Subject: Re: [PATCH net-next v2 17/21] virtio_net: xsk: rx: skip dma unmap when rq is bind with AF_XDP

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 9 Nov 2023 07:00:51 -0500

On Thu, Nov 09, 2023 at 07:10:02PM +0800, Xuan Zhuo wrote:
> On Thu, 9 Nov 2023 03:15:03 -0500, "Michael S. Tsirkin" <[email-masked]> wrote:
> > On Tue, Nov 07, 2023 at 11:12:23AM +0800, Xuan Zhuo wrote:
> > > When rq is bound with AF_XDP, the buffer dma is managed
> > > by the AF_XDP APIs. So the buffer got from the virtio core should
> > > skip the dma unmap operation.
> > >
> > > Signed-off-by: Xuan Zhuo <[email-masked]>
> >
> >
> > I don't get it - is this like a bugfix?
> 
> I want focus on this. So let it as an independent commit.
> 
> > And why do we need our own flag and checks?
> > Doesn't virtio core DTRT?
> 
> 
> struct vring_virtqueue {
> 	[....]
> 
> 	/* Do DMA mapping by driver */
> 	bool premapped;
> 
> We can not.
> 
> So I add own flag.
> 
> Thanks.

Still don't get it. Why not check the premapped flag?

> 
> >
> > > ---
> > >  drivers/net/virtio/main.c       | 8 +++++---
> > >  drivers/net/virtio/virtio_net.h | 3 +++
> > >  drivers/net/virtio/xsk.c        | 1 +
> > >  3 files changed, 9 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/net/virtio/main.c b/drivers/net/virtio/main.c
> > > index 15943a22e17d..a318b2533b94 100644
> > > --- a/drivers/net/virtio/main.c
> > > +++ b/drivers/net/virtio/main.c
> > > @@ -430,7 +430,7 @@ static void *virtnet_rq_get_buf(struct virtnet_rq *rq, u32 *len, void **ctx)
> > >  	void *buf;
> > >
> > >  	buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
> > > -	if (buf && rq->do_dma)
> > > +	if (buf && rq->do_dma_unmap)
> > >  		virtnet_rq_unmap(rq, buf, *len);
> > >
> > >  	return buf;
> > > @@ -561,8 +561,10 @@ static void virtnet_set_premapped(struct virtnet_info *vi)
> > >
> > >  		/* disable for big mode */
> > >  		if (vi->mergeable_rx_bufs || !vi->big_packets) {
> > > -			if (!virtqueue_set_dma_premapped(vi->rq[i].vq))
> > > +			if (!virtqueue_set_dma_premapped(vi->rq[i].vq)) {
> > >  				vi->rq[i].do_dma = true;
> > > +				vi->rq[i].do_dma_unmap = true;
> > > +			}
> > >  		}
> > >  	}
> > >  }
> > > @@ -3944,7 +3946,7 @@ void virtnet_rq_free_unused_buf(struct virtqueue *vq, void *buf)
> > >
> > >  	rq = &vi->rq[i];
> > >
> > > -	if (rq->do_dma)
> > > +	if (rq->do_dma_unmap)
> > >  		virtnet_rq_unmap(rq, buf, 0);
> > >
> > >  	virtnet_rq_free_buf(vi, rq, buf);
> > > diff --git a/drivers/net/virtio/virtio_net.h b/drivers/net/virtio/virtio_net.h
> > > index 1242785e311e..2005d0cd22e2 100644
> > > --- a/drivers/net/virtio/virtio_net.h
> > > +++ b/drivers/net/virtio/virtio_net.h
> > > @@ -135,6 +135,9 @@ struct virtnet_rq {
> > >  	/* Do dma by self */
> > >  	bool do_dma;
> > >
> > > +	/* Do dma unmap after getting buf from virtio core. */
> > > +	bool do_dma_unmap;
> > > +
> > >  	struct {
> > >  		struct xsk_buff_pool *pool;
> > >
> > > diff --git a/drivers/net/virtio/xsk.c b/drivers/net/virtio/xsk.c
> > > index e737c3353212..b09c473c29fb 100644
> > > --- a/drivers/net/virtio/xsk.c
> > > +++ b/drivers/net/virtio/xsk.c
> > > @@ -210,6 +210,7 @@ static int virtnet_rq_bind_xsk_pool(struct virtnet_info *vi, struct virtnet_rq *
> > >  		xdp_rxq_info_unreg(&rq->xsk.xdp_rxq);
> > >
> > >  	rq->xsk.pool = pool;
> > > +	rq->do_dma_unmap = !pool;
> > >
> > >  	virtnet_rx_resume(vi, rq);
> > >
> > > --
> > > 2.32.0.3.g01195cf9f
> >
> >