netdev - Re: [PATCH bpf-next v6 1/2] virtio_net: keep vnet header zeroed if XDP is loaded for small buffer

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Date:   Tue, 25 Feb 2020 06:18:01 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Yuya Kusakabe <yuya.kusakabe@...il.com>
Cc:     jasowang@...hat.com, andriin@...com, ast@...nel.org,
        bpf@...r.kernel.org, daniel@...earbox.net, davem@...emloft.net,
        hawk@...nel.org, john.fastabend@...il.com, kafai@...com,
        kuba@...nel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, songliubraving@...com, yhs@...com
Subject: Re: [PATCH bpf-next v6 1/2] virtio_net: keep vnet header zeroed if
 XDP is loaded for small buffer

On Tue, Feb 25, 2020 at 12:32:11PM +0900, Yuya Kusakabe wrote:
> We do not want to care about the vnet header in receive_small() if XDP
> is loaded, since we can not know whether or not the packet is modified
> by XDP.
> 
> Fixes: f6b10209b90d ("virtio-net: switch to use build_skb() for small buffer")
> Signed-off-by: Yuya Kusakabe <yuya.kusakabe@...il.com>

Acked-by: Michael S. Tsirkin <mst@...hat.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 2fe7a3188282..f39d0218bdaa 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -735,10 +735,10 @@ static struct sk_buff *receive_small(struct net_device *dev,
>  	}
>  	skb_reserve(skb, headroom - delta);
>  	skb_put(skb, len);
> -	if (!delta) {
> +	if (!xdp_prog) {
>  		buf += header_offset;
>  		memcpy(skb_vnet_hdr(skb), buf, vi->hdr_len);
> -	} /* keep zeroed vnet hdr since packet was changed by bpf */
> +	} /* keep zeroed vnet hdr since XDP is loaded */
>  
>  err:
>  	return skb;
> -- 
> 2.24.1