From 1cd1c472343b06d6d32038636ce51bfa2251e3cf Mon Sep 17 00:00:00 2001 From: Jon Kohler Date: Tue, 25 Nov 2025 15:27:53 -0700 Subject: 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 Acked-by: Michael S. Tsirkin Acked-by: Jason Wang Link: https://patch.msgid.link/20251125222754.1737443-1-jon@nutanix.com Signed-off-by: Jakub Kicinski --- include/linux/virtio_net.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'include/linux') 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) -- cgit v1.2.3