctl.h>
+#include <sys/wait.h>
+#include <asm/unistd.h>
+#include <init.h>
+#include <longjmp.h>
+#include <os.h>
+#include <skas/skas.h>
+
+void os_alarm_process(int pid)
+{
+	if (pid <= 0)
+		return;
+
+	kill(pid, SIGALRM);
+}
+
+void os_kill_process(int pid, int reap_child)
+{
+	if (pid <= 0)
+		return;
+
+	/* Block signals until child is reaped */
+	block_signals();
+
+	kill(pid, SIGKILL);
+	if (reap_child)
+		CATCH_EINTR(waitpid(pid, NULL, __WALL));
+
+	unblock_signals();
+}
+
+/* Kill off a ptraced child by all means available.  kill it normally first,
+ * then PTRACE_KILL it, then PTRACE_CONT it in case it's in a run state from
+ * which it can't exit directly.
+ */
+
+void os_kill_ptraced_process(int pid, int reap_child)
+{
+	if (pid <= 0)
+		return;
+
+	/* Block signals until child is reaped */
+	block_signals();
+
+	kill(pid, SIGKILL);
+	ptrace(PTRACE_KILL, pid);
+	ptrace(PTRACE_CONT, pid);
+	if (reap_child)
+		CATCH_EINTR(waitpid(pid, NULL, __WALL));
+
+	unblock_signals();
+}
+
+pid_t os_reap_child(void)
+{
+	int status;
+
+	/* Try to reap a child */
+	return waitpid(-1, &status, WNOHANG);
+}
+
+/* Don't use the glibc version, which caches the result in TLS. It misses some
+ * syscalls, and also breaks with clone(), which does not unshare the TLS.
+ */
+
+int os_getpid(void)
+{
+	return syscall(__NR_getpid);
+}
+
+int os_map_memory(void *virt, int fd, unsigned long long off, unsigned long len,
+		  int r, int w, int x)
+{
+	void *loc;
+	int prot;
+
+	prot = (r ? PROT_READ : 0) | (w ? PROT_WRITE : 0) |
+		(x ? PROT_EXEC : 0);
+
+	loc = mmap64((void *) virt, len, prot, MAP_SHARED | MAP_FIXED,
+		     fd, off);
+	if (loc == MAP_FAILED)
+		return -errno;
+	return 0;
+}
+
+int os_protect_memory(void *addr, unsigned long len, int r, int w, int x)
+{
+	int prot = ((r ? PROT_READ : 0) | (w ? PROT_WRITE : 0) |
+		    (x ? PROT_EXEC : 0));
+
+	if (mprotect(addr, len, prot) < 0)
+		return -errno;
+
+	return 0;
+}
+
+int os_unmap_memory(void *addr, int len)
+{
+	int err;
+
+	err = munmap(addr, len);
+	if (err < 0)
+		return -errno;
+	return 0;
+}
+
+#ifndef MADV_REMOVE
+#define MADV_REMOVE KERNEL_MADV_REMOVE
+#endif
+
+int os_drop_memory(void *addr, int length)
+{
+	int err;
+
+	err = madvise(addr, length, MADV_REMOVE);
+	if (err < 0)
+		err = -errno;
+	return err;
+}
+
+int __init can_drop_memory(void)
+{
+	void *addr;
+	int fd, ok = 0;
+
+	printk(UM_KERN_INFO "Checking host MADV_REMOVE support...");
+	fd = create_mem_file(UM_KERN_PAGE_SIZE);
+	if (fd < 0) {
+		printk(UM_KERN_ERR "Creating test memory file failed, "
+		       "err = %d\n", -fd);
+		goto out;
+	}
+
+	addr = mmap64(NULL, UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE,
+		      MAP_SHARED, fd, 0);
+	if (addr == MAP_FAILED) {
+		printk(UM_KERN_ERR "Mapping test memory file failed, "
+		       "err = %d\n", -errno);
+		goto out_close;
+	}
+
+	if (madvise(addr, UM_KERN_PAGE_SIZE, MADV_REMOVE) != 0) {
+		printk(UM_KERN_ERR "MADV_REMOVE failed, err = %d\n", -errno);
+		goto out_unmap;
+	}
+
+	printk(UM_KERN_CONT "OK\n");
+	ok = 1;
+
+out_unmap:
+	munmap(addr, UM_KERN_PAGE_SIZE);
+out_close:
+	close(fd);
+out:
+	return ok;
+}
+
+void init_new_thread_signals(void)
+{
+	set_handler(SIGSEGV);
+	set_handler(SIGTRAP);
+	set_handler(SIGFPE);
+	set_handler(SIGILL);
+	set_handler(SIGBUS);
+	signal(SIGHUP, SIG_IGN);
+	set_handler(SIGIO);
+	/* We (currently) only use the child reaper IRQ in seccomp mode */
+	if (using_seccomp)
+		set_handler(SIGCHLD);
+	signal(SIGWINCH, SIG_IGN);
+}
+
+void os_set_pdeathsig(void)
+{
+	prctl(PR_SET_PDEATHSIG, SIGKILL);
+}
+
+int os_futex_wait(void *uaddr, unsigned int val)
+{
+	int r;
+
+	CATCH_EINTR(r = syscall(__NR_futex, uaddr, FUTEX_WAIT, val,
+				NULL, NULL, 0));
+	return r < 0 ? -errno : r;
+}
+
+int os_futex_wake(void *uaddr)
+{
+	int r;
+
+	CATCH_EINTR(r = syscall(__NR_futex, uaddr, FUTEX_WAKE, INT_MAX,
+				NULL, NULL, 0));
+	return r < 0 ? -errno : r;
+}
diff --git a/arch/um/os-Linux/registers.c b/arch/um/os-Linux/registers.c
new file mode 100644
index 000000000..bfba2cbc9
--- /dev/null
+++ b/arch/um/os-Linux/registers.c
@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2004 PathScale, Inc
+ * Copyright (C) 2004 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <errno.h>
+#include <string.h>
+#include <sys/ptrace.h>
+#include <sysdep/ptrace.h>
+#include <sysdep/ptrace_user.h>
+#include <registers.h>
+#include <stdlib.h>
+
+/* This is set once at boot time and not changed thereafter */
+
+unsigned long exec_regs[MAX_REG_NR];
+unsigned long *exec_fp_regs;
+
+int init_pid_registers(int pid)
+{
+	int err;
+
+	err = ptrace(PTRACE_GETREGS, pid, 0, exec_regs);
+	if (err < 0)
+		return -errno;
+
+	err = arch_init_registers(pid);
+	if (err < 0)
+		return err;
+
+	exec_fp_regs = malloc(host_fp_size);
+	get_fp_registers(pid, exec_fp_regs);
+	return 0;
+}
+
+void get_safe_registers(unsigned long *regs, unsigned long *fp_regs)
+{
+	memcpy(regs, exec_regs, sizeof(exec_regs));
+
+	if (fp_regs)
+		memcpy(fp_regs, exec_fp_regs, host_fp_size);
+}
diff --git a/arch/um/os-Linux/sigio.c b/arch/um/os-Linux/sigio.c
new file mode 100644
index 000000000..6de145f8f
--- /dev/null
+++ b/arch/um/os-Linux/sigio.c
@@ -0,0 +1,304 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2008 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <unistd.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <pty.h>
+#include <sched.h>
+#include <signal.h>
+#include <string.h>
+#include <sys/epoll.h>
+#include <asm/unistd.h>
+#include <kern_util.h>
+#include <init.h>
+#include <os.h>
+#include <sigio.h>
+#include <um_malloc.h>
+
+/*
+ * Protected by sigio_lock(), also used by sigio_cleanup, which is an
+ * exitcall.
+ */
+static struct os_helper_thread *write_sigio_td;
+
+static int epollfd = -1;
+
+#define MAX_EPOLL_EVENTS 64
+
+static struct epoll_event epoll_events[MAX_EPOLL_EVENTS];
+
+static void *write_sigio_thread(void *unused)
+{
+	int pid = getpid();
+	int r;
+
+	os_fix_helper_thread_signals();
+
+	while (1) {
+		r = epoll_wait(epollfd, epoll_events, MAX_EPOLL_EVENTS, -1);
+		if (r < 0) {
+			if (errno == EINTR)
+				continue;
+			printk(UM_KERN_ERR "%s: epoll_wait failed, errno = %d\n",
+			       __func__, errno);
+		}
+
+		CATCH_EINTR(r = syscall(__NR_tgkill, pid, pid, SIGIO));
+		if (r < 0)
+			printk(UM_KERN_ERR "%s: tgkill failed, errno = %d\n",
+			       __func__, errno);
+	}
+
+	return NULL;
+}
+
+int __add_sigio_fd(int fd)
+{
+	struct epoll_event event = {
+		.data.fd = fd,
+		.events = EPOLLIN | EPOLLET,
+	};
+	int r;
+
+	CATCH_EINTR(r = epoll_ctl(epollfd, EPOLL_CTL_ADD, fd, &event));
+	return r < 0 ? -errno : 0;
+}
+
+int add_sigio_fd(int fd)
+{
+	int err;
+
+	sigio_lock();
+	err = __add_sigio_fd(fd);
+	sigio_unlock();
+
+	return err;
+}
+
+int __ignore_sigio_fd(int fd)
+{
+	struct epoll_event event;
+	int r;
+
+	CATCH_EINTR(r = epoll_ctl(epollfd, EPOLL_CTL_DEL, fd, &event));
+	return r < 0 ? -errno : 0;
+}
+
+int ignore_sigio_fd(int fd)
+{
+	int err;
+
+	sigio_lock();
+	err = __ignore_sigio_fd(fd);
+	sigio_unlock();
+
+	return err;
+}
+
+static void write_sigio_workaround(void)
+{
+	int err;
+
+	sigio_lock();
+	if (write_sigio_td)
+		goto out;
+
+	epollfd = epoll_create(MAX_EPOLL_EVENTS);
+	if (epollfd < 0) {
+		printk(UM_KERN_ERR "%s: epoll_create failed, errno = %d\n",
+		       __func__, errno);
+		goto out;
+	}
+
+	err = os_run_helper_thread(&write_sigio_td, write_sigio_thread, NULL);
+	if (err < 0) {
+		printk(UM_KERN_ERR "%s: os_run_helper_thread failed, errno = %d\n",
+		       __func__, -err);
+		close(epollfd);
+		epollfd = -1;
+		goto out;
+	}
+
+out:
+	sigio_unlock();
+}
+
+void sigio_broken(void)
+{
+	write_sigio_workaround();
+}
+
+/* Changed during early boot */
+static int pty_output_sigio;
+
+void maybe_sigio_broken(int fd)
+{
+	if (!isatty(fd))
+		return;
+
+	if (pty_output_sigio)
+		return;
+
+	sigio_broken();
+}
+
+static void sigio_cleanup(void)
+{
+	if (!write_sigio_td)
+		return;
+
+	os_kill_helper_thread(write_sigio_td);
+	write_sigio_td = NULL;
+}
+
+__uml_exitcall(sigio_cleanup);
+
+/* Used as a flag during SIGIO testing early in boot */
+static int got_sigio;
+
+static void __init handler(int sig)
+{
+	got_sigio = 1;
+}
+
+struct openpty_arg {
+	int master;
+	int slave;
+	int err;
+};
+
+static void openpty_cb(void *arg)
+{
+	struct openpty_arg *info = arg;
+
+	info->err = 0;
+	if (openpty(&info->master, &info->slave, NULL, NULL, NULL))
+		info->err = -errno;
+}
+
+static int async_pty(int master, int slave)
+{
+	int flags;
+
+	flags = fcntl(master, F_GETFL);
+	if (flags < 0)
+		return -errno;
+
+	if ((fcntl(master, F_SETFL, flags | O_NONBLOCK | O_ASYNC) < 0) ||
+	    (fcntl(master, F_SETOWN, os_getpid()) < 0))
+		return -errno;
+
+	if ((fcntl(slave, F_SETFL, flags | O_NONBLOCK) < 0))
+		return -errno;
+
+	return 0;
+}
+
+static void __init check_one_sigio(void (*proc)(int, int))
+{
+	struct sigaction old, new;
+	struct openpty_arg pty = { .master = -1, .slave = -1 };
+	int master, slave, err;
+
+	initial_thread_cb(openpty_cb, &pty);
+	if (pty.err) {
+		printk(UM_KERN_ERR "check_one_sigio failed, errno = %d\n",
+		       -pty.err);
+		return;
+	}
+
+	master = pty.master;
+	slave = pty.slave;
+
+	if ((master == -1) || (slave == -1)) {
+		printk(UM_KERN_ERR "check_one_sigio failed to allocate a "
+		       "pty\n");
+		return;
+	}
+
+	/* Not now, but complain so we now where we failed. */
+	err = raw(master);
+	if (err < 0) {
+		printk(UM_KERN_ERR "check_one_sigio : raw failed, errno = %d\n",
+		      -err);
+		return;
+	}
+
+	err = async_pty(master, slave);
+	if (err < 0) {
+		printk(UM_KERN_ERR "check_one_sigio : sigio_async failed, "
+		       "err = %d\n", -err);
+		return;
+	}
+
+	if (sigaction(SIGIO, NULL, &old) < 0) {
+		printk(UM_KERN_ERR "check_one_sigio : sigaction 1 failed, "
+		       "errno = %d\n", errno);
+		return;
+	}
+
+	new = old;
+	new.sa_handler = handler;
+	if (sigaction(SIGIO, &new, NULL) < 0) {
+		printk(UM_KERN_ERR "check_one_sigio : sigaction 2 failed, "
+		       "errno = %d\n", errno);
+		return;
+	}
+
+	got_sigio = 0;
+	(*proc)(master, slave);
+
+	close(master);
+	close(slave);
+
+	if (sigaction(SIGIO, &old, NULL) < 0)
+		printk(UM_KERN_ERR "check_one_sigio : sigaction 3 failed, "
+		       "errno = %d\n", errno);
+}
+
+static void tty_output(int master, int slave)
+{
+	int n;
+	char buf[512];
+
+	printk(UM_KERN_INFO "Checking that host ptys support output SIGIO...");
+
+	memset(buf, 0, sizeof(buf));
+
+	while (write(master, buf, sizeof(buf)) > 0) ;
+	if (errno != EAGAIN)
+		printk(UM_KERN_ERR "tty_output : write failed, errno = %d\n",
+		       errno);
+	while (((n = read(slave, buf, sizeof(buf))) > 0) &&
+	       !({ barrier(); got_sigio; }))
+		;
+
+	if (got_sigio) {
+		printk(UM_KERN_CONT "Yes\n");
+		pty_output_sigio = 1;
+	} else if (n == -EAGAIN)
+		printk(UM_KERN_CONT "No, enabling workaround\n");
+	else
+		printk(UM_KERN_CONT "tty_output : read failed, err = %d\n", n);
+}
+
+static void __init check_sigio(void)
+{
+	if ((access("/dev/ptmx", R_OK) < 0) &&
+	    (access("/dev/ptyp0", R_OK) < 0)) {
+		printk(UM_KERN_WARNING "No pseudo-terminals available - "
+		       "skipping pty SIGIO check\n");
+		return;
+	}
+	check_one_sigio(tty_output);
+}
+
+/* Here because it only does the SIGIO testing for now */
+void __init os_check_bugs(void)
+{
+	check_sigio();
+}
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
new file mode 100644
index 000000000..6c993bc8c
--- /dev/null
+++ b/arch/um/os-Linux/signal.c
@@ -0,0 +1,506 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
+ * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
+ * Copyright (C) 2004 PathScale, Inc
+ * Copyright (C) 2004 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stdlib.h>
+#include <stdarg.h>
+#include <stdbool.h>
+#include <errno.h>
+#include <signal.h>
+#include <string.h>
+#include <strings.h>
+#include <as-layout.h>
+#include <kern_util.h>
+#include <os.h>
+#include <skas.h>
+#include <sysdep/mcontext.h>
+#include <um_malloc.h>
+#include <sys/ucontext.h>
+#include <timetravel.h>
+#include "internal.h"
+
+void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *, void *mc) = {
+	[SIGTRAP]	= relay_signal,
+	[SIGFPE]	= relay_signal,
+	[SIGILL]	= relay_signal,
+	[SIGWINCH]	= winch,
+	[SIGBUS]	= relay_signal,
+	[SIGSEGV]	= segv_handler,
+	[SIGIO]		= sigio_handler,
+	[SIGCHLD]	= sigchld_handler,
+};
+
+static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
+{
+	struct uml_pt_regs r;
+
+	r.is_user = 0;
+	if (sig == SIGSEGV) {
+		/* For segfaults, we want the data from the sigcontext. */
+		get_regs_from_mc(&r, mc);
+		GET_FAULTINFO_FROM_MC(r.faultinfo, mc);
+	}
+
+	/* enable signals if sig isn't IRQ signal */
+	if ((sig != SIGIO) && (sig != SIGWINCH) && (sig != SIGCHLD))
+		unblock_signals_trace();
+
+	(*sig_info[sig])(sig, si, &r, mc);
+}
+
+/*
+ * These are the asynchronous signals.  SIGPROF is excluded because we want to
+ * be able to profile all of UML, not just the non-critical sections.  If
+ * profiling is not thread-safe, then that is not my problem.  We can disable
+ * profiling when SMP is enabled in that case.
