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

From: Jason Wang
Date: Sun Dec 25 2016 - 21:38:28 EST

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).


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.


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");

Acked-by: John Fastabend <john.r.fastabend@xxxxxxxxx>