Subject: Re: [PATCH bpf-next v5] virtio_net: add XDP meta data support

From: "Michael S. Tsirkin" <[email-masked]>
Date: Fri, 21 Feb 2020 06:01:42 -0500

On Fri, Feb 21, 2020 at 05:36:08PM +0900, Yuya Kusakabe wrote:
> On 2/21/20 1:23 PM, Jason Wang wrote:
> > 
> > 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()?
> 
> virtio_net doesn't support by calling xdp_set_data_meta_invalid() for now.
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/drivers/net/virtio_net.c?id=e42da4c62abb547d9c9138e0e7fcd1f36057b5e8#n686
> https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/drivers/net/virtio_net.c?id=e42da4c62abb547d9c9138e0e7fcd1f36057b5e8#n842
> 
> And xdp_set_data_meta_invalid() are added by de8f3a83b0a0.
> 
> $ git blame ./drivers/net/virtio_net.c | grep xdp_set_data_meta_invalid
> de8f3a83b0a0f (Daniel Borkmann           2017-09-25 02:25:51 +0200  686)                xdp_set_data_meta_invalid(&xdp);
> de8f3a83b0a0f (Daniel Borkmann           2017-09-25 02:25:51 +0200  842)                xdp_set_data_meta_invalid(&xdp);
> 
> So I added `Fixes: de8f3a83b0a0 ("bpf: add meta pointer for direct access")` to the comment.

Fixes basically means "must be backported to any kernel that has
de8f3a83b0a0 in order to fix a bug". This looks more like
a feature than a bug though, so I'm not sure Fixes
is approproate. Correct me if I'm wrong.

> > 
> > 
> >> Signed-off-by: Yuya Kusakabe <[email-masked]>
> >> ---
> >> 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
> 
> I see. So I need to revert to delta from xdp_prog?
> 
> Thank you.
> 
> > 
> >>   +    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))
> >