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vhost: restore avail index from vring used index on disconnection

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vhost_virtqueue_stop() gets avail index value from the backend,
except if the backend is not responding.

It happens when the backend crashes, and in this case, internal
state of the virtio queue is inconsistent, making packets
to corrupt the vring state.

With a Linux guest, it results in following error message on
backend reconnection:

[   22.444905] virtio_net virtio0: output.0:id 0 is not a head!
[   22.446746] net enp0s3: Unexpected TXQ (0) queue failure: -5
[   22.476360] net enp0s3: Unexpected TXQ (0) queue failure: -5

Fixes: 283e2c2adc ("net: virtio-net discards TX data after link down")
Cc: qemu-stable@nongnu.org
Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Maxime Coquelin 2017-11-16 19:48:35 +01:00 committed by Michael S. Tsirkin
parent 2d4ba6cc74
commit 2ae39a113a
1 changed files with 4 additions and 0 deletions
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4
hw/virtio/vhost.c
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@ -1138,6 +1138,10 @@ static void vhost_virtqueue_stop(struct vhost_dev *dev,
r = dev->vhost_ops->vhost_get_vring_base(dev, &state);
if (r < 0) {
VHOST_OPS_DEBUG("vhost VQ %d ring restore failed: %d", idx, r);
/* Connection to the backend is broken, so let's sync internal
* last avail idx to the device used idx.
*/
virtio_queue_restore_last_avail_idx(vdev, idx);
} else {
virtio_queue_set_last_avail_idx(vdev, idx, state.num);
}