[Xen-changelog] [qemu-xen stable-4.10] vhost: restore avail index from vring used index on disconnection

[patchbot@xxxxxxx]

commit 0bc76c8d0899f1f3a2bc5092ae9de7a900213a3b
Author:     Maxime Coquelin <maxime.coquelin@xxxxxxxxxx>
AuthorDate: Thu Nov 16 19:48:35 2017 +0100
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Wed Dec 6 09:55:22 2017 -0600

    vhost: restore avail index from vring used index on disconnection
    
    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: 283e2c2adcb8 ("net: virtio-net discards TX data after link down")
    Cc: qemu-stable@xxxxxxxxxx
    Signed-off-by: Maxime Coquelin <maxime.coquelin@xxxxxxxxxx>
    Reviewed-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
    Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
    (cherry picked from commit 2ae39a113af311cb56a0c35b7f212dafcef15303)
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
 hw/virtio/vhost.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index b737ca9..76f6e1f 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1137,6 +1137,10 @@ 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);
     }
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#stable-4.10

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