netdev - Re: [PATCH v2 1/9] virtio_net: disable the hole mechanism for xdp

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Message-ID: <c1b27a21-833c-2f3d-1943-7ab68c73836b@redhat.com>
Date:   Wed, 28 Dec 2022 14:28:30 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Heng Qi <hengqi@...ux.alibaba.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     "Michael S . Tsirkin" <mst@...hat.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH v2 1/9] virtio_net: disable the hole mechanism for xdp


在 2022/12/27 15:32, Heng Qi 写道:
>
>
> 在 2022/12/27 下午2:30, Jason Wang 写道:
>>
>> 在 2022/12/20 22:14, Heng Qi 写道:
>>> XDP core assumes that the frame_size of xdp_buff and the length of
>>> the frag are PAGE_SIZE. The hole may cause the processing of xdp to
>>> fail, so we disable the hole mechanism when xdp is set.
>>>
>>> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
>>> Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
>>> ---
>>>   drivers/net/virtio_net.c | 5 ++++-
>>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>> index 9cce7dec7366..443aa7b8f0ad 100644
>>> --- a/drivers/net/virtio_net.c
>>> +++ b/drivers/net/virtio_net.c
>>> @@ -1419,8 +1419,11 @@ static int add_recvbuf_mergeable(struct 
>>> virtnet_info *vi,
>>>           /* To avoid internal fragmentation, if there is very 
>>> likely not
>>>            * enough space for another buffer, add the remaining 
>>> space to
>>>            * the current buffer.
>>> +         * XDP core assumes that frame_size of xdp_buff and the length
>>> +         * of the frag are PAGE_SIZE, so we disable the hole 
>>> mechanism.
>>>            */
>>> -        len += hole;
>>> +        if (!headroom)
>>> +            len += hole;
>>
>>
>> Is this only a requirement of multi-buffer XDP? If not, it need to be 
>> backported to stable.
>
> It applies to single buffer xdp and multi-buffer xdp, but even if 
> single buffer xdp has a hole
> mechanism, there will be no problem (limiting mtu and turning off 
> GUEST GSO), so there is
> no need to backport it.


Let's add this in the changelog.

With that,

Acked-by: Jason Wang <jasowang@...hat.com>

Thanks


>
> Thanks.
>
>>
>> Thanks
>>
>>
>>>           alloc_frag->offset += hole;
>>>       }
>