+ */
+#define SIGIO_BIT 0
+#define SIGIO_MASK (1 << SIGIO_BIT)
+
+#define SIGALRM_BIT 1
+#define SIGALRM_MASK (1 << SIGALRM_BIT)
+
+#define SIGCHLD_BIT 2
+#define SIGCHLD_MASK (1 << SIGCHLD_BIT)
+
+__thread int signals_enabled;
+#if IS_ENABLED(CONFIG_UML_TIME_TRAVEL_SUPPORT)
+static int signals_blocked, signals_blocked_pending;
+#endif
+static __thread unsigned int signals_pending;
+static __thread unsigned int signals_active;
+
+static void sig_handler(int sig, struct siginfo *si, mcontext_t *mc)
+{
+	int enabled = signals_enabled;
+
+#if IS_ENABLED(CONFIG_UML_TIME_TRAVEL_SUPPORT)
+	if ((signals_blocked ||
+	     __atomic_load_n(&signals_blocked_pending, __ATOMIC_SEQ_CST)) &&
+	    (sig == SIGIO)) {
+		/* increment so unblock will do another round */
+		__atomic_add_fetch(&signals_blocked_pending, 1,
+				   __ATOMIC_SEQ_CST);
+		return;
+	}
+#endif
+
+	if (!enabled && (sig == SIGIO)) {
+		/*
+		 * In TT_MODE_EXTERNAL, need to still call time-travel
+		 * handlers. This will mark signals_pending by itself
+		 * (only if necessary.)
+		 * Note we won't get here if signals are hard-blocked
+		 * (which is handled above), in that case the hard-
+		 * unblock will handle things.
+		 */
+		if (time_travel_mode == TT_MODE_EXTERNAL)
+			sigio_run_timetravel_handlers();
+		else
+			signals_pending |= SIGIO_MASK;
+		return;
+	}
+
+	if (!enabled && (sig == SIGCHLD)) {
+		signals_pending |= SIGCHLD_MASK;
+		return;
+	}
+
+	block_signals_trace();
+
+	sig_handler_common(sig, si, mc);
+
+	um_set_signals_trace(enabled);
+}
+
+static void timer_real_alarm_handler(mcontext_t *mc)
+{
+	struct uml_pt_regs regs;
+
+	if (mc != NULL)
+		get_regs_from_mc(&regs, mc);
+	else
+		memset(&regs, 0, sizeof(regs));
+	timer_handler(SIGALRM, NULL, &regs);
+}
+
+static void timer_alarm_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
+{
+	int enabled;
+
+	enabled = signals_enabled;
+	if (!signals_enabled) {
+		signals_pending |= SIGALRM_MASK;
+		return;
+	}
+
+	block_signals_trace();
+
+	signals_active |= SIGALRM_MASK;
+
+	timer_real_alarm_handler(mc);
+
+	signals_active &= ~SIGALRM_MASK;
+
+	um_set_signals_trace(enabled);
+}
+
+void deliver_alarm(void) {
+    timer_alarm_handler(SIGALRM, NULL, NULL);
+}
+
+void timer_set_signal_handler(void)
+{
+	set_handler(SIGALRM);
+}
+
+int timer_alarm_pending(void)
+{
+	return !!(signals_pending & SIGALRM_MASK);
+}
+
+void set_sigstack(void *sig_stack, int size)
+{
+	stack_t stack = {
+		.ss_flags = 0,
+		.ss_sp = sig_stack,
+		.ss_size = size
+	};
+
+	if (sigaltstack(&stack, NULL) != 0)
+		panic("enabling signal stack failed, errno = %d\n", errno);
+}
+
+static void sigusr1_handler(int sig, struct siginfo *unused_si, mcontext_t *mc)
+{
+	uml_pm_wake();
+}
+
+void register_pm_wake_signal(void)
+{
+	set_handler(SIGUSR1);
+}
+
+static void (*handlers[_NSIG])(int sig, struct siginfo *si, mcontext_t *mc) = {
+	[SIGSEGV] = sig_handler,
+	[SIGBUS] = sig_handler,
+	[SIGILL] = sig_handler,
+	[SIGFPE] = sig_handler,
+	[SIGTRAP] = sig_handler,
+
+	[SIGIO] = sig_handler,
+	[SIGWINCH] = sig_handler,
+	/* SIGCHLD is only actually registered in seccomp mode. */
+	[SIGCHLD] = sig_handler,
+	[SIGALRM] = timer_alarm_handler,
+
+	[SIGUSR1] = sigusr1_handler,
+};
+
+static void hard_handler(int sig, siginfo_t *si, void *p)
+{
+	ucontext_t *uc = p;
+	mcontext_t *mc = &uc->uc_mcontext;
+	int save_errno = errno;
+
+	(*handlers[sig])(sig, (struct siginfo *)si, mc);
+
+	errno = save_errno;
+}
+
+void set_handler(int sig)
+{
+	struct sigaction action;
+	int flags = SA_SIGINFO | SA_ONSTACK;
+	sigset_t sig_mask;
+
+	action.sa_sigaction = hard_handler;
+
+	/* block irq ones */
+	sigemptyset(&action.sa_mask);
+	sigaddset(&action.sa_mask, SIGIO);
+	sigaddset(&action.sa_mask, SIGWINCH);
+	sigaddset(&action.sa_mask, SIGALRM);
+	if (using_seccomp)
+		sigaddset(&action.sa_mask, SIGCHLD);
+
+	if (sig == SIGSEGV)
+		flags |= SA_NODEFER;
+
+	if (sigismember(&action.sa_mask, sig))
+		flags |= SA_RESTART; /* if it's an irq signal */
+
+	action.sa_flags = flags;
+	action.sa_restorer = NULL;
+	if (sigaction(sig, &action, NULL) < 0)
+		panic("sigaction failed - errno = %d\n", errno);
+
+	sigemptyset(&sig_mask);
+	sigaddset(&sig_mask, sig);
+	if (sigprocmask(SIG_UNBLOCK, &sig_mask, NULL) < 0)
+		panic("sigprocmask failed - errno = %d\n", errno);
+}
+
+void send_sigio_to_self(void)
+{
+	kill(os_getpid(), SIGIO);
+}
+
+int change_sig(int signal, int on)
+{
+	sigset_t sigset;
+
+	sigemptyset(&sigset);
+	sigaddset(&sigset, signal);
+	if (sigprocmask(on ? SIG_UNBLOCK : SIG_BLOCK, &sigset, NULL) < 0)
+		return -errno;
+
+	return 0;
+}
+
+static inline void __block_signals(void)
+{
+	if (!signals_enabled)
+		return;
+
+	os_local_ipi_disable();
+	barrier();
+	signals_enabled = 0;
+}
+
+static inline void __unblock_signals(void)
+{
+	if (signals_enabled)
+		return;
+
+	signals_enabled = 1;
+	barrier();
+	os_local_ipi_enable();
+}
+
+void block_signals(void)
+{
+	__block_signals();
+	/*
+	 * This must return with signals disabled, so this barrier
+	 * ensures that writes are flushed out before the return.
+	 * This might matter if gcc figures out how to inline this and
+	 * decides to shuffle this code into the caller.
+	 */
+	barrier();
+}
+
+void unblock_signals(void)
+{
+	int save_pending;
+
+	if (signals_enabled == 1)
+		return;
+
+	__unblock_signals();
+
+#if IS_ENABLED(CONFIG_UML_TIME_TRAVEL_SUPPORT)
+	deliver_time_travel_irqs();
+#endif
+
+	/*
+	 * We loop because the IRQ handler returns with interrupts off.  So,
+	 * interrupts may have arrived and we need to re-enable them and
+	 * recheck signals_pending.
+	 */
+	while (1) {
+		/*
+		 * Save and reset save_pending after enabling signals.  This
+		 * way, signals_pending won't be changed while we're reading it.
+		 *
+		 * Setting signals_enabled and reading signals_pending must
+		 * happen in this order, so have the barrier here.
+		 */
+		barrier();
+
+		save_pending = signals_pending;
+		if (save_pending == 0)
+			return;
+
+		signals_pending = 0;
+
+		/*
+		 * We have pending interrupts, so disable signals, as the
+		 * handlers expect them off when they are called.  They will
+		 * be enabled again above. We need to trace this, as we're
+		 * expected to be enabling interrupts already, but any more
+		 * tracing that happens inside the handlers we call for the
+		 * pending signals will mess up the tracing state.
+		 */
+		__block_signals();
+		um_trace_signals_off();
+
+		/*
+		 * Deal with SIGIO first because the alarm handler might
+		 * schedule, leaving the pending SIGIO stranded until we come
+		 * back here.
+		 *
+		 * SIGIO's handler doesn't use siginfo or mcontext,
+		 * so they can be NULL.
+		 */
+		if (save_pending & SIGIO_MASK)
+			sig_handler_common(SIGIO, NULL, NULL);
+
+		if (save_pending & SIGCHLD_MASK) {
+			struct uml_pt_regs regs = {};
+
+			sigchld_handler(SIGCHLD, NULL, &regs, NULL);
+		}
+
+		/* Do not reenter the handler */
+
+		if ((save_pending & SIGALRM_MASK) && (!(signals_active & SIGALRM_MASK)))
+			timer_real_alarm_handler(NULL);
+
+		/* Rerun the loop only if there is still pending SIGIO and not in TIMER handler */
+
+		if (!(signals_pending & SIGIO_MASK) && (signals_active & SIGALRM_MASK))
+			return;
+
+		/* Re-enable signals and trace that we're doing so. */
+		um_trace_signals_on();
+		__unblock_signals();
+	}
+}
+
+int um_get_signals(void)
+{
+	return signals_enabled;
+}
+
+int um_set_signals(int enable)
+{
+	int ret;
+	if (signals_enabled == enable)
+		return enable;
+
+	ret = signals_enabled;
+	if (enable)
+		unblock_signals();
+	else block_signals();
+
+	return ret;
+}
+
+int um_set_signals_trace(int enable)
+{
+	int ret;
+	if (signals_enabled == enable)
+		return enable;
+
+	ret = signals_enabled;
+	if (enable)
+		unblock_signals_trace();
+	else
+		block_signals_trace();
+
+	return ret;
+}
+
+#if IS_ENABLED(CONFIG_UML_TIME_TRAVEL_SUPPORT)
+void mark_sigio_pending(void)
+{
+	/*
+	 * It would seem that this should be atomic so
+	 * it isn't a read-modify-write with a signal
+	 * that could happen in the middle, losing the
+	 * value set by the signal.
+	 *
+	 * However, this function is only called when in
+	 * time-travel=ext simulation mode, in which case
+	 * the only signal ever pending is SIGIO, which
+	 * is blocked while this can be called, and the
+	 * timer signal (SIGALRM) cannot happen.
+	 */
+	signals_pending |= SIGIO_MASK;
+}
+
+void block_signals_hard(void)
+{
+	signals_blocked++;
+	barrier();
+}
+
+void unblock_signals_hard(void)
+{
+	static bool unblocking;
+
+	if (!signals_blocked)
+		panic("unblocking signals while not blocked");
+
+	if (--signals_blocked)
+		return;
+	/*
+	 * Must be set to 0 before we check pending so the
+	 * SIGIO handler will run as normal unless we're still
+	 * going to process signals_blocked_pending.
+	 */
+	barrier();
+
+	/*
+	 * Note that block_signals_hard()/unblock_signals_hard() can be called
+	 * within the unblock_signals()/sigio_run_timetravel_handlers() below.
+	 * This would still be prone to race conditions since it's actually a
+	 * call _within_ e.g. vu_req_read_message(), where we observed this
+	 * issue, which loops. Thus, if the inner call handles the recorded
+	 * pending signals, we can get out of the inner call with the real
+	 * signal hander no longer blocked, and still have a race. Thus don't
+	 * handle unblocking in the inner call, if it happens, but only in
+	 * the outermost call - 'unblocking' serves as an ownership for the
+	 * signals_blocked_pending decrement.
+	 */
+	if (unblocking)
+		return;
+	unblocking = true;
+
+	while (__atomic_load_n(&signals_blocked_pending, __ATOMIC_SEQ_CST)) {
+		if (signals_enabled) {
+			/* signals are enabled so we can touch this */
+			signals_pending |= SIGIO_MASK;
+			/*
+			 * this is a bit inefficient, but that's
+			 * not really important
+			 */
+			block_signals();
+			unblock_signals();
+		} else {
+			/*
+			 * we need to run time-travel handlers even
+			 * if not enabled
+			 */
+			sigio_run_timetravel_handlers();
+		}
+
+		/*
+		 * The decrement of signals_blocked_pending must be atomic so
+		 * that the signal handler will either happen before or after
+		 * the decrement, not during a read-modify-write:
+		 *  - If it happens before, it can increment it and we'll
+		 *    decrement it and do another round in the loop.
