  On a closed connected oriented manifold $M$ we study the space
$\mathcal{M}_\|(M)$ of all Riemannian metrics which admit a non-zero parallel
spinor on the universal covering. Such metrics are Ricci-flat, and all known
Ricci-flat metrics are of this form. We show the following: The space
$\mathcal{M}_\|(M)$ is a smooth submanifold of the space of all metrics, and
its premoduli space is a smooth finite-dimensional manifold. The holonomy group
is locally constant on $\mathcal{M}_\|(M)$. If $M$ is spin, then the dimension
of the space of parallel spinors is a locally constant function on
$\mathcal{M}_\|(M)$.
