Re: [Qemu-devel] [PATCH 3/3] virtio: set ISR on dataplane notifications

[Paolo Bonzini]

> > +void virtio_notify_irqfd(VirtIODevice *vdev, VirtQueue *vq)
> > +{
> > +    if (!virtio_should_notify(vdev, vq)) {
> > +        return;
> > +    }
> > +
> > +    trace_virtio_notify_irqfd(vdev, vq);
> > +    virtio_set_isr(vq->vdev, 0x1);
> 
> So here, I think we need a comment with parts of
> the commit log.
> 
> /*
>  * virtio spec 1.0 says ISR bit 0 should be ignored with MSI, but
>  * windows drivers included in virtio-win 1.8.0 (circa 2015)
>  * for Windows 8.1 only are incorrectly polling this bit during shutdown
         ^^^^^^^^^^^^^^^^

Not sure it's only for Windows 8.1, in fact probably not.
Looks good if you replace this line with

"are incorrectly polling this bit during crashdump or hibernation"

Paolo

>  * in MSI mode, causing a hang if this bit is never updated.
>  * Next driver release from 2016 fixed this problem, so working around it
>  * is not a must, but it's easy to do so let's do it here.
>  *
>  * Note: it's safe to update ISR from any thread as it was switched
>  * to an atomic operation.
>  */


> 
> 
> 
> > +    event_notifier_set(&vq->guest_notifier);
> > +}
> > +
> >  void virtio_notify(VirtIODevice *vdev, VirtQueue *vq)
> >  {
> >      if (!virtio_should_notify(vdev, vq)) {
> > @@ -1990,7 +1994,7 @@ static void
> > virtio_queue_guest_notifier_read(EventNotifier *n)
> >  {
> >      VirtQueue *vq = container_of(n, VirtQueue, guest_notifier);
> >      if (event_notifier_test_and_clear(n)) {
> > -        virtio_irq(vq);
> > +        virtio_notify_vector(vq->vdev, vq->vector);
> >      }
> >  }
> >  
> > diff --git a/include/hw/virtio/virtio-scsi.h
> > b/include/hw/virtio/virtio-scsi.h
> > index 9fbc7d7..7375196 100644
> > --- a/include/hw/virtio/virtio-scsi.h
> > +++ b/include/hw/virtio/virtio-scsi.h
> > @@ -137,6 +137,5 @@ void virtio_scsi_push_event(VirtIOSCSI *s, SCSIDevice
> > *dev,
> >  void virtio_scsi_dataplane_setup(VirtIOSCSI *s, Error **errp);
> >  int virtio_scsi_dataplane_start(VirtIODevice *s);
> >  void virtio_scsi_dataplane_stop(VirtIODevice *s);
> > -void virtio_scsi_dataplane_notify(VirtIODevice *vdev, VirtIOSCSIReq *req);
> >  
> >  #endif /* QEMU_VIRTIO_SCSI_H */
> > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> > index 835b085..ab0e030 100644
> > --- a/include/hw/virtio/virtio.h
> > +++ b/include/hw/virtio/virtio.h
> > @@ -181,6 +181,7 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned
> > int *in_bytes,
> >                                 unsigned max_in_bytes, unsigned
> >                                 max_out_bytes);
> >  
> >  bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq);
> > +void virtio_notify_irqfd(VirtIODevice *vdev, VirtQueue *vq);
> >  void virtio_notify(VirtIODevice *vdev, VirtQueue *vq);
> >  
> >  void virtio_save(VirtIODevice *vdev, QEMUFile *f);
> > @@ -280,7 +281,6 @@ void virtio_queue_host_notifier_read(EventNotifier *n);
> >  void virtio_queue_aio_set_host_notifier_handler(VirtQueue *vq, AioContext
> >  *ctx,
> >                                                  void (*fn)(VirtIODevice *,
> >                                                             VirtQueue *));
> > -void virtio_irq(VirtQueue *vq);
> >  VirtQueue *virtio_vector_first_queue(VirtIODevice *vdev, uint16_t vector);
> >  VirtQueue *virtio_vector_next_queue(VirtQueue *vq);
> >  
> > --
> > 2.9.3
>