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>

4 files changed, 281 insertions, 0 deletions

diff --git a/tools/testing/selftests/kho/arm64.conf b/tools/testing/selftests/kho/arm64.conf
new file mode 100644
index 000000000..ee696807c
--- /dev/null
+++ b/tools/testing/selftests/kho/arm64.conf
@@ -0,0 +1,9 @@
+QEMU_CMD="qemu-system-aarch64 -M virt -cpu max"
+QEMU_KCONFIG="
+CONFIG_SERIAL_AMBA_PL010=y
+CONFIG_SERIAL_AMBA_PL010_CONSOLE=y
+CONFIG_SERIAL_AMBA_PL011=y
+CONFIG_SERIAL_AMBA_PL011_CONSOLE=y
+"
+KERNEL_IMAGE="Image"
+KERNEL_CMDLINE="console=ttyAMA0"
diff --git a/tools/testing/selftests/kho/init.c b/tools/testing/selftests/kho/init.c
new file mode 100644
index 000000000..88a41b6eb
--- /dev/null
+++ b/tools/testing/selftests/kho/init.c
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/syscall.h>
+#include <sys/mount.h>
+#include <sys/reboot.h>
+#include <linux/kexec.h>
+
+/* from arch/x86/include/asm/setup.h */
+#define COMMAND_LINE_SIZE	2048
+
+#define KERNEL_IMAGE "/kernel"
+
+static int mount_filesystems(void)
+{
+	if (mount("debugfs", "/debugfs", "debugfs", 0, NULL) < 0)
+		return -1;
+
+	return mount("proc", "/proc", "proc", 0, NULL);
+}
+
+static long kexec_file_load(int kernel_fd, int initrd_fd,
+			    unsigned long cmdline_len, const char *cmdline,
+			    unsigned long flags)
+{
+	return syscall(__NR_kexec_file_load, kernel_fd, initrd_fd, cmdline_len,
+		       cmdline, flags);
+}
+
+static int kexec_load(void)
+{
+	char cmdline[COMMAND_LINE_SIZE];
+	ssize_t len;
+	int fd, err;
+
+	fd = open("/proc/cmdline", O_RDONLY);
+	if (fd < 0)
+		return -1;
+
+	len = read(fd, cmdline, sizeof(cmdline));
+	close(fd);
+	if (len < 0)
+		return -1;
+
+	/* replace \n with \0 */
+	cmdline[len - 1] = 0;
+	fd = open(KERNEL_IMAGE, O_RDONLY);
+	if (fd < 0)
+		return -1;
+
+	err = kexec_file_load(fd, -1, len, cmdline, KEXEC_FILE_NO_INITRAMFS);
+	close(fd);
+
+	return err ? : 0;
+}
+
+int main(int argc, char *argv[])
+{
+	if (mount_filesystems())
+		goto err_reboot;
+
+	if (kexec_load())
+		goto err_reboot;
+
+	if (reboot(RB_KEXEC))
+		goto err_reboot;
+
+	return 0;
+
+err_reboot:
+	reboot(RB_AUTOBOOT);
+	return -1;
+}
diff --git a/tools/testing/selftests/kho/vmtest.sh b/tools/testing/selftests/kho/vmtest.sh
new file mode 100755
index 000000000..0014bd76e
--- /dev/null
+++ b/tools/testing/selftests/kho/vmtest.sh
@@ -0,0 +1,190 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+set -ue
+
+CROSS_COMPILE="${CROSS_COMPILE:-""}"
+
+test_dir=$(realpath "$(dirname "$0")")
+kernel_dir=$(realpath "$test_dir/../../../..")
+
+tmp_dir=$(mktemp -d /tmp/kho-test.XXXXXXXX)
+headers_dir="$tmp_dir/usr"
+initrd="$tmp_dir/initrd.cpio"
+
+source "$test_dir/../kselftest/ktap_helpers.sh"
+
+function usage() {
+	cat <<EOF
+$0 [-d build_dir] [-j jobs] [-t target_arch] [-h]
+Options:
+	-d)	path to the kernel build directory
+	-j)	number of jobs for compilation, similar to -j in make
+	-t)	run test for target_arch, requires CROSS_COMPILE set
+		supported targets: aarch64, x86_64
+	-h)	display this help
+EOF
+}
+
+function cleanup() {
+	rm -fr "$tmp_dir"
+	ktap_finished
+}
+trap cleanup EXIT
+
+function skip() {
+	local msg=${1:-""}
+
+	ktap_test_skip "$msg"
+	exit "$KSFT_SKIP"
+}
+
+function fail() {
+	local msg=${1:-""}
+
+	ktap_test_fail "$msg"
+	exit "$KSFT_FAIL"
+}
+
+function build_kernel() {
+	local build_dir=$1
+	local make_cmd=$2
+	local arch_kconfig=$3
+	local kimage=$4
+
+	local kho_config="$tmp_dir/kho.config"
+	local kconfig="$build_dir/.config"
