Quoting Paolo Bonzini (2017-02-28 07:21:32)
> Commit ad07cd6 ("virtio-scsi: always use dataplane path if ioeventfd is
> active", 2016-10-30) and 9ffe337 ("virtio-blk: always use dataplane
> path if ioeventfd is active", 2016-10-30) broke the virtio 1.0
> indirect access registers.
>
> The indirect access registers bypass the ioeventfd, so that virtio-blk
> and virtio-scsi now repeatedly try to initialize dataplane instead of
> triggering the guest->host EventNotifier. Detect the situation by
> checking vq->handle_aio_output; if it is not NULL, trigger the
> EventNotifier, which is how the device expects to get notifications
> and in fact the only thread-safe manner to deliver them.
>
> Fixes: ad07cd6
> Fixes: 9ffe337
> Cc: qemu-sta...@nongnu.org
> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
Ping for 2.9 / 2.8.1
> ---
> hw/virtio/virtio.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 23483c7..1206f6c 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -1458,7 +1458,18 @@ static void virtio_queue_notify_vq(VirtQueue *vq)
>
> void virtio_queue_notify(VirtIODevice *vdev, int n)
> {
> - virtio_queue_notify_vq(&vdev->vq[n]);
> + VirtQueue *vq = &vdev->vq[n];
> +
> + if (unlikely(!vq->vring.desc || vdev->broken)) {
> + return;
> + }
> +
> + trace_virtio_queue_notify(vdev, vq - vdev->vq, vq);
> + if (vq->handle_aio_output) {
> + event_notifier_set(&vq->host_notifier);
> + } else if (vq->handle_output) {
> + vq->handle_output(vdev, vq);
> + }
> }
>
> uint16_t virtio_queue_vector(VirtIODevice *vdev, int n)
> --
> 2.9.3
>
>
