Re: [RFC PATCH v4 16/20] vhost: Check for device VRING_USED_F_NO_NOTIFY at shadow virtqueue kick

[Jason Wang]

在 2021/10/1 下午3:05, Eugenio Pérez 写道:
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>   hw/virtio/vhost-shadow-virtqueue.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
> b/hw/virtio/vhost-shadow-virtqueue.c
> index df7e6fa3ec..775f8d36a0 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -173,6 +173,15 @@ static void vhost_svq_add(VhostShadowVirtqueue *svq, 
> VirtQueueElement *elem)
>       svq->ring_id_maps[qemu_head] = elem;
>   }
>   
> +static void vhost_svq_kick(VhostShadowVirtqueue *svq)
> +{
> +    /* Make sure we are reading updated device flag */


I guess this would be better:

        /* We need to expose available array entries before checking used
         * flags. */

(Borrowed from kernel codes).

Thanks


> +    smp_mb();
> +    if (!(svq->vring.used->flags & VRING_USED_F_NO_NOTIFY)) {
> +        event_notifier_set(&svq->kick_notifier);
> +    }
> +}
> +
>   /* Handle guest->device notifications */
>   static void vhost_handle_guest_kick(EventNotifier *n)
>   {
> @@ -197,7 +206,7 @@ static void vhost_handle_guest_kick(EventNotifier *n)
>               }
>   
>               vhost_svq_add(svq, elem);
> -            event_notifier_set(&svq->kick_notifier);
> +            vhost_svq_kick(svq);
>           }
>   
>           virtio_queue_set_notification(svq->vq, true);