[0/2] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag

Message

Will Deacon Dec. 9, 2020, 4:39 p.m. UTC

Hi folks,

This series allows 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].

Since this patch has demonstrated considerable benefits for arm64-based
Android devices with hardware access flag capabilities, patch two enables
this functionality there.

Cheers,

Will

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

Cc: Catalin Marinas <[e-mail]>
Cc: Jan Kara <[e-mail]>
Cc: Minchan Kim <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Kirill A. Shutemov <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Vinayak Menon <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: <[e-mail]>

--->8

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

 arch/arm64/include/asm/cpufeature.h | 12 +++++++++++
 arch/arm64/include/asm/pgtable.h    |  8 +++++++-
 include/linux/mm.h                  |  5 ++++-
 mm/memory.c                         | 31 ++++++++++++++++++++++++++---
 4 files changed, 51 insertions(+), 5 deletions(-)