test(snapshot): verify guest clock advances after cross-kernel restore

Sample guest time twice and assert it advanced by roughly the sleep
duration. Comparing guest time to host time doesn't work here: phase1
and restore run as separate pipeline steps with elapsed time between
them, and snapshot restore preserves the guest's KVM-clock from capture
time. Sampling twice still catches what we care about - the clock being
frozen, going backwards, or running at the wrong rate - which is how
KVM-clock regressions across host kernels manifest.

Signed-off-by: Jack Thomson <jackabt@amazon.com>

Author: JackThomson2

tests/integration_tests/functional/test_snapshot_restore_cross_kernel.py

@@ -5,6 +5,7 @@
 
 import json
 import logging
+import time
 from pathlib import Path
 
 import pytest
@@ -27,6 +28,20 @@
 pytestmark = pytest.mark.nonci
 
 
+def _check_guest_clock_advances(ssh_connection, sleep_sec=1, tolerance_sec=1):
+    # Can't compare guest time to host time here: phase1 and restore run as
+    # separate pipeline steps with elapsed time between them, and snapshot
+    # restore preserves the guest's KVM-clock from capture time. Instead,
+    # sample twice and verify the clock advanced by roughly sleep_sec.
+    _, first, _ = ssh_connection.check_output("date +%s")
+    time.sleep(sleep_sec)
+    _, second, _ = ssh_connection.check_output("date +%s")
+    elapsed = int(second.strip()) - int(first.strip())
+    assert (
+        abs(elapsed - sleep_sec) <= tolerance_sec
+    ), f"Guest clock advanced by {elapsed}s over {sleep_sec}s sleep"
+
+
 def _test_balloon(microvm):
     # Check memory usage.
     first_reading = get_stable_rss_mem(microvm)
@@ -129,4 +144,7 @@ def test_snap_restore_from_artifacts(
     logger.info("Testing entropy...")
     check_entropy(vm.ssh)
 
+    logger.info("Testing guest clock advances...")
+    _check_guest_clock_advances(vm.ssh)
+
     vm.kill()