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Subject: Re: [net PATCH 2/4] virtio_net: fix XDP code path in receive_small()
To: Jesper Dangaard Brouer <brouer@redhat.com>,
        Jason Wang <jasowang@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>, netdev@vger.kernel.org,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Saeed Mahameed <saeedm@mellanox.com>,
        Daniel Borkmann <borkmann@iogearbox.net>,
        "David S. Miller" <davem@davemloft.net>,
        Tariq Toukan <tariqt@mellanox.com>
References: <151913348634.28247.17519468037896960567.stgit@firesoul>
 <151913352995.28247.4449049695120368682.stgit@firesoul>
From: John Fastabend <john.fastabend@gmail.com>
Message-ID: <8532eda0-94fa-44e2-d73e-b7b14a13b9ab@gmail.com>
Date: Tue, 20 Feb 2018 08:57:18 -0800
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On 02/20/2018 05:32 AM, Jesper Dangaard Brouer wrote:
> When configuring virtio_net to use the code path 'receive_small()',
> in-order to get correct XDP_REDIRECT support, I discovered TCP packets
> would get silently dropped when loading an XDP program action XDP_PASS.
> 
> The bug seems to be that receive_small() when XDP is loaded check that
> hdr->hdr.flags is zero, which seems wrong as hdr.flags contains the
> flags VIRTIO_NET_HDR_F_* :
>  #define VIRTIO_NET_HDR_F_NEEDS_CSUM 1 /* Use csum_start, csum_offset */
>  #define VIRTIO_NET_HDR_F_DATA_VALID 2 /* Csum is valid */
> 
> TCP got dropped as it had the VIRTIO_NET_HDR_F_DATA_VALID flag set.
> 
> The flags that are relevant here are the VIRTIO_NET_HDR_GSO_* flags
> stored in hdr->hdr.gso_type. Thus, the fix is just check that none of
> the gso_type flags have been set.
> 
> Fixes: bb91accf2733 ("virtio-net: XDP support for small buffers")
> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> ---

Acked-by: John Fastabend <john.fastabend@gmail.com>

Thanks!

>  drivers/net/virtio_net.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 0ca91942a884..10c8fc46b588 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -558,7 +558,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
>  		void *orig_data;
>  		u32 act;
>  
> -		if (unlikely(hdr->hdr.gso_type || hdr->hdr.flags))
> +		if (unlikely(hdr->hdr.gso_type))
>  			goto err_xdp;
>  
>  		if (unlikely(xdp_headroom < virtnet_get_headroom(vi))) {
>