KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

Manually perform cache maintenance on the source VM during intra-host
migration to ensure no stale data is left in CPU caches after the VM is
destroyed.  Because the source VM is "converted" to a non-SEV VM, KVM's
memory reclaim flows won't trigger cache maintenance, e.g. when all guest
memory is reclaimed in response to detaching from the mmu_notifier.

Note, relying on the destination VM to do cache maintenance isn't an option
as KVM doesn't require identical guest memory configurations, i.e. the
source VM may have access to memory that the destination VM does not.
Enforcing equivalent memory configurations is infeasible, as it would
require a *deep* comparison of memslots, e.g. to verify that not only are
the memslot identical, but what the memslots point at is also identical.

Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 157 insertions, 0 deletions

diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
new file mode 100644
index 000000000..d7d45067d
--- /dev/null
+++ b/scripts/Makefile.modpost
@@ -0,0 +1,157 @@
+# SPDX-License-Identifier: GPL-2.0
+# ===========================================================================
+# Module versions
+# ===========================================================================
+#
+# Stage one of module building created the following:
+# a) The individual .o files used for the module
+# b) A <module>.o file which is the .o files above linked together
+# c) A <module>.mod file, listing the name of the preliminary <module>.o file,
+#    plus all .o files
+# d) modules.order, which lists all the modules
+
+# Stage 2 is handled by this file and does the following
+# 1) Find all modules listed in modules.order
+# 2) modpost is then used to
+# 3)  create one <module>.mod.c file per module
+# 4)  create one Module.symvers file with CRC for all exported symbols
+
+# Step 3 is used to place certain information in the module's ELF
+# section, including information such as:
+#   Version magic (see include/linux/vermagic.h for full details)
+#     - Kernel release
+#     - SMP is CONFIG_SMP
+#     - PREEMPT is CONFIG_PREEMPT[_RT]
+#     - GCC Version
+#   Module info
+#     - Module version (MODULE_VERSION)
+#     - Module alias'es (MODULE_ALIAS)
+#     - Module license (MODULE_LICENSE)
+#     - See include/linux/module.h for more details
+
+# Step 4 is solely used to allow module versioning in external modules,
+# where the CRC of each module is retrieved from the Module.symvers file.
+
+PHONY := __modpost
+__modpost:
+
+include $(objtree)/include/config/auto.conf
+include $(srctree)/scripts/Kbuild.include
+
+MODPOST = $(objtree)/scripts/mod/modpost
+
+modpost-args =										\
+	$(if $(CONFIG_MODULES),-M)							\
+	$(if $(CONFIG_MODVERSIONS),-m)							\
+	$(if $(CONFIG_BASIC_MODVERSIONS),-b)						\
+	$(if $(CONFIG_EXTENDED_MODVERSIONS),-x)						\
+	$(if $(CONFIG_MODULE_SRCVERSION_ALL),-a)					\
+	$(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)					\
+	$(if $(KBUILD_MODPOST_WARN),-w)							\
+	$(if $(KBUILD_NSDEPS),-d modules.nsdeps)					\
+	$(if $(CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS)$(KBUILD_NSDEPS),-N)	\
+	$(if $(findstring 1, $(KBUILD_EXTRA_WARN)),-W)					\
+	-o $@
+
+modpost-deps := $(MODPOST)
+
+# 'make -i -k' ignores compile errors, and builds as many modules as possible.
+ifneq ($(findstring i,$(filter-out --%,$(MAKEFLAGS))),)
+modpost-args += -n
+endif
+
+# Read out modules.order to pass in modpost.
+# Otherwise, allmodconfig would fail with "Argument list too long".
+ifdef KBUILD_MODULES
+modpost-args += -T modules.order
+modpost-deps += modules.order
+endif
+
+ifeq ($(KBUILD_EXTMOD),)
+
+# Generate the list of in-tree objects in vmlinux
+# ---------------------------------------------------------------------------
+
+# This is used to retrieve symbol versions generated by genksyms.
+ifdef CONFIG_MODVERSIONS
+vmlinux.symvers Module.symvers: .vmlinux.objs
+endif
+
+# Ignore libgcc.a
+# Some architectures do '$(CC) --print-libgcc-file-name' to borrow libgcc.a
+# from the toolchain, but there is no EXPORT_SYMBOL in it.
+
+quiet_cmd_vmlinux_objs = GEN     $@
+      cmd_vmlinux_objs =		\
+	for f in $(real-prereqs); do	\
+		case $${f} in		\
+		*libgcc.a) ;;		\
+		*) $(AR) t $${f} ;;	\
+		esac			\
+	done > $@
+
+targets += .vmlinux.objs
+.vmlinux.objs: vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
+	$(call if_changed,vmlinux_objs)
+
+ifdef CONFIG_TRIM_UNUSED_KSYMS
+ksym-wl := $(CONFIG_UNUSED_KSYMS_WHITELIST)
+ksym-wl := $(if $(filter-out /%, $(ksym-wl)),$(if $(wildcard $(ksym-wl)),,$(srctree)/))$(ksym-wl)
+modpost-args += -t $(addprefix -u , $(ksym-wl))
+modpost-deps += $(ksym-wl)
+endif
+
+ifeq ($(wildcard vmlinux.o),)
+missing-input := vmlinux.o
+output-symdump := modules-only.symvers
+else
+modpost-args += vmlinux.o
+modpost-deps += vmlinux.o
+output-symdump := $(if $(KBUILD_MODULES), Module.symvers, vmlinux.symvers)
+endif
+
+else
+
+# set src + obj - they may be used in the modules's Makefile
+obj := .
+src := $(srcroot)
+
+# Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
+include $(kbuild-file)
+
+output-symdump := Module.symvers
+
+ifeq ($(wildcard $(objtree)/Module.symvers),)
+missing-input := $(objtree)/Module.symvers
+else
+modpost-args += -i $(objtree)/Module.symvers
+modpost-deps += $(objtree)/Module.symvers
+endif
+
+modpost-args += -e $(addprefix -i , $(KBUILD_EXTRA_SYMBOLS))
+
+endif # ($(KBUILD_EXTMOD),)
+
+quiet_cmd_modpost = MODPOST $@
+      cmd_modpost = \
+	$(if $(missing-input), \
+		echo >&2 "WARNING: $(missing-input) is missing."; \
+		echo >&2 "         Modules may not have dependencies or modversions."; \
+		echo >&2 "         You may get many unresolved symbol errors."; \
+		echo >&2 "         You can set KBUILD_MODPOST_WARN=1 to turn errors into warning"; \
+		echo >&2 "         if you want to proceed at your own risk.";) \
+	$(MODPOST) $(modpost-args)
+
+targets += $(output-symdump)
+$(output-symdump): $(modpost-deps) FORCE
+	$(call if_changed,modpost)
+
+__modpost: $(output-symdump)
+PHONY += FORCE
+FORCE:
+
+existing-targets := $(wildcard $(sort $(targets)))
+
+-include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
+
+.PHONY: $(PHONY)