* [PATCH net v9 1/2] virtio-net: correct hdr_len handling for VIRTIO_NET_F_GUEST_HDRLEN
2026-03-11 11:54 [PATCH net v9 0/2] virtio-net: fix for VIRTIO_NET_F_GUEST_HDRLEN Xuan Zhuo
@ 2026-03-11 11:54 ` Xuan Zhuo
2026-03-11 11:54 ` [PATCH net v9 2/2] virtio-net: correct hdr_len handling for tunnel gso Xuan Zhuo
1 sibling, 0 replies; 4+ messages in thread
From: Xuan Zhuo @ 2026-03-11 11:54 UTC (permalink / raw)
To: netdev
Cc: Willem de Bruijn, Jason Wang, Andrew Lunn, David S. Miller,
Eric Dumazet, Jakub Kicinski, Paolo Abeni, Michael S. Tsirkin,
Xuan Zhuo, Eugenio Pérez, Jiri Pirko, Alvaro Karsz,
virtualization
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>
---
drivers/net/tun_vnet.h | 2 +-
drivers/net/virtio_net.c | 6 +++++-
include/linux/virtio_net.h | 33 +++++++++++++++++++++++++++++----
3 files changed, 35 insertions(+), 6 deletions(-)
diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h
index a5f93b6c4482..fa5cab9d3e55 100644
--- a/drivers/net/tun_vnet.h
+++ b/drivers/net/tun_vnet.h
@@ -244,7 +244,7 @@ tun_vnet_hdr_tnl_from_skb(unsigned int flags,
if (virtio_net_hdr_tnl_from_skb(skb, tnl_hdr, has_tnl_offload,
tun_vnet_is_little_endian(flags),
- vlan_hlen, true)) {
+ vlan_hlen, true, false)) {
struct virtio_net_hdr_v1 *hdr = &tnl_hdr->hash_hdr.hdr;
struct skb_shared_info *sinfo = skb_shinfo(skb);
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 72d6a9c6a5a2..7106333ef904 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3267,8 +3267,12 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb, bool orphan)
struct virtio_net_hdr_v1_hash_tunnel *hdr;
int num_sg;
unsigned hdr_len = vi->hdr_len;
+ bool feature_hdrlen;
bool can_push;
+ feature_hdrlen = virtio_has_feature(vi->vdev,
+ VIRTIO_NET_F_GUEST_HDRLEN);
+
pr_debug("%s: xmit %p %pM\n", vi->dev->name, skb, dest);
/* Make sure it's safe to cast between formats */
@@ -3288,7 +3292,7 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb, bool orphan)
if (virtio_net_hdr_tnl_from_skb(skb, hdr, vi->tx_tnl,
virtio_is_little_endian(vi->vdev), 0,
- false))
+ false, feature_hdrlen))
return -EPROTO;
if (vi->mergeable_rx_bufs)
diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 75dabb763c65..48de4a16a96a 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -207,6 +207,22 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
return __virtio_net_hdr_to_skb(skb, hdr, little_endian, hdr->gso_type);
}
+static inline void virtio_net_set_hdrlen(const struct sk_buff *skb,
+ struct virtio_net_hdr *hdr,
+ bool little_endian)
+{
+ u16 hdr_len;
+
+ hdr_len = skb_transport_offset(skb);
+
+ if (hdr->gso_type == VIRTIO_NET_HDR_GSO_UDP_L4)
+ hdr_len += sizeof(struct udphdr);
+ else
+ hdr_len += tcp_hdrlen(skb);
+
+ hdr->hdr_len = __cpu_to_virtio16(little_endian, hdr_len);
+}
+
static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb,
struct virtio_net_hdr *hdr,
bool little_endian,
@@ -385,7 +401,8 @@ virtio_net_hdr_tnl_from_skb(const struct sk_buff *skb,
bool tnl_hdr_negotiated,
bool little_endian,
int vlan_hlen,
- bool has_data_valid)
+ bool has_data_valid,
+ bool feature_hdrlen)
{
struct virtio_net_hdr *hdr = (struct virtio_net_hdr *)vhdr;
unsigned int inner_nh, outer_th;
@@ -394,9 +411,17 @@ virtio_net_hdr_tnl_from_skb(const struct sk_buff *skb,
tnl_gso_type = skb_shinfo(skb)->gso_type & (SKB_GSO_UDP_TUNNEL |
SKB_GSO_UDP_TUNNEL_CSUM);
- if (!tnl_gso_type)
- return virtio_net_hdr_from_skb(skb, hdr, little_endian,
