Re: [PATCH] virtio: Work around frames incorrectly marked as gso

From: Anton Ivanov <anton.ivanov@cambridgegreys.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: netdev@vger.kernel.org, Jason Wang <jasowang@redhat.com>,
	linux-um@lists.infradead.org,
	virtualization@lists.linux-foundation.org
Subject: Re: [PATCH] virtio: Work around frames incorrectly marked as gso
Date: Wed, 12 Feb 2020 10:03:31 +0000	[thread overview]
Message-ID: <8e730fe1-3129-de8d-bcb6-d5e10695238a@cambridgegreys.com> (raw)
In-Reply-To: <20200211053502-mutt-send-email-mst@kernel.org>

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 <anton.ivanov@cambridgegreys.com>
>>>>>
>>>>> 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 <anton.ivanov@cambridgegreys.com>
>>>>> ---
>>>>>    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?

I will rebuild my rig and retest (it's been a while since I worked on this bug).

In theory, it should be veth - the test is over a vEth pair and all frames are locally originated by iperf.

In practice - I will retest and post the results sometimes later today.

Brgds,

 >
> 
> 
>> -- 
>> Anton R. Ivanov
>> Cambridgegreys Limited. Registered in England. Company Number 10273661
>> https://www.cambridgegreys.com/
> 
> 
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-- 
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/