virtio-net: Add queues for RSS during migration

virtio_net_pre_load_queues() inspects vdev->guest_features to tell if
VIRTIO_NET_F_RSS or VIRTIO_NET_F_MQ is enabled to infer the required
number of queues. This works for VIRTIO_NET_F_MQ but it doesn't for
VIRTIO_NET_F_RSS because only the lowest 32 bits of vdev->guest_features
is set at the point and VIRTIO_NET_F_RSS uses bit 60 while
VIRTIO_NET_F_MQ uses bit 22.

Instead of inferring the required number of queues from
vdev->guest_features, use the number loaded from the vm state. This
change also has a nice side effect to remove a duplicate peer queue
pair change by circumventing virtio_net_set_multiqueue().

Also update the comment in include/hw/virtio/virtio.h to prevent an
implementation of pre_load_queues() from refering to any fields being
loaded during migration by accident in the future.

Fixes: 8c49756825da ("virtio-net: Add only one queue pair when realizing")

Tested-by: Lei Yang <leiyang@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

1 files changed, 7 insertions, 7 deletions

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 82a285a31d..7e38b1ca97 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -3270,13 +3270,6 @@ virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id)
         config_len--;
     }
 
-    if (vdc->pre_load_queues) {
-        ret = vdc->pre_load_queues(vdev);
-        if (ret) {
-            return ret;
-        }
-    }
-
     num = qemu_get_be32(f);
 
     if (num > VIRTIO_QUEUE_MAX) {
@@ -3284,6 +3277,13 @@ virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id)
         return -1;
     }
 
+    if (vdc->pre_load_queues) {
+        ret = vdc->pre_load_queues(vdev, num);
+        if (ret) {
+            return ret;
+        }
+    }
+
     for (i = 0; i < num; i++) {
         vdev->vq[i].vring.num = qemu_get_be32(f);
         if (k->has_variable_vring_alignment) {