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Message-ID: <CACGkMEsd75VYCeSSQo_H6+0reNxQsAMSamNr-_k3ndJ-ToJHHQ@mail.gmail.com>
Date:   Tue, 6 Dec 2022 14:42:14 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Heng Qi <hengqi@...ux.alibaba.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        "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>
Subject: Re: [RFC PATCH 9/9] virtio_net: support multi-buffer xdp

On Tue, Nov 22, 2022 at 3:44 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
>
> Driver can pass the skb to stack by build_skb_from_xdp_buff().
>
> Driver forwards multi-buffer packets using the send queue
> when XDP_TX and XDP_REDIRECT, and clears the reference of multi
> pages when XDP_DROP.
>
> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>  drivers/net/virtio_net.c | 65 ++++++----------------------------------
>  1 file changed, 9 insertions(+), 56 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 431f2126a2b5..bbd5cd9bfd47 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1065,7 +1065,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>         struct bpf_prog *xdp_prog;
>         unsigned int truesize = mergeable_ctx_to_truesize(ctx);
>         unsigned int headroom = mergeable_ctx_to_headroom(ctx);
> -       unsigned int metasize = 0;
>         unsigned int frame_sz;
>         int err;
>
> @@ -1137,63 +1136,22 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>
>                 switch (act) {
>                 case XDP_PASS:
> -                       metasize = xdp.data - xdp.data_meta;
> -
> -                       /* recalculate offset to account for any header
> -                        * adjustments and minus the metasize to copy the
> -                        * metadata in page_to_skb(). Note other cases do not
> -                        * build an skb and avoid using offset
> -                        */
> -                       offset = xdp.data - page_address(xdp_page) -
> -                                vi->hdr_len - metasize;
> -
> -                       /* recalculate len if xdp.data, xdp.data_end or
> -                        * xdp.data_meta were adjusted
> -                        */
> -                       len = xdp.data_end - xdp.data + vi->hdr_len + metasize;
> -
> -                       /* recalculate headroom if xdp.data or xdp_data_meta
> -                        * were adjusted, note that offset should always point
> -                        * to the start of the reserved bytes for virtio_net
> -                        * header which are followed by xdp.data, that means
> -                        * that offset is equal to the headroom (when buf is
> -                        * starting at the beginning of the page, otherwise
> -                        * there is a base offset inside the page) but it's used
> -                        * with a different starting point (buf start) than
> -                        * xdp.data (buf start + vnet hdr size). If xdp.data or
> -                        * data_meta were adjusted by the xdp prog then the
> -                        * headroom size has changed and so has the offset, we
> -                        * can use data_hard_start, which points at buf start +
> -                        * vnet hdr size, to calculate the new headroom and use
> -                        * it later to compute buf start in page_to_skb()
> -                        */
> -                       headroom = xdp.data - xdp.data_hard_start - metasize;
> -
> -                       /* We can only create skb based on xdp_page. */
> -                       if (unlikely(xdp_page != page)) {
> -                               rcu_read_unlock();
> -                               put_page(page);
> -                               head_skb = page_to_skb(vi, rq, xdp_page, offset,
> -                                                      len, PAGE_SIZE);
> -                               return head_skb;
> -                       }
> -                       break;
> +                       head_skb = build_skb_from_xdp_buff(dev, vi, &xdp, xdp_frags_truesz);
> +                       rcu_read_unlock();
> +                       return head_skb;
>                 case XDP_TX:
>                         stats->xdp_tx++;
>                         xdpf = xdp_convert_buff_to_frame(&xdp);
>                         if (unlikely(!xdpf)) {
> -                               if (unlikely(xdp_page != page))
> -                                       put_page(xdp_page);
> -                               goto err_xdp;
> +                               pr_debug("%s: convert buff to frame failed for xdp\n", dev->name);

netdev_dbg()?

Thanks

> +                               goto err_xdp_frags;
>                         }
>                         err = virtnet_xdp_xmit(dev, 1, &xdpf, 0);
>                         if (unlikely(!err)) {
>                                 xdp_return_frame_rx_napi(xdpf);
>                         } else if (unlikely(err < 0)) {
>                                 trace_xdp_exception(vi->dev, xdp_prog, act);
> -                               if (unlikely(xdp_page != page))
> -                                       put_page(xdp_page);
> -                               goto err_xdp;
> +                               goto err_xdp_frags;
>                         }
>                         *xdp_xmit |= VIRTIO_XDP_TX;
>                         if (unlikely(xdp_page != page))
> @@ -1203,11 +1161,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>                 case XDP_REDIRECT:
>                         stats->xdp_redirects++;
>                         err = xdp_do_redirect(dev, &xdp, xdp_prog);
> -                       if (err) {
> -                               if (unlikely(xdp_page != page))
> -                                       put_page(xdp_page);
> -                               goto err_xdp;
> -                       }
> +                       if (err)
> +                               goto err_xdp_frags;
>                         *xdp_xmit |= VIRTIO_XDP_REDIR;
>                         if (unlikely(xdp_page != page))
>                                 put_page(page);
> @@ -1220,9 +1175,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>                         trace_xdp_exception(vi->dev, xdp_prog, act);
>                         fallthrough;
>                 case XDP_DROP:
> -                       if (unlikely(xdp_page != page))
> -                               __free_pages(xdp_page, 0);
> -                       goto err_xdp;
> +                       goto err_xdp_frags;
>                 }
>  err_xdp_frags:
>                 shinfo = xdp_get_shared_info_from_buff(&xdp);
> --
> 2.19.1.6.gb485710b
>

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