On Fri, 26 Sep 2025 12:52:53 +0800, Jason Wang <[email protected]> wrote:
> On Thu, Sep 25, 2025 at 10:25 AM Xuan Zhuo <[email protected]> wrote:
> >
> > The commit be50da3e9d4a ("net: virtio_net: implement exact header length
> > guest feature") introduces support for the VIRTIO_NET_F_GUEST_HDRLEN
> > feature in virtio-net.
> >
> > This feature requires virtio-net to set hdr_len to the actual header
> > length of the packet when transmitting, the number of
> > bytes from the start of the packet to the beginning of the
> > transport-layer payload.
> >
> > However, in practice, hdr_len was being set using skb_headlen(skb),
> > which is clearly incorrect. This commit fixes that issue.
> >
> > Fixes: be50da3e9d4a ("net: virtio_net: implement exact header length guest
> > feature")
> > Signed-off-by: Xuan Zhuo <[email protected]>
> > ---
> > include/linux/virtio_net.h | 19 ++++++++++++-------
> > 1 file changed, 12 insertions(+), 7 deletions(-)
> >
> > diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
> > index 20e0584db1dd..4273420a9ff9 100644
> > --- a/include/linux/virtio_net.h
> > +++ b/include/linux/virtio_net.h
> > @@ -217,20 +217,25 @@ static inline int virtio_net_hdr_from_skb(const
> > struct sk_buff *skb,
> >
> > if (skb_is_gso(skb)) {
> > struct skb_shared_info *sinfo = skb_shinfo(skb);
> > + u16 hdr_len;
> >
> > - /* This is a hint as to how much should be linear. */
> > - hdr->hdr_len = __cpu_to_virtio16(little_endian,
> > - skb_headlen(skb));
> > + hdr_len = skb_transport_offset(skb);
> > hdr->gso_size = __cpu_to_virtio16(little_endian,
> > sinfo->gso_size);
> > - if (sinfo->gso_type & SKB_GSO_TCPV4)
> > + if (sinfo->gso_type & SKB_GSO_TCPV4) {
> > hdr->gso_type = VIRTIO_NET_HDR_GSO_TCPV4;
> > - else if (sinfo->gso_type & SKB_GSO_TCPV6)
> > + hdr_len += tcp_hdrlen(skb);
> > + } else if (sinfo->gso_type & SKB_GSO_TCPV6) {
> > hdr->gso_type = VIRTIO_NET_HDR_GSO_TCPV6;
> > - else if (sinfo->gso_type & SKB_GSO_UDP_L4)
> > + hdr_len += tcp_hdrlen(skb);
> > + } else if (sinfo->gso_type & SKB_GSO_UDP_L4) {
> > hdr->gso_type = VIRTIO_NET_HDR_GSO_UDP_L4;
> > - else
>
> I think we need to deal with the GSO tunnel as well?
>
> """
> If the \field{gso_type} has the VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV4 bit or
> VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV6 bit set, \field{hdr_len} accounts for
> all the headers up to and including the inner transport.
> """
I checked the new code, VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV6
and VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV4 are not supported, so the next version
will not include these feature.
Thanks.
>
> > + hdr_len += sizeof(struct udphdr);
> > + } else {
> > return -EINVAL;
> > + }
> > +
> > + hdr->hdr_len = __cpu_to_virtio16(little_endian, hdr_len);
>
> Should we at least check against the feature of VIRTIO_NET_F_GUEST_HDRLEN?
>
> > if (sinfo->gso_type & SKB_GSO_TCP_ECN)
> > hdr->gso_type |= VIRTIO_NET_HDR_GSO_ECN;
> > } else
> > --
> > 2.32.0.3.g01195cf9f
> >
>
