netdev - Re: [net PATCH] net: virtio: cap mtu when XDP programs are running

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Message-ID: <402027b4-58c7-aa1b-5079-74e31448f544@redhat.com>
Date:   Tue, 3 Jan 2017 14:14:47 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     John Fastabend <john.fastabend@...il.com>, mst@...hat.com
Cc:     john.r.fastabend@...el.com, netdev@...r.kernel.org,
        alexei.starovoitov@...il.com, daniel@...earbox.net
Subject: Re: [net PATCH] net: virtio: cap mtu when XDP programs are running



On 2017年01月03日 06:30, 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.
>
> This patch sets/clears the max_mtu value at XDP load/unload time.
>
> Signed-off-by: John Fastabend <john.r.fastabend@...el.com>
> ---
>   drivers/net/virtio_net.c |    9 ++++++---
>   1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 5deeda6..783e842 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1699,6 +1699,9 @@ 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 int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>   {
>   	unsigned long int max_sz = PAGE_SIZE - sizeof(struct padded_vnet_hdr);
> @@ -1748,6 +1751,9 @@ 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;

Or use ETH_DATA_LEN here consider we only allocate a size of 
GOOD_PACKET_LEN for each small buffer?

Thanks

>   	}
>   
>   	vi->xdp_queue_pairs = xdp_qp;
> @@ -2133,9 +2139,6 @@ 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;
>