  In this short note, we prove that a quasi-periodic torus, with a non-resonant
frequency (that can be Diophantine or Liouville) and which is invariant by a
sufficiently regular Hamiltonian flow, is KAM stable provided it is Kolmogorov
non-degenerate. When the Hamiltonian is smooth (respectively Gevrey-smooth,
respectively real-analytic), the in-variant tori are smooth (respectively
Gevrey-smooth, respectively real-analytic). This answers a question raised in a
recent work by Eliasson, Fayad and Krikorian ([EFK]). We also take the
opportunity to ask other questions concerning the stability of non-resonant
invariant quasi-periodic tori in (analytic or smooth) Hamiltonian systems.
