netdev - Re: [PATCH v3 2/9] virtio-net: set up xdp for multi buffer packets

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Message-ID: <8ae89098-594f-b28b-4040-b0625b816e14@linux.alibaba.com>
Date:   Mon, 9 Jan 2023 10:48:05 +0800
From:   Heng Qi <hengqi@...ux.alibaba.com>
To:     Jason Wang <jasowang@...hat.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     "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>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH v3 2/9] virtio-net: set up xdp for multi buffer packets



在 2023/1/3 下午2:40, Heng Qi 写道:
> When the xdp program sets xdp.frags, which means it can process
> multi-buffer packets over larger MTU, so we continue to support xdp.
> But for single-buffer xdp, we should keep checking for MTU.
>
> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>   drivers/net/virtio_net.c | 10 ++++++----
>   1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 443aa7b8f0ad..60e199811212 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3074,7 +3074,9 @@ static int virtnet_restore_guest_offloads(struct virtnet_info *vi)
>   static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
>   			   struct netlink_ext_ack *extack)
>   {
> -	unsigned long int max_sz = PAGE_SIZE - sizeof(struct padded_vnet_hdr);
> +	unsigned int room = SKB_DATA_ALIGN(VIRTIO_XDP_HEADROOM +
> +					   sizeof(struct skb_shared_info));
> +	unsigned int max_sz = PAGE_SIZE - room - ETH_HLEN;

Hi Jason, I've updated the calculation of 'max_sz' in this patch instead 
of a separate bugfix, since doing so also seemed clear.

Thanks.

>   	struct virtnet_info *vi = netdev_priv(dev);
>   	struct bpf_prog *old_prog;
>   	u16 xdp_qp = 0, curr_qp;
> @@ -3095,9 +3097,9 @@ 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");
> -		netdev_warn(dev, "XDP requires MTU less than %lu\n", max_sz);
> +	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, "single-buffer XDP requires MTU less than %u\n", max_sz);
>   		return -EINVAL;
>   	}
>