On Wed, Jan 04, 2017 at 07:11:18PM -0800, John Fastabend wrote:
> XDP programs can not consume multiple pages so we cap the MTU to
> avoid this case. Virtio-net however only checks the MTU at XDP
> program load and does not block MTU changes after the program
> has loaded.
Do drivers really have to tweak max mtu all the time?
Seems strange, I would say drivers just report device caps
and net core enforces rules.
Can't net core do these checks?
>
> This patch sets/clears the max_mtu value at XDP load/unload time.
>
> Signed-off-by: John Fastabend <john.r.fastab...@intel.com>
> ---
> drivers/net/virtio_net.c | 26 ++++++++++++++++++++++----
> 1 file changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 4a10500..261103d9 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1699,11 +1699,28 @@ static void virtnet_init_settings(struct net_device
> *dev)
> .set_settings = virtnet_set_settings,
> };
>
> +#define MIN_MTU ETH_MIN_MTU
> +#define MAX_MTU ETH_MAX_MTU
> +
> +static unsigned long int virtnet_xdp_mtu(struct bpf_prog *prog,
> + struct virtnet_info *vi)
> +{
> + if (!prog && virtio_has_feature(vi->vdev, VIRTIO_NET_F_MTU))
> + return virtio_cread16(vi->vdev,
> + offsetof(struct virtio_net_config, mtu));
> + else if (!prog)
> + return ETH_MAX_MTU;
> + else if (vi->mergeable_rx_bufs)
> + return PAGE_SIZE - sizeof(struct padded_vnet_hdr);
> + else
> + return GOOD_PACKET_LEN;
> +}
> +
> static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
> {
> - unsigned long int max_sz = PAGE_SIZE - sizeof(struct padded_vnet_hdr);
> struct virtnet_info *vi = netdev_priv(dev);
> struct bpf_prog *old_prog;
> + unsigned long int max_sz;
> u16 xdp_qp = 0, curr_qp;
> int i, err;
>
> @@ -1720,6 +1737,7 @@ static int virtnet_xdp_set(struct net_device *dev,
> struct bpf_prog *prog)
> return -EINVAL;
> }
>
> + max_sz = virtnet_xdp_mtu(prog, vi);
> if (dev->mtu > max_sz) {
> netdev_warn(dev, "XDP requires MTU less than %lu\n", max_sz);
> return -EINVAL;
> @@ -1748,6 +1766,9 @@ static int virtnet_xdp_set(struct net_device *dev,
> struct bpf_prog *prog)
> virtnet_set_queues(vi, curr_qp);
> return PTR_ERR(prog);
> }
> + dev->max_mtu = max_sz;
> + } else {
> + dev->max_mtu = ETH_MAX_MTU;
> }
>
> vi->xdp_queue_pairs = xdp_qp;
> @@ -2133,9 +2154,6 @@ static bool virtnet_validate_features(struct
> virtio_device *vdev)
> return true;
> }
>
> -#define MIN_MTU ETH_MIN_MTU
> -#define MAX_MTU ETH_MAX_MTU
> -
> static int virtnet_probe(struct virtio_device *vdev)
> {
> int i, err;