+		 *  - If it happens after it'll see 0 for both signals_blocked
+		 *    and signals_blocked_pending and thus run the handler as
+		 *    usual (subject to signals_enabled, but that's unrelated.)
+		 *
+		 * Note that a call to unblock_signals_hard() within the calls
+		 * to unblock_signals() or sigio_run_timetravel_handlers() above
+		 * will do nothing due to the 'unblocking' state, so this cannot
+		 * underflow as the only one decrementing will be the outermost
+		 * one.
+		 */
+		if (__atomic_sub_fetch(&signals_blocked_pending, 1,
+				       __ATOMIC_SEQ_CST) < 0)
+			panic("signals_blocked_pending underflow");
+	}
+
+	unblocking = false;
+}
+#endif
diff --git a/arch/um/os-Linux/skas/Makefile b/arch/um/os-Linux/skas/Makefile
new file mode 100644
index 000000000..75f11989d
--- /dev/null
+++ b/arch/um/os-Linux/skas/Makefile
@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2002 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
+#
+
+obj-y := mem.o process.o
+
+USER_OBJS := $(obj-y)
+
+include $(srctree)/arch/um/scripts/Makefile.rules
diff --git a/arch/um/os-Linux/skas/mem.c b/arch/um/os-Linux/skas/mem.c
new file mode 100644
index 000000000..8b9921ac3
--- /dev/null
+++ b/arch/um/os-Linux/skas/mem.c
@@ -0,0 +1,284 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2021 Benjamin Berg <benjamin@sipsolutions.net>
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stddef.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <init.h>
+#include <as-layout.h>
+#include <mm_id.h>
+#include <os.h>
+#include <ptrace_user.h>
+#include <registers.h>
+#include <skas.h>
+#include <sysdep/ptrace.h>
+#include <sysdep/stub.h>
+#include "../internal.h"
+
+extern char __syscall_stub_start[];
+
+void syscall_stub_dump_error(struct mm_id *mm_idp)
+{
+	struct stub_data *proc_data = (void *)mm_idp->stack;
+	struct stub_syscall *sc;
+
+	if (proc_data->syscall_data_len < 0 ||
+	    proc_data->syscall_data_len >= ARRAY_SIZE(proc_data->syscall_data))
+		panic("Syscall data was corrupted by stub (len is: %d, expected maximum: %d)!",
+			proc_data->syscall_data_len,
+			mm_idp->syscall_data_len);
+
+	sc = &proc_data->syscall_data[proc_data->syscall_data_len];
+
+	printk(UM_KERN_ERR "%s : length = %d, last offset = %d",
+		__func__, mm_idp->syscall_data_len,
+		proc_data->syscall_data_len);
+	printk(UM_KERN_ERR "%s : stub syscall type %d failed, return value = 0x%lx\n",
+		__func__, sc->syscall, proc_data->err);
+
+	print_hex_dump(UM_KERN_ERR, "    syscall data: ", 0,
+		       16, 4, sc, sizeof(*sc), 0);
+
+	if (using_seccomp) {
+		printk(UM_KERN_ERR "%s: FD map num: %d", __func__,
+		       mm_idp->syscall_fd_num);
+		print_hex_dump(UM_KERN_ERR,
+				"    FD map: ", 0, 16,
+				sizeof(mm_idp->syscall_fd_map[0]),
+				mm_idp->syscall_fd_map,
+				sizeof(mm_idp->syscall_fd_map), 0);
+	}
+}
+
+static inline unsigned long *check_init_stack(struct mm_id * mm_idp,
+					      unsigned long *stack)
+{
+	if (stack == NULL) {
+		stack = (unsigned long *) mm_idp->stack + 2;
+		*stack = 0;
+	}
+	return stack;
+}
+
+static unsigned long syscall_regs[MAX_REG_NR];
+
+static int __init init_syscall_regs(void)
+{
+	get_safe_registers(syscall_regs, NULL);
+
+	syscall_regs[REGS_IP_INDEX] = STUB_CODE +
+		((unsigned long) stub_syscall_handler -
+		 (unsigned long) __syscall_stub_start);
+	syscall_regs[REGS_SP_INDEX] = STUB_DATA +
+		offsetof(struct stub_data, sigstack) +
+		sizeof(((struct stub_data *) 0)->sigstack) -
+		sizeof(void *);
+
+	return 0;
+}
+
+__initcall(init_syscall_regs);
+
+static inline long do_syscall_stub(struct mm_id *mm_idp)
+{
+	struct stub_data *proc_data = (void *)mm_idp->stack;
+	int n, i;
+	int err, pid = mm_idp->pid;
+
+	/* Inform process how much we have filled in. */
+	proc_data->syscall_data_len = mm_idp->syscall_data_len;
+
+	if (using_seccomp) {
+		proc_data->restart_wait = 1;
+		wait_stub_done_seccomp(mm_idp, 0, 1);
+	} else {
+		n = ptrace_setregs(pid, syscall_regs);
+		if (n < 0) {
+			printk(UM_KERN_ERR "Registers -\n");
+			for (i = 0; i < MAX_REG_NR; i++)
+				printk(UM_KERN_ERR "\t%d\t0x%lx\n", i, syscall_regs[i]);
+			panic("%s : PTRACE_SETREGS failed, errno = %d\n",
+			      __func__, -n);
+		}
+
+		err = ptrace(PTRACE_CONT, pid, 0, 0);
+		if (err)
+			panic("Failed to continue stub, pid = %d, errno = %d\n",
+			      pid, errno);
+
+		wait_stub_done(pid);
+	}
+
+	/*
+	 * proc_data->err will be negative if there was an (unexpected) error.
+	 * In that case, syscall_data_len points to the last executed syscall,
+	 * otherwise it will be zero (but we do not need to rely on that).
+	 */
+	if (proc_data->err < 0) {
+		syscall_stub_dump_error(mm_idp);
+
+		/* Store error code in case someone tries to add more syscalls */
+		mm_idp->syscall_data_len = proc_data->err;
+	} else {
+		mm_idp->syscall_data_len = 0;
+	}
+
+	if (using_seccomp)
+		mm_idp->syscall_fd_num = 0;
+
+	return mm_idp->syscall_data_len;
+}
+
+int syscall_stub_flush(struct mm_id *mm_idp)
+{
+	int res;
+
+	if (mm_idp->syscall_data_len == 0)
+		return 0;
+
+	/* If an error happened already, report it and reset the state. */
+	if (mm_idp->syscall_data_len < 0) {
+		res = mm_idp->syscall_data_len;
+		mm_idp->syscall_data_len = 0;
+		return res;
+	}
+
+	res = do_syscall_stub(mm_idp);
+	mm_idp->syscall_data_len = 0;
+
+	return res;
+}
+
+struct stub_syscall *syscall_stub_alloc(struct mm_id *mm_idp)
+{
+	struct stub_syscall *sc;
+	struct stub_data *proc_data = (struct stub_data *) mm_idp->stack;
+
+	if (mm_idp->syscall_data_len > 0 &&
+	    mm_idp->syscall_data_len == ARRAY_SIZE(proc_data->syscall_data))
+		do_syscall_stub(mm_idp);
+
+	if (mm_idp->syscall_data_len < 0) {
+		/* Return dummy to retain error state. */
+		sc = &proc_data->syscall_data[0];
+	} else {
+		sc = &proc_data->syscall_data[mm_idp->syscall_data_len];
+		mm_idp->syscall_data_len += 1;
+	}
+	memset(sc, 0, sizeof(*sc));
+
+	return sc;
+}
+
+static struct stub_syscall *syscall_stub_get_previous(struct mm_id *mm_idp,
+						      int syscall_type,
+						      unsigned long virt)
+{
+	if (mm_idp->syscall_data_len > 0) {
+		struct stub_data *proc_data = (void *) mm_idp->stack;
+		struct stub_syscall *sc;
+
+		sc = &proc_data->syscall_data[mm_idp->syscall_data_len - 1];
+
+		if (sc->syscall == syscall_type &&
+		    sc->mem.addr + sc->mem.length == virt)
+			return sc;
+	}
+
+	return NULL;
+}
+
+static int get_stub_fd(struct mm_id *mm_idp, int fd)
+{
+	int i;
+
+	/* Find an FD slot (or flush and use first) */
+	if (!using_seccomp)
+		return fd;
+
+	/* Already crashed, value does not matter */
+	if (mm_idp->syscall_data_len < 0)
+		return 0;
+
+	/* Find existing FD in map if we can allocate another syscall */
+	if (mm_idp->syscall_data_len <
+	    ARRAY_SIZE(((struct stub_data *)NULL)->syscall_data)) {
+		for (i = 0; i < mm_idp->syscall_fd_num; i++) {
+			if (mm_idp->syscall_fd_map[i] == fd)
+				return i;
+		}
+
+		if (mm_idp->syscall_fd_num < STUB_MAX_FDS) {
+			i = mm_idp->syscall_fd_num;
+			mm_idp->syscall_fd_map[i] = fd;
+
+			mm_idp->syscall_fd_num++;
+
+			return i;
+		}
+	}
+
+	/* FD map full or no syscall space available, continue after flush */
+	do_syscall_stub(mm_idp);
+	mm_idp->syscall_fd_map[0] = fd;
+	mm_idp->syscall_fd_num = 1;
+
+	return 0;
+}
+
+int map(struct mm_id *mm_idp, unsigned long virt, unsigned long len, int prot,
+	int phys_fd, unsigned long long offset)
+{
+	struct stub_syscall *sc;
+
+	/* Compress with previous syscall if that is possible */
+	sc = syscall_stub_get_previous(mm_idp, STUB_SYSCALL_MMAP, virt);
+	if (sc && sc->mem.prot == prot &&
+	    sc->mem.offset == MMAP_OFFSET(offset - sc->mem.length)) {
+		int prev_fd = sc->mem.fd;
+
+		if (using_seccomp)
+			prev_fd = mm_idp->syscall_fd_map[sc->mem.fd];
+
+		if (phys_fd == prev_fd) {
+			sc->mem.length += len;
+			return 0;
+		}
+	}
+
+	phys_fd = get_stub_fd(mm_idp, phys_fd);
+
+	sc = syscall_stub_alloc(mm_idp);
+	sc->syscall = STUB_SYSCALL_MMAP;
+	sc->mem.addr = virt;
+	sc->mem.length = len;
+	sc->mem.prot = prot;
+	sc->mem.fd = phys_fd;
+	sc->mem.offset = MMAP_OFFSET(offset);
+
+	return 0;
+}
+
+int unmap(struct mm_id *mm_idp, unsigned long addr, unsigned long len)
+{
+	struct stub_syscall *sc;
+
+	/* Compress with previous syscall if that is possible */
+	sc = syscall_stub_get_previous(mm_idp, STUB_SYSCALL_MUNMAP, addr);
+	if (sc) {
+		sc->mem.length += len;
+		return 0;
+	}
+
+	sc = syscall_stub_alloc(mm_idp);
+	sc->syscall = STUB_SYSCALL_MUNMAP;
+	sc->mem.addr = addr;
+	sc->mem.length = len;
+
+	return 0;
+}
diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
new file mode 100644
index 000000000..d6c22f8aa
--- /dev/null
+++ b/arch/um/os-Linux/skas/process.c
@@ -0,0 +1,908 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2021 Benjamin Berg <benjamin@sipsolutions.net>
+ * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
+ * Copyright (C) 2002- 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stdlib.h>
+#include <stdbool.h>
+#include <unistd.h>
+#include <sched.h>
+#include <errno.h>
+#include <string.h>
+#include <fcntl.h>
+#include <mem_user.h>
+#include <sys/mman.h>
+#include <sys/wait.h>
+#include <sys/stat.h>
+#include <sys/socket.h>
+#include <asm/unistd.h>
+#include <as-layout.h>
+#include <init.h>
+#include <kern_util.h>
+#include <mem.h>
+#include <os.h>
+#include <ptrace_user.h>
+#include <registers.h>
+#include <skas.h>
+#include <sysdep/stub.h>
+#include <sysdep/mcontext.h>
+#include <linux/futex.h>
+#include <linux/threads.h>
+#include <timetravel.h>
+#include <asm-generic/rwonce.h>
+#include "../internal.h"
+
+int is_skas_winch(int pid, int fd, void *data)
+{
+	return pid == getpgrp();
+}
+
+static const char *ptrace_reg_name(int idx)
+{
+#define R(n) case HOST_##n: return #n
+
+	switch (idx) {
+#ifdef __x86_64__
+	R(BX);
+	R(CX);
+	R(DI);
+	R(SI);
+	R(DX);
+	R(BP);
+	R(AX);
+	R(R8);
+	R(R9);
+	R(R10);
+	R(R11);
+	R(R12);
+	R(R13);
+	R(R14);
+	R(R15);
+	R(ORIG_AX);
+	R(CS);
+	R(SS);
+	R(EFLAGS);
+#elif defined(__i386__)
+	R(IP);
+	R(SP);
+	R(EFLAGS);
+	R(AX);
+	R(BX);
+	R(CX);
+	R(DX);
+	R(SI);
+	R(DI);
+	R(BP);
+	R(CS);
+	R(SS);
+	R(DS);
+	R(FS);
+	R(ES);
+	R(GS);
+	R(ORIG_AX);
+#endif
+	}
+	return "";
+}
+
+static int ptrace_dump_regs(int pid)
+{
+	unsigned long regs[MAX_REG_NR];
+	int i;
+
+	if (ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
+		return -errno;
+
+	printk(UM_KERN_ERR "Stub registers -\n");
+	for (i = 0; i < ARRAY_SIZE(regs); i++) {
+		const char *regname = ptrace_reg_name(i);
+
+		printk(UM_KERN_ERR "\t%s\t(%2d): %lx\n", regname, i, regs[i]);
+	}
+
+	return 0;
+}
+
+/*
+ * Signals that are OK to receive in the stub - we'll just continue it.
+ * SIGWINCH will happen when UML is inside a detached screen.
