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, 153 insertions, 0 deletions

diff --git a/scripts/Makefile.dtbs b/scripts/Makefile.dtbs
new file mode 100644
index 000000000..c4e466390
--- /dev/null
+++ b/scripts/Makefile.dtbs
@@ -0,0 +1,153 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+all-dtb := $(dtb-y) $(dtb-)
+
+# If CONFIG_OF_ALL_DTBS is enabled, all DT blobs are built
+dtb-$(CONFIG_OF_ALL_DTBS) += $(dtb-)
+
+# Composite DTB (i.e. DTB constructed by overlay)
+multi-dtb-y := $(call multi-search, $(dtb-y), .dtb, -dtbs)
+# Primitive DTB compiled from *.dts
+real-dtb-y := $(call real-search, $(dtb-y), .dtb, -dtbs)
+# Base DTB that overlay is applied onto
+base-dtb-y := $(filter %.dtb, $(call real-search, $(multi-dtb-y), .dtb, -dtbs))
+
+# Ensure that any .dtbo is applied to at least one base .dtb. Otherwise, it
+# does not get validated.
+applied-dtbo := $(filter %.dtbo, \
+	$(call real-search, $(call multi-search, $(all-dtb), .dtb, -dtbs), .dtb, -dtbs))
+unapplied-dtbo := $(filter-out $(applied-dtbo),$(filter %.dtbo, $(dtb-y)))
+$(if $(unapplied-dtbo), $(warning .dtbo is not applied to any base: $(unapplied-dtbo)))
+
+dtb-y           := $(addprefix $(obj)/, $(dtb-y))
+multi-dtb-y     := $(addprefix $(obj)/, $(multi-dtb-y))
+real-dtb-y      := $(addprefix $(obj)/, $(real-dtb-y))
+
+always-y        += $(dtb-y)
+targets         += $(real-dtb-y)
+
+# dtbs-list
+# ---------------------------------------------------------------------------
+
+ifdef need-dtbslist
+subdir-dtbslist := $(addsuffix /dtbs-list, $(subdir-ym))
+dtb-y           += $(subdir-dtbslist)
+always-y        += $(obj)/dtbs-list
+endif
+
+$(subdir-dtbslist): $(obj)/%/dtbs-list: $(obj)/% ;
+
+$(obj)/dtbs-list: $(dtb-y) FORCE
+	$(call if_changed,gen_order)
+
+# Assembly file to wrap dtb(o)
+# ---------------------------------------------------------------------------
+
+builtin-dtb-section = $(if $(filter arch/$(SRCARCH)/boot/dts%, $(obj)),.dtb.init.rodata,.rodata)
+
+# Generate an assembly file to wrap the output of the device tree compiler
+quiet_cmd_wrap_S_dtb = WRAP    $@
+      cmd_wrap_S_dtb = {								\
+		symbase=__$(patsubst .%,%,$(suffix $<))_$(subst -,_,$(notdir $*));	\
+		echo '\#include <asm-generic/vmlinux.lds.h>';				\
+		echo '.section $(builtin-dtb-section),"a"';				\
+		echo '.balign STRUCT_ALIGNMENT';					\
+		echo ".global $${symbase}_begin";					\
+		echo "$${symbase}_begin:";						\
+		echo '.incbin "$<" ';							\
+		echo ".global $${symbase}_end";						\
+		echo "$${symbase}_end:";						\
+		echo '.balign STRUCT_ALIGNMENT';					\
+	} > $@
+
+$(obj)/%.dtb.S: $(obj)/%.dtb FORCE
+	$(call if_changed,wrap_S_dtb)
+
+$(obj)/%.dtbo.S: $(obj)/%.dtbo FORCE
+	$(call if_changed,wrap_S_dtb)
+
+# Schema check
+# ---------------------------------------------------------------------------
+
+ifneq ($(CHECK_DTBS),)
+DT_CHECKER ?= dt-validate
+DT_CHECKER_FLAGS ?= $(if $(DT_SCHEMA_FILES),-l $(DT_SCHEMA_FILES),-m)
+DT_BINDING_DIR := Documentation/devicetree/bindings
+DT_TMP_SCHEMA := $(objtree)/$(DT_BINDING_DIR)/processed-schema.json
+dtb-check-enabled = $(if $(filter %.dtb, $@),y)
+endif
+
+quiet_dtb_check_tag = $(if $(dtb-check-enabled),[C],   )
+cmd_dtb_check = $(if $(dtb-check-enabled),; $(DT_CHECKER) $(DT_CHECKER_FLAGS) -u $(srctree)/$(DT_BINDING_DIR) -p $(DT_TMP_SCHEMA) $@ || true)
+
+# Overlay
+# ---------------------------------------------------------------------------
+
+# NOTE:
+# Do not replace $(filter %.dtb %.dtbo, $^) with $(real-prereqs). When a single
+# DTB is turned into a multi-blob DTB, $^ will contain header file dependencies
+# recorded in the .*.cmd file.
