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Commita2fb4bc4e2("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>