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

[Huacai Chen]

On Sun, Dec 18, 2022 at 5:59 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
>
> On 18.12.22 04:32, Huacai Chen wrote:
> > 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
> > ...
>
> Hi Huacai,
>
> thanks for having a look!
>
> Please note that this series doesn't add these primitives but merely
> implements them on all remaining architectures.
>
> Having that said, the semantics are "exclusive" vs. "maybe shared", not
> "exclusive" vs. "shared" or sth. else. It would have to be
> pte_swp_mkmaybe_shared().
>
>
> Note that this naming matches just the way we handle it for the other
> pte_swp_ flags we have, namely:
>
> pte_swp_mksoft_dirty()
> pte_swp_soft_dirty()
> pte_swp_clear_soft_dirty()
>
> and
>
> pte_swp_mkuffd_wp()
> pte_swp_uffd_wp()
> pte_swp_clear_uffd_wp()
>
>
> For example, we also (thankfully) didn't call it pte_mksoft_clean().
> Grepping for "pte_swp.*soft_dirty" gives you the full picture.
>
> Thanks!
OK, got it.

Huacai
>
> David
>
> >
> > 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
> >>
> >>
> >
>
> --
> Thanks,
>
> David / dhildenb
>