+ */
+#define STUB_SIG_MASK ((1 << SIGALRM) | (1 << SIGWINCH))
+
+/* Signals that the stub will finish with - anything else is an error */
+#define STUB_DONE_MASK (1 << SIGTRAP)
+
+void wait_stub_done(int pid)
+{
+	int n, status, err;
+
+	while (1) {
+		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
+		if ((n < 0) || !WIFSTOPPED(status))
+			goto bad_wait;
+
+		if (((1 << WSTOPSIG(status)) & STUB_SIG_MASK) == 0)
+			break;
+
+		err = ptrace(PTRACE_CONT, pid, 0, 0);
+		if (err) {
+			printk(UM_KERN_ERR "%s : continue failed, errno = %d\n",
+			       __func__, errno);
+			fatal_sigsegv();
+		}
+	}
+
+	if (((1 << WSTOPSIG(status)) & STUB_DONE_MASK) != 0)
+		return;
+
+bad_wait:
+	err = ptrace_dump_regs(pid);
+	if (err)
+		printk(UM_KERN_ERR "Failed to get registers from stub, errno = %d\n",
+		       -err);
+	printk(UM_KERN_ERR "%s : failed to wait for SIGTRAP, pid = %d, n = %d, errno = %d, status = 0x%x\n",
+	       __func__, pid, n, errno, status);
+	fatal_sigsegv();
+}
+
+void wait_stub_done_seccomp(struct mm_id *mm_idp, int running, int wait_sigsys)
+{
+	struct stub_data *data = (void *)mm_idp->stack;
+	int ret;
+
+	do {
+		const char byte = 0;
+		struct iovec iov = {
+			.iov_base = (void *)&byte,
+			.iov_len = sizeof(byte),
+		};
+		union {
+			char data[CMSG_SPACE(sizeof(mm_idp->syscall_fd_map))];
+			struct cmsghdr align;
+		} ctrl;
+		struct msghdr msgh = {
+			.msg_iov = &iov,
+			.msg_iovlen = 1,
+		};
+
+		if (!running) {
+			if (mm_idp->syscall_fd_num) {
+				unsigned int fds_size =
+					sizeof(int) * mm_idp->syscall_fd_num;
+				struct cmsghdr *cmsg;
+
+				msgh.msg_control = ctrl.data;
+				msgh.msg_controllen = CMSG_SPACE(fds_size);
+				cmsg = CMSG_FIRSTHDR(&msgh);
+				cmsg->cmsg_level = SOL_SOCKET;
+				cmsg->cmsg_type = SCM_RIGHTS;
+				cmsg->cmsg_len = CMSG_LEN(fds_size);
+				memcpy(CMSG_DATA(cmsg), mm_idp->syscall_fd_map,
+				       fds_size);
+
+				CATCH_EINTR(syscall(__NR_sendmsg, mm_idp->sock,
+						&msgh, 0));
+			}
+
+			data->signal = 0;
+			data->futex = FUTEX_IN_CHILD;
+			CATCH_EINTR(syscall(__NR_futex, &data->futex,
+					    FUTEX_WAKE, 1, NULL, NULL, 0));
+		}
+
+		do {
+			/*
+			 * We need to check whether the child is still alive
+			 * before and after the FUTEX_WAIT call. Before, in
+			 * case it just died but we still updated data->futex
+			 * to FUTEX_IN_CHILD. And after, in case it died while
+			 * we were waiting (and SIGCHLD woke us up, see the
+			 * IRQ handler in mmu.c).
+			 *
+			 * Either way, if PID is negative, then we have no
+			 * choice but to kill the task.
+			 */
+			if (__READ_ONCE(mm_idp->pid) < 0)
+				goto out_kill;
+
+			ret = syscall(__NR_futex, &data->futex,
+				      FUTEX_WAIT, FUTEX_IN_CHILD,
+				      NULL, NULL, 0);
+			if (ret < 0 && errno != EINTR && errno != EAGAIN) {
+				printk(UM_KERN_ERR "%s : FUTEX_WAIT failed, errno = %d\n",
+				       __func__, errno);
+				goto out_kill;
+			}
+		} while (data->futex == FUTEX_IN_CHILD);
+
+		if (__READ_ONCE(mm_idp->pid) < 0)
+			goto out_kill;
+
+		running = 0;
+
+		/* We may receive a SIGALRM before SIGSYS, iterate again. */
+	} while (wait_sigsys && data->signal == SIGALRM);
+
+	if (data->mctx_offset > sizeof(data->sigstack) - sizeof(mcontext_t)) {
+		printk(UM_KERN_ERR "%s : invalid mcontext offset", __func__);
+		goto out_kill;
+	}
+
+	if (wait_sigsys && data->signal != SIGSYS) {
+		printk(UM_KERN_ERR "%s : expected SIGSYS but got %d",
+		       __func__, data->signal);
+		goto out_kill;
+	}
+
+	return;
+
+out_kill:
+	printk(UM_KERN_ERR "%s : failed to wait for stub, pid = %d, errno = %d\n",
+	       __func__, mm_idp->pid, errno);
+	/* This is not true inside start_userspace */
+	if (current_mm_id() == mm_idp)
+		fatal_sigsegv();
+}
+
+extern unsigned long current_stub_stack(void);
+
+static void get_skas_faultinfo(int pid, struct faultinfo *fi)
+{
+	int err;
+
+	err = ptrace(PTRACE_CONT, pid, 0, SIGSEGV);
+	if (err) {
+		printk(UM_KERN_ERR "Failed to continue stub, pid = %d, "
+		       "errno = %d\n", pid, errno);
+		fatal_sigsegv();
+	}
+	wait_stub_done(pid);
+
+	/*
+	 * faultinfo is prepared by the stub_segv_handler at start of
+	 * the stub stack page. We just have to copy it.
+	 */
+	memcpy(fi, (void *)current_stub_stack(), sizeof(*fi));
+}
+
+static void handle_trap(struct uml_pt_regs *regs)
+{
+	if ((UPT_IP(regs) >= STUB_START) && (UPT_IP(regs) < STUB_END))
+		fatal_sigsegv();
+
+	handle_syscall(regs);
+}
+
+extern char __syscall_stub_start[];
+
+static int stub_exe_fd;
+
+struct tramp_data {
+	struct stub_data *stub_data;
+	/* 0 is inherited, 1 is the kernel side */
+	int sockpair[2];
+};
+
+#ifndef CLOSE_RANGE_CLOEXEC
+#define CLOSE_RANGE_CLOEXEC	(1U << 2)
+#endif
+
+static int userspace_tramp(void *data)
+{
+	struct tramp_data *tramp_data = data;
+	char *const argv[] = { "uml-userspace", NULL };
+	unsigned long long offset;
+	struct stub_init_data init_data = {
+		.seccomp = using_seccomp,
+		.stub_start = STUB_START,
+	};
+	int ret;
+
+	if (using_seccomp) {
+		init_data.signal_handler = STUB_CODE +
+					   (unsigned long) stub_signal_interrupt -
+					   (unsigned long) __syscall_stub_start;
+		init_data.signal_restorer = STUB_CODE +
+					   (unsigned long) stub_signal_restorer -
+					   (unsigned long) __syscall_stub_start;
+	} else {
+		init_data.signal_handler = STUB_CODE +
+					   (unsigned long) stub_segv_handler -
+					   (unsigned long) __syscall_stub_start;
+		init_data.signal_restorer = 0;
+	}
+
+	init_data.stub_code_fd = phys_mapping(uml_to_phys(__syscall_stub_start),
+					      &offset);
+	init_data.stub_code_offset = MMAP_OFFSET(offset);
+
+	init_data.stub_data_fd = phys_mapping(uml_to_phys(tramp_data->stub_data),
+					      &offset);
+	init_data.stub_data_offset = MMAP_OFFSET(offset);
+
+	/*
+	 * Avoid leaking unneeded FDs to the stub by setting CLOEXEC on all FDs
+	 * and then unsetting it on all memory related FDs.
+	 * This is not strictly necessary from a safety perspective.
+	 */
+	syscall(__NR_close_range, 0, ~0U, CLOSE_RANGE_CLOEXEC);
+
+	fcntl(init_data.stub_data_fd, F_SETFD, 0);
+
+	/* dup2 signaling FD/socket to STDIN */
+	if (dup2(tramp_data->sockpair[0], 0) < 0)
+		exit(3);
+	close(tramp_data->sockpair[0]);
+
+	/* Write init_data and close write side */
+	ret = write(tramp_data->sockpair[1], &init_data, sizeof(init_data));
+	close(tramp_data->sockpair[1]);
+
+	if (ret != sizeof(init_data))
+		exit(4);
+
+	/* Raw execveat for compatibility with older libc versions */
+	syscall(__NR_execveat, stub_exe_fd, (unsigned long)"",
+		(unsigned long)argv, NULL, AT_EMPTY_PATH);
+
+	exit(5);
+}
+
+extern char stub_exe_start[];
+extern char stub_exe_end[];
+
+extern char *tempdir;
+
+#define STUB_EXE_NAME_TEMPLATE "/uml-userspace-XXXXXX"
+
+#ifndef MFD_EXEC
+#define MFD_EXEC 0x0010U
+#endif
+
+static int __init init_stub_exe_fd(void)
+{
+	size_t written = 0;
+	char *tmpfile = NULL;
+
+	stub_exe_fd = memfd_create("uml-userspace",
+				   MFD_EXEC | MFD_CLOEXEC | MFD_ALLOW_SEALING);
+
+	if (stub_exe_fd < 0) {
+		printk(UM_KERN_INFO "Could not create executable memfd, using temporary file!");
+
+		tmpfile = malloc(strlen(tempdir) +
+				  strlen(STUB_EXE_NAME_TEMPLATE) + 1);
+		if (tmpfile == NULL)
+			panic("Failed to allocate memory for stub binary name");
+
+		strcpy(tmpfile, tempdir);
+		strcat(tmpfile, STUB_EXE_NAME_TEMPLATE);
+
+		stub_exe_fd = mkstemp(tmpfile);
+		if (stub_exe_fd < 0)
+			panic("Could not create temporary file for stub binary: %d",
+			      -errno);
+	}
+
+	while (written < stub_exe_end - stub_exe_start) {
+		ssize_t res = write(stub_exe_fd, stub_exe_start + written,
+				    stub_exe_end - stub_exe_start - written);
+		if (res < 0) {
+			if (errno == EINTR)
+				continue;
+
+			if (tmpfile)
+				unlink(tmpfile);
+			panic("Failed write stub binary: %d", -errno);
+		}
+
+		written += res;
+	}
+
+	if (!tmpfile) {
+		fcntl(stub_exe_fd, F_ADD_SEALS,
+		      F_SEAL_WRITE | F_SEAL_SHRINK | F_SEAL_GROW | F_SEAL_SEAL);
+	} else {
+		if (fchmod(stub_exe_fd, 00500) < 0) {
+			unlink(tmpfile);
+			panic("Could not make stub binary executable: %d",
+			      -errno);
+		}
+
+		close(stub_exe_fd);
+		stub_exe_fd = open(tmpfile, O_RDONLY | O_CLOEXEC | O_NOFOLLOW);
+		if (stub_exe_fd < 0) {
+			unlink(tmpfile);
+			panic("Could not reopen stub binary: %d", -errno);
+		}
+
+		unlink(tmpfile);
+		free(tmpfile);
+	}
+
+	return 0;
+}
+__initcall(init_stub_exe_fd);
+
+int using_seccomp;
+
+/**
+ * start_userspace() - prepare a new userspace process
+ * @mm_id: The corresponding struct mm_id
+ *
+ * Setups a new temporary stack page that is used while userspace_tramp() runs
+ * Clones the kernel process into a new userspace process, with FDs only.
+ *
+ * Return: When positive: the process id of the new userspace process,
+ *         when negative: an error number.
+ * FIXME: can PIDs become negative?!
+ */
+int start_userspace(struct mm_id *mm_id)
+{
+	struct stub_data *proc_data = (void *)mm_id->stack;
+	struct tramp_data tramp_data = {
+		.stub_data = proc_data,
+	};
+	void *stack;
+	unsigned long sp;
+	int status, n, err;
+
+	/* setup a temporary stack page */
+	stack = mmap(NULL, UM_KERN_PAGE_SIZE,
+		     PROT_READ | PROT_WRITE | PROT_EXEC,
+		     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	if (stack == MAP_FAILED) {
+		err = -errno;
+		printk(UM_KERN_ERR "%s : mmap failed, errno = %d\n",
+		       __func__, errno);
+		return err;
+	}
+
+	/* set stack pointer to the end of the stack page, so it can grow downwards */
+	sp = (unsigned long)stack + UM_KERN_PAGE_SIZE;
+
+	/* socket pair for init data and SECCOMP FD passing (no CLOEXEC here) */
+	if (socketpair(AF_UNIX, SOCK_STREAM, 0, tramp_data.sockpair)) {
+		err = -errno;
+		printk(UM_KERN_ERR "%s : socketpair failed, errno = %d\n",
+		       __func__, errno);
+		return err;
+	}
+
+	if (using_seccomp)
+		proc_data->futex = FUTEX_IN_CHILD;
+
+	mm_id->pid = clone(userspace_tramp, (void *) sp,
+		    CLONE_VFORK | CLONE_VM | SIGCHLD,
+		    (void *)&tramp_data);
+	if (mm_id->pid < 0) {
+		err = -errno;
+		printk(UM_KERN_ERR "%s : clone failed, errno = %d\n",
+		       __func__, errno);
+		goto out_close;
+	}
+
+	if (using_seccomp) {
+		wait_stub_done_seccomp(mm_id, 1, 1);
+	} else {
+		do {
+			CATCH_EINTR(n = waitpid(mm_id->pid, &status,
+						WUNTRACED | __WALL));
+			if (n < 0) {
+				err = -errno;
+				printk(UM_KERN_ERR "%s : wait failed, errno = %d\n",
+				       __func__, errno);
+				goto out_kill;
+			}
+		} while (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGALRM));
+
+		if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP)) {
+			err = -EINVAL;
+			printk(UM_KERN_ERR "%s : expected SIGSTOP, got status = %d\n",
+			       __func__, status);
+			goto out_kill;
+		}
+
+		if (ptrace(PTRACE_SETOPTIONS, mm_id->pid, NULL,
+			   (void *) PTRACE_O_TRACESYSGOOD) < 0) {
+			err = -errno;
+			printk(UM_KERN_ERR "%s : PTRACE_SETOPTIONS failed, errno = %d\n",
+			       __func__, errno);
+			goto out_kill;
+		}
+	}
+
+	if (munmap(stack, UM_KERN_PAGE_SIZE) < 0) {
+		err = -errno;
+		printk(UM_KERN_ERR "%s : munmap failed, errno = %d\n",
+		       __func__, errno);
+		goto out_kill;
+	}
+
+	close(tramp_data.sockpair[0]);
+	if (using_seccomp)
+		mm_id->sock = tramp_data.sockpair[1];
+	else
+		close(tramp_data.sockpair[1]);
+
+	return 0;
+
+out_kill:
+	os_kill_ptraced_process(mm_id->pid, 1);
+out_close:
+	close(tramp_data.sockpair[0]);
+	close(tramp_data.sockpair[1]);
+
+	mm_id->pid = -1;
+
+	return err;
+}
+
+static int unscheduled_userspace_iterations;
+extern unsigned long tt_extra_sched_jiffies;
+
+void userspace(struct uml_pt_regs *regs)
+{
+	int err, status, op;
+	siginfo_t si_local;
+	siginfo_t *si;
+	int sig;
+
+	/* Handle any immediate reschedules or signals */
+	interrupt_end();
+
+	while (1) {
+		struct mm_id *mm_id = current_mm_id();
+
+		/*
+		 * At any given time, only one CPU thread can enter the
+		 * turnstile to operate on the same stub process, including
+		 * executing stub system calls (mmap and munmap).
