Re: [PATCH v5 0/9] Merge arm64/riscv hugetlbfs contpte support

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 21/03/2025 à 14:06, Alexandre Ghiti a écrit :
> This patchset intends to merge the contiguous ptes hugetlbfs implementation
> of arm64 and riscv.

Can we also add powerpc in the dance ?

powerpc also use contiguous PTEs allthough there is not (yet) a special 
name for it:
- b250c8c08c79 powerpc/8xx: Manage 512k huge pages as standard pages
- e47168f3d1b1 powerpc/8xx: Support 16k hugepages with 4k pages

powerpc also use configuous PMDs/PUDs for larger hugepages:
- 57fb15c32f4f ("powerpc/64s: use contiguous PMD/PUD instead of HUGEPD")
- 7c44202e3609 ("powerpc/e500: use contiguous PMD instead of hugepd")
- 0549e7666373 ("powerpc/8xx: rework support for 8M pages using 
contiguous PTE entries")

Christophe

> 
> Both arm64 and riscv support the use of contiguous ptes to map pages that
> are larger than the default page table size, respectively called contpte
> and svnapot.
> 
> The riscv implementation differs from the arm64's in that the LSBs of the
> pfn of a svnapot pte are used to store the size of the mapping, allowing
> for future sizes to be added (for now only 64KB is supported). That's an
> issue for the core mm code which expects to find the *real* pfn a pte points
> to. Patch 1 fixes that by always returning svnapot ptes with the real pfn
> and restores the size of the mapping when it is written to a page table.
> 
> The following patches are just merges of the 2 different implementations
> that currently exist in arm64 and riscv which are very similar. It paves
> the way to the reuse of the recent contpte THP work by Ryan [1] to avoid
> reimplementing the same in riscv.
> 
> This patchset was tested by running the libhugetlbfs testsuite with 64KB
> and 2MB pages on both architectures (on a 4KB base page size arm64 kernel).
> 
> [1] https://lore.kernel.org/linux-arm-kernel/20240215103205.2607016-1-ryan.roberts@arm.com/
> 
> v4: https://lore.kernel.org/linux-riscv/20250127093530.19548-1-alexghiti@rivosinc.com/
> v3: https://lore.kernel.org/all/20240802151430.99114-1-alexghiti@rivosinc.com/
> v2: https://lore.kernel.org/linux-riscv/20240508113419.18620-1-alexghiti@rivosinc.com/
> v1: https://lore.kernel.org/linux-riscv/20240301091455.246686-1-alexghiti@rivosinc.com/
> 
> Changes in v5:
>    - Fix "int i" unused variable in patch 2 (as reported by PW)
>    - Fix !svnapot build
>    - Fix arch_make_huge_pte() which returned a real napot pte
>    - Make __ptep_get(), ptep_get_and_clear() and __set_ptes() napot aware to
>      avoid leaking real napot pfns to core mm
>    - Fix arch_contpte_get_num_contig() that used to always try to get the
>      mapping size from the ptep, which does not work if the ptep comes the core mm
>    - Rebase on top of 6.14-rc7 + fix for
>      huge_ptep_get_and_clear()/huge_pte_clear()
>      https://lore.kernel.org/linux-riscv/20250317072551.572169-1-alexghiti@rivosinc.com/
> 
> Changes in v4:
>    - Rebase on top of 6.13
> 
> Changes in v3:
>    - Split set_ptes and ptep_get into internal and external API (Ryan)
>    - Rename ARCH_HAS_CONTPTE into ARCH_WANT_GENERAL_HUGETLB_CONTPTE so that
>      we split hugetlb functions from contpte functions (actually riscv contpte
>      functions to support THP will come into another series) (Ryan)
>    - Rebase on top of 6.11-rc1
> 
> Changes in v2:
>    - Rebase on top of 6.9-rc3
> 
> Alexandre Ghiti (9):
>    riscv: Safely remove huge_pte_offset() when manipulating NAPOT ptes
>    riscv: Restore the pfn in a NAPOT pte when manipulated by core mm code
>    mm: Use common huge_ptep_get() function for riscv/arm64
>    mm: Use common set_huge_pte_at() function for riscv/arm64
>    mm: Use common huge_pte_clear() function for riscv/arm64
>    mm: Use common huge_ptep_get_and_clear() function for riscv/arm64
>    mm: Use common huge_ptep_set_access_flags() function for riscv/arm64
>    mm: Use common huge_ptep_set_wrprotect() function for riscv/arm64
>    mm: Use common huge_ptep_clear_flush() function for riscv/arm64
> 
>   arch/arm64/Kconfig                  |   1 +
>   arch/arm64/include/asm/hugetlb.h    |  22 +--
>   arch/arm64/include/asm/pgtable.h    |  68 ++++++-
>   arch/arm64/mm/hugetlbpage.c         | 294 +---------------------------
>   arch/riscv/Kconfig                  |   1 +
>   arch/riscv/include/asm/hugetlb.h    |  36 +---
>   arch/riscv/include/asm/pgtable-64.h |  11 ++
>   arch/riscv/include/asm/pgtable.h    | 222 ++++++++++++++++++---
>   arch/riscv/mm/hugetlbpage.c         | 243 +----------------------
>   arch/riscv/mm/pgtable.c             |   6 +-
>   include/linux/hugetlb_contpte.h     |  39 ++++
>   mm/Kconfig                          |   3 +
>   mm/Makefile                         |   1 +
>   mm/hugetlb_contpte.c                | 258 ++++++++++++++++++++++++
>   14 files changed, 583 insertions(+), 622 deletions(-)
>   create mode 100644 include/linux/hugetlb_contpte.h
>   create mode 100644 mm/hugetlb_contpte.c
>