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>

2 files changed, 236 insertions, 0 deletions

diff --git a/tools/testing/selftests/cpu-hotplug/Makefile b/tools/testing/selftests/cpu-hotplug/Makefile
new file mode 100644
index 000000000..8b66c4738
--- /dev/null
+++ b/tools/testing/selftests/cpu-hotplug/Makefile
@@ -0,0 +1,11 @@
+# SPDX-License-Identifier: GPL-2.0
+all:
+
+TEST_PROGS := cpu-on-off-test.sh
+
+include ../lib.mk
+
+run_full_test:
+	@/bin/bash ./cpu-on-off-test.sh -a && echo "cpu-hotplug selftests: [PASS]" || echo "cpu-hotplug selftests: [FAIL]"
+
+clean:
diff --git a/tools/testing/selftests/cpu-hotplug/cpu-on-off-test.sh b/tools/testing/selftests/cpu-hotplug/cpu-on-off-test.sh
new file mode 100755
index 000000000..287cfd580
--- /dev/null
+++ b/tools/testing/selftests/cpu-hotplug/cpu-on-off-test.sh
@@ -0,0 +1,225 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+SYSFS=
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+retval=0
+
+prerequisite()
+{
+	msg="skip all tests:"
+
+	if [ $UID != 0 ]; then
+		echo $msg must be run as root >&2
+		exit $ksft_skip
+	fi
+
+	taskset -p 01 $$
+
+	SYSFS=`mount -t sysfs | head -1 | awk '{ print $3 }'`
+
+	if [ ! -d "$SYSFS" ]; then
+		echo $msg sysfs is not mounted >&2
+		exit $ksft_skip
+	fi
+
+	if ! ls $SYSFS/devices/system/cpu/cpu*/online > /dev/null 2>&1; then
+		echo $msg cpu hotplug is not supported >&2
+		exit $ksft_skip
+	fi
+
+	echo "CPU online/offline summary:"
+	online_cpus=`cat $SYSFS/devices/system/cpu/online`
+	online_max=${online_cpus##*-}
+
+	if [[ "$online_cpus" = "$online_max" ]]; then
+		echo "$msg: since there is only one cpu: $online_cpus"
+		exit $ksft_skip
+	fi
+
+	present_cpus=`cat $SYSFS/devices/system/cpu/present`
+	present_max=${present_cpus##*-}
+	echo "present_cpus = $present_cpus present_max = $present_max"
+
+	echo -e "\t Cpus in online state: $online_cpus"
+
+	offline_cpus=`cat $SYSFS/devices/system/cpu/offline`
+	if [[ "a$offline_cpus" = "a" ]]; then
+		offline_cpus=0
+	else
+		offline_max=${offline_cpus##*-}
+	fi
+	echo -e "\t Cpus in offline state: $offline_cpus"
+}
+
+#
+# list all hot-pluggable CPUs
+#
+hotpluggable_cpus()
+{
+	local state=${1:-.\*}
+
+	for cpu in $SYSFS/devices/system/cpu/cpu*; do
+		if [ -f $cpu/online ] && grep -q $state $cpu/online; then
+			echo ${cpu##/*/cpu}
+		fi
+	done
+}
+
+hotpluggable_offline_cpus()
+{
+	hotpluggable_cpus 0
+}
+
+hotpluggable_online_cpus()
+{
+	hotpluggable_cpus 1
+}
+
+cpu_is_online()
+{
+	grep -q 1 $SYSFS/devices/system/cpu/cpu$1/online
+}
+
+cpu_is_offline()
+{
+	grep -q 0 $SYSFS/devices/system/cpu/cpu$1/online
+}
+
+online_cpu()
+{
+	echo 1 > $SYSFS/devices/system/cpu/cpu$1/online
+}
+
+offline_cpu()
+{
+	echo 0 > $SYSFS/devices/system/cpu/cpu$1/online
+}
+
+online_cpu_expect_success()
+{
+	local cpu=$1
+
+	if ! online_cpu $cpu; then
+		echo $FUNCNAME $cpu: unexpected fail >&2
+		retval=1
+	elif ! cpu_is_online $cpu; then
+		echo $FUNCNAME $cpu: unexpected offline >&2
+		retval=1
+	fi
+}
+
+online_cpu_expect_fail()
+{
+	local cpu=$1
+
+	if online_cpu $cpu 2> /dev/null; then
+		echo $FUNCNAME $cpu: unexpected success >&2
+		retval=1
+	elif ! cpu_is_offline $cpu; then
+		echo $FUNCNAME $cpu: unexpected online >&2
+		retval=1
+	fi
+}
+
+offline_cpu_expect_success()
+{
+	local cpu=$1
+
+	if ! offline_cpu $cpu; then
+		echo $FUNCNAME $cpu: unexpected fail >&2
+		retval=1
+	elif ! cpu_is_offline $cpu; then
+		echo $FUNCNAME $cpu: unexpected offline >&2
+		retval=1
+	fi
+}
+
+offline_cpu_expect_fail()
+{
+	local cpu=$1
+
+	if offline_cpu $cpu 2> /dev/null; then
+		echo $FUNCNAME $cpu: unexpected success >&2
+		retval=1
+	elif ! cpu_is_online $cpu; then
+		echo $FUNCNAME $cpu: unexpected offline >&2
+		retval=1
+	fi
+}
+
+online_all_hot_pluggable_cpus()
+{
+	for cpu in `hotpluggable_offline_cpus`; do
+		online_cpu_expect_success $cpu
+	done
+}
+
+offline_all_hot_pluggable_cpus()
+{
+	local reserve_cpu=$online_max
+	for cpu in `hotpluggable_online_cpus`; do
+		# Reserve one cpu oneline at least.
+		if [ $cpu -eq $reserve_cpu ];then
+			continue
+		fi
+		offline_cpu_expect_success $cpu
+	done
+}
+
+allcpus=0
+online_cpus=0
+online_max=0
+offline_cpus=0
+offline_max=0
+present_cpus=0
+present_max=0
+
+while getopts ah opt; do
+	case $opt in
+	a)
+		allcpus=1
+		;;
+	h)
+		echo "Usage $0 [ -a ]"
+		echo -e "\t default offline one cpu"
+		echo -e "\t run with -a option to offline all cpus"
+		exit
+		;;
+	esac
+done
+
+prerequisite
+
+#
+# Safe test (default) - offline and online one cpu
+#
+if [ $allcpus -eq 0 ]; then
+	echo "Limited scope test: one hotplug cpu"
+	echo -e "\t (leaves cpu in the original state):"
+	echo -e "\t online to offline to online: cpu $online_max"
+	offline_cpu_expect_success $online_max
+	online_cpu_expect_success $online_max
+
+	if [[ $offline_cpus -gt 0 ]]; then
+		echo -e "\t online to offline to online: cpu $present_max"
+		online_cpu_expect_success $present_max
+		offline_cpu_expect_success $present_max
+		online_cpu $present_max
+	fi
+	exit $retval
+else
+	echo "Full scope test: all hotplug cpus"
+	echo -e "\t online all offline cpus"
+	echo -e "\t offline all online cpus"
+	echo -e "\t online all offline cpus"
+fi
+
+online_all_hot_pluggable_cpus
+
+offline_all_hot_pluggable_cpus
+
+online_all_hot_pluggable_cpus
+
+exit $retval