[PATCH v4 0/8] Create 'old' ptes for faultaround mappings on arm64 with hardware access flag

From: Will Deacon
Date: Wed Jan 20 2021 - 14:01:20 EST

Hi all,

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

v1: https://lore.kernel.org/r/20201209163950.8494-1-will@xxxxxxxxxx
v2: https://lore.kernel.org/r/20210108171517.5290-1-will@xxxxxxxxxx
v3: https://lore.kernel.org/r/20210114175934.13070-1-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 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:




[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

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: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Cc: <kernel-team@xxxxxxxxxxx>


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(-)