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[146.241.9.4]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-453646cb672sm4573535e9.6.2025.06.19.13.30.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Jun 2025 13:30:44 -0700 (PDT) Message-ID: Date: Thu, 19 Jun 2025 22:30:41 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 net-next 7/8] tun: enable gso over UDP tunnel support. From: Paolo Abeni To: Akihiko Odaki , netdev@vger.kernel.org Cc: Willem de Bruijn , Jason Wang , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , "Michael S. Tsirkin" , Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Yuri Benditovich References: <1c6ffd4bd0480ecc4c8442cef7c689fbfb5e0e56.1750176076.git.pabeni@redhat.com> <0aa1055e-3e52-4275-a074-e6f27115a748@redhat.com> Content-Language: en-US In-Reply-To: <0aa1055e-3e52-4275-a074-e6f27115a748@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/19/25 7:41 PM, Paolo Abeni wrote: > On 6/19/25 6:02 PM, Akihiko Odaki wrote: >> On 2025/06/18 1:12, Paolo Abeni wrote: >>> @@ -2426,7 +2453,17 @@ static int tun_xdp_one(struct tun_struct *tun, >>> if (metasize > 0) >>> skb_metadata_set(skb, metasize); >>> >>> - if (tun_vnet_hdr_to_skb(tun->flags, skb, gso)) { >>> + /* >>> + * Assume tunnel offloads are enabled if the received hdr is large >>> + * enough. >>> + */ >>> + if (READ_ONCE(tun->vnet_hdr_sz) >= TUN_VNET_TNL_SIZE && >>> + xdp->data - xdp->data_hard_start >= TUN_VNET_TNL_SIZE) >>> + features = NETIF_F_GSO_UDP_TUNNEL | >>> + NETIF_F_GSO_UDP_TUNNEL_CSUM; >> >> xdp->data - xdp->data_hard_start may not represent the header size. >> >> struct tun_xdp_hdr is filled in vhost_net_build_xdp() in >> drivers/vhost/net.c. This function sets the two fields with >> xdp_prepare_buff(), but the arguments passed to xdp_prepare_buff() does >> not seem to represent the exact size of the header. > > Indeed the xdp->data - xdp->data_hard_start range additionally contains > some padding and eventually the xdp specific headroom. The problem is > that both info are vhost_net specific and tun can't (or at least shoul) > not be aware of them. > > The only IMHO feasible refinement could be using xdp->data_meta instead > of xdp->data when available. Alternatively I could drop entirely the test. As the vhost_net padding is considerably larger than the largest possible vnet_hdr_sz, I'll drop entirely the xdp check - so that I can use the newly introduced tun_vnet_hdr_guest_features() helper here, too. /P