net/mlx5e: Attach/detach XDP program safely

When an XDP program is set, a full reopen of all channels happens in two
cases:

1. When there was no program set, and a new one is being set.

2. When there was a program set, but it's being unset.

The full reopen is necessary, because the channel parameters may change
if XDP is enabled or disabled. However, it's performed in an unsafe way:
if the new channels fail to open, the old ones are already closed, and
the interface goes down. Use the safe way to switch channels instead.
The same way is already used for other configuration changes.
Signed-off-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

drivers/net/ethernet/mellanox/mlx5/core/en_main.c

@@ -4190,8 +4190,6 @@ static int mlx5e_xdp_set(struct net_device *netdev, struct bpf_prog *prog)
 	/* no need for full reset when exchanging programs */
 	reset = (!priv->channels.params.xdp_prog || !prog);
 
-	if (was_opened && reset)
-		mlx5e_close_locked(netdev);
 	if (was_opened && !reset) {
 		/* num_channels is invariant here, so we can take the
 		 * batched reference right upfront.
@@ -4203,20 +4201,31 @@ static int mlx5e_xdp_set(struct net_device *netdev, struct bpf_prog *prog)
 		}
 	}
 
-	/* exchange programs, extra prog reference we got from caller
-	 * as long as we don't fail from this point onwards.
-	 */
-	old_prog = xchg(&priv->channels.params.xdp_prog, prog);
+	if (was_opened && reset) {
+		struct mlx5e_channels new_channels = {};
+
+		new_channels.params = priv->channels.params;
+		new_channels.params.xdp_prog = prog;
+		mlx5e_set_rq_type(priv->mdev, &new_channels.params);
+		old_prog = priv->channels.params.xdp_prog;
+
+		err = mlx5e_safe_switch_channels(priv, &new_channels, NULL);
+		if (err)
+			goto unlock;
+	} else {
+		/* exchange programs, extra prog reference we got from caller
+		 * as long as we don't fail from this point onwards.
+		 */
+		old_prog = xchg(&priv->channels.params.xdp_prog, prog);
+	}
+
 	if (old_prog)
 		bpf_prog_put(old_prog);
 
-	if (reset) /* change RQ type according to priv->xdp_prog */
+	if (!was_opened && reset) /* change RQ type according to priv->xdp_prog */
 		mlx5e_set_rq_type(priv->mdev, &priv->channels.params);
 
-	if (was_opened && reset)
-		err = mlx5e_open_locked(netdev);
-
-	if (!test_bit(MLX5E_STATE_OPENED, &priv->state) || reset)
+	if (!was_opened || reset)
 		goto unlock;
 
 	/* exchanging programs w/o reset, we update ref counts on behalf