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, 118 insertions, 0 deletions

diff --git a/scripts/gfp-translate b/scripts/gfp-translate
new file mode 100755
index 000000000..8385ae0d5
--- /dev/null
+++ b/scripts/gfp-translate
@@ -0,0 +1,118 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0-only
+# Translate the bits making up a GFP mask
+# (c) 2009, Mel Gorman <mel@csn.ul.ie>
+SOURCE=
+GFPMASK=none
+
+# Helper function to report failures and exit
+die() {
+	echo ERROR: $@
+	if [ "$TMPFILE" != "" ]; then
+		rm -f $TMPFILE
+	fi
+	exit -1
+}
+
+usage() {
+	echo "usage: gfp-translate [-h] [ --source DIRECTORY ] gfpmask"
+	exit 0
+}
+
+# Parse command-line arguments
+while [ $# -gt 0 ]; do
+	case $1 in
+		--source)
+			SOURCE=$2
+			shift 2
+			;;
+		-h)
+			usage
+			;;
+		--help)
+			usage
+			;;
+		*)
+			GFPMASK=$1
+			shift
+			;;
+	esac
+done
+
+# Guess the kernel source directory if it's not set. Preference is in order of
+# o current directory
+# o /usr/src/linux
+if [ "$SOURCE" = "" ]; then
+	if [ -r "/usr/src/linux/Makefile" ]; then
+		SOURCE=/usr/src/linux
+	fi
+	if [ -r "`pwd`/Makefile" ]; then
+		SOURCE=`pwd`
+	fi
+fi
+
+# Confirm that a source directory exists
+if [ ! -r "$SOURCE/Makefile" ]; then
+	die "Could not locate kernel source directory or it is invalid"
+fi
+
+# Confirm that a GFP mask has been specified
+if [ "$GFPMASK" = "none" ]; then
+	usage
+fi
+
+# Extract GFP flags from the kernel source
+TMPFILE=`mktemp -t gfptranslate-XXXXXX.c` || exit 1
+
+echo Source: $SOURCE
+echo Parsing: $GFPMASK
+
+(
+    cat <<EOF
+#include <stdint.h>
+#include <stdio.h>
+
+// Try to fool compiler.h into not including extra stuff
+#define __ASSEMBLY__	1
+
+#include <generated/autoconf.h>
+#include <linux/gfp_types.h>
+
+static const char *masks[] = {
+EOF
+
+    sed -nEe 's/^[[:space:]]+(___GFP_.*)_BIT,.*$/\1/p' $SOURCE/include/linux/gfp_types.h |
+	while read b; do
+	    cat <<EOF
+#if defined($b) && ($b > 0)
+	[${b}_BIT]	= "$b",
+#endif
+EOF
+	done
+
+    cat <<EOF
+};
+
+int main(int argc, char *argv[])
+{
+	unsigned long long mask = $GFPMASK;
+
+	for (int i = 0; i < sizeof(mask) * 8; i++) {
+		unsigned long long bit = 1ULL << i;
+		if (mask & bit)
+			printf("\t%-25s0x%llx\n",
+			       (i < ___GFP_LAST_BIT && masks[i]) ?
+					masks[i] : "*** INVALID ***",
+			       bit);
+	}
+
+	return 0;
+}
+EOF
+) > $TMPFILE
+
+${CC:-gcc} -Wall -o ${TMPFILE}.bin -I $SOURCE/include $TMPFILE && ${TMPFILE}.bin
+
+rm -f $TMPFILE ${TMPFILE}.bin
+
+exit 0