virtio-net: set up xdp for multi buffer packets

When the xdp program sets xdp.frags, which means it can process
multi-buffer packets over larger MTU, so we continue to support xdp.

Signed-off-by: Heng Qi <hengqi@linux.alibaba.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: Heng Qi

drivers/net/virtio_net.c

@@ -3106,9 +3106,9 @@ static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
 		return -EINVAL;
 	}
 
-	if (dev->mtu > max_sz) {
-		NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP");
-		netdev_warn(dev, "XDP requires MTU less than %u\n", max_sz);
+	if (prog && !prog->aux->xdp_has_frags && dev->mtu > max_sz) {
+		NL_SET_ERR_MSG_MOD(extack, "MTU too large to enable XDP without frags");
+		netdev_warn(dev, "single-buffer XDP requires MTU less than %u\n", max_sz);
 		return -EINVAL;
 	}