+		 */
+		enter_turnstile(mm_id);
+
+		/*
+		 * When we are in time-travel mode, userspace can theoretically
+		 * do a *lot* of work without being scheduled. The problem with
+		 * this is that it will prevent kernel bookkeeping (primarily
+		 * the RCU) from running and this can for example cause OOM
+		 * situations.
+		 *
+		 * This code accounts a jiffie against the scheduling clock
+		 * after the defined userspace iterations in the same thread.
+		 * By doing so the situation is effectively prevented.
+		 */
+		if (time_travel_mode == TT_MODE_INFCPU ||
+		    time_travel_mode == TT_MODE_EXTERNAL) {
+#ifdef CONFIG_UML_MAX_USERSPACE_ITERATIONS
+			if (CONFIG_UML_MAX_USERSPACE_ITERATIONS &&
+			    unscheduled_userspace_iterations++ >
+			    CONFIG_UML_MAX_USERSPACE_ITERATIONS) {
+				tt_extra_sched_jiffies += 1;
+				unscheduled_userspace_iterations = 0;
+			}
+#endif
+		}
+
+		time_travel_print_bc_msg();
+
+		current_mm_sync();
+
+		if (using_seccomp) {
+			struct stub_data *proc_data = (void *) mm_id->stack;
+
+			err = set_stub_state(regs, proc_data, singlestepping());
+			if (err) {
+				printk(UM_KERN_ERR "%s - failed to set regs: %d",
+				       __func__, err);
+				fatal_sigsegv();
+			}
+
+			/* Must have been reset by the syscall caller */
+			if (proc_data->restart_wait != 0)
+				panic("Programming error: Flag to only run syscalls in child was not cleared!");
+
+			/* Mark pending syscalls for flushing */
+			proc_data->syscall_data_len = mm_id->syscall_data_len;
+
+			wait_stub_done_seccomp(mm_id, 0, 0);
+
+			sig = proc_data->signal;
+
+			if (sig == SIGTRAP && proc_data->err != 0) {
+				printk(UM_KERN_ERR "%s - Error flushing stub syscalls",
+				       __func__);
+				syscall_stub_dump_error(mm_id);
+				mm_id->syscall_data_len = proc_data->err;
+				fatal_sigsegv();
+			}
+
+			mm_id->syscall_data_len = 0;
+			mm_id->syscall_fd_num = 0;
+
+			err = get_stub_state(regs, proc_data, NULL);
+			if (err) {
+				printk(UM_KERN_ERR "%s - failed to get regs: %d",
+				       __func__, err);
+				fatal_sigsegv();
+			}
+
+			if (proc_data->si_offset > sizeof(proc_data->sigstack) - sizeof(*si))
+				panic("%s - Invalid siginfo offset from child", __func__);
+
+			si = &si_local;
+			memcpy(si, &proc_data->sigstack[proc_data->si_offset], sizeof(*si));
+
+			regs->is_user = 1;
+
+			/* Fill in ORIG_RAX and extract fault information */
+			PT_SYSCALL_NR(regs->gp) = si->si_syscall;
+			if (sig == SIGSEGV) {
+				mcontext_t *mcontext = (void *)&proc_data->sigstack[proc_data->mctx_offset];
+
+				GET_FAULTINFO_FROM_MC(regs->faultinfo, mcontext);
+			}
+		} else {
+			int pid = mm_id->pid;
+
+			/* Flush out any pending syscalls */
+			err = syscall_stub_flush(mm_id);
+			if (err) {
+				if (err == -ENOMEM)
+					report_enomem();
+
+				printk(UM_KERN_ERR "%s - Error flushing stub syscalls: %d",
+					__func__, -err);
+				fatal_sigsegv();
+			}
+
+			/*
+			 * This can legitimately fail if the process loads a
+			 * bogus value into a segment register.  It will
+			 * segfault and PTRACE_GETREGS will read that value
+			 * out of the process.  However, PTRACE_SETREGS will
+			 * fail.  In this case, there is nothing to do but
+			 * just kill the process.
+			 */
+			if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp)) {
+				printk(UM_KERN_ERR "%s - ptrace set regs failed, errno = %d\n",
+				       __func__, errno);
+				fatal_sigsegv();
+			}
+
+			if (put_fp_registers(pid, regs->fp)) {
+				printk(UM_KERN_ERR "%s - ptrace set fp regs failed, errno = %d\n",
+				       __func__, errno);
+				fatal_sigsegv();
+			}
+
+			if (singlestepping())
+				op = PTRACE_SYSEMU_SINGLESTEP;
+			else
+				op = PTRACE_SYSEMU;
+
+			if (ptrace(op, pid, 0, 0)) {
+				printk(UM_KERN_ERR "%s - ptrace continue failed, op = %d, errno = %d\n",
+				       __func__, op, errno);
+				fatal_sigsegv();
+			}
+
+			CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
+			if (err < 0) {
+				printk(UM_KERN_ERR "%s - wait failed, errno = %d\n",
+				       __func__, errno);
+				fatal_sigsegv();
+			}
+
+			regs->is_user = 1;
+			if (ptrace(PTRACE_GETREGS, pid, 0, regs->gp)) {
+				printk(UM_KERN_ERR "%s - PTRACE_GETREGS failed, errno = %d\n",
+				       __func__, errno);
+				fatal_sigsegv();
+			}
+
+			if (get_fp_registers(pid, regs->fp)) {
+				printk(UM_KERN_ERR "%s -  get_fp_registers failed, errno = %d\n",
+				       __func__, errno);
+				fatal_sigsegv();
+			}
+
+			if (WIFSTOPPED(status)) {
+				sig = WSTOPSIG(status);
+
+				/*
+				 * These signal handlers need the si argument
+				 * and SIGSEGV needs the faultinfo.
+				 * The SIGIO and SIGALARM handlers which constitute
+				 * the majority of invocations, do not use it.
+				 */
+				switch (sig) {
+				case SIGSEGV:
+					get_skas_faultinfo(pid,
+							   &regs->faultinfo);
+					fallthrough;
+				case SIGTRAP:
+				case SIGILL:
+				case SIGBUS:
+				case SIGFPE:
+				case SIGWINCH:
+					ptrace(PTRACE_GETSIGINFO, pid, 0,
+					       (struct siginfo *)&si_local);
+					si = &si_local;
+					break;
+				default:
+					si = NULL;
+					break;
+				}
+			} else {
+				sig = 0;
+			}
+		}
+
+		exit_turnstile(mm_id);
+
+		UPT_SYSCALL_NR(regs) = -1; /* Assume: It's not a syscall */
+
+		if (sig) {
+			switch (sig) {
+			case SIGSEGV:
+				if (using_seccomp || PTRACE_FULL_FAULTINFO)
+					(*sig_info[SIGSEGV])(SIGSEGV,
+							     (struct siginfo *)si,
+							     regs, NULL);
+				else
+					segv(regs->faultinfo, 0, 1, NULL, NULL);
+
+				break;
+			case SIGSYS:
+				handle_syscall(regs);
+				break;
+			case SIGTRAP + 0x80:
+				handle_trap(regs);
+				break;
+			case SIGTRAP:
+				relay_signal(SIGTRAP, (struct siginfo *)si, regs, NULL);
+				break;
+			case SIGALRM:
+				break;
+			case SIGIO:
+			case SIGILL:
+			case SIGBUS:
+			case SIGFPE:
+			case SIGWINCH:
+				block_signals_trace();
+				(*sig_info[sig])(sig, (struct siginfo *)si, regs, NULL);
+				unblock_signals_trace();
+				break;
+			default:
+				printk(UM_KERN_ERR "%s - child stopped with signal %d\n",
+				       __func__, sig);
+				fatal_sigsegv();
+			}
+			interrupt_end();
+
+			/* Avoid -ERESTARTSYS handling in host */
+			if (PT_SYSCALL_NR_OFFSET != PT_SYSCALL_RET_OFFSET)
+				PT_SYSCALL_NR(regs->gp) = -1;
+		}
+	}
+}
+
+void new_thread(void *stack, jmp_buf *buf, void (*handler)(void))
+{
+	(*buf)[0].JB_IP = (unsigned long) handler;
+	(*buf)[0].JB_SP = (unsigned long) stack + UM_THREAD_SIZE -
+		sizeof(void *);
+}
+
+#define INIT_JMP_NEW_THREAD 0
+#define INIT_JMP_CALLBACK 1
+#define INIT_JMP_HALT 2
+#define INIT_JMP_REBOOT 3
+
+void switch_threads(jmp_buf *me, jmp_buf *you)
+{
+	unscheduled_userspace_iterations = 0;
+
+	if (UML_SETJMP(me) == 0)
+		UML_LONGJMP(you, 1);
+}
+
+static jmp_buf initial_jmpbuf;
+
+static __thread void (*cb_proc)(void *arg);
+static __thread void *cb_arg;
+static __thread jmp_buf *cb_back;
+
+int start_idle_thread(void *stack, jmp_buf *switch_buf)
+{
+	int n;
+
+	set_handler(SIGWINCH);
+
+	/*
+	 * Can't use UML_SETJMP or UML_LONGJMP here because they save
+	 * and restore signals, with the possible side-effect of
+	 * trying to handle any signals which came when they were
+	 * blocked, which can't be done on this stack.
+	 * Signals must be blocked when jumping back here and restored
+	 * after returning to the jumper.
+	 */
+	n = setjmp(initial_jmpbuf);
+	switch (n) {
+	case INIT_JMP_NEW_THREAD:
+		(*switch_buf)[0].JB_IP = (unsigned long) uml_finishsetup;
+		(*switch_buf)[0].JB_SP = (unsigned long) stack +
+			UM_THREAD_SIZE - sizeof(void *);
+		break;
+	case INIT_JMP_CALLBACK:
+		(*cb_proc)(cb_arg);
+		longjmp(*cb_back, 1);
+		break;
+	case INIT_JMP_HALT:
+		kmalloc_ok = 0;
+		return 0;
+	case INIT_JMP_REBOOT:
+		kmalloc_ok = 0;
+		return 1;
+	default:
+		printk(UM_KERN_ERR "Bad sigsetjmp return in %s - %d\n",
+		       __func__, n);
+		fatal_sigsegv();
+	}
+	longjmp(*switch_buf, 1);
+
+	/* unreachable */
+	printk(UM_KERN_ERR "impossible long jump!");
+	fatal_sigsegv();
+	return 0;
+}
+
+void initial_thread_cb_skas(void (*proc)(void *), void *arg)
+{
+	jmp_buf here;
+
+	cb_proc = proc;
+	cb_arg = arg;
+	cb_back = &here;
+
+	initial_jmpbuf_lock();
+	if (UML_SETJMP(&here) == 0)
+		UML_LONGJMP(&initial_jmpbuf, INIT_JMP_CALLBACK);
+	initial_jmpbuf_unlock();
+
+	cb_proc = NULL;
+	cb_arg = NULL;
+	cb_back = NULL;
+}
+
+void halt_skas(void)
+{
+	initial_jmpbuf_lock();
+	UML_LONGJMP(&initial_jmpbuf, INIT_JMP_HALT);
+	/* unreachable */
+}
+
+static bool noreboot;
+
+static int __init noreboot_cmd_param(char *str, int *add)
+{
+	*add = 0;
+	noreboot = true;
+	return 0;
+}
+
+__uml_setup("noreboot", noreboot_cmd_param,
+"noreboot\n"
+"    Rather than rebooting, exit always, akin to QEMU's -no-reboot option.\n"
+"    This is useful if you're using CONFIG_PANIC_TIMEOUT in order to catch\n"
+"    crashes in CI\n\n");
+
+void reboot_skas(void)
+{
+	initial_jmpbuf_lock();
+	UML_LONGJMP(&initial_jmpbuf, noreboot ? INIT_JMP_HALT : INIT_JMP_REBOOT);
+	/* unreachable */
+}
diff --git a/arch/um/os-Linux/smp.c b/arch/um/os-Linux/smp.c
new file mode 100644
index 000000000..18d3858a7
--- /dev/null
+++ b/arch/um/os-Linux/smp.c
@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2025 Ant Group
+ * Author: Tiwei Bie <tiwei.btw@antgroup.com>
+ */
+
+#include <errno.h>
+#include <pthread.h>
+#include <signal.h>
+#include <kern_util.h>
+#include <um_malloc.h>
+#include <init.h>
+#include <os.h>
+#include <smp.h>
+#include "internal.h"
+
+struct cpu_thread_data {
+	int cpu;
+	sigset_t sigset;
+};
+
+static __thread int __curr_cpu;
+
+int uml_curr_cpu(void)
+{
+	return __curr_cpu;
+}
+
+static pthread_t cpu_threads[CONFIG_NR_CPUS];
+
+static void *cpu_thread(void *arg)
+{
+	struct cpu_thread_data *data = arg;
+
+	__curr_cpu = data->cpu;
+
+	uml_start_secondary(data);
+
+	return NULL;
+}
+
+int os_start_cpu_thread(int cpu)
+{
+	struct cpu_thread_data *data;
+	sigset_t sigset, oset;
+	int err;
+
+	data = uml_kmalloc(sizeof(*data), UM_GFP_ATOMIC);
+	if (!data)
+		return -ENOMEM;
+
+	sigfillset(&sigset);
+	if (sigprocmask(SIG_SETMASK, &sigset, &oset) < 0) {
+		err = errno;
+		goto err;
+	}
+
+	data->cpu = cpu;
+	data->sigset = oset;
+
+	err = pthread_create(&cpu_threads[cpu], NULL, cpu_thread, data);
+	if (sigprocmask(SIG_SETMASK, &oset, NULL) < 0)
+		panic("Failed to restore the signal mask, errno = %d", errno);
+	if (err != 0)
+		goto err;
+
+	return 0;
+
+err:
+	kfree(data);
+	return -err;
+}
+
+void os_start_secondary(void *arg, jmp_buf *switch_buf)
+{
+	struct cpu_thread_data *data = arg;
+
+	sigaddset(&data->sigset, IPI_SIGNAL);
+	sigaddset(&data->sigset, SIGIO);
+
+	if (sigprocmask(SIG_SETMASK, &data->sigset, NULL) < 0)
+		panic("Failed to restore the signal mask, errno = %d", errno);
+
+	kfree(data);
+	longjmp(*switch_buf, 1);
+
+	/* unreachable */
+	printk(UM_KERN_ERR "impossible long jump!");
+	fatal_sigsegv();
+}
+
+int os_send_ipi(int cpu, int vector)
+{
+	union sigval value = { .sival_int = vector };
+
+	return pthread_sigqueue(cpu_threads[cpu], IPI_SIGNAL, value);
+}
+
+static void __local_ipi_set(int enable)
+{
+	sigset_t sigset;
+
+	sigemptyset(&sigset);
+	sigaddset(&sigset, IPI_SIGNAL);
+
+	if (sigprocmask(enable ? SIG_UNBLOCK : SIG_BLOCK, &sigset, NULL) < 0)
+		panic("%s: sigprocmask failed, errno = %d", __func__, errno);
+}
+
+void os_local_ipi_enable(void)
+{
+	__local_ipi_set(1);
+}
+
+void os_local_ipi_disable(void)
+{
+	__local_ipi_set(0);
+}
+
+static void ipi_sig_handler(int sig, siginfo_t *si, void *uc)
+{
+	int save_errno = errno;
+
+	signals_enabled = 0;
+	um_trace_signals_off();
+
+	uml_ipi_handler(si->si_value.sival_int);
+
+	um_trace_signals_on();
+	signals_enabled = 1;
+
+	errno = save_errno;
+}
+
+void __init os_init_smp(void)
+{
+	struct sigaction action = {
+		.sa_sigaction = ipi_sig_handler,
+		.sa_flags = SA_SIGINFO | SA_ONSTACK | SA_RESTART,
+	};
+
+	sigfillset(&action.sa_mask);
+
+	if (sigaction(IPI_SIGNAL, &action, NULL) < 0)
+		panic("%s: sigaction failed, errno = %d", __func__, errno);
+
+	cpu_threads[0] = pthread_self();
+}
diff --git a/arch/um/os-Linux/start_up.c b/arch/um/os-Linux/start_up.c
new file mode 100644
index 000000000..054ac03bb
--- /dev/null
+++ b/arch/um/os-Linux/start_up.c
@@ -0,0 +1,495 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2021 Benjamin Berg <benjamin@sipsolutions.net>
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <unistd.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <sched.h>
+#include <signal.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <sys/time.h>
+#include <sys/resource.h>
+#include <asm/ldt.h>
+#include <asm/unistd.h>
+#include <init.h>
+#include <os.h>
+#include <smp.h>
+#include <kern_util.h>
+#include <mem_user.h>
+#include <ptrace_user.h>
+#include <stdbool.h>
+#include <stub-data.h>
+#include <sys/prctl.h>
+#include <linux/seccomp.h>
+#include <linux/filter.h>
+#include <sysdep/mcontext.h>
+#include <sysdep/stub.h>
+#include <registers.h>
+#include <skas.h>
+#include "internal.h"
+
+static void ptrace_child(void)
+{
+	int ret;
+	/* Calling os_getpid because some libcs cached getpid incorrectly */
+	int pid = os_getpid(), ppid = getppid();
+	int sc_result;
+
+	if (change_sig(SIGWINCH, 0) < 0 ||
+	    ptrace(PTRACE_TRACEME, 0, 0, 0) < 0) {
+		perror("ptrace");
+		kill(pid, SIGKILL);
+	}
+	kill(pid, SIGSTOP);
+
+	/*
+	 * This syscall will be intercepted by the parent. Don't call more than
+	 * once, please.
