Re: [PATCH net 7/9] virtio-net: forbid XDP when VIRTIO_NET_F_GUEST_UFO is support

[Jason Wang]

On 2016å12æ24æ 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@xxxxxxxxx>
> > > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > > ---
> > >   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@xxxxxxxxx>