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

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Date:   Thu, 8 Dec 2022 16:21:13 +0800
From:   Heng Qi <hengqi@...ux.alibaba.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        "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>
Subject: Re: [RFC PATCH 2/9] virtio_net: set up xdp for multi buffer packets



在 2022/12/6 下午1:29, Jason Wang 写道:
> On Tue, Nov 22, 2022 at 3:44 PM Heng Qi <hengqi@...ux.alibaba.com> wrote:
>> When the xdp program sets xdp.frags, which means it can process
>> multi-buffer packets, so we continue to open xdp support when
>> features such as GRO_HW are negotiated.
>>
>> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
>> Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
>> ---
>>   drivers/net/virtio_net.c | 30 +++++++++++++++++-------------
>>   1 file changed, 17 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index c5046d21b281..8f7d207d58d6 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -3080,14 +3080,21 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
>>          u16 xdp_qp = 0, curr_qp;
>>          int i, err;
>>
>> -       if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS)
>> -           && (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
>> -               virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6) ||
>> -               virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
>> -               virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO) ||
>> -               virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_CSUM))) {
>> -               NL_SET_ERR_MSG_MOD(extack, "Can't set XDP while host is implementing GRO_HW/CSUM, disable GRO_HW/CSUM first");
>> -               return -EOPNOTSUPP;
>> +       if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS)) {
>> +               if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_CSUM)) {
>> +                       NL_SET_ERR_MSG_MOD(extack, "Can't set XDP without frags while guest is implementing GUEST_CSUM");
>> +                       return -EOPNOTSUPP;
>> +               }
>> +
>> +               if (prog && !prog->aux->xdp_has_frags) {
>> +                       if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
>> +                           virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6) ||
>> +                           virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
>> +                           virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO)) {
>> +                               NL_SET_ERR_MSG_MOD(extack, "Can't set XDP without frags while guest is implementing GUEST_GRO_HW");
>> +                               return -EOPNOTSUPP;
>> +                       }
>> +               }
>>          }
>>
>>          if (vi->mergeable_rx_bufs && !vi->any_header_sg) {
>> @@ -3095,8 +3102,8 @@ 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) {
>> +               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;
>>          }
>> @@ -3218,9 +3225,6 @@ static int virtnet_set_features(struct net_device *dev,
>>          int err;
>>
>>          if ((dev->features ^ features) & NETIF_F_GRO_HW) {
>> -               if (vi->xdp_enabled)
>> -                       return -EBUSY;
> This seems suspicious, GRO_HW could be re-enabled accidentally even if
> it was disabled when attaching an XDP program that is not capable of
> doing multi-buffer XDP?

Yes, we shouldn't drop this check, because GRO_HW is unfriendly to xdp 
programs without xdp.frags.

Thanks.

>
> Thanks
>
>> -
>>                  if (features & NETIF_F_GRO_HW)
>>                          offloads = vi->guest_offloads_capable;
>>                  else
>> --
>> 2.19.1.6.gb485710b
>>