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

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Date:   Tue, 6 Dec 2022 13:29:42 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Heng Qi <hengqi@...ux.alibaba.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

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?

Thanks

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