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

[Alexandre Ghiti]

+cc Andrew: Would  you mind taking this patchset in your tree for the 
next rc? This patchset depends on a previous fix for arm64 that you 
merged in rc4 which is not in the riscv -fixes branch yet.

I saw with Palmer and he should ack this shortly.

If I can do anything else to help, let me know.

Thanks,

Alex

On 28/09/2023 17:18, Alexandre Ghiti wrote:
> 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@xxxxxxx/
>
>
> 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(-)