[eli_gottlieb]

If any quantity about what the processor does, outside the intended effect, has a different distribution when X happens versus Y, then the distribution of that quantity is exploitable. Period.

Any nonuniform distribution in any quantity that is not part of the spec is exploitable!

[_0w8t]

It is only exploitable if one can measure the difference and extract useful information. Until Spectre guys discovered the double read technique, the expectation was that speculative execution did not allow to extract useful information besides extremely artificial theoretical cases.