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[35.247.100.8]) by smtp.gmail.com with ESMTPSA id b25sm3552541pfo.38.2020.02.13.07.44.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 13 Feb 2020 07:44:10 -0800 (PST) Subject: Re: [PATCH] virtio: Work around frames incorrectly marked as gso To: "Michael S. Tsirkin" , Anton Ivanov Cc: netdev@vger.kernel.org, Jason Wang , linux-um@lists.infradead.org, virtualization@lists.linux-foundation.org References: <20191209104824.17059-1-anton.ivanov@cambridgegreys.com> <57230228-7030-c65f-a24f-910ca52bbe9e@cambridgegreys.com> <918222d9-816a-be70-f8af-b8dfcb586240@cambridgegreys.com> <20200211053502-mutt-send-email-mst@kernel.org> <9547228b-aa93-f2b6-6fdc-8d33cde3716a@cambridgegreys.com> <20200213045937-mutt-send-email-mst@kernel.org> From: Eric Dumazet Message-ID: <94fb9656-99ee-a001-e428-9d76c3620e61@gmail.com> Date: Thu, 13 Feb 2020 07:44:06 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200213045937-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2/13/20 2:00 AM, Michael S. Tsirkin wrote: > On Wed, Feb 12, 2020 at 05:38:09PM +0000, Anton Ivanov wrote: >> >> >> On 11/02/2020 10:37, Michael S. Tsirkin wrote: >>> On Tue, Feb 11, 2020 at 07:42:37AM +0000, Anton Ivanov wrote: >>>> On 11/02/2020 02:51, Jason Wang wrote: >>>>> >>>>> On 2020/2/11 上午12:55, Anton Ivanov wrote: >>>>>> >>>>>> >>>>>> On 09/12/2019 10:48, anton.ivanov@cambridgegreys.com wrote: >>>>>>> From: Anton Ivanov >>>>>>> >>>>>>> Some of the frames marked as GSO which arrive at >>>>>>> virtio_net_hdr_from_skb() have no GSO_TYPE, no >>>>>>> fragments (data_len = 0) and length significantly shorter >>>>>>> than the MTU (752 in my experiments). >>>>>>> >>>>>>> This is observed on raw sockets reading off vEth interfaces >>>>>>> in all 4.x and 5.x kernels I tested. >>>>>>> >>>>>>> These frames are reported as invalid while they are in fact >>>>>>> gso-less frames. >>>>>>> >>>>>>> This patch marks the vnet header as no-GSO for them instead >>>>>>> of reporting it as invalid. >>>>>>> >>>>>>> Signed-off-by: Anton Ivanov >>>>>>> --- >>>>>>>   include/linux/virtio_net.h | 8 ++++++-- >>>>>>>   1 file changed, 6 insertions(+), 2 deletions(-) >>>>>>> >>>>>>> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h >>>>>>> index 0d1fe9297ac6..d90d5cff1b9a 100644 >>>>>>> --- a/include/linux/virtio_net.h >>>>>>> +++ b/include/linux/virtio_net.h >>>>>>> @@ -112,8 +112,12 @@ static inline int >>>>>>> virtio_net_hdr_from_skb(const struct sk_buff *skb, >>>>>>>               hdr->gso_type = VIRTIO_NET_HDR_GSO_TCPV4; >>>>>>>           else if (sinfo->gso_type & SKB_GSO_TCPV6) >>>>>>>               hdr->gso_type = VIRTIO_NET_HDR_GSO_TCPV6; >>>>>>> -        else >>>>>>> -            return -EINVAL; >>>>>>> +        else { >>>>>>> +            if (skb->data_len == 0) >>>>>>> +                hdr->gso_type = VIRTIO_NET_HDR_GSO_NONE; >>>>>>> +            else >>>>>>> +                return -EINVAL; >>>>>>> +        } >>>>>>>           if (sinfo->gso_type & SKB_GSO_TCP_ECN) >>>>>>>               hdr->gso_type |= VIRTIO_NET_HDR_GSO_ECN; >>>>>>>       } else >>>>>>> >>>>>> >>>>>> ping. >>>>>> >>>>> >>>>> Do you mean gso_size is set but gso_type is not? Looks like a bug >>>>> elsewhere. >>>>> >>>>> Thanks >>>>> >>>>> >>>> Yes. >>>> >>>> I could not trace it where it is coming from. >>>> >>>> I see it when doing recvmmsg on raw sockets in the UML vector network >>>> drivers. >>>> >>> >>> I think we need to find the culprit and fix it there, lots of other things >>> can break otherwise. >>> Just printing out skb->dev->name should do the trick, no? >> >> The printk in virtio_net_hdr_from_skb says NULL. >> >> That is probably normal for a locally originated frame. >> >> I cannot reproduce this with network traffic by the way - it happens only if the traffic is locally originated on the host. >> >> A, > > OK so is it code in __tcp_transmit_skb that sets gso_size to non-null > when gso_type is 0? > Correct way to determine if a packet is a gso one is by looking at gso_size. Then only it is legal looking at gso_type static inline bool skb_is_gso(const struct sk_buff *skb) { return skb_shinfo(skb)->gso_size; } /* Note: Should be called only if skb_is_gso(skb) is true */ static inline bool skb_is_gso_v6(const struct sk_buff *skb) ... There is absolutely no relation between GSO and skb->data_len, skb can be linearized for various orthogonal reasons.