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    SubjectRe: [PATCH bpf-next v5] virtio_net: add XDP meta data support
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    On 2020/2/20 下午4:55, Yuya Kusakabe wrote:
    > Implement support for transferring XDP meta data into skb for
    > virtio_net driver; before calling into the program, xdp.data_meta points
    > to xdp.data, where on program return with pass verdict, we call
    > into skb_metadata_set().
    >
    > Tested with the script at
    > https://github.com/higebu/virtio_net-xdp-metadata-test.
    >
    > Fixes: de8f3a83b0a0 ("bpf: add meta pointer for direct access")


    I'm not sure this is correct since virtio-net claims to not support
    metadata by calling xdp_set_data_meta_invalid()?


    > Signed-off-by: Yuya Kusakabe <yuya.kusakabe@gmail.com>
    > ---
    > v5:
    > - page_to_skb(): copy vnet header if hdr_valid without checking metasize.
    > - receive_small(): do not copy vnet header if xdp_prog is availavle.
    > - __virtnet_xdp_xmit_one(): remove the xdp_set_data_meta_invalid().
    > - improve comments.
    > v4:
    > - improve commit message
    > v3:
    > - fix preserve the vnet header in receive_small().
    > v2:
    > - keep copy untouched in page_to_skb().
    > - preserve the vnet header in receive_small().
    > - fix indentation.
    > ---
    > drivers/net/virtio_net.c | 54 ++++++++++++++++++++++++----------------
    > 1 file changed, 33 insertions(+), 21 deletions(-)
    >
    > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
    > index 2fe7a3188282..4ea0ae60c000 100644
    > --- a/drivers/net/virtio_net.c
    > +++ b/drivers/net/virtio_net.c
    > @@ -371,7 +371,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
    > struct receive_queue *rq,
    > struct page *page, unsigned int offset,
    > unsigned int len, unsigned int truesize,
    > - bool hdr_valid)
    > + bool hdr_valid, unsigned int metasize)
    > {
    > struct sk_buff *skb;
    > struct virtio_net_hdr_mrg_rxbuf *hdr;
    > @@ -393,6 +393,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
    > else
    > hdr_padded_len = sizeof(struct padded_vnet_hdr);
    >
    > + /* hdr_valid means no XDP, so we can copy the vnet header */
    > if (hdr_valid)
    > memcpy(hdr, p, hdr_len);
    >
    > @@ -405,6 +406,11 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
    > copy = skb_tailroom(skb);
    > skb_put_data(skb, p, copy);
    >
    > + if (metasize) {
    > + __skb_pull(skb, metasize);
    > + skb_metadata_set(skb, metasize);
    > + }
    > +
    > len -= copy;
    > offset += copy;
    >
    > @@ -450,10 +456,6 @@ static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
    > struct virtio_net_hdr_mrg_rxbuf *hdr;
    > int err;
    >
    > - /* virtqueue want to use data area in-front of packet */
    > - if (unlikely(xdpf->metasize > 0))
    > - return -EOPNOTSUPP;
    > -
    > if (unlikely(xdpf->headroom < vi->hdr_len))
    > return -EOVERFLOW;
    >
    > @@ -644,6 +646,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
    > unsigned int delta = 0;
    > struct page *xdp_page;
    > int err;
    > + unsigned int metasize = 0;
    >
    > len -= vi->hdr_len;
    > stats->bytes += len;
    > @@ -683,8 +686,8 @@ static struct sk_buff *receive_small(struct net_device *dev,
    >
    > xdp.data_hard_start = buf + VIRTNET_RX_PAD + vi->hdr_len;
    > xdp.data = xdp.data_hard_start + xdp_headroom;
    > - xdp_set_data_meta_invalid(&xdp);
    > xdp.data_end = xdp.data + len;
    > + xdp.data_meta = xdp.data;
    > xdp.rxq = &rq->xdp_rxq;
    > orig_data = xdp.data;
    > act = bpf_prog_run_xdp(xdp_prog, &xdp);
    > @@ -695,6 +698,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
    > /* Recalculate length in case bpf program changed it */
    > delta = orig_data - xdp.data;
    > len = xdp.data_end - xdp.data;
    > + metasize = xdp.data - xdp.data_meta;
    > break;
    > case XDP_TX:
    > stats->xdp_tx++;
    > @@ -735,11 +739,14 @@ static struct sk_buff *receive_small(struct net_device *dev,
    > }
    > skb_reserve(skb, headroom - delta);
    > skb_put(skb, len);
    > - if (!delta) {
    > + if (!xdp_prog) {
    > buf += header_offset;
    > memcpy(skb_vnet_hdr(skb), buf, vi->hdr_len);
    > } /* keep zeroed vnet hdr since packet was changed by bpf */


    I prefer to make this an independent patch and cc stable.

    Other looks good.

    Thanks


    >
    > + if (metasize)
    > + skb_metadata_set(skb, metasize);
    > +
    > err:
    > return skb;
    >
    > @@ -760,8 +767,8 @@ static struct sk_buff *receive_big(struct net_device *dev,
    > struct virtnet_rq_stats *stats)
    > {
    > struct page *page = buf;
    > - struct sk_buff *skb = page_to_skb(vi, rq, page, 0, len,
    > - PAGE_SIZE, true);
    > + struct sk_buff *skb =
    > + page_to_skb(vi, rq, page, 0, len, PAGE_SIZE, true, 0);
    >
    > stats->bytes += len - vi->hdr_len;
    > if (unlikely(!skb))
    > @@ -793,6 +800,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
    > unsigned int truesize;
    > unsigned int headroom = mergeable_ctx_to_headroom(ctx);
    > int err;
    > + unsigned int metasize = 0;
    >
    > head_skb = NULL;
    > stats->bytes += len - vi->hdr_len;
    > @@ -839,8 +847,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
    > data = page_address(xdp_page) + offset;
    > xdp.data_hard_start = data - VIRTIO_XDP_HEADROOM + vi->hdr_len;
    > xdp.data = data + vi->hdr_len;
    > - xdp_set_data_meta_invalid(&xdp);
    > xdp.data_end = xdp.data + (len - vi->hdr_len);
    > + xdp.data_meta = xdp.data;
    > xdp.rxq = &rq->xdp_rxq;
    >
    > act = bpf_prog_run_xdp(xdp_prog, &xdp);
    > @@ -848,24 +856,27 @@ 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. Note other cases do not build an
    > - * skb and avoid using offset
    > + * 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;
    > + offset = xdp.data - page_address(xdp_page) -
    > + vi->hdr_len - metasize;
    >
    > - /* recalculate len if xdp.data or xdp.data_end were
    > - * adjusted
    > + /* recalculate len if xdp.data, xdp.data_end or
    > + * xdp.data_meta were adjusted
    > */
    > - len = xdp.data_end - xdp.data + vi->hdr_len;
    > + len = xdp.data_end - xdp.data + vi->hdr_len + 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, false);
    > + head_skb = page_to_skb(vi, rq, xdp_page, offset,
    > + len, PAGE_SIZE, false,
    > + metasize);
    > return head_skb;
    > }
    > break;
    > @@ -921,7 +932,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
    > goto err_skb;
    > }
    >
    > - head_skb = page_to_skb(vi, rq, page, offset, len, truesize, !xdp_prog);
    > + head_skb = page_to_skb(vi, rq, page, offset, len, truesize, !xdp_prog,
    > + metasize);
    > curr_skb = head_skb;
    >
    > if (unlikely(!curr_skb))

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