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, 75 insertions, 0 deletions

diff --git a/scripts/package/install-extmod-build b/scripts/package/install-extmod-build
new file mode 100755
index 000000000..f12e1ffe4
--- /dev/null
+++ b/scripts/package/install-extmod-build
@@ -0,0 +1,75 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+
+set -eu
+
+destdir=${1}
+
+is_enabled() {
+	grep -q "^$1=y" include/config/auto.conf
+}
+
+find_in_scripts() {
+	find scripts \
+		\( -name atomic -o -name dtc -o -name kconfig -o -name package \) -prune -o \
+		! -name unifdef -a ! -name mk_elfconfig -a \( -type f -o -type l \) -print
+}
+
+mkdir -p "${destdir}"
+
+(
+	cd "${srctree}"
+	echo Makefile
+	find "arch/${SRCARCH}" -maxdepth 1 -name 'Makefile*'
+	find "arch/${SRCARCH}" -name generated -prune -o -name include -type d -print
+	find "arch/${SRCARCH}" -name Kbuild.platforms -o -name Platform
+	find include \( -name config -o -name generated \) -prune -o \( -type f -o -type l \) -print
+	find_in_scripts
+) | tar -c -f - -C "${srctree}" -T - | tar -xf - -C "${destdir}"
+
+{
+	if is_enabled CONFIG_OBJTOOL; then
+		echo tools/objtool/objtool
+	fi
+
+	if is_enabled CONFIG_DEBUG_INFO_BTF_MODULES; then
+		echo tools/bpf/resolve_btfids/resolve_btfids
+	fi
+
+	echo Module.symvers
+	echo "arch/${SRCARCH}/include/generated"
+	echo include/config/auto.conf
+	echo include/config/kernel.release
+	echo include/generated
+	find_in_scripts
+
+	if is_enabled CONFIG_GCC_PLUGINS; then
+		find scripts/gcc-plugins -name '*.so'
+	fi
+} | tar -c -f - -T - | tar -xf - -C "${destdir}"
+
+# When ${CC} and ${HOSTCC} differ, rebuild host programs using ${CC}.
+#
+# This caters to host programs that participate in Kbuild. objtool and
+# resolve_btfids are out of scope.
+if [ "${CC}" != "${HOSTCC}" ]; then
+	cat "${destdir}/scripts/Makefile" - <<-'EOF' > "${destdir}/scripts/Kbuild"
+	subdir-y += basic
+	hostprogs-always-y += mod/modpost
+	mod/modpost-objs := $(addprefix mod/, modpost.o file2alias.o sumversion.o symsearch.o)
+	EOF
+
+	# HOSTCXX is not overridden. The C++ compiler is used to build:
+	# - scripts/kconfig/qconf, which is unneeded for external module builds
+	# - GCC plugins, which will not work on the installed system even after
+	#   being rebuilt.
+	#
+	# Clear VPATH and srcroot because the source files reside in the output
+	# directory.
+	# shellcheck disable=SC2016 # $(MAKE) and $(build) will be expanded by Make
+	"${MAKE}" run-command KBUILD_RUN_COMMAND='+$(MAKE) HOSTCC="'"${CC}"'" VPATH= srcroot=. $(build)='"$(realpath --relative-to=. "${destdir}")"/scripts
+
+	rm -f "${destdir}/scripts/Kbuild"
+fi
+
+find "${destdir}" \( -name '.*.cmd' -o -name '*.o' \) -delete