- has_data_valid, vlan_hlen);
+ if (!tnl_gso_type) {
+ ret = virtio_net_hdr_from_skb(skb, hdr, little_endian,
+ has_data_valid, vlan_hlen);
+ if (ret)
+ return ret;
+
+ if (feature_hdrlen && hdr->hdr_len)
+ virtio_net_set_hdrlen(skb, hdr, little_endian);
+
+ return ret;
+ }
/* Tunnel support not negotiated but skb ask for it. */
if (!tnl_hdr_negotiated)
--
2.32.0.3.g01195cf9f
^ permalink raw reply related [flat|nested] 4+ messages in thread* [PATCH net v9 2/2] virtio-net: correct hdr_len handling for tunnel gso
2026-03-11 11:54 [PATCH net v9 0/2] virtio-net: fix for VIRTIO_NET_F_GUEST_HDRLEN Xuan Zhuo
2026-03-11 11:54 ` [PATCH net v9 1/2] virtio-net: correct hdr_len handling " Xuan Zhuo
@ 2026-03-11 11:54 ` Xuan Zhuo
2026-03-12 14:28 ` kernel test robot
1 sibling, 1 reply; 4+ messages in thread
From: Xuan Zhuo @ 2026-03-11 11:54 UTC (permalink / raw)
To: netdev
Cc: Willem de Bruijn, Jason Wang, Andrew Lunn, David S. Miller,
Eric Dumazet, Jakub Kicinski, Paolo Abeni, Michael S. Tsirkin,
Xuan Zhuo, Eugenio Pérez, Jiri Pirko, Alvaro Karsz,
virtualization
The commit a2fb4bc4e2a6a03 ("net: implement virtio helpers to handle UDP
GSO tunneling.") introduces support for the UDP GSO tunnel feature in
virtio-net.
The virtio spec says:
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.
The commit did not update the hdr_len to include the inner transport.
I observed that the "hdr_len" is 116 for this packet:
17:36:18.241105 52:55:00:d1:27:0a > 2e:2c:df:46:a9:e1, ethertype IPv4 (0x0800), length 2912: (tos 0x0, ttl 64, id 45197, offset 0, flags [none], proto UDP (17), length 2898)
192.168.122.100.50613 > 192.168.122.1.4789: [bad udp cksum 0x8106 -> 0x26a0!] VXLAN, flags [I] (0x08), vni 1
fa:c3:ba:82:05:ee > ce:85:0c:31:77:e5, ethertype IPv4 (0x0800), length 2862: (tos 0x0, ttl 64, id 14678, offset 0, flags [DF], proto TCP (6), length 2848)
192.168.3.1.49880 > 192.168.3.2.9898: Flags [P.], cksum 0x9266 (incorrect -> 0xaa20), seq 515667:518463, ack 1, win 64, options [nop,nop,TS val 2990048824 ecr 2798801412], length 2796
116 = 14(mac) + 20(ip) + 8(udp) + 8(vxlan) + 14(inner mac) + 20(inner ip) + 32(innner tcp)
Fixes: a2fb4bc4e2a6a03 ("net: implement virtio helpers to handle UDP GSO tunneling.")
Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
include/linux/virtio_net.h | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 48de4a16a96a..0fe69876d839 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -223,6 +223,21 @@ static inline void virtio_net_set_hdrlen(const struct sk_buff *skb,
hdr->hdr_len = __cpu_to_virtio16(little_endian, hdr_len);
}
+static inline void virtio_net_set_tnl_hdrlen(const struct sk_buff *skb,
+ struct virtio_net_hdr *hdr)
+{
+ u16 hdr_len;
+
+ hdr_len = skb_inner_transport_offset(skb);
+
+ if (hdr->gso_type == VIRTIO_NET_HDR_GSO_UDP_L4)
+ hdr_len += sizeof(struct udphdr);
+ else
+ hdr_len += inner_tcp_hdrlen(skb);
+
+ hdr->hdr_len = cpu_to_le16(hdr_len);
+}
+
static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb,
struct virtio_net_hdr *hdr,
bool little_endian,
@@ -439,6 +454,9 @@ virtio_net_hdr_tnl_from_skb(const struct sk_buff *skb,
if (ret)
return ret;
+ if (feature_hdrlen && hdr->hdr_len)
+ virtio_net_set_tnl_hdrlen(skb, hdr);
+
if (skb->protocol == htons(ETH_P_IPV6))
hdr->gso_type |= VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV6;
else
--
2.32.0.3.g01195cf9f
^ permalink raw reply related [flat|nested] 4+ messages in thread