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

[Huacai Chen]

Hi, David,

What is the opposite of exclusive here? Shared or inclusive? I prefer
pte_swp_mkshared() or pte_swp_mkinclusive() rather than
pte_swp_clear_exclusive(). Existing examples: dirty/clean, young/old
...

Huacai

On Tue, Dec 6, 2022 at 10:48 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> 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
>
>