[RFC PATCH] tests/qtest/migration: Add cpu hotplug test

[Fabiano Rosas]

Bug #2594 is about a failure during migration after a cpu hotplug. Add
a test that covers that scenario. Start the source with -smp 2 and
destination with -smp 3, plug one extra cpu to match and migrate.

The issue seems to be a mismatch in the number of virtqueues between
the source and destination due to the hotplug not changing the
num_queues:

  get_pci_config_device: Bad config data: i=0x9a read: 4 device: 5
  cmask: ff wmask: 0 w1cmask:0

Usage:
$ QTEST_QEMU_IMG=./qemu-img QTEST_QEMU_BINARY=./qemu-system-x86_64 \
  ./tests/qtest/migration-test -p /x86_64/migration/hotplug/cpu

References: https://gitlab.com/qemu-project/qemu/-/issues/2594
References: https://issues.redhat.com/browse/RHEL-68302
Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
As you can see there's no fix attached to this. I haven't reached that
part yet, suggestions welcome =). Posting the test case if anyone
wants to play with this.

(if someone at RH is already working on this, that's fine. I'm just
trying to get some upstream bugs to move)
---
 tests/qtest/migration/misc-tests.c | 76 ++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/tests/qtest/migration/misc-tests.c 
b/tests/qtest/migration/misc-tests.c
index 6173430748..bde567b124 100644
--- a/tests/qtest/migration/misc-tests.c
+++ b/tests/qtest/migration/misc-tests.c
@@ -251,6 +251,79 @@ static void test_validate_uri_channels_none_set(void)
     do_test_validate_uri_channel(&args);
 }
 
+static void test_cpu_hotplug_virtqueues(void)
+{
+    MigrateStart args = {
+        .hide_stderr = false,
+    };
+    QTestState *from, *to;
+    g_autofree char *device_virtio_scsi = NULL;
+    g_autofree char *device_virtio_blk = NULL;
+    g_autofree char *filename_scsi = g_strdup_printf("%s/qtest_disk0.qcow2", 
tmpfs);
+    g_autofree char *filename_blk = g_strdup_printf("%s/qtest_disk1.qcow2", 
tmpfs);
+
+    /*
+     * Matching the queues between src/dst allows the test to pass.
+     * Defaults are:
+     *   virtio-scsi-pci:   #vcpus + 2 queues that are always present.
+     *   virtio-blk-pci:    same number of queues as vcpus.
+     * See virtio_pci_optimal_num_queues() for the exact computation.
+     */
+    bool match_queues = false;
+    const char *qs_scsi = "num_queues=5";
+    const char *qs_blk = "num-queues=3"; /* _ vs. - is not a mistake */
+
+    g_assert(mkimg(filename_scsi, "qcow2", 1));
+    g_assert(mkimg(filename_blk, "qcow2", 1));
+
+    device_virtio_scsi = g_strdup_printf(
+        "-drive id=drive0,if=none,format=qcow2,file=%s "
+        "-device virtio-scsi-pci,id=scsi0,%s "
+        "-device scsi-hd,drive=drive0,bus=scsi0.0 ",
+        filename_scsi, match_queues ? qs_scsi : "");
+
+    device_virtio_blk = g_strdup_printf(
+        "-drive id=drive1,if=none,format=qcow2,file=%s "
+        "-device virtio-blk-pci,drive=drive1,id=blk0,%s ",
+        filename_blk, match_queues ? qs_blk : "");
+
+    /* The missing cpu will be hotplugged before migration */
+    args.opts_source = g_strconcat("-smp 2,threads=1,sockets=1,maxcpus=4 ",
+                                   device_virtio_scsi,
+                                   device_virtio_blk, NULL);
+
+    args.opts_target = g_strconcat("-smp 3,threads=1,sockets=1,maxcpus=4 ",
+                                   device_virtio_scsi,
+                                   device_virtio_blk, NULL);
+
+    if (migrate_start(&from, &to, "defer", &args)) {
+        return;
+    }
+
+    g_free((char *)args.opts_source);
+    g_free((char *)args.opts_target);
+
+
+    migrate_ensure_converge(from);
+    wait_for_serial("src_serial");
+
+    qtest_qmp_assert_success(from, "{ 'execute': 'device_add',"
+                             "  'arguments': { "
+                             "    'node-id': 0, 'socket-id': 0,"
+                             "    'core-id': 2, 'thread-id': 0,"
+                             "    'id': {},"
+                             "    'driver': 'qemu64-x86_64-cpu' } }");
+
+    migrate_incoming_qmp(to, "tcp:127.0.0.1:0", "{}");
+
+    migrate_qmp(from, to, NULL, NULL, "{}");
+    wait_for_migration_complete(from);
+
+    migrate_end(from, to, true);
+    unlink(filename_scsi);
+    unlink(filename_blk);
+}
+
 void migration_test_add_misc(MigrationTestEnv *env)
 {
     tmpfs = env->tmpfs;
@@ -279,4 +352,7 @@ void migration_test_add_misc(MigrationTestEnv *env)
                        test_validate_uri_channels_both_set);
     migration_test_add("/migration/validate_uri/channels/none_set",
                        test_validate_uri_channels_none_set);
+
+    migration_test_add("/migration/hotplug/cpu/virtqueues",
+                       test_cpu_hotplug_virtqueues);
 }
-- 
2.35.3