Yes, that's pretty much it. A very similar technique was already used 2 years ago by Zhang et al. in their paper Cross-VM Side Channels and Their Use to Extract

Yes, that's pretty much it. A very similar technique was already used 2 years ago by Zhang et al. in their paper Cross-VM Side Channels and Their Use to Extract Private Keys [1] at CCS. [1] https://www.cs.unc.edu/~reiter/papers/2012/CCS.pdf https://www.cs.unc.edu/~reiter/papers/2012/CCS.pdf