Re: [PATCH] virtio: reset device on bad guest index in virtio_load()

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Nov 20, 2020 at 06:51:07PM +0000, John Levon wrote:
> 
> If we find a queue with an inconsistent guest index value, explicitly mark the
> device as needing a reset - and broken - via virtio_error().
> 
> There's at least one driver implementation - the virtio-win NetKVM driver - that
> is able to handle a VIRTIO_CONFIG_S_NEEDS_RESET notification and successfully
> restore the device to a working state. Other implementations do not correctly
> handle this, but as the VQ is not in a functional state anyway, this is still
> worth doing.
> 
> Signed-off-by: John Levon <john.levon@nutanix.com>

I tagged this for after the release. pls ping me after the release
to help make sure it does not get lost.

> ---
>  hw/virtio/virtio.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index ceb58fda6c..eff35fab7c 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -3161,12 +3161,15 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id)
>              nheads = vring_avail_idx(&vdev->vq[i]) - vdev->vq[i].last_avail_idx;
>              /* Check it isn't doing strange things with descriptor numbers. */
>              if (nheads > vdev->vq[i].vring.num) {
> -                qemu_log_mask(LOG_GUEST_ERROR,
> -                              "VQ %d size 0x%x Guest index 0x%x "
> -                              "inconsistent with Host index 0x%x: delta 0x%x",
> -                              i, vdev->vq[i].vring.num,
> -                              vring_avail_idx(&vdev->vq[i]),
> -                              vdev->vq[i].last_avail_idx, nheads);
> +                virtio_error(vdev, "VQ %d size 0x%x Guest index 0x%x "
> +                             "inconsistent with Host index 0x%x: delta 0x%x",
> +                             i, vdev->vq[i].vring.num,
> +                             vring_avail_idx(&vdev->vq[i]),
> +                             vdev->vq[i].last_avail_idx, nheads);
> +                vdev->vq[i].used_idx = 0;
> +                vdev->vq[i].shadow_avail_idx = 0;
> +                vdev->vq[i].inuse = 0;
> +                continue;
>              }
>              vdev->vq[i].used_idx = vring_used_idx(&vdev->vq[i]);
>              vdev->vq[i].shadow_avail_idx = vring_avail_idx(&vdev->vq[i]);
> -- 
> 2.22.3
>