  We show that for a Lie group $G=\R^{n}\ltimes_{\phi} \R^{m}$ with a
semisimple action $\phi$ which has a cocompact discrete subgroup $\Gamma$, the
solvmanifold $G/\Gamma$ admits a canonical invariant formal (i.e. all products
of harmonic forms are again harmonic) metric. We show that a compact oriented
aspherical manifold of dimension less than or equal to 4 with the virtually
solvable fundamental group admits a formal metric if and only if it is
diffeomorphic to a torus or an infra-solvmanifold which is not a nilmanifold.