+quiet_cmd_fdtoverlay = OVL $(quiet_dtb_check_tag) $@
+      cmd_fdtoverlay = $(objtree)/scripts/dtc/fdtoverlay -o $@ -i $(filter %.dtb %.dtbo, $^) $(cmd_dtb_check)
+
+$(multi-dtb-y): $(DT_TMP_SCHEMA) FORCE
+	$(call if_changed,fdtoverlay)
+$(call multi_depend, $(multi-dtb-y), .dtb, -dtbs)
+
+# DTC
+# ---------------------------------------------------------------------------
+
+DTC ?= $(objtree)/scripts/dtc/dtc
+DTC_FLAGS += -Wno-unique_unit_address
+
+# Disable noisy checks by default
+ifeq ($(findstring 1,$(KBUILD_EXTRA_WARN)),)
+DTC_FLAGS += -Wno-unit_address_vs_reg \
+             -Wno-avoid_unnecessary_addr_size \
+             -Wno-alias_paths \
+             -Wno-interrupt_map \
+             -Wno-simple_bus_reg
+else
+DTC_FLAGS += -Wunique_unit_address_if_enabled
+endif
+
+ifneq ($(findstring 2,$(KBUILD_EXTRA_WARN)),)
+DTC_FLAGS += -Wnode_name_chars_strict \
+             -Wproperty_name_chars_strict \
+             -Wunique_unit_address
+endif
+
+DTC_FLAGS += $(DTC_FLAGS_$(target-stem))
+
+# Set -@ if the target is a base DTB that overlay is applied onto
+DTC_FLAGS += $(if $(filter $(patsubst $(obj)/%,%,$@), $(base-dtb-y)), -@)
+
+DTC_INCLUDE := $(srctree)/scripts/dtc/include-prefixes
+
+dtc_cpp_flags = -Wp,-MMD,$(depfile).pre.tmp -nostdinc -I $(DTC_INCLUDE) -undef -D__DTS__
+
+dtc-tmp = $(subst $(comma),_,$(dot-target).dts.tmp)
+
+quiet_cmd_dtc = DTC $(quiet_dtb_check_tag) $@
+      cmd_dtc = \
+	$(HOSTCC) -E $(dtc_cpp_flags) -x assembler-with-cpp -o $(dtc-tmp) $< ; \
+	$(DTC) -o $@ -b 0 $(addprefix -i,$(dir $<) $(DTC_INCLUDE)) \
+	       $(DTC_FLAGS) -d $(depfile).dtc.tmp $(dtc-tmp) ; \
+	cat $(depfile).pre.tmp $(depfile).dtc.tmp > $(depfile) \
+	$(cmd_dtb_check)
+
+$(obj)/%.dtb: $(obj)/%.dts $(DTC) $(DT_TMP_SCHEMA) FORCE
+	$(call if_changed_dep,dtc)
+
+$(obj)/%.dtbo: $(src)/%.dtso $(DTC) FORCE
+	$(call if_changed_dep,dtc)
+
+# targets
+# ---------------------------------------------------------------------------
+
+targets += $(always-y)
+
+# %.dtb.o <- %.dtb.S <- %.dtb <- %.dts
+# %.dtbo.o <- %.dtbo.S <- %.dtbo <- %.dtso
+targets += $(call intermediate_targets, .dtb.o, .dtb.S .dtb) \
+           $(call intermediate_targets, .dtbo.o, .dtbo.S .dtbo)