Re: [Qemu-devel] [PATCH] virtio: allow broken device to notify guest

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Wed, 26 Apr 2017 14:51:17 +0200
Greg Kurz <groug@kaod.org> wrote:

> According to section 2.1.2 of the virtio-1 specification:
> 
> "The device SHOULD set DEVICE_NEEDS_RESET when it enters an error state that
> a reset is needed. If DRIVER_OK is set, after it sets DEVICE_NEEDS_RESET,
> the device MUST send a device configuration change notification to the
> driver."
> 
> Commit "f5ed36635d8f virtio: stop virtqueue processing if device is broken"
> introduced a virtio_error() call that just does that:
> 
> - internally mark the device as broken
> - set the DEVICE_NEEDS_RESET bit in the status
> - send a configuration change notification
> 
> Unfortunately, virtio_notify_vector(), called by virtio_notify_config(),
> returns right away when the device is marked as broken and the notification
> isn't sent in this case.
> 
> The spec doesn't say whether a broken device can send notifications
> in other situations or not. But since the driver isn't supposed to do
> anything but to reset the device, it makes sense to keep the check in
> virtio_notify_config().
> 
> Marking the device as broken AFTER the configuration change notification was
> sent is enough to fix the issue.
> 
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
>  hw/virtio/virtio.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 03592c542a55..890b4d7eb751 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -2451,12 +2451,12 @@ void GCC_FMT_ATTR(2, 3) virtio_error(VirtIODevice *vdev, const char *fmt, ...)
>      error_vreport(fmt, ap);
>      va_end(ap);
> 
> -    vdev->broken = true;
> -
>      if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) {
>          virtio_set_status(vdev, vdev->status | VIRTIO_CONFIG_S_NEEDS_RESET);
>          virtio_notify_config(vdev);
>      }
> +
> +    vdev->broken = true;
>  }
> 
>  static void virtio_memory_listener_commit(MemoryListener *listener)
> 

Good catch.

Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>

Should this be cc:stable, as it's a spec violation?