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

From: Maciej Fijalkowski <[email-masked]>
Date: Mon, 13 Nov 2023 17:11:04 +0100

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 <[email-masked]>
> ---
>  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().

> +	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.

> +		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
> 
>