> Ok I think I understand the subtleties of these attacks now. But: can anyone tell me why the accessibility check for protected memory doesn't happen before th

> Ok I think I understand the subtleties of these attacks now. But: can anyone tell me why the accessibility check for protected memory doesn't happen before the cache loads the contents of RAM? If that happened then none of these attacks would be possible. If that happened, Meltdown wouldn't be possible on the processors on which it is possible. Those checks in no way mitigate against Spectre. Spectre is both simpler and in many ways more profoundly devastating -- as long as an attacker can influence the statistics that the CPU uses for branch prediction, the very act of trying to "work ahead" in another process can be influenced by the attacker, and will produce some side-effects even if you throw out the result, and those side-effects suffice to infer information about the work you did but threw out.