virtio-net: avoid unnecessary checksum calculation on guest RX

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: stable@vger.kernel.org
Fixes: a2fb4bc4e2a6 ("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>

diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h
index 81662328b2c7992be8db5432d07b8e8f7ef2016b..a5f93b6c4482c318679a44dadbb2cc34b70bbd90 100644 (file)
--- 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 0369dda5ed606868e02bd8dde9789169e52eba05..8e04adb57f52ad344db8c9e983d5fb979d24a974 100644 (file)
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -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)

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index b673c31569f32048b3e4c3647fadc08456248c4d..75dabb763c650478844950f9a8b92edcde48abf0 100644 (file)
--- 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)