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Subject: Re: [PATCH bpf-next v6 1/2] virtio_net: keep vnet header zeroed if
 XDP is loaded for small buffer
To:     Yuya Kusakabe <yuya.kusakabe@gmail.com>
Cc:     andriin@fb.com, ast@kernel.org, bpf@vger.kernel.org,
        daniel@iogearbox.net, davem@davemloft.net, hawk@kernel.org,
        john.fastabend@gmail.com, kafai@fb.com, kuba@kernel.org,
        linux-kernel@vger.kernel.org, mst@redhat.com,
        netdev@vger.kernel.org, songliubraving@fb.com, yhs@fb.com
References: <20200225033103.437305-1-yuya.kusakabe@gmail.com>
 <20200225033212.437563-1-yuya.kusakabe@gmail.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <1b3045d0-edc0-3f6f-5442-06f6f927ff94@redhat.com>
Date:   Tue, 25 Feb 2020 13:44:53 +0800
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On 2020/2/25 =E4=B8=8A=E5=8D=8811:32, 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 b=
uffer")
> Signed-off-by: Yuya Kusakabe <yuya.kusakabe@gmail.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_d=
evice *dev,
>   	}
>   	skb_reserve(skb, headroom - delta);
>   	skb_put(skb, len);
> -	if (!delta) {
> +	if (!xdp_prog) {
>   		buf +=3D 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 */
>  =20
>   err:
>   	return skb;


Acked-by: Jason Wang <jasowang@redhat.com>