[$] More timing side-channels for the page cache

In 2019, researchers published a way toidentify which file-backed pageswere being accessed on a system using timing information from the page cache,leading to a handful of unpleasant consequences and a change to the design ofthemincore() system call. Discussion at the timeled to a number of ad-hoc patches to address theproblem. The lack of new page-cache attacks suggested that attempts to fixthings in a piecemeal fashion had succeeded. Now, however, Sudheendra Raghav Neela,Jonas Juffinger, Lukas Maar, and Daniel Gruss havefound a new set ofholes in the Linux kernel's page-cache-timing protections that allowthe same general class of attack.