Create 'old' ptes for faultaround mappings on arm64 with hardware access flag

Hi all,

This is version four of the patches I previously posted here:

v1: https://lore.kernel.org/r/[email protected]
v2: https://lore.kernel.org/r/[email protected]
v3: https://lore.kernel.org/r/[email protected]

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 change since v3 is that the immutable fields of 'struct vm_fault' now live in a 'const' anonymous struct. Although Clang will silently accept modifications to these fields [3], GCC emits an error. The resulting diffstat is _considerably_ more manageable with this approach.

As before, I've also updated this branch:

https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/log/?h=faultaround

Cheers,

Will

[1] https://www.spinics.net/lists/linux-mm/msg143831.html
[2] 315d09bf30c2 ("Revert "mm: make faultaround produce old ptes"")
[3] https://bugs.llvm.org/show_bug.cgi?id=48755

--->8

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

Will Deacon (7):
mm: Allow architectures to request 'old' entries when prefaulting
arm64: mm: Implement arch_wants_old_prefaulted_pte()
mm: Move immutable fields of 'struct vm_fault' into anonymous struct
mm: Pass 'address' to map to do_set_pte() and drop FAULT_FLAG_PREFAULT
mm: Avoid modifying vmf.address in __collapse_huge_page_swapin()
mm: Use static initialisers for immutable fields of 'struct vm_fault'
mm: Mark anonymous struct field of 'struct vm_fault' as 'const'

 arch/arm64/include/asm/pgtable.h |  12 +-
 fs/xfs/xfs_file.c                |   6 +-
 include/linux/mm.h               |  25 ++--
 include/linux/pgtable.h          |  11 ++
 mm/filemap.c                     | 178 ++++++++++++++++++------
 mm/khugepaged.c                  |  37 +++--
 mm/memory.c                      | 223 +++++++++++--------------------
 mm/shmem.c                       |   6 +-
 mm/swapfile.c                    |  11 +-
 9 files changed, 280 insertions(+), 229 deletions(-)

2.30.0.284.gd98b1dd5eaa7-goog