Commit 1cd1c472343b for kernel

commit 1cd1c472343b06d6d32038636ce51bfa2251e3cf
Author: Jon Kohler <jon@nutanix.com>
Date:   Tue Nov 25 15:27:53 2025 -0700

    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 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 0369dda5ed60..8e04adb57f52 100644
--- 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 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)