tests: Add integration test for nested virtualization

Since we run integration tests on Intel & AMD this should test the
behaviour of `--cpus nested={on|off}` correctly.

Signed-off-by: Rob Bradford <rbradford@meta.com>

cloud-hypervisor/tests/integration.rs

@@ -2616,6 +2616,51 @@ mod common_parallel {
         handle_child_output(r, &output);
     }
 
+    fn _test_nested_virtualization(nested: bool) {
+        let disk_config = UbuntuDiskConfig::new(JAMMY_IMAGE_NAME.to_string());
+        let guest = Guest::new(Box::new(disk_config)).with_nested(nested);
+        let mut child = GuestCommand::new(&guest)
+            .default_cpus()
+            .default_memory()
+            .args(["--kernel", direct_kernel_boot_path().to_str().unwrap()])
+            .args(["--cmdline", DIRECT_KERNEL_BOOT_CMDLINE])
+            .default_disks()
+            .default_net()
+            .capture_output()
+            .spawn()
+            .unwrap();
+
+        let r = std::panic::catch_unwind(|| {
+            guest.wait_vm_boot().unwrap();
+
+            let expected = if nested { "yes" } else { "no" };
+            assert_eq!(
+                guest
+                    .ssh_command("test -c /dev/kvm && echo yes || echo no")
+                    .unwrap()
+                    .trim(),
+                expected
+            );
+        });
+
+        kill_child(&mut child);
+        let output = child.wait_with_output().unwrap();
+
+        handle_child_output(r, &output);
+    }
+
+    #[test]
+    #[cfg(target_arch = "x86_64")]
+    fn test_nested_virtualization_on() {
+        _test_nested_virtualization(true);
+    }
+
+    #[test]
+    #[cfg(target_arch = "x86_64")]
+    fn test_nested_virtualization_off() {
+        _test_nested_virtualization(false);
+    }
+
     #[test]
     fn test_cpu_affinity() {
         let disk_config = UbuntuDiskConfig::new(JAMMY_IMAGE_NAME.to_string());