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([2a0d:3344:5521:6b10:58fd:68f:7756:389d]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47f63eeece9sm37465633f8f.37.2026.07.21.04.19.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Jul 2026 04:19:17 -0700 (PDT) Message-ID: <03f49d98-c6e1-4dd2-bf25-f42e424fd59c@redhat.com> Date: Tue, 21 Jul 2026 13:19:15 +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 net] vhost-net: fix TX stall when vhost owns virtio-net header To: "Michael S. Tsirkin" , enrico.zanda@arm.com Cc: jasowangio@gmail.com, virtualization@lists.linux.dev, netdev@vger.kernel.org, kuba@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, eperezma@redhat.com, nd@arm.com References: <20260708152242.2268848-1-enrico.zanda@arm.com> <20260708124901-mutt-send-email-mst@kernel.org> Content-Language: en-US From: Paolo Abeni In-Reply-To: <20260708124901-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/8/26 6:50 PM, Michael S. Tsirkin wrote: > On Wed, Jul 08, 2026 at 04:22:42PM +0100, enrico.zanda@arm.com wrote: >> From: Enrico Zanda >> >> When vhost owns the virtio-net header, i.e. when >> VHOST_NET_F_VIRTIO_NET_HDR is negotiated, sock_hlen is 0, >> meaning that no header will be forwarded to the TAP device. >> >> In the current vhost_net_build_xdp() implementation, >> when sock_hlen == 0, the gso pointer can point at the start of the >> Ethernet frame instead of a virtio-net header. >> This results in a wrong interpretation of the destination MAC address >> bytes as struct virtio_net_hdr fields. >> >> This can, for some MAC addresses, trigger -EINVAL and return early >> before the TX descriptor is completed, which can stall vhost-net TX. >> >> Before 97b2409f28e0, the gso pointer was set to the zeroed padding area, >> using it as a synthetic virtio-net header. Restore that behavior. >> >> Fixes: 97b2409f28e0 ("vhost-net: reduce one userspace copy when building XDP buff") >> Signed-off-by: Enrico Zanda > > > The fix looks good: > Acked-by: Michael S. Tsirkin > > Sashiko thinks there's something something security here, but I think > it is misguided. It's just guest hurting itself. driver breaks the > device it gets to keep both pieces. Out of sheer curiosity: which sashiko instance? AFAICS both gemini and nipa are clean: https://sashiko.dev/#/patchset/20260708152242.2268848-1-enrico.zanda%40arm.com https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260708152242.2268848-1-enrico.zanda%40arm.com /P