netdev - Re: [PATCH v2 1/9] virtio_net: disable the hole mechanism for xdp

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Date:   Tue, 27 Dec 2022 14:30:10 +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 1/9] virtio_net: disable the hole mechanism for xdp


在 2022/12/20 22:14, Heng Qi 写道:
> XDP core assumes that the frame_size of xdp_buff and the length of
> the frag are PAGE_SIZE. The hole may cause the processing of xdp to
> fail, so we disable the hole mechanism when xdp is set.
>
> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>   drivers/net/virtio_net.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 9cce7dec7366..443aa7b8f0ad 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1419,8 +1419,11 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
>   		/* To avoid internal fragmentation, if there is very likely not
>   		 * enough space for another buffer, add the remaining space to
>   		 * the current buffer.
> +		 * XDP core assumes that frame_size of xdp_buff and the length
> +		 * of the frag are PAGE_SIZE, so we disable the hole mechanism.
>   		 */
> -		len += hole;
> +		if (!headroom)
> +			len += hole;


Is this only a requirement of multi-buffer XDP? If not, it need to be 
backported to stable.

Thanks


>   		alloc_frag->offset += hole;
>   	}
>