hv_netvsc: Fix hibernation for mlx5 VF driver

mlx5_suspend()/resume() keep the network interface, so during hibernation
netvsc_unregister_vf() and netvsc_register_vf() are not called, and hence
netvsc_resume() should call netvsc_vf_changed() to switch the data path
back to the VF after hibernation. Note: after we close and re-open the
vmbus channel of the netvsc NIC in netvsc_suspend() and netvsc_resume(),
the data path is implicitly switched to the netvsc NIC. Similarly,
netvsc_suspend() should not call netvsc_unregister_vf(), otherwise the VF
can no longer be used after hibernation.

For mlx4, since the VF network interafce is explicitly destroyed and
re-created during hibernation (see mlx4_suspend()/resume()), hv_netvsc
already explicitly switches the data path from and to the VF automatically
via netvsc_register_vf() and netvsc_unregister_vf(), so mlx4 doesn't need
this fix. Note: mlx4 can still work with the fix because in
netvsc_suspend()/resume() ndev_ctx->vf_netdev is NULL for mlx4.

Fixes: 0efeea5 ("hv_netvsc: Add the support of hibernation")
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/hyperv/netvsc_drv.c

@@ -2587,8 +2587,8 @@ static int netvsc_remove(struct hv_device *dev)
 static int netvsc_suspend(struct hv_device *dev)
 {
 	struct net_device_context *ndev_ctx;
-	struct net_device *vf_netdev, *net;
 	struct netvsc_device *nvdev;
+	struct net_device *net;
 	int ret;
 
 	net = hv_get_drvdata(dev);
@@ -2604,10 +2604,6 @@ static int netvsc_suspend(struct hv_device *dev)
 		goto out;
 	}
 
-	vf_netdev = rtnl_dereference(ndev_ctx->vf_netdev);
-	if (vf_netdev)
-		netvsc_unregister_vf(vf_netdev);
-
 	/* Save the current config info */
 	ndev_ctx->saved_netvsc_dev_info = netvsc_devinfo_get(nvdev);
 
@@ -2623,6 +2619,7 @@ static int netvsc_resume(struct hv_device *dev)
 	struct net_device *net = hv_get_drvdata(dev);
 	struct net_device_context *net_device_ctx;
 	struct netvsc_device_info *device_info;
+	struct net_device *vf_netdev;
 	int ret;
 
 	rtnl_lock();
@@ -2635,6 +2632,15 @@ static int netvsc_resume(struct hv_device *dev)
 	netvsc_devinfo_put(device_info);
 	net_device_ctx->saved_netvsc_dev_info = NULL;
 
+	/* A NIC driver (e.g. mlx5) may keep the VF network interface across
+	 * hibernation, but here the data path is implicitly switched to the
+	 * netvsc NIC since the vmbus channel is closed and re-opened, so
+	 * netvsc_vf_changed() must be used to switch the data path to the VF.
+	 */
+	vf_netdev = rtnl_dereference(net_device_ctx->vf_netdev);
+	if (vf_netdev && netvsc_vf_changed(vf_netdev) != NOTIFY_OK)
+		ret = -EINVAL;
+
 	rtnl_unlock();
 
 	return ret;