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Date:   Mon, 26 Dec 2016 10:38:16 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     John Fastabend <john.fastabend@...il.com>, mst@...hat.com,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     john.r.fastabend@...el.com
Subject: Re: [PATCH net 7/9] virtio-net: forbid XDP when
 VIRTIO_NET_F_GUEST_UFO is support



On 2016年12月24日 00:10, John Fastabend wrote:
> On 16-12-23 08:02 AM, John Fastabend wrote:
>> On 16-12-23 06:37 AM, Jason Wang wrote:
>>> When VIRTIO_NET_F_GUEST_UFO is negotiated, host could still send UFO
>>> packet that exceeds a single page which could not be handled
>>> correctly by XDP. So this patch forbids setting XDP when GUEST_UFO is
>>> supported. While at it, forbid XDP for ECN (which comes only from GRO)
>>> too to prevent user from misconfiguration.
>>>
> Is sending packets greater than single page though normal in this case?

Yes, when NETIF_F_UFO was enabled for tap, it won't segment UFO packet 
and will send it directly to guest. (This could be reproduced with 
UDP_STREAM between two guests or host to guest).

Thanks

> I don't have any need to support big packet mode other than MST asked
> for it. And I wasn't seeing this in my tests. MTU is capped at 4k - hdr
> when XDP is enabled.
>
> .John
>
>>> Cc: John Fastabend <john.r.fastabend@...el.com>
>>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>>> ---
>>>   drivers/net/virtio_net.c | 4 +++-
>>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>>> index 77ae358..c1f66d8 100644
>>> --- a/drivers/net/virtio_net.c
>>> +++ b/drivers/net/virtio_net.c
>>> @@ -1684,7 +1684,9 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog)
>>>   	int i, err;
>>>   
>>>   	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
>>> -	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6)) {
>>> +	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6) ||
>>> +	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
>>> +	    virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO)) {
>>>   		netdev_warn(dev, "can't set XDP while host is implementing LRO, disable LRO first\n");
>>>   		return -EOPNOTSUPP;
>>>   	}
>>>
>> Acked-by: John Fastabend <john.r.fastabend@...el.com>
>>

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