[$] get_user_pages() and COW, 2022 edition

The numerous correctness problems
with the kernel's
get_user_pages() functionality have been a fixture at the Linux
Storage, Filesystem, Memory-management and BPF Summit (LSFMM) for some
years. The 2022 event
did not break that tradition. The first-day discussion on page pinning
was covered here.
On the final day, in the memory-management
track, David Hildenbrand led a session on the current status of
get_user_pages() and its interaction with copy-on-write (COW)
memory.