[$] Generalizing address-space isolation

Linux systems have traditionally run with a single address space thatis shared by user and kernel space. That changed with the advent of theMeltdown vulnerability, which forced the merging of kernel page-table isolation (KPTI) at the end of2017. But, Mike Rapoport said during his 2019Open Source Summit Europe talk, that may not be the end of the story for address-space isolation.There is a good case to be made for increasing the separation of addressspaces, but implementing that may require some fundamental changes in howkernel memory management works.