Re: [PATCH] virtio: support VIRTIO_F_ORDER_PLATFORM

[Tiwei Bie <tiwei.bie@intel.com>]

On Tue, Jan 22, 2019 at 11:04:29PM -0500, Michael S. Tsirkin wrote:
> On Wed, Jan 23, 2019 at 01:03:46AM +0800, Tiwei Bie wrote:
> > This patch introduces the support for VIRTIO_F_ORDER_PLATFORM.
> > When this feature is negotiated, driver will use the barriers
> > suitable for hardware devices.
> > 
> > Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
> 
> Could you pls add a bit more explanation in the commit log?
> E.g. which configurations are broken without this patch?
> How severe is the problem?

Sure. Will do that.

Thanks

> 
> I'm trying to decide whether this belongs in 5.0 or 5.1.
> 
> > ---
> >  drivers/virtio/virtio_ring.c       | 8 ++++++++
> >  include/uapi/linux/virtio_config.h | 6 ++++++
> >  2 files changed, 14 insertions(+)
> > 
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index cd7e755484e3..27d3f057493e 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -1609,6 +1609,9 @@ static struct virtqueue *vring_create_virtqueue_packed(
> >  		!context;
> >  	vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
> >  
> > +	if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
> > +		vq->weak_barriers = false;
> > +
> >  	vq->packed.ring_dma_addr = ring_dma_addr;
> >  	vq->packed.driver_event_dma_addr = driver_event_dma_addr;
> >  	vq->packed.device_event_dma_addr = device_event_dma_addr;
> > @@ -2079,6 +2082,9 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
> >  		!context;
> >  	vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
> >  
> > +	if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
> > +		vq->weak_barriers = false;
> > +
> >  	vq->split.queue_dma_addr = 0;
> >  	vq->split.queue_size_in_bytes = 0;
> >  
> > @@ -2213,6 +2219,8 @@ void vring_transport_features(struct virtio_device *vdev)
> >  			break;
> >  		case VIRTIO_F_RING_PACKED:
> >  			break;
> > +		case VIRTIO_F_ORDER_PLATFORM:
> > +			break;
> >  		default:
> >  			/* We don't understand this bit. */
> >  			__virtio_clear_bit(vdev, i);
> > diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h
> > index 1196e1c1d4f6..ff8e7dc9d4dd 100644
> > --- a/include/uapi/linux/virtio_config.h
> > +++ b/include/uapi/linux/virtio_config.h
> > @@ -78,6 +78,12 @@
> >  /* This feature indicates support for the packed virtqueue layout. */
> >  #define VIRTIO_F_RING_PACKED		34
> >  
> > +/*
> > + * This feature indicates that memory accesses by the driver and the
> > + * device are ordered in a way described by the platform.
> > + */
> > +#define VIRTIO_F_ORDER_PLATFORM		36
> > +
> >  /*
> >   * Does the device support Single Root I/O Virtualization?
> >   */
> > -- 
> > 2.17.1