Interactions between speculative execution and virtual memory translation and caches are exploitable. It's not an inherent vulnerability in prediction.
Sure, as long as it’s not observable in any way, it’s not observable. But the problem is that speculation has been repeatedly been found to be observable in unexpected ways from both brands.
Amd, for example, has observability issues in all zen1/2/3 processors that leaks enough data to break KASLR that remain unpatched in all chips except for Milan (specifically epyc only, not ryzen). They didn’t expect cache ways to be visible in that fashion, and it’s observable that the model is incorrectly implemented.
the idea cannot fail, only be failed, because if it’s observable then obviously you just did it wrong.
The point was, you can engineer around problems that aren't _inherent_ in the design, but arise as an interaction between systems. You just change the rules of interaction between systems to mitigate the vulnerabilities.
So, to your original question, we're always going to have prediction, and we're going to have to solve any vulnerabilities that arise downstream. Which, thankfully, is always an available option.
