No. Process isolation still works, assuming your CPU is not broken. The real mitigation is that going forwards, you have to assume that any attacker-controlled

No. Process isolation still works, assuming your CPU is not broken. The real mitigation is that going forwards, you have to assume that any attacker-controlled code always has full read access to the entire process it runs in, and you need to architect your systems so that this does not result in any bad things. It is entirely possible to do this. You can still have branch prediction and caches, which is a very good thing, because not having those would cut the performance of modern CPUs to less than 1% of what it currently is.