5.4 Merge window, part 1

To make things even more interesting, ARM can have three different base page sizes: 4KB, 16KB, and 64KB (this has led to some fun compatibility issues when packages autodetect and hardcode the page size during their build, for instance jemalloc: https://github.com/jemalloc/jemalloc/issues/467). In some distributions (for instance, current Fedora, if I read their kernel config correctly), the kernel is compiled to use 4KB pages; in other distributions (for instance, current RedHat, if I read their kernel config correctly), the kernel is compiled to use 64KB pages. The 52-bit addresses are only available when the kernel is compiled to use 64KB pages (which is probably why RedHat chose that option).