Re: [PATCH v2 2/9] virtio_net: set up xdp for multi buffer packets

Heng Qi
2022-12-27T12:24:39Z

在 2022/12/27 下午2:32, Jason Wang 写道:
>
> 在 2022/12/20 22:14, Heng Qi 写道:
>> When the xdp program sets xdp.frags, which means it can process
>> multi-buffer packets over larger MTU, so we continue to support xdp.
>> But for single-buffer xdp, we should keep checking for MTU.
>>
>> Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
>> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
>> ---
>>   drivers/net/virtio_net.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index 443aa7b8f0ad..c5c4e9db4ed3 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -3095,8 +3095,8 @@ static int virtnet_xdp_set(struct net_device
>> *dev, struct bpf_prog *prog,
>>           return -EINVAL;
>>       }
>>   -    if (dev->mtu > max_sz) {
>> -        NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP");
>> +    if (prog && !prog->aux->xdp_has_frags && dev->mtu > max_sz) {
>
>
> Not related to this patch, but I see:
>
>         unsigned long int max_sz = PAGE_SIZE - sizeof(struct
> padded_vnet_hdr);
>
> Which is suspicious, do we need to count reserved headroom/tailroom as
> well?

This seems to be suspicious. After loading xdp, the size of the filled
avail buffer
is (PAGE_SIZE - headroom - tailroom), so the size of the received used
buffer, ie MTU,
should also be (PAGE_SIZE - headroom - tailroom).

Thanks.

>
> Thanks
>
>
>> +        NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP
>> without frags");
>>           netdev_warn(dev, "XDP requires MTU less than %lu\n", max_sz);
>>           return -EINVAL;
>>       }