Re: [PATCH net-next v2 18/21] virtio_net: xsk: rx: introduce receive_xsk() to recv xsk buffer

[Xuan Zhuo <xuanzhuo@linux.alibaba.com>]

On Mon, 13 Nov 2023 17:11:04 +0100, Maciej Fijalkowski <maciej.fijalkowski@intel.com> wrote:
> On Tue, Nov 07, 2023 at 11:12:24AM +0800, Xuan Zhuo wrote:
> > The virtnet_xdp_handler() is re-used. But
> >
> > 1. We need to copy data to create skb for XDP_PASS.
> > 2. We need to call xsk_buff_free() to release the buffer.
> > 3. The handle for xdp_buff is difference.
> >
> > If we pushed this logic into existing receive handle(merge and small),
> > we would have to maintain code scattered inside merge and small (and big).
> > So I think it is a good choice for us to put the xsk code into an
> > independent function.
> >
> > Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> > ---
> >  drivers/net/virtio/main.c       |  12 ++--
> >  drivers/net/virtio/virtio_net.h |   4 ++
> >  drivers/net/virtio/xsk.c        | 120 ++++++++++++++++++++++++++++++++
> >  drivers/net/virtio/xsk.h        |   4 ++
> >  4 files changed, 135 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/net/virtio/main.c b/drivers/net/virtio/main.c
> > index a318b2533b94..095f4acb0577 100644
> > --- a/drivers/net/virtio/main.c
> > +++ b/drivers/net/virtio/main.c
> > @@ -831,10 +831,10 @@ static void put_xdp_frags(struct xdp_buff *xdp)
> >  	}
> >  }
> >
> > -static int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
> > -			       struct net_device *dev,
> > -			       unsigned int *xdp_xmit,
> > -			       struct virtnet_rq_stats *stats)
> > +int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
> > +			struct net_device *dev,
> > +			unsigned int *xdp_xmit,
> > +			struct virtnet_rq_stats *stats)
> >  {
> >  	struct xdp_frame *xdpf;
> >  	int err;
> > @@ -1598,7 +1598,9 @@ static void receive_buf(struct virtnet_info *vi, struct virtnet_rq *rq,
> >  		return;
> >  	}
> >
> > -	if (vi->mergeable_rx_bufs)
> > +	if (rq->xsk.pool)
> > +		skb = virtnet_receive_xsk(dev, vi, rq, buf, len, xdp_xmit, stats);
> > +	else if (vi->mergeable_rx_bufs)
> >  		skb = receive_mergeable(dev, vi, rq, buf, ctx, len, xdp_xmit,
> >  					stats);
> >  	else if (vi->big_packets)
> > diff --git a/drivers/net/virtio/virtio_net.h b/drivers/net/virtio/virtio_net.h
> > index 2005d0cd22e2..f520fec06662 100644
> > --- a/drivers/net/virtio/virtio_net.h
> > +++ b/drivers/net/virtio/virtio_net.h
> > @@ -339,4 +339,8 @@ void virtnet_tx_pause(struct virtnet_info *vi, struct virtnet_sq *sq);
> >  void virtnet_tx_resume(struct virtnet_info *vi, struct virtnet_sq *sq);
> >  void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf);
> >  void virtnet_rq_free_unused_buf(struct virtqueue *vq, void *buf);
> > +int virtnet_xdp_handler(struct bpf_prog *xdp_prog, struct xdp_buff *xdp,
> > +			struct net_device *dev,
> > +			unsigned int *xdp_xmit,
> > +			struct virtnet_rq_stats *stats);
> >  #endif
> > diff --git a/drivers/net/virtio/xsk.c b/drivers/net/virtio/xsk.c
> > index b09c473c29fb..5c7eb19ab04b 100644
> > --- a/drivers/net/virtio/xsk.c
> > +++ b/drivers/net/virtio/xsk.c
> > @@ -14,6 +14,18 @@ static void sg_fill_dma(struct scatterlist *sg, dma_addr_t addr, u32 len)
> >  	sg->length = len;
> >  }
> >
> > +static unsigned int virtnet_receive_buf_num(struct virtnet_info *vi, char *buf)
> > +{
> > +	struct virtio_net_hdr_mrg_rxbuf *hdr;
> > +
> > +	if (vi->mergeable_rx_bufs) {
> > +		hdr = (struct virtio_net_hdr_mrg_rxbuf *)buf;
> > +		return virtio16_to_cpu(vi->vdev, hdr->num_buffers);
> > +	}
> > +
> > +	return 1;
> > +}
> > +
> >  static void virtnet_xsk_check_queue(struct virtnet_sq *sq)
> >  {
> >  	struct virtnet_info *vi = sq->vq->vdev->priv;
> > @@ -38,6 +50,114 @@ static void virtnet_xsk_check_queue(struct virtnet_sq *sq)
> >  		netif_stop_subqueue(dev, qnum);
> >  }
> >
> > +static void merge_drop_follow_xdp(struct net_device *dev,
> > +				  struct virtnet_rq *rq,
> > +				  u32 num_buf,
> > +				  struct virtnet_rq_stats *stats)
> > +{
> > +	struct xdp_buff *xdp;
> > +	u32 len;
> > +
> > +	while (num_buf-- > 1) {
> > +		xdp = virtqueue_get_buf(rq->vq, &len);
> > +		if (unlikely(!xdp)) {
> > +			pr_debug("%s: rx error: %d buffers missing\n",
> > +				 dev->name, num_buf);
> > +			dev->stats.rx_length_errors++;
> > +			break;
> > +		}
> > +		u64_stats_add(&stats->bytes, len);
> > +		xsk_buff_free(xdp);
> > +	}
> > +}
> > +
> > +static struct sk_buff *construct_skb(struct virtnet_rq *rq,
>
> could you name this to virtnet_construct_skb_zc
>
> > +				     struct xdp_buff *xdp)
> > +{
> > +	unsigned int metasize = xdp->data - xdp->data_meta;
> > +	struct sk_buff *skb;
> > +	unsigned int size;
> > +
> > +	size = xdp->data_end - xdp->data_hard_start;
> > +	skb = napi_alloc_skb(&rq->napi, size);
> > +	if (unlikely(!skb))
> > +		return NULL;
> > +
> > +	skb_reserve(skb, xdp->data_meta - xdp->data_hard_start);
> > +
> > +	size = xdp->data_end - xdp->data_meta;
> > +	memcpy(__skb_put(skb, size), xdp->data_meta, size);
> > +
> > +	if (metasize) {
> > +		__skb_pull(skb, metasize);
> > +		skb_metadata_set(skb, metasize);
> > +	}
> > +
> > +	return skb;
> > +}
> > +
> > +struct sk_buff *virtnet_receive_xsk(struct net_device *dev, struct virtnet_info *vi,
> > +				    struct virtnet_rq *rq, void *buf,
> > +				    unsigned int len, unsigned int *xdp_xmit,
> > +				    struct virtnet_rq_stats *stats)
> > +{
> > +	struct virtio_net_hdr_mrg_rxbuf *hdr;
> > +	struct sk_buff *skb = NULL;
> > +	u32 ret, headroom, num_buf;
> > +	struct bpf_prog *prog;
> > +	struct xdp_buff *xdp;
> > +
> > +	len -= vi->hdr_len;
> > +
> > +	xdp = (struct xdp_buff *)buf;
> > +
> > +	xsk_buff_set_size(xdp, len);
> > +
> > +	hdr = xdp->data - vi->hdr_len;
> > +
> > +	num_buf = virtnet_receive_buf_num(vi, (char *)hdr);
> > +	if (num_buf > 1)
> > +		goto drop;
> > +
> > +	headroom = xdp->data - xdp->data_hard_start;
> > +
> > +	xdp_prepare_buff(xdp, xdp->data_hard_start, headroom, len, true);
>
> Please don't.
>
> xsk_buff_pool has ::data_hard_start initialized and you already
> initialized ::data and ::data_end within xsk_buff_set_size().

