On Thu, Sep 25, 2025 at 10:25 AM Xuan Zhuo <xuanz...@linux.alibaba.com> 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 <xuanz...@linux.alibaba.com>
> ---
> 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.
"""
> + 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
>
