virtio_net: xsk: prevent disable tx napi

Since xsk's TX queue is consumed by TX NAPI, if sq is bound to xsk, then
we must stop tx napi from being disabled.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://patch.msgid.link/20241112012928.102478-11-xuanzhuo@linux.alibaba.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: fengidri

drivers/net/virtio_net.c

@@ -5090,7 +5090,7 @@ static int virtnet_set_coalesce(struct net_device *dev,
 				struct netlink_ext_ack *extack)
 {
 	struct virtnet_info *vi = netdev_priv(dev);
-	int ret, queue_number, napi_weight;
+	int ret, queue_number, napi_weight, i;
 	bool update_napi = false;
 
 	/* Can't change NAPI weight if the link is up */
@@ -5119,6 +5119,14 @@ static int virtnet_set_coalesce(struct net_device *dev,
 		return ret;
 
 	if (update_napi) {
+		/* xsk xmit depends on the tx napi. So if xsk is active,
+		 * prevent modifications to tx napi.
+		 */
+		for (i = queue_number; i < vi->max_queue_pairs; i++) {
+			if (vi->sq[i].xsk_pool)
+				return -EBUSY;
+		}
+
 		for (; queue_number < vi->max_queue_pairs; queue_number++)
 			vi->sq[queue_number].napi.weight = napi_weight;
 	}