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

Heng Qi
2022-12-27T07:33:08Z

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@linux.alibaba.com>
>> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.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.

Thanks.

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