[PATCH v5 0/4] mm: userfaultfd: refactor and add UFFDIO_CONTINUE_MODE_WP

[Axel Rasmussen <axelrasmussen@google.com>]

This series, currently based on 6.3-rc1, is divided into two parts:

- Commits 1-3 refactor userfaultfd ioctl code without behavior changes, with the
  main goal of improving consistency and reducing the number of function args.
- Commit 4 adds UFFDIO_CONTINUE_MODE_WP.

The refactors are sorted by increasing controversial-ness, the idea being we
could drop some of the refactors if they are deemed not worth it.

Changelog:

v4->v5:
 - rename "uffd_flags_has_mode" to "uffd_flags_mode_is"
 - modify "uffd_flags_set_mode" to clear mode bits before setting new mode
 - update userfaultfd documentation to describe new mode flag

v3->v4:
 - massage the uffd_flags_t implementation to eliminate all sparse warnings
 - add a couple inline helpers to make uffd_flags_t usage easier
 - drop the refactor passing `struct uffdio_range *` around (previously 4/5)
 - define a temporary `struct mm_struct *` in function with >=3 `vma->vm_mm`
 - consistent argument order between `flags` and `pagep`
 - expand on the use case in patch 4/4 message

v2->v3:
 - rebase onto 6.3-rc1
 - typedef a new type for mfill flags in patch 3/5 (suggested by Nadav)

v1->v2:
 - refactor before adding the new flag, to avoid perpetuating messiness

Axel Rasmussen (4):
  mm: userfaultfd: rename functions for clarity + consistency
  mm: userfaultfd: don't pass around both mm and vma
  mm: userfaultfd: combine 'mode' and 'wp_copy' arguments
  mm: userfaultfd: add UFFDIO_CONTINUE_MODE_WP to install WP PTEs

 Documentation/admin-guide/mm/userfaultfd.rst |   8 +
 fs/userfaultfd.c                             |  29 ++--
 include/linux/hugetlb.h                      |  27 ++-
 include/linux/shmem_fs.h                     |   9 +-
 include/linux/userfaultfd_k.h                |  69 +++++---
 include/uapi/linux/userfaultfd.h             |   7 +
 mm/hugetlb.c                                 |  28 +--
 mm/shmem.c                                   |  14 +-
 mm/userfaultfd.c                             | 170 +++++++++----------
 tools/testing/selftests/mm/userfaultfd.c     |   4 +
 10 files changed, 196 insertions(+), 169 deletions(-)

--
2.40.0.rc1.284.g88254d51c5-goog