[$] get_user_pages() and COW, 2022 edition

The numerous correctness problemswith the kernel's get_user_pages() functionality have been a fixture at the LinuxStorage, Filesystem, Memory-management and BPF Summit (LSFMM) for someyears. The 2022 eventdid not break that tradition. The first-day discussion on page pinning was covered here.On the final day, in the memory-managementtrack, David Hildenbrand led a session on the current status ofget_user_pages() and its interaction with copy-on-write (COW)memory.