Gromov's positivity conjecture for the Gromov norm

Let $M$ be a closed, nonpositively curved, locally symmetric manifold with no local $\mathbb{R}$ factors. The Gromov norm of $M$, namely the simplicial volume, is positive. Gromov's positivity conjecture.

$$\|M\|>0.$$

The source presents this as a related conjecture attributed to Gromov; no resolution is supplied in the given text.