An unexpected perf feature

Just as an addendum... Don't get me wrong, you are right to complain that a mechanism that was usable for security purposes was removed while nobody bothered to add a suitable substitute, and that all of the pretty architectural ideas that had already been present and demonstrated to be workable for 25+ years now had been ignored, but the "proper" way going forward is not to revive segmentation but implement comparable semantics with mechanisms that are performance-neutral. SMEP and SMAP are actually quite "easy" from a hardware conceputal point of view, so it is kind of annoying that it took so long.