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

Jason Wang
2022-12-06T05:31:03Z

On Tue, Nov 22, 2022 at 3:44 PM Heng Qi <hengqi@linux.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@linux.alibaba.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@linux.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
>