From: Bobby Eshleman <bobbyeshleman@meta.com>

Add tests to verify CID collision rules across different vsock namespace
modes.

1. Two VMs with the same CID cannot start in different global namespaces
   (ns_global_same_cid_fails)
2. Two VMs with the same CID can start in different local namespaces
   (ns_local_same_cid_ok)
3. VMs with the same CID can coexist when one is in a global namespace
   and another is in a local namespace (ns_global_local_same_cid_ok and
   ns_local_global_same_cid_ok)

The tests ns_global_local_same_cid_ok and ns_local_global_same_cid_ok
make sure that ordering does not matter.

The tests use a shared helper function namespaces_can_boot_same_cid()
that attempts to start two VMs with identical CIDs in the specified
namespaces and verifies whether VM initialization failed or succeeded.

Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
---
 tools/testing/selftests/vsock/vmtest.sh | 74 +++++++++++++++++++++++++++++++++
 1 file changed, 74 insertions(+)

diff --git a/tools/testing/selftests/vsock/vmtest.sh b/tools/testing/selftests/vsock/vmtest.sh
index b775fb0cd4ed..f2a99cde9fb4 100755
--- a/tools/testing/selftests/vsock/vmtest.sh
+++ b/tools/testing/selftests/vsock/vmtest.sh
@@ -44,6 +44,10 @@ readonly TEST_NAMES=(
 	vm_loopback
 	ns_host_vsock_ns_mode_ok
 	ns_host_vsock_ns_mode_write_once_ok
+	ns_global_same_cid_fails
+	ns_local_same_cid_ok
+	ns_global_local_same_cid_ok
+	ns_local_global_same_cid_ok
 )
 readonly TEST_DESCS=(
 	# vm_server_host_client
@@ -60,6 +64,18 @@ readonly TEST_DESCS=(
 
 	# ns_host_vsock_ns_mode_write_once_ok
 	"Check /proc/sys/net/vsock/ns_mode is write-once on the host."
+
+	# ns_global_same_cid_fails
+	"Check QEMU fails to start two VMs with same CID in two different global namespaces."
+
+	# ns_local_same_cid_ok
+	"Check QEMU successfully starts two VMs with same CID in two different local namespaces."
+
+	# ns_global_local_same_cid_ok
+	"Check QEMU successfully starts one VM in a global ns and then another VM in a local ns with the same CID."
+
+	# ns_local_global_same_cid_ok
+	"Check QEMU successfully starts one VM in a local ns and then another VM in a global ns with the same CID."
 )
 
 readonly USE_SHARED_VM=(vm_server_host_client vm_client_host_server vm_loopback)
@@ -548,6 +564,64 @@ test_ns_host_vsock_ns_mode_ok() {
 	return "${KSFT_PASS}"
 }
 
+namespaces_can_boot_same_cid() {
+	local ns0=$1
+	local ns1=$2
+	local pidfile1 pidfile2
+	local rc
+
+	pidfile1=$(mktemp $PIDFILE_TEMPLATE)
+	vm_start "${pidfile1}" "${ns0}"
+
+	pidfile2=$(mktemp $PIDFILE_TEMPLATE)
+	vm_start "${pidfile2}" "${ns1}"
+
+	rc=$?
+	terminate_pidfiles "${pidfile1}" "${pidfile2}"
+
+	return $rc
+}
+
+test_ns_global_same_cid_fails() {
+	init_namespaces
+
+	if namespaces_can_boot_same_cid "global0" "global1"; then
+		return "${KSFT_FAIL}"
+	fi
+
+	return "${KSFT_PASS}"
+}
+
+test_ns_local_global_same_cid_ok() {
+	init_namespaces
+
+	if namespaces_can_boot_same_cid "local0" "global0"; then
+		return "${KSFT_PASS}"
+	fi
+
+	return "${KSFT_FAIL}"
+}
+
+test_ns_global_local_same_cid_ok() {
+	init_namespaces
+
+	if namespaces_can_boot_same_cid "global0" "local0"; then
+		return "${KSFT_PASS}"
+	fi
+
+	return "${KSFT_FAIL}"
+}
+
+test_ns_local_same_cid_ok() {
+	init_namespaces
+
+	if namespaces_can_boot_same_cid "local0" "local0"; then
+		return "${KSFT_FAIL}"
+	fi
+
+	return "${KSFT_PASS}"
+}
+
 test_ns_host_vsock_ns_mode_write_once_ok() {
 	add_namespaces
 

-- 
2.47.3