[$] Seeking an API for protection keys supervisor

Memory protection keys are a CPU feature that allows additional accessrestrictions to be imposed on regions of memory and changed in a fast andefficient way. Support for protection keys in user space has been in thekernel for some time, but kernel-side protection (often called "protectionkeys supervisor" or PKS) remains unsupported - on x86, at least. At the 2022 LinuxStorage, Filesystem, Memory-management and BPF Summit (LSFMM), IraWeiny provided an update on the state of PKS and led a discussion on whatthe proper in-kernel API for PKS should be.