Re: [PATCH v2 9/9] virtio_net: support multi-buffer xdp

Jason Wang
2022-12-27T09:05:07Z

On Tue, Dec 20, 2022 at 10:15 PM Heng Qi <hengqi@linux.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@linux.alibaba.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>

Acked-by: Jason Wang <jasowang@redhat.com>

Thanks

> ---
> 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 398ffe2a5084..daa380b9d1cc 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1074,7 +1074,6 @@ 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;
>
> @@ -1165,63 +1164,22 @@ 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;
> + netdev_dbg(dev, "convert buff to frame failed for xdp\n");
> + 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))
> @@ -1231,11 +1189,8 @@ 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);
> @@ -1248,9 +1203,7 @@ 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
>