[PATCH mm-unstable RFC 00/26] mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE on all architectures with swap PTEs

[David Hildenbrand]

This is the follow-up on [1]:
	[PATCH v2 0/8] mm: COW fixes part 3: reliable GUP R/W FOLL_GET of
	anonymous pages

After we implemented __HAVE_ARCH_PTE_SWP_EXCLUSIVE on most prominent
enterprise architectures, implement __HAVE_ARCH_PTE_SWP_EXCLUSIVE on all
remaining architectures that support swap PTEs.

This makes sure that exclusive anonymous pages will stay exclusive, even
after they were swapped out -- for example, making GUP R/W FOLL_GET of
anonymous pages reliable. Details can be found in [1].

This primarily fixes remaining known O_DIRECT memory corruptions that can
happen on concurrent swapout, whereby we can lose DMA reads to a page
(modifying the user page by writing to it).

To verify, there are two test cases (requiring swap space, obviously):
(1) The O_DIRECT+swapout test case [2] from Andrea. This test case tries
    triggering a race condition.
(2) My vmsplice() test case [3] that tries to detect if the exclusive
    marker was lost during swapout, not relying on a race condition.


For example, on 32bit x86 (with and without PAE), my test case fails
without these patches:
	$ ./test_swp_exclusive
	FAIL: page was replaced during COW
But succeeds with these patches:
	$ ./test_swp_exclusive 
	PASS: page was not replaced during COW


Why implement __HAVE_ARCH_PTE_SWP_EXCLUSIVE for all architectures, even
the ones where swap support might be in a questionable state? This is the
first step towards removing "readable_exclusive" migration entries, and
instead using pte_swp_exclusive() also with (readable) migration entries
instead (as suggested by Peter). The only missing piece for that is
supporting pmd_swp_exclusive() on relevant architectures with THP
migration support.

As all relevant architectures now implement __HAVE_ARCH_PTE_SWP_EXCLUSIVE,,
we can drop __HAVE_ARCH_PTE_SWP_EXCLUSIVE in the last patch.


RFC because some of the swap PTE layouts are really tricky and I really
need some feedback related to deciphering these layouts and "using yet
unused PTE bits in swap PTEs". I tried cross-compiling all relevant setups
(phew, I might only miss some power/nohash variants), but only tested on
x86 so far.

CCing arch maintainers only on this cover letter and on the respective
patch(es).


[1] https://lkml.kernel.org/r/20220329164329.208407-1-david@xxxxxxxxxx
[2] https://gitlab.com/aarcange/kernel-testcases-for-v5.11/-/blob/main/page_count_do_wp_page-swap.c
[3] https://gitlab.com/davidhildenbrand/scratchspace/-/blob/main/test_swp_exclusive.c

David Hildenbrand (26):
  mm/debug_vm_pgtable: more pte_swp_exclusive() sanity checks
  alpha/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  arc/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  arm/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  csky/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  hexagon/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  ia64/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  loongarch/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  m68k/mm: remove dummy __swp definitions for nommu
  m68k/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  microblaze/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  mips/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  nios2/mm: refactor swap PTE layout
  nios2/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  openrisc/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  parisc/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  powerpc/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE on 32bit book3s
  powerpc/nohash/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  riscv/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  sh/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  sparc/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE on 32bit
  sparc/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE on 64bit
  um/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  x86/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE also on 32bit
  xtensa/mm: support __HAVE_ARCH_PTE_SWP_EXCLUSIVE
  mm: remove __HAVE_ARCH_PTE_SWP_EXCLUSIVE

 arch/alpha/include/asm/pgtable.h              | 40 ++++++++-
 arch/arc/include/asm/pgtable-bits-arcv2.h     | 26 +++++-
 arch/arm/include/asm/pgtable-2level.h         |  3 +
 arch/arm/include/asm/pgtable-3level.h         |  3 +
 arch/arm/include/asm/pgtable.h                | 34 ++++++--
 arch/arm64/include/asm/pgtable.h              |  1 -
 arch/csky/abiv1/inc/abi/pgtable-bits.h        | 13 ++-
 arch/csky/abiv2/inc/abi/pgtable-bits.h        | 19 ++--
 arch/csky/include/asm/pgtable.h               | 17 ++++
 arch/hexagon/include/asm/pgtable.h            | 36 ++++++--
 arch/ia64/include/asm/pgtable.h               | 31 ++++++-
 arch/loongarch/include/asm/pgtable-bits.h     |  4 +
 arch/loongarch/include/asm/pgtable.h          | 38 +++++++-
 arch/m68k/include/asm/mcf_pgtable.h           | 35 +++++++-
 arch/m68k/include/asm/motorola_pgtable.h      | 37 +++++++-
 arch/m68k/include/asm/pgtable_no.h            |  6 --
 arch/m68k/include/asm/sun3_pgtable.h          | 38 +++++++-
 arch/microblaze/include/asm/pgtable.h         | 44 +++++++---
 arch/mips/include/asm/pgtable-32.h            | 86 ++++++++++++++++---
 arch/mips/include/asm/pgtable-64.h            | 23 ++++-
 arch/mips/include/asm/pgtable.h               | 35 ++++++++
 arch/nios2/include/asm/pgtable-bits.h         |  3 +
 arch/nios2/include/asm/pgtable.h              | 37 ++++++--
 arch/openrisc/include/asm/pgtable.h           | 40 +++++++--
 arch/parisc/include/asm/pgtable.h             | 40 ++++++++-
 arch/powerpc/include/asm/book3s/32/pgtable.h  | 37 ++++++--
 arch/powerpc/include/asm/book3s/64/pgtable.h  |  1 -
 arch/powerpc/include/asm/nohash/32/pgtable.h  | 22 +++--
 arch/powerpc/include/asm/nohash/32/pte-40x.h  |  6 +-
 arch/powerpc/include/asm/nohash/32/pte-44x.h  | 18 +---
 arch/powerpc/include/asm/nohash/32/pte-85xx.h |  4 +-
 arch/powerpc/include/asm/nohash/64/pgtable.h  | 24 +++++-
 arch/powerpc/include/asm/nohash/pgtable.h     | 15 ++++
 arch/powerpc/include/asm/nohash/pte-e500.h    |  1 -
 arch/riscv/include/asm/pgtable-bits.h         |  3 +
 arch/riscv/include/asm/pgtable.h              | 28 ++++--
 arch/s390/include/asm/pgtable.h               |  1 -
 arch/sh/include/asm/pgtable_32.h              | 53 +++++++++---
 arch/sparc/include/asm/pgtable_32.h           | 26 +++++-
 arch/sparc/include/asm/pgtable_64.h           | 37 +++++++-
 arch/sparc/include/asm/pgtsrmmu.h             | 14 +--
 arch/um/include/asm/pgtable.h                 | 36 +++++++-
 arch/x86/include/asm/pgtable-2level.h         | 26 ++++--
 arch/x86/include/asm/pgtable-3level.h         | 26 +++++-
 arch/x86/include/asm/pgtable.h                |  3 -
 arch/xtensa/include/asm/pgtable.h             | 31 +++++--
 include/linux/pgtable.h                       | 29 -------
 mm/debug_vm_pgtable.c                         | 25 +++++-
 mm/memory.c                                   |  4 -
 mm/rmap.c                                     | 11 ---
 50 files changed, 943 insertions(+), 227 deletions(-)

-- 
2.38.1