Yes, you are right.


>
> > +	xsk_buff_dma_sync_for_cpu(xdp, rq->xsk.pool);
> > +
> > +	ret = XDP_PASS;
> > +	rcu_read_lock();
>
> We don't need RCU sections for running XDP progs anymore.
>
> > +	prog = rcu_dereference(rq->xdp_prog);
> > +	if (prog)
>
> Prog is always !NULL for ZC case. Just dereference it at the beginning of
> rx processing instead of doing it for each buf.


That is a problem of virtio-net. I notice that, I will post patch to fix
that.

Thanks.


>
> > +		ret = virtnet_xdp_handler(prog, xdp, dev, xdp_xmit, stats);
> > +	rcu_read_unlock();
> > +
> > +	switch (ret) {
> > +	case XDP_PASS:
> > +		skb = construct_skb(rq, xdp);
> > +		xsk_buff_free(xdp);
> > +		break;
> > +
> > +	case XDP_TX:
> > +	case XDP_REDIRECT:
> > +		goto consumed;
> > +
> > +	default:
> > +		goto drop;
> > +	}
> > +
> > +	return skb;
> > +
> > +drop:
> > +	u64_stats_inc(&stats->drops);
> > +
> > +	xsk_buff_free(xdp);
> > +
> > +	if (num_buf > 1)
> > +		merge_drop_follow_xdp(dev, rq, num_buf, stats);
> > +consumed:
> > +	return NULL;
> > +}
> > +
> >  int virtnet_add_recvbuf_xsk(struct virtnet_info *vi, struct virtnet_rq *rq,
> >  			    struct xsk_buff_pool *pool, gfp_t gfp)
> >  {
> > diff --git a/drivers/net/virtio/xsk.h b/drivers/net/virtio/xsk.h
> > index bef41a3f954e..dbd2839a5f61 100644
> > --- a/drivers/net/virtio/xsk.h
> > +++ b/drivers/net/virtio/xsk.h
> > @@ -25,4 +25,8 @@ bool virtnet_xsk_xmit(struct virtnet_sq *sq, struct xsk_buff_pool *pool,
> >  int virtnet_xsk_wakeup(struct net_device *dev, u32 qid, u32 flag);
> >  int virtnet_add_recvbuf_xsk(struct virtnet_info *vi, struct virtnet_rq *rq,
> >  			    struct xsk_buff_pool *pool, gfp_t gfp);
> > +struct sk_buff *virtnet_receive_xsk(struct net_device *dev, struct virtnet_info *vi,
> > +				    struct virtnet_rq *rq, void *buf,
> > +				    unsigned int len, unsigned int *xdp_xmit,
> > +				    struct virtnet_rq_stats *stats);
> >  #endif
> > --
> > 2.32.0.3.g01195cf9f
> >
> >