Re: [PATCH net 2/2] virtio-net: correct hdr_len handling for VIRTIO_NET_F_GUEST_HDRLEN
From: Jason Wang <jasowang@redhat.com>
Date: 2025-09-26 04:53:09
Also in:
virtualization
On Thu, Sep 25, 2025 at 10:25 AM Xuan Zhuo [off-list ref] wrote:
quoted hunk ↗ jump to hunk
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 <xuanzhuo@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