vdpa/mlx5: Fix is_index_valid() to refer to features

Make sure the decision whether an index received through a callback is
valid or not consults the negotiated features.

The motivation for this was due to a case encountered where I shut down
the VM. After the reset operation was called features were already
clear, I got get_vq_state() call which caused out array bounds
access since is_index_valid() reported the index value.

So this is more of not hit a bug since the call shouldn't have been made
first place.

Signed-off-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20220111183400.38418-4-elic@nvidia.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Si-Wei Liu<si-wei.liu@oracle.com>
Acked-by: Jason Wang <jasowang@redhat.com>

drivers/vdpa/mlx5/net/mlx5_vnet.c

@@ -133,10 +133,14 @@ struct mlx5_vdpa_virtqueue {
 
 static bool is_index_valid(struct mlx5_vdpa_dev *mvdev, u16 idx)
 {
-	if (unlikely(idx > mvdev->max_idx))
-		return false;
+	if (!(mvdev->actual_features & BIT_ULL(VIRTIO_NET_F_MQ))) {
+		if (!(mvdev->actual_features & BIT_ULL(VIRTIO_NET_F_CTRL_VQ)))
+			return idx < 2;
+		else
+			return idx < 3;
+	}
 
-	return true;
+	return idx <= mvdev->max_idx;
 }
 
 struct mlx5_vdpa_net {