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virtio-net: avoid unnecessary checksum calculation on guest RX 

Commit a2fb4bc4e2 ("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: stable@vger.kernel.org
Fixes: a2fb4bc4e2 ("net: implement virtio helpers to handle UDP GSO tunneling.")
Signed-off-by: Jon Kohler <jon@nutanix.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://patch.msgid.link/20251125222754.1737443-1-jon@nutanix.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jon Kohler 2025-11-25 15:27:53 -07:00 committed by Jakub Kicinski
parent 6d66e093e0
commit 1cd1c47234
3 changed files with 7 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/net/tun_vnet.h
View File

@ -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);

3
drivers/net/virtio_net.c
View File

@ -3339,7 +3339,8 @@ 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)

7
include/linux/virtio_net.h
View File

@ -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)