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

Huacai Chen
2022-12-18T03:33:26Z

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@redhat.com> 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@redhat.com
> [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
>
>