Last time I said as it was undecidable it is actually Semi Decidable. We can't really say. As the condition M1 <M2 so Semi Decidability is satisfied. Hence, M1 is reduciblie to M2 is recursive enumerable.
One way theorem satisfies these conditions of semi-decidability are:
1. P <--- P
2. NP <---- NP
3. Recursive Enumerable <---- Recursive enumerable
4. Recursive lang <--- Recursive Language