[PATCH v2 0/3] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag

[Will Deacon]

Hi all,

This is version two of the series I originally posted here:

  https://lore.kernel.org/r/20201209163950.8494-1-will@xxxxxxxxxx

The patches allow architectures to opt-in at runtime for faultaround
mappings to be created as 'old' instead of 'young'. Although there have
been previous attempts at this, they failed either because the decision
was deferred to userspace [1] or because it was done unconditionally and
shown to regress benchmarks for particular architectures [2].

The big difference in this version is that I have reworked it based on
Kirill's patch which he posted as a follow-up to the original. However,
I can't tell where we've landed on that -- Linus seemed to like it, but
Hugh was less enthusiastic. I think that my subsequent patches are an
awful lot cleaner after the rework, but I don't think I necessarily
depend on everything in there so if that patch is likely to be a
sticking point then I can try to extract the parts I need.

Feedback welcome.

Cheers,

Will

[1] https://www.spinics.net/lists/linux-mm/msg143831.html
[2] 315d09bf30c2 ("Revert "mm: make faultaround produce old ptes"")

Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Vinayak Menon <vinmenon@xxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: <kernel-team@xxxxxxxxxxx>

--->8

Kirill A. Shutemov (1):
  mm: Cleanup faultaround and finish_fault() codepaths

Will Deacon (2):
  mm: Allow architectures to request 'old' entries when prefaulting
  arm64: mm: Implement arch_wants_old_prefaulted_pte()

 arch/arm64/include/asm/pgtable.h |  12 +-
 fs/xfs/xfs_file.c                |   6 +-
 include/linux/mm.h               |  17 ++-
 include/linux/pgtable.h          |  11 ++
 mm/filemap.c                     | 181 +++++++++++++++++++------
 mm/memory.c                      | 219 +++++++++++--------------------
 6 files changed, 251 insertions(+), 195 deletions(-)

-- 
2.29.2.729.g45daf8777d-goog