"Good" speculative execution shouldn't be able to speculate isolated memory - isolation does work against Spectre. Meltdown-type exploits (Older Intel and arm)

"Good" speculative execution shouldn't be able to speculate isolated memory - isolation does work against Spectre. Meltdown-type exploits (Older Intel and arm) can "see" across this isolation in some cases, which is why they were such an egregious mistake. Spectre is kind of inevitable whereas Meltdown isn't.