[PATCH v2 0/9] Merge arm64/riscv hugetlbfs contpte support

[Alexandre Ghiti]

This patchset intends to merge the contiguous ptes hugetlbfs implementation
of arm64 and riscv.

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/

Changes in v2:
  - Rebase on top of 6.9-rc3

Alexandre Ghiti (9):
  riscv: Restore the pfn in a NAPOT pte when manipulated by core mm code
  riscv: Safely remove huge_pte_offset() when manipulating NAPOT ptes
  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/pgtable.h    |  56 +++++-
 arch/arm64/mm/hugetlbpage.c         | 291 +---------------------------
 arch/riscv/Kconfig                  |   1 +
 arch/riscv/include/asm/hugetlb.h    |   2 +-
 arch/riscv/include/asm/pgtable-64.h |  11 ++
 arch/riscv/include/asm/pgtable.h    | 153 +++++++++++++--
 arch/riscv/mm/hugetlbpage.c         | 227 ----------------------
 arch/riscv/mm/pgtable.c             |   6 +-
 mm/Kconfig                          |   3 +
 mm/Makefile                         |   1 +
 mm/contpte.c                        | 272 ++++++++++++++++++++++++++
 12 files changed, 480 insertions(+), 544 deletions(-)
 create mode 100644 mm/contpte.c

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2.39.2