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Thu, 19 Mar 2026 17:38:47 -0700 (PDT) X-Received: by 2002:a17:90a:e7d1:b0:35b:90e7:c458 with SMTP id 98e67ed59e1d1-35bd2bba0admr840853a91.3.1773967127303; Thu, 19 Mar 2026 17:38:47 -0700 (PDT) Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20260313075930.105466-1-xuanzhuo@linux.alibaba.com> <20260313075930.105466-2-xuanzhuo@linux.alibaba.com> <6be7d6f0-08ce-466c-87cc-bc2ad3f26aab@redhat.com> In-Reply-To: <6be7d6f0-08ce-466c-87cc-bc2ad3f26aab@redhat.com> From: Jason Wang Date: Fri, 20 Mar 2026 08:38:35 +0800 X-Gm-Features: AaiRm51Cgmr_6KcHsvMLEhMg1ooE2wNm_OXHGeR3ESMy6iFQsh2XE_XRq9XTcsI Message-ID: Subject: Re: [PATCH net v10 1/2] virtio-net: correct hdr_len handling for VIRTIO_NET_F_GUEST_HDRLEN To: Paolo Abeni Cc: Xuan Zhuo , netdev@vger.kernel.org, Willem de Bruijn , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , "Michael S. Tsirkin" , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Jiri Pirko , Alvaro Karsz , virtualization@lists.linux.dev X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: OBDZJ06N6uI5VaLWoO0TXUGzvoFtF1FuLGTbsbgq5vM_1773967128 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, Mar 19, 2026 at 4:15=E2=80=AFPM Paolo Abeni wro= te: > > Hi, > > On 3/18/26 5:11 AM, Jason Wang wrote: > > On Wed, Mar 18, 2026 at 12:07=E2=80=AFPM Jason Wang wrote: > >> On Fri, Mar 13, 2026 at 3:59=E2=80=AFPM Xuan Zhuo wrote: > >>> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h > >>> index 75dabb763c65..48de4a16a96a 100644 > >>> --- a/include/linux/virtio_net.h > >>> +++ b/include/linux/virtio_net.h > >>> @@ -207,6 +207,22 @@ static inline int virtio_net_hdr_to_skb(struct s= k_buff *skb, > >>> return __virtio_net_hdr_to_skb(skb, hdr, little_endian, hdr->= gso_type); > >>> } > >>> > >>> +static inline void virtio_net_set_hdrlen(const struct sk_buff *skb, > >>> + struct virtio_net_hdr *hdr, > >>> + bool little_endian) > >>> +{ > >>> + u16 hdr_len; > >>> + > >>> + hdr_len =3D skb_transport_offset(skb); > >>> + > >>> + if (hdr->gso_type =3D=3D VIRTIO_NET_HDR_GSO_UDP_L4) > >>> + hdr_len +=3D sizeof(struct udphdr); > >>> + else > >>> + hdr_len +=3D tcp_hdrlen(skb); > >> > >> Ok, I think this depends on the logic inside virtio_net_hdr_from_skb() > >> > >> if (sinfo->gso_type & SKB_GSO_TCPV4) > >> hdr->gso_type =3D VIRTIO_NET_HDR_GSO_TCPV4; > >> else if (sinfo->gso_type & SKB_GSO_TCPV6) > >> hdr->gso_type =3D VIRTIO_NET_HDR_GSO_TCPV6; > >> else if (sinfo->gso_type & SKB_GSO_UDP_L4) > >> hdr->gso_type =3D VIRTIO_NET_HDR_GSO_UDP_L4; > >> else > >> return -EINVAL; > >> > >> To be more robust, I'd suggest moving it there. > >> > >> But I have another question, the logic above depends on the headlen is > >> correctly set: > >> > >> /* This is a hint as to how much should be linear. */ > >> hdr->hdr_len =3D __cpu_to_virtio16(little_endian, > >> skb_headlen(skb)); > >> > >> Is the headlen guaranteed to be correct in all cases (e.g for nested > >> setups or dodgy packets?) > > > > Speak too fast, I miss > > > > hdr_len =3D skb_transport_offset(skb); > > > > This is probably another call to > > > > 1) Move virtio_net_set_hdrlen() inside virtio_net_hdr_from_skb() or > > 2) call virtio_net_set_hdrlen() inside virtio_net_hdr_from_skb(). > > It looks like that the above leads to more complex code with a bunch of > additional conditionals, which possibly the compiler can't optimize out, > and IMHO not nice layering violation, see the already mentioned previous > iteration: > > https://lore.kernel.org/all/cf62a942-e1e8-4b37-837a-b0bd76297656@redhat.c= om/ > > What about instead simply rename virtio_net_set_hdrlen() to > __virtio_net_set_hdrlen(), virtio_net_set_tnl_hdrlen() to > __virtio_net_set_tnl_hdrlen(), and add explicitly mention in a comment > that such functions must be invoked only after virtio_net_hdr_from_skb() > validation? Works for me. Thanks > > /P >