+	 */
+	sc_result = os_getpid();
+
+	if (sc_result == pid)
+		/* Nothing modified by the parent, we are running normally. */
+		ret = 1;
+	else if (sc_result == ppid)
+		/*
+		 * Expected in check_ptrace and check_sysemu when they succeed
+		 * in modifying the stack frame
+		 */
+		ret = 0;
+	else
+		/* Serious trouble! This could be caused by a bug in host 2.6
+		 * SKAS3/2.6 patch before release -V6, together with a bug in
+		 * the UML code itself.
+		 */
+		ret = 2;
+
+	exit(ret);
+}
+
+static void fatal_perror(const char *str)
+{
+	perror(str);
+	exit(1);
+}
+
+static void fatal(char *fmt, ...)
+{
+	va_list list;
+
+	va_start(list, fmt);
+	vfprintf(stderr, fmt, list);
+	va_end(list);
+
+	exit(1);
+}
+
+static void non_fatal(char *fmt, ...)
+{
+	va_list list;
+
+	va_start(list, fmt);
+	vfprintf(stderr, fmt, list);
+	va_end(list);
+}
+
+static int start_ptraced_child(void)
+{
+	int pid, n, status;
+
+	fflush(stdout);
+
+	pid = fork();
+	if (pid == 0)
+		ptrace_child();
+	else if (pid < 0)
+		fatal_perror("start_ptraced_child : fork failed");
+
+	CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
+	if (n < 0)
+		fatal_perror("check_ptrace : waitpid failed");
+	if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP))
+		fatal("check_ptrace : expected SIGSTOP, got status = %d",
+		      status);
+
+	return pid;
+}
+
+static void stop_ptraced_child(int pid, int exitcode)
+{
+	int status, n;
+
+	if (ptrace(PTRACE_CONT, pid, 0, 0) < 0)
+		fatal_perror("stop_ptraced_child : ptrace failed");
+
+	CATCH_EINTR(n = waitpid(pid, &status, 0));
+	if (!WIFEXITED(status) || (WEXITSTATUS(status) != exitcode)) {
+		int exit_with = WEXITSTATUS(status);
+		fatal("stop_ptraced_child : child exited with exitcode %d, "
+		      "while expecting %d; status 0x%x\n", exit_with,
+		      exitcode, status);
+	}
+}
+
+static void __init check_sysemu(void)
+{
+	int pid, n, status, count=0;
+
+	os_info("Checking syscall emulation for ptrace...");
+	pid = start_ptraced_child();
+
+	if ((ptrace(PTRACE_SETOPTIONS, pid, 0,
+		   (void *) PTRACE_O_TRACESYSGOOD) < 0))
+		fatal_perror("check_sysemu: PTRACE_SETOPTIONS failed");
+
+	while (1) {
+		count++;
+		if (ptrace(PTRACE_SYSEMU_SINGLESTEP, pid, 0, 0) < 0)
+			goto fail;
+		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
+		if (n < 0)
+			fatal_perror("check_sysemu: wait failed");
+
+		if (WIFSTOPPED(status) &&
+		    (WSTOPSIG(status) == (SIGTRAP|0x80))) {
+			if (!count) {
+				non_fatal("check_sysemu: SYSEMU_SINGLESTEP "
+					  "doesn't singlestep");
+				goto fail;
+			}
+			n = ptrace(PTRACE_POKEUSER, pid, PT_SYSCALL_RET_OFFSET,
+				   os_getpid());
+			if (n < 0)
+				fatal_perror("check_sysemu : failed to modify "
+					     "system call return");
+			break;
+		}
+		else if (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGTRAP))
+			count++;
+		else {
+			non_fatal("check_sysemu: expected SIGTRAP or "
+				  "(SIGTRAP | 0x80), got status = %d\n",
+				  status);
+			goto fail;
+		}
+	}
+	stop_ptraced_child(pid, 0);
+
+	os_info("OK\n");
+
+	return;
+
+fail:
+	stop_ptraced_child(pid, 1);
+	fatal("missing\n");
+}
+
+static void __init check_ptrace(void)
+{
+	int pid, syscall, n, status;
+
+	os_info("Checking that ptrace can change system call numbers...");
+	pid = start_ptraced_child();
+
+	if ((ptrace(PTRACE_SETOPTIONS, pid, 0,
+		   (void *) PTRACE_O_TRACESYSGOOD) < 0))
+		fatal_perror("check_ptrace: PTRACE_SETOPTIONS failed");
+
+	while (1) {
+		if (ptrace(PTRACE_SYSCALL, pid, 0, 0) < 0)
+			fatal_perror("check_ptrace : ptrace failed");
+
+		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
+		if (n < 0)
+			fatal_perror("check_ptrace : wait failed");
+
+		if (!WIFSTOPPED(status) ||
+		   (WSTOPSIG(status) != (SIGTRAP | 0x80)))
+			fatal("check_ptrace : expected (SIGTRAP|0x80), "
+			       "got status = %d", status);
+
+		syscall = ptrace(PTRACE_PEEKUSER, pid, PT_SYSCALL_NR_OFFSET,
+				 0);
+		if (syscall == __NR_getpid) {
+			n = ptrace(PTRACE_POKEUSER, pid, PT_SYSCALL_NR_OFFSET,
+				   __NR_getppid);
+			if (n < 0)
+				fatal_perror("check_ptrace : failed to modify "
+					     "system call");
+			break;
+		}
+	}
+	stop_ptraced_child(pid, 0);
+	os_info("OK\n");
+	check_sysemu();
+}
+
+extern unsigned long host_fp_size;
+extern unsigned long exec_regs[MAX_REG_NR];
+extern unsigned long *exec_fp_regs;
+
+__initdata static struct stub_data *seccomp_test_stub_data;
+
+static void __init sigsys_handler(int sig, siginfo_t *info, void *p)
+{
+	ucontext_t *uc = p;
+
+	/* Stow away the location of the mcontext in the stack */
+	seccomp_test_stub_data->mctx_offset = (unsigned long)&uc->uc_mcontext -
+					      (unsigned long)&seccomp_test_stub_data->sigstack[0];
+
+	/* Prevent libc from clearing memory (mctx_offset in particular) */
+	syscall(__NR_exit, 0);
+}
+
+static int __init seccomp_helper(void *data)
+{
+	static struct sock_filter filter[] = {
+		BPF_STMT(BPF_LD | BPF_W | BPF_ABS,
+			 offsetof(struct seccomp_data, nr)),
+		BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_clock_nanosleep, 1, 0),
+		BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
+		BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_TRAP),
+	};
+	static struct sock_fprog prog = {
+		.len = ARRAY_SIZE(filter),
+		.filter = filter,
+	};
+	struct sigaction sa;
+
+	/* close_range is needed for the stub */
+	if (stub_syscall3(__NR_close_range, 1, ~0U, 0))
+		exit(1);
+
+	set_sigstack(seccomp_test_stub_data->sigstack,
+			sizeof(seccomp_test_stub_data->sigstack));
+
+	sa.sa_flags = SA_ONSTACK | SA_NODEFER | SA_SIGINFO;
+	sa.sa_sigaction = (void *) sigsys_handler;
+	sa.sa_restorer = NULL;
+	if (sigaction(SIGSYS, &sa, NULL) < 0)
+		exit(2);
+
+	prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0);
+	if (syscall(__NR_seccomp, SECCOMP_SET_MODE_FILTER,
+			SECCOMP_FILTER_FLAG_TSYNC, &prog) != 0)
+		exit(3);
+
+	sleep(0);
+
+	/* Never reached. */
+	_exit(4);
+}
+
+static bool __init init_seccomp(void)
+{
+	int pid;
+	int status;
+	int n;
+	unsigned long sp;
+
+	/*
+	 * We check that we can install a seccomp filter and then exit(0)
+	 * from a trapped syscall.
+	 *
+	 * Note that we cannot verify that no seccomp filter already exists
+	 * for a syscall that results in the process/thread to be killed.
+	 */
+
+	os_info("Checking that seccomp filters can be installed...");
+
+	seccomp_test_stub_data = mmap(0, sizeof(*seccomp_test_stub_data),
+				      PROT_READ | PROT_WRITE,
+				      MAP_SHARED | MAP_ANON, 0, 0);
+
+	/* Use the syscall data area as stack, we just need something */
+	sp = (unsigned long)&seccomp_test_stub_data->syscall_data +
+	     sizeof(seccomp_test_stub_data->syscall_data) -
+	     sizeof(void *);
+	pid = clone(seccomp_helper, (void *)sp, CLONE_VFORK | CLONE_VM, NULL);
+
+	if (pid < 0)
+		fatal_perror("check_seccomp : clone failed");
+
+	CATCH_EINTR(n = waitpid(pid, &status, __WCLONE));
+	if (n < 0)
+		fatal_perror("check_seccomp : waitpid failed");
+
+	if (WIFEXITED(status) && WEXITSTATUS(status) == 0) {
+		struct uml_pt_regs *regs;
+		unsigned long fp_size;
+		int r;
+
+		/* Fill in the host_fp_size from the mcontext. */
+		regs = calloc(1, sizeof(struct uml_pt_regs));
+		get_stub_state(regs, seccomp_test_stub_data, &fp_size);
+		host_fp_size = fp_size;
+		free(regs);
+
+		/* Repeat with the correct size */
+		regs = calloc(1, sizeof(struct uml_pt_regs) + host_fp_size);
+		r = get_stub_state(regs, seccomp_test_stub_data, NULL);
+
+		/* Store as the default startup registers */
+		exec_fp_regs = malloc(host_fp_size);
+		memcpy(exec_regs, regs->gp, sizeof(exec_regs));
+		memcpy(exec_fp_regs, regs->fp, host_fp_size);
+
+		munmap(seccomp_test_stub_data, sizeof(*seccomp_test_stub_data));
+
+		free(regs);
+
+		if (r) {
+			os_info("failed to fetch registers: %d\n", r);
+			return false;
+		}
+
+		os_info("OK\n");
+		return true;
+	}
+
+	if (WIFEXITED(status) && WEXITSTATUS(status) == 2)
+		os_info("missing\n");
+	else
+		os_info("error\n");
+
+	munmap(seccomp_test_stub_data, sizeof(*seccomp_test_stub_data));
+	return false;
+}
+
+
+static void __init check_coredump_limit(void)
+{
+	struct rlimit lim;
+	int err = getrlimit(RLIMIT_CORE, &lim);
+
+	if (err) {
+		perror("Getting core dump limit");
+		return;
+	}
+
+	os_info("Core dump limits :\n\tsoft - ");
+	if (lim.rlim_cur == RLIM_INFINITY)
+		os_info("NONE\n");
+	else
+		os_info("%llu\n", (unsigned long long)lim.rlim_cur);
+
+	os_info("\thard - ");
+	if (lim.rlim_max == RLIM_INFINITY)
+		os_info("NONE\n");
+	else
+		os_info("%llu\n", (unsigned long long)lim.rlim_max);
+}
+
+void  __init get_host_cpu_features(
+		void (*flags_helper_func)(char *line),
+		void (*cache_helper_func)(char *line))
+{
+	FILE *cpuinfo;
+	char *line = NULL;
+	size_t len = 0;
+	int done_parsing = 0;
+
+	cpuinfo = fopen("/proc/cpuinfo", "r");
+	if (cpuinfo == NULL) {
+		os_info("Failed to get host CPU features\n");
+	} else {
+		while ((getline(&line, &len, cpuinfo)) != -1) {
+			if (strstr(line, "flags")) {
+				flags_helper_func(line);
+				done_parsing++;
+			}
+			if (strstr(line, "cache_alignment")) {
+				cache_helper_func(line);
+				done_parsing++;
+			}
+			free(line);
+			line = NULL;
+			if (done_parsing > 1)
+				break;
+		}
+		fclose(cpuinfo);
+	}
+}
+
+static int seccomp_config __initdata;
+
+static int __init uml_seccomp_config(char *line, int *add)
+{
+	*add = 0;
+
+	if (strcmp(line, "off") == 0)
+		seccomp_config = 0;
+	else if (strcmp(line, "auto") == 0)
+		seccomp_config = 1;
+	else if (strcmp(line, "on") == 0)
+		seccomp_config = 2;
+	else
+		fatal("Invalid seccomp option '%s', expected on/auto/off\n",
+		      line);
+
+	return 0;
+}
+
+__uml_setup("seccomp=", uml_seccomp_config,
+"seccomp=<on/auto/off>\n"
+"    Configure whether or not SECCOMP is used. With SECCOMP, userspace\n"
+"    processes work collaboratively with the kernel instead of being\n"
+"    traced using ptrace. All syscalls from the application are caught and\n"
+"    redirected using a signal. This signal handler in turn is permitted to\n"
+"    do the selected set of syscalls to communicate with the UML kernel and\n"
+"    do the required memory management.\n"
+"\n"
+"    This method is overall faster than the ptrace based userspace, primarily\n"
+"    because it reduces the number of context switches for (minor) page faults.\n"
+"\n"
+"    However, the SECCOMP filter is not (yet) restrictive enough to prevent\n"
+"    userspace from reading and writing all physical memory. Userspace\n"
+"    processes could also trick the stub into disabling SIGALRM which\n"
+"    prevents it from being interrupted for scheduling purposes.\n"
+"\n"
+"    This is insecure and should only be used with a trusted userspace\n\n"
+);
+
+void __init os_early_checks(void)
+{
+	int pid;
+
+	/* Print out the core dump limits early */
+	check_coredump_limit();
+
+	/* Need to check this early because mmapping happens before the
+	 * kernel is running.
