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

From: Jason Wang <jasowang@redhat.com>
To: "Eugenio Pérez" <eperezma@redhat.com>, qemu-devel@nongnu.org
Cc: Parav Pandit <parav@mellanox.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Markus Armbruster <armbru@redhat.com>,
	virtualization@lists.linux-foundation.org,
	Harpreet Singh Anand <hanand@xilinx.com>,
	Xiao W Wang <xiao.w.wang@intel.com>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Eli Cohen <eli@mellanox.com>, Eric Blake <eblake@redhat.com>,
	Michael Lilja <ml@napatech.com>
Subject: Re: [RFC PATCH v4 16/20] vhost: Check for device VRING_USED_F_NO_NOTIFY at shadow virtqueue kick
Date: Wed, 13 Oct 2021 12:35:29 +0800	[thread overview]
Message-ID: <f77b8efb-9d6b-5f35-2285-72f2dc59c26a@redhat.com> (raw)
In-Reply-To: <20211001070603.307037-17-eperezma@redhat.com>

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);

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