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Tsirkin" To: Xuan Zhuo Cc: netdev@vger.kernel.org, Richard Weinberger , Anton Ivanov , Johannes Berg , Willem de Bruijn , Jason Wang , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Eugenio =?iso-8859-1?Q?P=E9rez?= , Simon Horman , Jiri Pirko , Alvaro Karsz , linux-um@lists.infradead.org, virtualization@lists.linux.dev Subject: Re: [PATCH net v5 1/2] virtio-net: correct hdr_len handling for VIRTIO_NET_F_GUEST_HDRLEN Message-ID: <20251111062859-mutt-send-email-mst@kernel.org> References: <20251111111212.102083-1-xuanzhuo@linux.alibaba.com> <20251111111212.102083-2-xuanzhuo@linux.alibaba.com> MIME-Version: 1.0 In-Reply-To: <20251111111212.102083-2-xuanzhuo@linux.alibaba.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: cjxgjH7VzGkLhb07R6HYjzrI_tZqRoNt3ss_N0TMFt8_1762860789 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251111_033456_106372_A1AC73DF X-CRM114-Status: GOOD ( 31.63 ) X-BeenThere: linux-um@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-um" Errors-To: linux-um-bounces+linux-um=archiver.kernel.org@lists.infradead.org On Tue, Nov 11, 2025 at 07:12:11PM +0800, Xuan Zhuo wrote: > The commit be50da3e9d4a ("net: virtio_net: implement exact header length > guest feature") introduces support for the VIRTIO_NET_F_GUEST_HDRLEN > feature in virtio-net. > > This feature requires virtio-net to set hdr_len to the actual header > length of the packet when transmitting, the number of > bytes from the start of the packet to the beginning of the > transport-layer payload. > > However, in practice, hdr_len was being set using skb_headlen(skb), > which is clearly incorrect. This commit fixes that issue. > > Fixes: be50da3e9d4a ("net: virtio_net: implement exact header length guest feature") > Signed-off-by: Xuan Zhuo > --- > arch/um/drivers/vector_transports.c | 1 + > drivers/net/tun_vnet.h | 4 ++-- > drivers/net/virtio_net.c | 9 +++++++-- > include/linux/virtio_net.h | 26 +++++++++++++++++++++----- > net/packet/af_packet.c | 5 +++-- > 5 files changed, 34 insertions(+), 11 deletions(-) > > diff --git a/arch/um/drivers/vector_transports.c b/arch/um/drivers/vector_transports.c > index 0794d23f07cb..03c5baa1d0c1 100644 > --- a/arch/um/drivers/vector_transports.c > +++ b/arch/um/drivers/vector_transports.c > @@ -121,6 +121,7 @@ static int raw_form_header(uint8_t *header, > vheader, > virtio_legacy_is_little_endian(), > false, > + false, > 0 > ); > > diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h > index 81662328b2c7..0d376bc70dd7 100644 > --- a/drivers/net/tun_vnet.h > +++ b/drivers/net/tun_vnet.h > @@ -214,7 +214,7 @@ static inline int tun_vnet_hdr_from_skb(unsigned int flags, > > if (virtio_net_hdr_from_skb(skb, hdr, > tun_vnet_is_little_endian(flags), true, > - vlan_hlen)) { > + false, vlan_hlen)) { > struct skb_shared_info *sinfo = skb_shinfo(skb); > > if (net_ratelimit()) { > @@ -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)) { > + false, vlan_hlen)) { > 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..b335c88a8cd6 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -3317,9 +3317,13 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb, bool orphan) > const unsigned char *dest = ((struct ethhdr *)skb->data)->h_dest; > struct virtnet_info *vi = sq->vq->vdev->priv; > struct virtio_net_hdr_v1_hash_tunnel *hdr; > - int num_sg; > unsigned hdr_len = vi->hdr_len; > + bool hdrlen_negotiated; > bool can_push; > + int num_sg; > + > + hdrlen_negotiated = virtio_has_feature(vi->vdev, > + VIRTIO_NET_F_GUEST_HDRLEN); > > pr_debug("%s: xmit %p %pM\n", vi->dev->name, skb, dest); > > @@ -3339,7 +3343,8 @@ 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), > + hdrlen_negotiated, 0)) > return -EPROTO; > > if (vi->mergeable_rx_bufs) > diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h > index b673c31569f3..3cd8b2ebc197 100644 > --- a/include/linux/virtio_net.h > +++ b/include/linux/virtio_net.h > @@ -211,16 +211,15 @@ static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb, > struct virtio_net_hdr *hdr, > bool little_endian, > bool has_data_valid, > + bool hdrlen_negotiated, > int vlan_hlen) Took me a while to figure out why does tun pass false here. The reason is that this flag is really only dealing with guest hdrlen. so how about guest_hdrlen to mirror spec or if you like xmit_hdrlen? > { > memset(hdr, 0, sizeof(*hdr)); /* no info leak */ > > if (skb_is_gso(skb)) { > struct skb_shared_info *sinfo = skb_shinfo(skb); > + u16 hdr_len; > > - /* This is a hint as to how much should be linear. */ > - hdr->hdr_len = __cpu_to_virtio16(little_endian, > - skb_headlen(skb)); > hdr->gso_size = __cpu_to_virtio16(little_endian, > sinfo->gso_size); > if (sinfo->gso_type & SKB_GSO_TCPV4) > @@ -231,6 +230,21 @@ static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb, > hdr->gso_type = VIRTIO_NET_HDR_GSO_UDP_L4; > else > return -EINVAL; > + > + if (hdrlen_negotiated) { > + hdr_len = skb_transport_offset(skb); > + > + if (hdr->gso_type == VIRTIO_NET_HDR_GSO_UDP_L4) > + hdr_len += sizeof(struct udphdr); > + else > + hdr_len += tcp_hdrlen(skb); > + } else { > + /* This is a hint as to how much should be linear. */ > + hdr_len = skb_headlen(skb); > + } > + > + hdr->hdr_len = __cpu_to_virtio16(little_endian, hdr_len); > + > if (sinfo->gso_type & SKB_GSO_TCP_ECN) > hdr->gso_type |= VIRTIO_NET_HDR_GSO_ECN; > } else > @@ -384,6 +398,7 @@ 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, > + bool hdrlen_negotiated, > int vlan_hlen) > { > struct virtio_net_hdr *hdr = (struct virtio_net_hdr *)vhdr; > @@ -395,7 +410,7 @@ virtio_net_hdr_tnl_from_skb(const struct sk_buff *skb, > SKB_GSO_UDP_TUNNEL_CSUM); > if (!tnl_gso_type) > return virtio_net_hdr_from_skb(skb, hdr, little_endian, false, > - vlan_hlen); > + hdrlen_negotiated, vlan_hlen); > > /* Tunnel support not negotiated but skb ask for it. */ > if (!tnl_hdr_negotiated) > @@ -408,7 +423,8 @@ virtio_net_hdr_tnl_from_skb(const struct sk_buff *skb, > > /* Let the basic parsing deal with plain GSO features. */ > skb_shinfo(skb)->gso_type &= ~tnl_gso_type; > - ret = virtio_net_hdr_from_skb(skb, hdr, true, false, vlan_hlen); > + ret = virtio_net_hdr_from_skb(skb, hdr, true, false, hdrlen_negotiated, > + vlan_hlen); > skb_shinfo(skb)->gso_type |= tnl_gso_type; > if (ret) > return ret; > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c > index 173e6edda08f..6982f4ab1c73 100644 > --- a/net/packet/af_packet.c > +++ b/net/packet/af_packet.c > @@ -2093,7 +2093,8 @@ static int packet_rcv_vnet(struct msghdr *msg, const struct sk_buff *skb, > return -EINVAL; > *len -= vnet_hdr_sz; > > - if (virtio_net_hdr_from_skb(skb, (struct virtio_net_hdr *)&vnet_hdr, vio_le(), true, 0)) > + if (virtio_net_hdr_from_skb(skb, (struct virtio_net_hdr *)&vnet_hdr, > + vio_le(), true, false, 0)) > return -EINVAL; > > return memcpy_to_msg(msg, (void *)&vnet_hdr, vnet_hdr_sz); > @@ -2361,7 +2362,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev, > if (vnet_hdr_sz && > virtio_net_hdr_from_skb(skb, h.raw + macoff - > sizeof(struct virtio_net_hdr), > - vio_le(), true, 0)) { > + vio_le(), true, false, 0)) { > if (po->tp_version == TPACKET_V3) > prb_clear_blk_fill_status(&po->rx_ring); > goto drop_n_account; > -- > 2.32.0.3.g01195cf9f