+	 */
+	check_tmpexec();
+
+	if (seccomp_config) {
+		if (init_seccomp()) {
+			using_seccomp = 1;
+			return;
+		}
+
+		if (seccomp_config == 2)
+			fatal("SECCOMP userspace requested but not functional!\n");
+	}
+
+	if (uml_ncpus > 1)
+		fatal("SMP is not supported with PTRACE userspace.\n");
+
+	using_seccomp = 0;
+	check_ptrace();
+
+	pid = start_ptraced_child();
+	if (init_pid_registers(pid))
+		fatal("Failed to initialize default registers");
+	stop_ptraced_child(pid, 1);
+}
diff --git a/arch/um/os-Linux/time.c b/arch/um/os-Linux/time.c
new file mode 100644
index 000000000..13ebc8691
--- /dev/null
+++ b/arch/um/os-Linux/time.c
@@ -0,0 +1,157 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015 Anton Ivanov (aivanov@{brocade.com,kot-begemot.co.uk})
+ * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
+ * Copyright (C) 2012-2014 Cisco Systems
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike{addtoit,linux.intel}.com)
+ */
+
+#include <stddef.h>
+#include <unistd.h>
+#include <errno.h>
+#include <signal.h>
+#include <time.h>
+#include <sys/signalfd.h>
+#include <sys/time.h>
+#include <kern_util.h>
+#include <os.h>
+#include <smp.h>
+#include <string.h>
+#include "internal.h"
+
+static timer_t event_high_res_timer[CONFIG_NR_CPUS] = { 0 };
+
+static inline long long timespec_to_ns(const struct timespec *ts)
+{
+	return ((long long) ts->tv_sec * UM_NSEC_PER_SEC) + ts->tv_nsec;
+}
+
+long long os_persistent_clock_emulation(void)
+{
+	struct timespec realtime_tp;
+
+	clock_gettime(CLOCK_REALTIME, &realtime_tp);
+	return timespec_to_ns(&realtime_tp);
+}
+
+#ifndef sigev_notify_thread_id
+#define sigev_notify_thread_id _sigev_un._tid
+#endif
+
+/**
+ * os_timer_create() - create an new posix (interval) timer
+ */
+int os_timer_create(void)
+{
+	int cpu = uml_curr_cpu();
+	timer_t *t = &event_high_res_timer[cpu];
+	struct sigevent sev = {
+		.sigev_notify = SIGEV_THREAD_ID,
+		.sigev_signo = SIGALRM,
+		.sigev_value.sival_ptr = t,
+		.sigev_notify_thread_id = gettid(),
+	};
+
+	if (timer_create(CLOCK_MONOTONIC, &sev, t) == -1)
+		return -1;
+
+	return 0;
+}
+
+int os_timer_set_interval(int cpu, unsigned long long nsecs)
+{
+	struct itimerspec its;
+
+	its.it_value.tv_sec = nsecs / UM_NSEC_PER_SEC;
+	its.it_value.tv_nsec = nsecs % UM_NSEC_PER_SEC;
+
+	its.it_interval.tv_sec = nsecs / UM_NSEC_PER_SEC;
+	its.it_interval.tv_nsec = nsecs % UM_NSEC_PER_SEC;
+
+	if (timer_settime(event_high_res_timer[cpu], 0, &its, NULL) == -1)
+		return -errno;
+
+	return 0;
+}
+
+int os_timer_one_shot(int cpu, unsigned long long nsecs)
+{
+	struct itimerspec its = {
+		.it_value.tv_sec = nsecs / UM_NSEC_PER_SEC,
+		.it_value.tv_nsec = nsecs % UM_NSEC_PER_SEC,
+
+		.it_interval.tv_sec = 0,
+		.it_interval.tv_nsec = 0, // we cheat here
+	};
+
+	timer_settime(event_high_res_timer[cpu], 0, &its, NULL);
+	return 0;
+}
+
+/**
+ * os_timer_disable() - disable the posix (interval) timer
+ * @cpu: the CPU for which the timer is to be disabled
+ */
+void os_timer_disable(int cpu)
+{
+	struct itimerspec its;
+
+	memset(&its, 0, sizeof(struct itimerspec));
+	timer_settime(event_high_res_timer[cpu], 0, &its, NULL);
+}
+
+long long os_nsecs(void)
+{
+	struct timespec ts;
+
+	clock_gettime(CLOCK_MONOTONIC,&ts);
+	return timespec_to_ns(&ts);
+}
+
+static __thread int wake_signals;
+
+void os_idle_prepare(void)
+{
+	sigset_t set;
+
+	sigemptyset(&set);
+	sigaddset(&set, SIGALRM);
+	sigaddset(&set, IPI_SIGNAL);
+
+	/*
+	 * We need to use signalfd rather than sigsuspend in idle sleep
+	 * because the IPI signal is a real-time signal that carries data,
+	 * and unlike handling SIGALRM, we cannot simply flag it in
+	 * signals_pending.
+	 */
+	wake_signals = signalfd(-1, &set, SFD_CLOEXEC);
+	if (wake_signals < 0)
+		panic("Failed to create signal FD, errno = %d", errno);
+}
+
+/**
+ * os_idle_sleep() - sleep until interrupted
+ */
+void os_idle_sleep(void)
+{
+	sigset_t set;
+
+	/*
+	 * Block SIGALRM while performing the need_resched check.
+	 * Note that, because IRQs are disabled, the IPI signal is
+	 * already blocked.
+	 */
+	sigemptyset(&set);
+	sigaddset(&set, SIGALRM);
+	sigprocmask(SIG_BLOCK, &set, NULL);
+
+	/*
+	 * Because disabling IRQs does not block SIGALRM, it is also
+	 * necessary to check for any pending timer alarms.
+	 */
+	if (!uml_need_resched() && !timer_alarm_pending())
+		os_poll(1, &wake_signals);
+
+	/* Restore the signal mask. */
+	sigprocmask(SIG_UNBLOCK, &set, NULL);
+}
diff --git a/arch/um/os-Linux/tty.c b/arch/um/os-Linux/tty.c
new file mode 100644
index 000000000..f784db83e
--- /dev/null
+++ b/arch/um/os-Linux/tty.c
@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <kern_util.h>
+#include <os.h>
+
+struct grantpt_info {
+	int fd;
+	int res;
+	int err;
+};
+
+static void grantpt_cb(void *arg)
+{
+	struct grantpt_info *info = arg;
+
+	info->res = grantpt(info->fd);
+	info->err = errno;
+}
+
+int get_pty(void)
+{
+	struct grantpt_info info;
+	int fd, err;
+
+	fd = open("/dev/ptmx", O_RDWR);
+	if (fd < 0) {
+		err = -errno;
+		printk(UM_KERN_ERR "get_pty : Couldn't open /dev/ptmx - "
+		       "err = %d\n", errno);
+		return err;
+	}
+
+	info.fd = fd;
+	initial_thread_cb(grantpt_cb, &info);
+
+	if (info.res < 0) {
+		err = -info.err;
+		printk(UM_KERN_ERR "get_pty : Couldn't grant pty - "
+		       "errno = %d\n", -info.err);
+		goto out;
+	}
+
+	if (unlockpt(fd) < 0) {
+		err = -errno;
+		printk(UM_KERN_ERR "get_pty : Couldn't unlock pty - "
+		       "errno = %d\n", errno);
+		goto out;
+	}
+	return fd;
+out:
+	close(fd);
+	return err;
+}
diff --git a/arch/um/os-Linux/umid.c b/arch/um/os-Linux/umid.c
new file mode 100644
index 000000000..6b488be2c
--- /dev/null
+++ b/arch/um/os-Linux/umid.c
@@ -0,0 +1,409 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <init.h>
+#include <os.h>
+
+#define UML_DIR "~/.uml/"
+
+#define UMID_LEN 64
+
+/* Changed by set_umid, which is run early in boot */
+static char umid[UMID_LEN] = { 0 };
+
+/* Changed by set_uml_dir and make_uml_dir, which are run early in boot */
+static char *uml_dir = UML_DIR;
+
+static int __init make_uml_dir(void)
+{
+	char dir[512] = { '\0' };
+	int len, err;
+
+	if (*uml_dir == '~') {
+		char *home = getenv("HOME");
+
+		err = -ENOENT;
+		if (home == NULL) {
+			printk(UM_KERN_ERR
+				"%s: no value in environment for $HOME\n",
+				__func__);
+			goto err;
+		}
+		strscpy(dir, home);
+		uml_dir++;
+	}
+	strlcat(dir, uml_dir, sizeof(dir));
+	len = strlen(dir);
+	if (len > 0 && dir[len - 1] != '/')
+		strlcat(dir, "/", sizeof(dir));
+
+	err = -ENOMEM;
+	uml_dir = malloc(strlen(dir) + 1);
+	if (uml_dir == NULL) {
+		printk(UM_KERN_ERR "%s : malloc failed, errno = %d\n",
+			__func__, errno);
+		goto err;
+	}
+	strcpy(uml_dir, dir);
+
+	if ((mkdir(uml_dir, 0777) < 0) && (errno != EEXIST)) {
+		printk(UM_KERN_ERR "Failed to mkdir '%s': %s\n",
+			uml_dir, strerror(errno));
+		err = -errno;
+		goto err_free;
+	}
+	return 0;
+
+err_free:
+	free(uml_dir);
+err:
+	uml_dir = NULL;
+	return err;
+}
+
+/*
+ * Unlinks the files contained in @dir and then removes @dir.
+ * Doesn't handle directory trees, so it's not like rm -rf, but almost such. We
+ * ignore ENOENT errors for anything (they happen, strangely enough - possibly
+ * due to races between multiple dying UML threads).
+ */
+static int remove_files_and_dir(char *dir)
+{
+	DIR *directory;
+	struct dirent *ent;
+	int len;
+	char file[256];
+	int ret;
+
+	directory = opendir(dir);
+	if (directory == NULL) {
+		if (errno != ENOENT)
+			return -errno;
+		else
+			return 0;
+	}
+
+	while ((ent = readdir(directory)) != NULL) {
+		if (!strcmp(ent->d_name, ".") || !strcmp(ent->d_name, ".."))
+			continue;
+		len = strlen(dir) + strlen("/") + strlen(ent->d_name) + 1;
+		if (len > sizeof(file)) {
+			ret = -E2BIG;
+			goto out;
+		}
+
+		sprintf(file, "%s/%s", dir, ent->d_name);
+		if (unlink(file) < 0 && errno != ENOENT) {
+			ret = -errno;
+			goto out;
+		}
+	}
+
+	if (rmdir(dir) < 0 && errno != ENOENT) {
+		ret = -errno;
+		goto out;
+	}
+
+	ret = 0;
+out:
+	closedir(directory);
+	return ret;
+}
+
+/*
+ * This says that there isn't already a user of the specified directory even if
+ * there are errors during the checking.  This is because if these errors
+ * happen, the directory is unusable by the pre-existing UML, so we might as
+ * well take it over.  This could happen either by
+ * 	the existing UML somehow corrupting its umid directory
+ * 	something other than UML sticking stuff in the directory
+ *	this boot racing with a shutdown of the other UML
+ * In any of these cases, the directory isn't useful for anything else.
+ *
+ * Boolean return: 1 if in use, 0 otherwise.
+ */
+static inline int is_umdir_used(char *dir)
+{
+	char pid[sizeof("nnnnnnnnn")], *end, *file;
+	int fd, p, n;
+	size_t filelen = strlen(dir) + sizeof("/pid") + 1;
+
+	file = malloc(filelen);
+	if (!file)
+		return -ENOMEM;
+
+	snprintf(file, filelen, "%s/pid", dir);
+
+	fd = open(file, O_RDONLY);
+	if (fd < 0) {
+		fd = -errno;
+		if (fd != -ENOENT) {
+			printk(UM_KERN_ERR "is_umdir_used : couldn't open pid "
+			       "file '%s', err = %d\n", file, -fd);
+		}
+		goto out;
+	}
+
+	n = read(fd, pid, sizeof(pid));
+	if (n < 0) {
+		printk(UM_KERN_ERR "is_umdir_used : couldn't read pid file "
+		       "'%s', err = %d\n", file, errno);
+		goto out_close;
+	} else if (n == 0) {
+		printk(UM_KERN_ERR "is_umdir_used : couldn't read pid file "
+		       "'%s', 0-byte read\n", file);
+		goto out_close;
+	}
+
+	p = strtoul(pid, &end, 0);
+	if (end == pid) {
+		printk(UM_KERN_ERR "is_umdir_used : couldn't parse pid file "
+		       "'%s', errno = %d\n", file, errno);
+		goto out_close;
+	}
+
+	if ((kill(p, 0) == 0) || (errno != ESRCH)) {
+		printk(UM_KERN_ERR "umid \"%s\" is already in use by pid %d\n",
+		       umid, p);
+		return 1;
+	}
+
+out_close:
+	close(fd);
+out:
+	free(file);
+	return 0;
+}
+
+/*
+ * Try to remove the directory @dir unless it's in use.
+ * Precondition: @dir exists.
+ * Returns 0 for success, < 0 for failure in removal or if the directory is in
+ * use.
