Commit a2fb4bc4e2a6 ("net: implement virtio helpers to handle UDP GSO tunneling.") inadvertently altered checksum offload behavior for guests not using UDP GSO tunneling.

Before, tun_put_user called tun_vnet_hdr_from_skb, which passed has_data_valid = true to virtio_net_hdr_from_skb.

After, tun_put_user began calling tun_vnet_hdr_tnl_from_skb instead, which passes has_data_valid = false into both call sites.

This caused virtio hdr flags to not include VIRTIO_NET_HDR_F_DATA_VALID for SKBs where skb->ip_summed == CHECKSUM_UNNECESSARY. As a result, guests are forced to recalculate checksums unnecessarily.

Restore the previous behavior by ensuring has_data_valid = true is passed in the !tnl_gso_type case, but only from tun side, as virtio_net_hdr_tnl_from_skb() is used also by the virtio_net driver, which in turn must not use VIRTIO_NET_HDR_F_DATA_VALID on tx.

Cc: Paolo Abeni pabeni@redhat.com Cc: stable@vger.kernel.org Acked-by: Michael S. Tsirkin mst@redhat.com Acked-by: Jason Wang jasowang@redhat.com Fixes: a2fb4bc4e2a6 ("net: implement virtio helpers to handle UDP GSO tunneling.") Signed-off-by: Jon Kohler jon@nutanix.com --- v3: https://patchwork.kernel.org/project/netdevbpf/patch/20251125222754.1737443-... v2: https://patchwork.kernel.org/project/netdevbpf/patch/20251125211418.1707482-... v3-v4: Collect acked-by (MST, Jason) and cc stable (Jason) v2-v3: Add net tag (whoops, sorry!) v1-v2: Add arg to avoid conflict from driver (Paolo) and send to net instead of net-next.

drivers/net/tun_vnet.h | 2 +- drivers/net/virtio_net.c | 3 ++- include/linux/virtio_net.h | 7 ++++--- 3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h index 81662328b2c7..a5f93b6c4482 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)) { + vlan_hlen, true)) { 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 b0947e15895f..1bb3aeca66c6 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -3344,7 +3344,8 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb, bool orphan) hdr = &skb_vnet_common_hdr(skb)->tnl_hdr;

if (virtio_net_hdr_tnl_from_skb(skb, hdr, vi->tx_tnl, - virtio_is_little_endian(vi->vdev), 0)) + virtio_is_little_endian(vi->vdev), 0, + false)) return -EPROTO;

if (vi->mergeable_rx_bufs) diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h index b673c31569f3..75dabb763c65 100644 --- a/include/linux/virtio_net.h +++ b/include/linux/virtio_net.h @@ -384,7 +384,8 @@ virtio_net_hdr_tnl_from_skb(const struct sk_buff *skb, struct virtio_net_hdr_v1_hash_tunnel *vhdr, bool tnl_hdr_negotiated, bool little_endian, - int vlan_hlen) + int vlan_hlen, + bool has_data_valid) { struct virtio_net_hdr *hdr = (struct virtio_net_hdr *)vhdr; unsigned int inner_nh, outer_th; @@ -394,8 +395,8 @@ 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, false, - vlan_hlen); + return virtio_net_hdr_from_skb(skb, hdr, little_endian, + has_data_valid, vlan_hlen);

/* Tunnel support not negotiated but skb ask for it. */ if (!tnl_hdr_negotiated)