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

[Eugenio Perez Martin]

On Wed, Oct 13, 2021 at 6:35 AM Jason Wang <jasowang@redhat.com> wrote:
>
>
> 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
>

Right, I will replace it, 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);
>