+ */
+static int umdir_take_if_dead(char *dir)
+{
+	int ret;
+	if (is_umdir_used(dir))
+		return -EEXIST;
+
+	ret = remove_files_and_dir(dir);
+	if (ret) {
+		printk(UM_KERN_ERR "is_umdir_used - remove_files_and_dir "
+		       "failed with err = %d\n", ret);
+	}
+	return ret;
+}
+
+static void __init create_pid_file(void)
+{
+	char pid[sizeof("nnnnnnnnn")], *file;
+	int fd, n;
+
+	n = strlen(uml_dir) + UMID_LEN + sizeof("/pid");
+	file = malloc(n);
+	if (!file)
+		return;
+
+	if (umid_file_name("pid", file, n))
+		goto out;
+
+	fd = open(file, O_RDWR | O_CREAT | O_EXCL, 0644);
+	if (fd < 0) {
+		printk(UM_KERN_ERR "Open of machine pid file \"%s\" failed: "
+		       "%s\n", file, strerror(errno));
+		goto out;
+	}
+
+	snprintf(pid, sizeof(pid), "%d\n", getpid());
+	n = write(fd, pid, strlen(pid));
+	if (n != strlen(pid))
+		printk(UM_KERN_ERR "Write of pid file failed - err = %d\n",
+		       errno);
+
+	close(fd);
+out:
+	free(file);
+}
+
+int __init set_umid(char *name)
+{
+	if (strlen(name) > UMID_LEN - 1)
+		return -E2BIG;
+
+	strscpy(umid, name);
+
+	return 0;
+}
+
+/* Changed in make_umid, which is called during early boot */
+static int umid_setup = 0;
+
+static int __init make_umid(void)
+{
+	int fd, err;
+	char tmp[256];
+
+	if (umid_setup)
+		return 0;
+
+	make_uml_dir();
+
+	if (*umid == '\0') {
+		strscpy(tmp, uml_dir);
+		strlcat(tmp, "XXXXXX", sizeof(tmp));
+		fd = mkstemp(tmp);
+		if (fd < 0) {
+			printk(UM_KERN_ERR "make_umid - mkstemp(%s) failed: "
+			       "%s\n", tmp, strerror(errno));
+			err = -errno;
+			goto err;
+		}
+
+		close(fd);
+
+		set_umid(&tmp[strlen(uml_dir)]);
+
+		/*
+		 * There's a nice tiny little race between this unlink and
+		 * the mkdir below.  It'd be nice if there were a mkstemp
+		 * for directories.
+		 */
+		if (unlink(tmp)) {
+			err = -errno;
+			goto err;
+		}
+	}
+
+	snprintf(tmp, sizeof(tmp), "%s%s", uml_dir, umid);
+	err = mkdir(tmp, 0777);
+	if (err < 0) {
+		err = -errno;
+		if (err != -EEXIST)
+			goto err;
+
+		if (umdir_take_if_dead(tmp) < 0)
+			goto err;
+
+		err = mkdir(tmp, 0777);
+	}
+	if (err) {
+		err = -errno;
+		printk(UM_KERN_ERR "Failed to create '%s' - err = %d\n", umid,
+		       errno);
+		goto err;
+	}
+
+	umid_setup = 1;
+
+	create_pid_file();
+
+	err = 0;
+ err:
+	return err;
+}
+
+static int __init make_umid_init(void)
+{
+	if (!make_umid())
+		return 0;
+
+	/*
+	 * If initializing with the given umid failed, then try again with
+	 * a random one.
+	 */
+	printk(UM_KERN_ERR "Failed to initialize umid \"%s\", trying with a "
+	       "random umid\n", umid);
+	*umid = '\0';
+	make_umid();
+
+	return 0;
+}
+
+__initcall(make_umid_init);
+
+int __init umid_file_name(char *name, char *buf, int len)
+{
+	int n, err;
+
+	err = make_umid();
+	if (err)
+		return err;
+
+	n = snprintf(buf, len, "%s%s/%s", uml_dir, umid, name);
+	if (n >= len) {
+		printk(UM_KERN_ERR "umid_file_name : buffer too short\n");
+		return -E2BIG;
+	}
+
+	return 0;
+}
+
+char *get_umid(void)
+{
+	return umid;
+}
+
+static int __init set_uml_dir(char *name, int *add)
+{
+	*add = 0;
+
+	if (*name == '\0') {
+		os_warn("uml_dir can't be an empty string\n");
+		return 0;
+	}
+
+	if (name[strlen(name) - 1] == '/') {
+		uml_dir = name;
+		return 0;
+	}
+
+	uml_dir = malloc(strlen(name) + 2);
+	if (uml_dir == NULL) {
+		os_warn("Failed to malloc uml_dir - error = %d\n", errno);
+
+		/*
+		 * Return 0 here because do_initcalls doesn't look at
+		 * the return value.
+		 */
+		return 0;
+	}
+	sprintf(uml_dir, "%s/", name);
+
+	return 0;
+}
+
+__uml_setup("uml_dir=", set_uml_dir,
+"uml_dir=<directory>\n"
+"    The location to place the pid and umid files.\n\n"
+);
+
+static void remove_umid_dir(void)
+{
+	char *dir, err;
+
+	dir = malloc(strlen(uml_dir) + UMID_LEN + 1);
+	if (!dir)
+		return;
+
+	sprintf(dir, "%s%s", uml_dir, umid);
+	err = remove_files_and_dir(dir);
+	if (err)
+		os_warn("%s - remove_files_and_dir failed with err = %d\n",
+			__func__, err);
+
+	free(dir);
+}
+
+__uml_exitcall(remove_umid_dir);
diff --git a/arch/um/os-Linux/user_syms.c b/arch/um/os-Linux/user_syms.c
new file mode 100644
index 000000000..67f611231
--- /dev/null
+++ b/arch/um/os-Linux/user_syms.c
@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0
+#define __NO_FORTIFY
+#include <linux/types.h>
+#include <linux/module.h>
+
+/*
+ * This file exports some critical string functions and compiler
+ * built-in functions (where calls are emitted by the compiler
+ * itself that we cannot avoid even in kernel code) to modules.
+ *
+ * "_user.c" code that previously used exports here such as hostfs
+ * really should be considered part of the 'hypervisor' and define
+ * its own API boundary like hostfs does now; don't add exports to
+ * this file for such cases.
+ */
+
+/* If it's not defined, the export is included in lib/string.c.*/
+#ifdef __HAVE_ARCH_STRSTR
+#undef strstr
+EXPORT_SYMBOL(strstr);
+#endif
+
+#ifndef __x86_64__
+#undef memcpy
+extern void *memcpy(void *, const void *, size_t);
+EXPORT_SYMBOL(memcpy);
+extern void *memmove(void *, const void *, size_t);
+EXPORT_SYMBOL(memmove);
+#undef memset
+extern void *memset(void *, int, size_t);
+EXPORT_SYMBOL(memset);
+#endif
+
+#ifdef _FORTIFY_SOURCE
+extern int __sprintf_chk(char *str, int flag, size_t len, const char *format);
+EXPORT_SYMBOL(__sprintf_chk);
+#endif
diff --git a/arch/um/os-Linux/util.c b/arch/um/os-Linux/util.c
new file mode 100644
index 000000000..e3ad71a0d
--- /dev/null
+++ b/arch/um/os-Linux/util.c
@@ -0,0 +1,209 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <signal.h>
+#include <string.h>
+#include <termios.h>
+#include <sys/wait.h>
+#include <sys/mman.h>
+#include <sys/utsname.h>
+#include <sys/random.h>
+#include <init.h>
+#include <os.h>
+
+void stack_protections(unsigned long address)
+{
+	if (mprotect((void *) address, UM_THREAD_SIZE, PROT_READ | PROT_WRITE) < 0)
+		panic("protecting stack failed, errno = %d", errno);
+}
+
+int raw(int fd)
+{
+	struct termios tt;
+	int err;
+
+	CATCH_EINTR(err = tcgetattr(fd, &tt));
+	if (err < 0)
+		return -errno;
+
+	cfmakeraw(&tt);
+
+	CATCH_EINTR(err = tcsetattr(fd, TCSADRAIN, &tt));
+	if (err < 0)
+		return -errno;
+
+	/*
+	 * XXX tcsetattr could have applied only some changes
+	 * (and cfmakeraw() is a set of changes)
+	 */
+	return 0;
+}
+
+void setup_machinename(char *machine_out)
+{
+	struct utsname host;
+
+	uname(&host);
+#if IS_ENABLED(CONFIG_UML_X86)
+# if !IS_ENABLED(CONFIG_64BIT)
+	if (!strcmp(host.machine, "x86_64")) {
+		strcpy(machine_out, "i686");
+		return;
+	}
+# else
+	if (!strcmp(host.machine, "i686")) {
+		strcpy(machine_out, "x86_64");
+		return;
+	}
+# endif
+#endif
+	strcpy(machine_out, host.machine);
+}
+
+void setup_hostinfo(char *buf, int len)
+{
+	struct utsname host;
+
+	uname(&host);
+	snprintf(buf, len, "%s %s %s %s %s", host.sysname, host.nodename,
+		 host.release, host.version, host.machine);
+}
+
+/*
+ * We cannot use glibc's abort(). It makes use of tgkill() which
+ * has no effect within UML's kernel threads.
+ * After that glibc would execute an invalid instruction to kill
+ * the calling process and UML crashes with SIGSEGV.
+ */
+static inline void __attribute__ ((noreturn)) uml_abort(void)
+{
+	sigset_t sig;
+
+	fflush(NULL);
+
+	if (!sigemptyset(&sig) && !sigaddset(&sig, SIGABRT))
+		sigprocmask(SIG_UNBLOCK, &sig, 0);
+
+	for (;;)
+		if (kill(getpid(), SIGABRT) < 0)
+			exit(127);
+}
+
+ssize_t os_getrandom(void *buf, size_t len, unsigned int flags)
+{
+	return getrandom(buf, len, flags);
+}
+
+/*
+ * UML helper threads must not handle SIGWINCH/INT/TERM
+ */
+void os_fix_helper_signals(void)
+{
+	signal(SIGWINCH, SIG_IGN);
+	signal(SIGINT, SIG_DFL);
+	signal(SIGTERM, SIG_DFL);
+}
+
+void os_dump_core(void)
+{
+	int pid;
+
+	signal(SIGSEGV, SIG_DFL);
+
+	/*
+	 * We are about to SIGTERM this entire process group to ensure that
+	 * nothing is around to run after the kernel exits.  The
+	 * kernel wants to abort, not die through SIGTERM, so we
+	 * ignore it here.
+	 */
+
+	signal(SIGTERM, SIG_IGN);
+	kill(0, SIGTERM);
+	/*
+	 * Most of the other processes associated with this UML are
+	 * likely sTopped, so give them a SIGCONT so they see the
+	 * SIGTERM.
+	 */
+	kill(0, SIGCONT);
+
+	/*
+	 * Now, having sent signals to everyone but us, make sure they
+	 * die by ptrace.  Processes can survive what's been done to
+	 * them so far - the mechanism I understand is receiving a
+	 * SIGSEGV and segfaulting immediately upon return.  There is
+	 * always a SIGSEGV pending, and (I'm guessing) signals are
+	 * processed in numeric order so the SIGTERM (signal 15 vs
+	 * SIGSEGV being signal 11) is never handled.
+	 *
+	 * Run a waitpid loop until we get some kind of error.
+	 * Hopefully, it's ECHILD, but there's not a lot we can do if
+	 * it's something else.  Tell os_kill_ptraced_process not to
+	 * wait for the child to report its death because there's
+	 * nothing reasonable to do if that fails.
+	 */
+
+	while ((pid = waitpid(-1, NULL, WNOHANG | __WALL)) > 0)
+		os_kill_ptraced_process(pid, 0);
+
+	uml_abort();
+}
+
+void um_early_printk(const char *s, unsigned int n)
+{
+	printf("%.*s", n, s);
+}
+
+static int quiet_info;
+
+static int __init quiet_cmd_param(char *str, int *add)
+{
+	quiet_info = 1;
+	return 0;
+}
+
+__uml_setup("quiet", quiet_cmd_param,
+"quiet\n"
+"    Turns off information messages during boot.\n\n");
+
+/*
+ * The os_info/os_warn functions will be called by helper threads. These
+ * have a very limited stack size and using the libc formatting functions
+ * may overflow the stack.
+ * So pull in the kernel vscnprintf and use that instead with a fixed
+ * on-stack buffer.
+ */
+int vscnprintf(char *buf, size_t size, const char *fmt, va_list args);
+
+void os_info(const char *fmt, ...)
+{
+	char buf[256];
+	va_list list;
+	int len;
+
+	if (quiet_info)
+		return;
+
+	va_start(list, fmt);
+	len = vscnprintf(buf, sizeof(buf), fmt, list);
+	fwrite(buf, len, 1, stderr);
+	va_end(list);
+}
+
+void os_warn(const char *fmt, ...)
+{
+	char buf[256];
+	va_list list;
+	int len;
+
+	va_start(list, fmt);
+	len = vscnprintf(buf, sizeof(buf), fmt, list);
+	fwrite(buf, len, 1, stderr);
+	va_end(list);
+}
diff --git a/arch/um/scripts/Makefile.rules b/arch/um/scripts/Makefile.rules
new file mode 100644
index 000000000..a8b7d9dab
--- /dev/null
+++ b/arch/um/scripts/Makefile.rules
@@ -0,0 +1,27 @@
+# SPDX-License-Identifier: GPL-2.0
+# ===========================================================================
+# arch/um: Generic definitions
+# ===========================================================================
+
+USER_SINGLE_OBJS := \
+	$(foreach f,$(patsubst %.o,%,$(obj-y)),$($(f)-objs))
+USER_OBJS += $(filter %_user.o,$(obj-y) $(USER_SINGLE_OBJS))
+USER_OBJS := $(foreach file,$(USER_OBJS),$(obj)/$(file))
+
+$(USER_OBJS:.o=.%): \
+	c_flags = -Wp,-MD,$(depfile) $(USER_CFLAGS) -include $(srctree)/include/linux/kern_levels.h -include user.h $(CFLAGS_$(basetarget).o)
+
+# These are like USER_OBJS but filter USER_CFLAGS through unprofile instead of
+# using it directly.
+UNPROFILE_OBJS := $(foreach file,$(UNPROFILE_OBJS),$(obj)/$(file))
+
+$(UNPROFILE_OBJS:.o=.%): \
+	c_flags = -Wp,-MD,$(depfile) $(call unprofile,$(USER_CFLAGS)) $(CFLAGS_$(basetarget).o)
+
+$(USER_OBJS) $(UNPROFILE_OBJS): \
+	CHECKFLAGS := $(patsubst $(NOSTDINC_FLAGS),,$(CHECKFLAGS))
+
+# The stubs can't try to call mcount or update basic block data
+define unprofile
+	$(patsubst -pg,,$(patsubst -fprofile-arcs -ftest-coverage,,$(1)))
+endef