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Date: Fri, 13 Jan 2023 10:58:47 +0800
From: Jason Wang <jasowang@...hat.com>
To: Heng Qi <hengqi@...ux.alibaba.com>, netdev@...r.kernel.org,
bpf@...r.kernel.org
Cc: "Michael S . Tsirkin" <mst@...hat.com>,
Paolo Abeni <pabeni@...hat.com>,
Jakub Kicinski <kuba@...nel.org>,
John Fastabend <john.fastabend@...il.com>,
"David S . Miller" <davem@...emloft.net>,
Daniel Borkmann <daniel@...earbox.net>,
Alexei Starovoitov <ast@...nel.org>,
Eric Dumazet <edumazet@...gle.com>,
Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH v3 4/9] virtio-net: build xdp_buff with multi buffers
在 2023/1/3 14:40, Heng Qi 写道:
> Support xdp for multi buffer packets in mergeable mode.
>
> Putting the first buffer as the linear part for xdp_buff,
> and the rest of the buffers as non-linear fragments to struct
> skb_shared_info in the tailroom belonging to xdp_buff.
>
> Let 'truesize' return to its literal meaning, that is, when
> xdp is set, it includes the length of headroom and tailroom.
>
> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Acked-by: Jason Wang <jasowang@...hat.com>
Thanks
> ---
> drivers/net/virtio_net.c | 108 ++++++++++++++++++++++++++++++++++++---
> 1 file changed, 100 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 6fc5302ca5ff..699e376b8f8b 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -931,6 +931,91 @@ static struct sk_buff *receive_big(struct net_device *dev,
> return NULL;
> }
>
> +/* TODO: build xdp in big mode */
> +static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
> + struct virtnet_info *vi,
> + struct receive_queue *rq,
> + struct xdp_buff *xdp,
> + void *buf,
> + unsigned int len,
> + unsigned int frame_sz,
> + u16 *num_buf,
> + unsigned int *xdp_frags_truesize,
> + struct virtnet_rq_stats *stats)
> +{
> + struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
> + unsigned int headroom, tailroom, room;
> + unsigned int truesize, cur_frag_size;
> + struct skb_shared_info *shinfo;
> + unsigned int xdp_frags_truesz = 0;
> + struct page *page;
> + skb_frag_t *frag;
> + int offset;
> + void *ctx;
> +
> + xdp_init_buff(xdp, frame_sz, &rq->xdp_rxq);
> + xdp_prepare_buff(xdp, buf - VIRTIO_XDP_HEADROOM,
> + VIRTIO_XDP_HEADROOM + vi->hdr_len, len - vi->hdr_len, true);
> +
> + if (*num_buf > 1) {
> + /* If we want to build multi-buffer xdp, we need
> + * to specify that the flags of xdp_buff have the
> + * XDP_FLAGS_HAS_FRAG bit.
> + */
> + if (!xdp_buff_has_frags(xdp))
> + xdp_buff_set_frags_flag(xdp);
> +
> + shinfo = xdp_get_shared_info_from_buff(xdp);
> + shinfo->nr_frags = 0;
> + shinfo->xdp_frags_size = 0;
> + }
> +
> + if ((*num_buf - 1) > MAX_SKB_FRAGS)
> + return -EINVAL;
> +
> + while ((--*num_buf) >= 1) {
> + buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx);
> + if (unlikely(!buf)) {
> + pr_debug("%s: rx error: %d buffers out of %d missing\n",
> + dev->name, *num_buf,
> + virtio16_to_cpu(vi->vdev, hdr->num_buffers));
> + dev->stats.rx_length_errors++;
> + return -EINVAL;
> + }
> +
> + stats->bytes += len;
> + page = virt_to_head_page(buf);
> + offset = buf - page_address(page);
> +
> + truesize = mergeable_ctx_to_truesize(ctx);
> + headroom = mergeable_ctx_to_headroom(ctx);
> + tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
> + room = SKB_DATA_ALIGN(headroom + tailroom);
> +
> + cur_frag_size = truesize;
> + xdp_frags_truesz += cur_frag_size;
> + if (unlikely(len > truesize - room || cur_frag_size > PAGE_SIZE)) {
> + put_page(page);
> + pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
> + dev->name, len, (unsigned long)(truesize - room));
> + dev->stats.rx_length_errors++;
> + return -EINVAL;
> + }
> +
> + frag = &shinfo->frags[shinfo->nr_frags++];
> + __skb_frag_set_page(frag, page);
> + skb_frag_off_set(frag, offset);
> + skb_frag_size_set(frag, len);
> + if (page_is_pfmemalloc(page))
> + xdp_buff_set_frag_pfmemalloc(xdp);
> +
> + shinfo->xdp_frags_size += len;
> + }
> +
> + *xdp_frags_truesize = xdp_frags_truesz;
> + return 0;
> +}
> +
> static struct sk_buff *receive_mergeable(struct net_device *dev,
> struct virtnet_info *vi,
> struct receive_queue *rq,
> @@ -949,15 +1034,17 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> unsigned int truesize = mergeable_ctx_to_truesize(ctx);
> unsigned int headroom = mergeable_ctx_to_headroom(ctx);
> unsigned int metasize = 0;
> + unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
> + unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
> unsigned int frame_sz;
> int err;
>
> head_skb = NULL;
> stats->bytes += len - vi->hdr_len;
>
> - if (unlikely(len > truesize)) {
> + if (unlikely(len > truesize - room)) {
> pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
> - dev->name, len, (unsigned long)ctx);
> + dev->name, len, (unsigned long)(truesize - room));
> dev->stats.rx_length_errors++;
> goto err_skb;
> }
> @@ -983,10 +1070,12 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> if (unlikely(hdr->hdr.gso_type))
> goto err_xdp;
>
> - /* Buffers with headroom use PAGE_SIZE as alloc size,
> - * see add_recvbuf_mergeable() + get_mergeable_buf_len()
> + /* Now XDP core assumes frag size is PAGE_SIZE, but buffers
> + * with headroom may add hole in truesize, which
> + * make their length exceed PAGE_SIZE. So we disabled the
> + * hole mechanism for xdp. See add_recvbuf_mergeable().
> */
> - frame_sz = headroom ? PAGE_SIZE : truesize;
> + frame_sz = truesize;
>
> /* This happens when rx buffer size is underestimated
> * or headroom is not enough because of the buffer
> @@ -1139,9 +1228,12 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> page = virt_to_head_page(buf);
>
> truesize = mergeable_ctx_to_truesize(ctx);
> - if (unlikely(len > truesize)) {
> + headroom = mergeable_ctx_to_headroom(ctx);
> + tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
> + room = SKB_DATA_ALIGN(headroom + tailroom);
> + if (unlikely(len > truesize - room)) {
> pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
> - dev->name, len, (unsigned long)ctx);
> + dev->name, len, (unsigned long)(truesize - room));
> dev->stats.rx_length_errors++;
> goto err_skb;
> }
> @@ -1428,7 +1520,7 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> }
>
> sg_init_one(rq->sg, buf, len);
> - ctx = mergeable_len_to_ctx(len, headroom);
> + ctx = mergeable_len_to_ctx(len + room, headroom);
> err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
> if (err < 0)
> put_page(virt_to_head_page(buf));
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