test: Check all vCPUs are oneline

As seen in firecracker-microvm#4925, a bad CPU template made secondary CPUs not come up. To
catch similar bugs of CPU templates, check all the vCPUs are online from
guests' perspective.

Signed-off-by: Takahiro Itazuri <[email protected]>

Author: zulinx86

tests/framework/microvm.py

@@ -939,6 +939,7 @@ def make_snapshot(
             snapshot_type=snapshot_type,
             meta={
                 "kernel_file": str(self.kernel_file),
+                "vcpus_count": self.vcpus_count,
             },
         )
 

tests/integration_tests/functional/test_cpu_multiple.py

@@ -0,0 +1,22 @@
+# Copyright 2024 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+# SPDX-License-Identifier: Apache-2.0
+
+"""
+Test all vCPUs are configured correctly and work properly.
+
+This test suite aims to catch bugs of Firecracker's vCPU configuration and
+CPU templates especially under multi-vCPU setup, by checking that all vCPUs
+are operating identically, except for the expected differences.
+"""
+
+
+def test_all_vcpus_online(uvm_any):
+    """Check all vCPUs are online inside guest"""
+    vm = uvm_any
+    for idx in range(vm.vcpus_count):
+        assert (
+            vm.ssh.check_output(
+                f"cat /sys/devices/system/cpu/cpu{idx}/online"
+            ).stdout.strip()
+            == "1"
+        )