netdev - Re: [PATCH v2 2/9] virtio_net: set up xdp for multi buffer packets

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Message-ID: <82eb2ffc-ce97-0c76-f7bc-8a163968cde7@redhat.com>
Date:   Tue, 27 Dec 2022 14:32:22 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Heng Qi <hengqi@...ux.alibaba.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 v2 2/9] virtio_net: set up xdp for multi buffer packets


在 2022/12/20 22:14, 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 | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 443aa7b8f0ad..c5c4e9db4ed3 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3095,8 +3095,8 @@ 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) {


Not related to this patch, but I see:

         unsigned long int max_sz = PAGE_SIZE - sizeof(struct 
padded_vnet_hdr);

Which is suspicious, do we need to count reserved headroom/tailroom as well?

Thanks


> +		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;
>   	}