I think the main takeaway should be "speculative execution creates exploitable side-channels, and you should assume your hardware is exploitable until proven otherwise." AMD and ARM are probably still exploitable with unknown exploits, possibly even at Meltdown-levels of exploitability, but people haven't taken the time to reverse-engineer the microarchitecture enough to find the exploits.
If I were developing processors, I'd be having emergency meetings on trying to craft exploits to figure out where our processors' weaknesses are. While being happy that Intel is getting all the bad PR for this and I'm not.
AIUI the fundamental difference between Meltdown and Spectre is Meltdown involves speculating execution that loads memory across privilege domains and Spectre doesn't. If both AMD and ARM won't speculate memory loads across privilege domains, then it sounds like they're strictly immune to Meltdown.
> main takeaway should be "speculative execution creates exploitable side-channels, and you should assume your hardware is exploitable until proven otherwise."
Speculative execution does not create side-channels in and of itself, side effects of speculative execution does that. In this case the side effect of cache state. Just don't change the cache during speculative execution and there's no problem.
And roll them back? It can, but it doesn't for performance reasons. What the performance impact would be is unknown but this requires a silicon change so unless you work at Intel you'll probably never know.
If I were developing processors, I'd be having emergency meetings on trying to craft exploits to figure out where our processors' weaknesses are. While being happy that Intel is getting all the bad PR for this and I'm not.