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[80.230.39.63]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42cb7f2e574sm38233964f8f.3.2025.11.25.22.28.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Nov 2025 22:29:00 -0800 (PST) Date: Wed, 26 Nov 2025 01:28:57 -0500 From: "Michael S. Tsirkin" To: Jon Kohler Cc: Willem de Bruijn , Jason Wang , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Xuan Zhuo , Eugenio =?iso-8859-1?Q?P=E9rez?= , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux.dev Subject: Re: [PATCH net v3] virtio-net: avoid unnecessary checksum calculation on guest RX Message-ID: <20251126012848-mutt-send-email-mst@kernel.org> References: <20251125222754.1737443-1-jon@nutanix.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251125222754.1737443-1-jon@nutanix.com> On Tue, Nov 25, 2025 at 03:27:53PM -0700, Jon Kohler wrote: > 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: Paolo Abeni > Fixes: a2fb4bc4e2a6 ("net: implement virtio helpers to handle UDP GSO tunneling.") > Signed-off-by: Jon Kohler Acked-by: Michael S. Tsirkin > --- > v2-v3: Add net tag (whoops, sorry!) > v1-v2: Add arg to avoid conflict from driver (Paolo) and send to net > instead of net-next. > drivers/net/tun_vnet.h | 2 +- > drivers/net/virtio_net.c | 3 ++- > include/linux/virtio_net.h | 7 ++++--- > 3 files changed, 7 insertions(+), 5 deletions(-) > > 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 cfa006b88688..96f2d2a59003 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) > -- > 2.43.0