Merge branch 'selftests-vsock-support-nested-vm-runner-for-vmtest-sh'

Bobby Eshleman says:

====================
selftests/vsock: support nested VM runner for vmtest.sh

This series fixes a few issues trying to launch vmtest.sh in a nested VM
environment and were discovered when trying to prepare the tests for
netdev CI/CD.

When taken together these patches make vmtest.sh work both on bare metal
and in nested VMs, regardless of the outer VM's user, coincidental path
overlaps, or filesystem settings.
====================

Link: https://patch.msgid.link/20260317-vsock-vmtest-nested-fixes-v2-0-0b3f53b80a0f@meta.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/vsock/vmtest.sh

@@ -42,6 +42,8 @@ readonly KERNEL_CMDLINE="\
 	virtme.ssh virtme_ssh_channel=tcp virtme_ssh_user=$USER \
 "
 readonly LOG=$(mktemp /tmp/vsock_vmtest_XXXX.log)
+readonly TEST_HOME="$(mktemp -d /tmp/vmtest_home_XXXX)"
+readonly SSH_KEY_PATH="${TEST_HOME}"/.ssh/id_ed25519
 
 # Namespace tests must use the ns_ prefix. This is checked in check_netns() and
 # is used to determine if a test needs namespace setup before test execution.
@@ -257,7 +259,12 @@ vm_ssh() {
 
 	shift
 
-	${ns_exec} ssh -q -o UserKnownHostsFile=/dev/null -p "${SSH_HOST_PORT}" localhost "$@"
+	${ns_exec} ssh -q \
+		-i "${SSH_KEY_PATH}" \
+		-o UserKnownHostsFile=/dev/null \
+		-o StrictHostKeyChecking=no \
+		-p "${SSH_HOST_PORT}" \
+		localhost "$@"
 
 	return $?
 }
@@ -265,6 +272,7 @@ vm_ssh() {
 cleanup() {
 	terminate_pidfiles "${!PIDFILES[@]}"
 	del_namespaces
+	rm -rf "${TEST_HOME}"
 }
 
 check_args() {
@@ -382,6 +390,12 @@ handle_build() {
 	popd &>/dev/null
 }
 
+setup_home() {
+	mkdir -p "$(dirname "${SSH_KEY_PATH}")"
+	ssh-keygen -t ed25519 -f "${SSH_KEY_PATH}" -N "" -q
+	cp "${VSOCK_TEST}" "${TEST_HOME}"/vsock_test
+}
+
 create_pidfile() {
 	local pidfile
 
@@ -470,11 +484,14 @@ vm_start() {
 		--run \
 		${kernel_opt} \
 		${verbose_opt} \
+		--rwdir=/root="${TEST_HOME}" \
+		--force-9p \
+		--cwd /root \
 		--qemu-opts="${qemu_opts}" \
 		--qemu="${qemu}" \
 		--user root \
 		--append "${KERNEL_CMDLINE}" \
-		--rw  &> ${logfile} &
+		&> ${logfile} &
 
 	timeout "${WAIT_QEMU}" \
 		bash -c 'while [[ ! -s '"${pidfile}"' ]]; do sleep 1; done; exit 0'
@@ -604,7 +621,7 @@ vm_vsock_test() {
 	# log output and use pipefail to respect vsock_test errors
 	set -o pipefail
 	if [[ "${host}" != server ]]; then
-		vm_ssh "${ns}" -- "${VSOCK_TEST}" \
+		vm_ssh "${ns}" -- ./vsock_test \
 			--mode=client \
 			--control-host="${host}" \
 			--peer-cid="${cid}" \
@@ -612,7 +629,7 @@ vm_vsock_test() {
 			2>&1 | log_guest
 		rc=$?
 	else
-		vm_ssh "${ns}" -- "${VSOCK_TEST}" \
+		vm_ssh "${ns}" -- ./vsock_test \
 			--mode=server \
 			--peer-cid="${cid}" \
 			--control-port="${port}" \
@@ -1551,6 +1568,7 @@ check_deps
 check_vng
 check_socat
 handle_build
+setup_home
 
 echo "1..${#ARGS[@]}"