+
+	# enable initrd, KHO and KHO test in kernel configuration
+	tee "$kconfig" > "$kho_config" <<EOF
+CONFIG_BLK_DEV_INITRD=y
+CONFIG_KEXEC_HANDOVER=y
+CONFIG_KEXEC_HANDOVER_DEBUG=y
+CONFIG_KEXEC_HANDOVER_DEBUGFS=y
+CONFIG_TEST_KEXEC_HANDOVER=y
+CONFIG_DEBUG_KERNEL=y
+CONFIG_DEBUG_VM=y
+CONFIG_DEBUG_VM_PGFLAGS=y
+CONFIG_SMP=y
+CONFIG_DEFERRED_STRUCT_PAGE_INIT=y
+$arch_kconfig
+EOF
+
+	make_cmd="$make_cmd -C $kernel_dir O=$build_dir"
+	$make_cmd olddefconfig
+
+	# verify that kernel confiration has all necessary options
+	while read -r opt ; do
+		grep "$opt" "$kconfig" &>/dev/null || skip "$opt is missing"
+	done < "$kho_config"
+
+	$make_cmd "$kimage"
+	$make_cmd headers_install INSTALL_HDR_PATH="$headers_dir"
+}
+
+function mkinitrd() {
+	local kernel=$1
+
+	"$CROSS_COMPILE"gcc -s -static -Os -nostdinc -nostdlib \
+			-fno-asynchronous-unwind-tables -fno-ident \
+			-I "$headers_dir/include" \
+			-I "$kernel_dir/tools/include/nolibc" \
+			-o "$tmp_dir/init" "$test_dir/init.c"
+
+	cat > "$tmp_dir/cpio_list" <<EOF
+dir /dev 0755 0 0
+dir /proc 0755 0 0
+dir /debugfs 0755 0 0
+nod /dev/console 0600 0 0 c 5 1
+file /init $tmp_dir/init 0755 0 0
+file /kernel $kernel 0644 0 0
+EOF
+
+	"$build_dir/usr/gen_init_cpio" "$tmp_dir/cpio_list" > "$initrd"
+}
+
+function run_qemu() {
+	local qemu_cmd=$1
+	local cmdline=$2
+	local kernel=$3
+	local serial="$tmp_dir/qemu.serial"
+
+	cmdline="$cmdline kho=on panic=-1"
+
+	$qemu_cmd -m 1G -smp 2 -no-reboot -nographic -nodefaults \
+		  -accel kvm -accel hvf -accel tcg  \
+		  -serial file:"$serial" \
+		  -append "$cmdline" \
+		  -kernel "$kernel" \
+		  -initrd "$initrd"
+
+	grep "KHO restore succeeded" "$serial" &> /dev/null || fail "KHO failed"
+}
+
+function target_to_arch() {
+	local target=$1
+
+	case $target in
+	     aarch64) echo "arm64" ;;
+	     x86_64) echo "x86" ;;
+	     *) skip "architecture $target is not supported"
+	esac
+}
+
+function main() {
+	local build_dir="$kernel_dir/.kho"
+	local jobs=$(($(nproc) * 2))
+	local target="$(uname -m)"
+
+	# skip the test if any of the preparation steps fails
+	set -o errtrace
+	trap skip ERR
+
+	while getopts 'hd:j:t:' opt; do
+		case $opt in
+		d)
+			build_dir="$OPTARG"
+			;;
+		j)
+		        jobs="$OPTARG"
+			;;
+		t)
+			target="$OPTARG"
+			;;
+		h)
+			usage
+			exit 0
+			;;
+		*)
+			echo Unknown argument "$opt"
+			usage
+			exit 1
+			;;
+		esac
+	done
+
+	ktap_print_header
+	ktap_set_plan 1
+
+	if [[ "$target" != "$(uname -m)" ]] && [[ -z "$CROSS_COMPILE" ]]; then
+		skip "Cross-platform testing needs to specify CROSS_COMPILE"
+	fi
+
+	mkdir -p "$build_dir"
+	local arch=$(target_to_arch "$target")
+	source "$test_dir/$arch.conf"
+
+	# build the kernel and create initrd
+	# initrd includes the kernel image that will be kexec'ed
+	local make_cmd="make ARCH=$arch CROSS_COMPILE=$CROSS_COMPILE -j$jobs"
+	build_kernel "$build_dir" "$make_cmd" "$QEMU_KCONFIG" "$KERNEL_IMAGE"
+
+	local kernel="$build_dir/arch/$arch/boot/$KERNEL_IMAGE"
+	mkinitrd "$kernel"
+
+	run_qemu "$QEMU_CMD" "$KERNEL_CMDLINE" "$kernel"
+
+	ktap_test_pass "KHO succeeded"
+}
+
+main "$@"
diff --git a/tools/testing/selftests/kho/x86.conf b/tools/testing/selftests/kho/x86.conf
new file mode 100644
index 000000000..b419e610c
--- /dev/null
+++ b/tools/testing/selftests/kho/x86.conf
@@ -0,0 +1,7 @@
+QEMU_CMD=qemu-system-x86_64
+QEMU_KCONFIG="
+CONFIG_SERIAL_8250=y
+CONFIG_SERIAL_8250_CONSOLE=y
+"
+KERNEL_IMAGE="bzImage"
+KERNEL_CMDLINE="console=ttyS0"