From: "Michael S. Tsirkin" <mst@redhat•com>
To: Xuan Zhuo <xuanzhuo@linux•alibaba.com>
Cc: netdev@vger•kernel.org, "Jason Wang" <jasowang@redhat•com>,
"Eugenio Pérez" <eperezma@redhat•com>,
"Andrew Lunn" <andrew+netdev@lunn•ch>,
"David S. Miller" <davem@davemloft•net>,
"Eric Dumazet" <edumazet@google•com>,
"Jakub Kicinski" <kuba@kernel•org>,
"Paolo Abeni" <pabeni@redhat•com>,
"Heng Qi" <hengqi@linux•alibaba.com>,
"Willem de Bruijn" <willemb@google•com>,
"Jiri Pirko" <jiri@resnulli•us>,
"Alvaro Karsz" <alvaro.karsz@solid-run•com>,
virtualization@lists•linux.dev
Subject: Re: [PATCH net v4 3/4] virtio-net: correct hdr_len handling for VIRTIO_NET_F_GUEST_HDRLEN
Date: Sun, 9 Nov 2025 16:42:47 -0500 [thread overview]
Message-ID: <20251109164133-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20251029030913.20423-4-xuanzhuo@linux.alibaba.com>
On Wed, Oct 29, 2025 at 11:09:12AM +0800, Xuan Zhuo 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 <xuanzhuo@linux•alibaba.com>
ca you supply some examples when this is wrong please?
> ---
> include/linux/virtio_net.h | 22 ++++++++++++++++------
> 1 file changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
> index 710ae0d2d336..6ef0b737d548 100644
> --- a/include/linux/virtio_net.h
> +++ b/include/linux/virtio_net.h
> @@ -217,25 +217,35 @@ 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 = 0;
>
> /* In certain code paths (such as the af_packet.c receive path),
> * this function may be called without a transport header.
> * In this case, we do not need to set the hdr_len.
> */
you actually do initialize it, just to 0.
the comment is confusing.
> if (skb_transport_header_was_set(skb))
> - hdr->hdr_len = __cpu_to_virtio16(little_endian,
> - skb_headlen(skb));
> + hdr_len = skb_transport_offset(skb);
better:
else
hdr_len = 0;
>
> 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)
> + if (hdr_len)
> + 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)
> + if (hdr_len)
> + hdr_len += tcp_hdrlen(skb);
> + } else if (sinfo->gso_type & SKB_GSO_UDP_L4) {
> hdr->gso_type = VIRTIO_NET_HDR_GSO_UDP_L4;
> - else
> + if (hdr_len)
> + hdr_len += sizeof(struct udphdr);
> + } else {
> return -EINVAL;
> + }
> +
> + hdr->hdr_len = __cpu_to_virtio16(little_endian, hdr_len);
> +
> if (sinfo->gso_type & SKB_GSO_TCP_ECN)
> hdr->gso_type |= VIRTIO_NET_HDR_GSO_ECN;
> } else
> --
> 2.32.0.3.g01195cf9f
next prev parent reply other threads:[~2025-11-09 21:42 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-29 3:09 [PATCH net v4 0/4] fixes two virtio-net related bugs Xuan Zhuo
2025-10-29 3:09 ` [PATCH net v4 1/4] virtio-net: fix incorrect flags recording in big mode Xuan Zhuo
2025-11-09 17:04 ` Alyssa Ross
2025-11-09 21:34 ` Michael S. Tsirkin
2025-10-29 3:09 ` [PATCH net v4 2/4] virtio-net: Ensure hdr_len is not set unless the header is forwarded to the device Xuan Zhuo
2025-10-30 2:42 ` Jason Wang
2025-11-09 21:37 ` Michael S. Tsirkin
2025-10-29 3:09 ` [PATCH net v4 3/4] virtio-net: correct hdr_len handling for VIRTIO_NET_F_GUEST_HDRLEN Xuan Zhuo
2025-10-30 2:53 ` Jason Wang
2025-11-09 21:41 ` Michael S. Tsirkin
2025-11-10 7:16 ` Jason Wang
2025-11-10 7:26 ` Michael S. Tsirkin
2025-11-10 7:39 ` Jason Wang
2025-11-10 16:10 ` Michael S. Tsirkin
2025-11-11 0:45 ` Jason Wang
2025-11-09 21:42 ` Michael S. Tsirkin [this message]
2025-10-29 3:09 ` [PATCH net v4 4/4] virtio-net: correct hdr_len handling for tunnel gso Xuan Zhuo
2025-10-29 9:51 ` Paolo Abeni
2025-10-30 8:02 ` [PATCH net v4 0/4] fixes two virtio-net related bugs Michael S. Tsirkin
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