[PATCH -fixes 0/2] Fix set_huge_pte_at()

[Alexandre Ghiti]

A recent report [1] from Ryan for arm64 revealed that we do not handle
swap entries when setting a hugepage backed by a NAPOT region (the
contpte riscv equivalent).

As explained in [1], the issue was discovered by a new test in kselftest
which uses poison entries, but the symptoms are different from arm64 though:

- the riscv kernel bugs because we do not handle VM_FAULT_HWPOISON*,
  this is fixed by patch 1,
- after that, the test passes because the first pte_napot() fails (the
  poison entry does not have the N bit set), and then we only set the
  first page table entry covering the NAPOT hugepage, which is enough
  for hugetlb_fault() to correctly raise a VM_FAULT_HWPOISON wherever we
  write in this mapping since only this first page table entry is
  checked
  (see https://elixir.bootlin.com/linux/v6.6-rc3/source/mm/hugetlb.c#L6071).
  But this seems fragile so patch 2 sets all page table entries of a
  NAPOT mapping.

[1]: https://lore.kernel.org/linux-arm-kernel/20230922115804.2043771-1-ryan.roberts@arm.com/


Alexandre Ghiti (2):
  riscv: Handle VM_FAULT_[HWPOISON|HWPOISON_LARGE] faults instead of
    panicking
  riscv: Fix set_huge_pte_at() for NAPOT mappings when a swap entry is
    set

 arch/riscv/mm/fault.c       |  2 +-
 arch/riscv/mm/hugetlbpage.c | 19 +++++++++++++------
 2 files changed, 14 insertions(+), 7 deletions(-)

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2.39.2