On Tue, 30 Apr 2024 14:31:38 +0100, Ryan Roberts wrote:
> __split_huge_pmd_locked() can be called for a present THP, devmap or
> (non-present) migration entry. It calls pmdp_invalidate()
> unconditionally on the pmdp and only determines if it is present or not
> based on the returned old pmd.
>
> But arm64's pmd_mkinvalid(), called by pmdp_invalidate(),
> unconditionally sets the PMD_PRESENT_INVALID flag, which causes future
> pmd_present() calls to return true - even for a swap pmd. Therefore any
> lockless pgtable walker could see the migration entry pmd in this state
> and start interpretting the fields (e.g. pmd_pfn()) as if it were
> present, leading to BadThings (TM). GUP-fast appears to be one such
> lockless pgtable walker.
>
> [...]
Applied to arm64 (for-next/fixes), thanks! It should land in 6.9-rc7. I
removed the debug/test code, please send it as a separate patch for
6.10.
[1/1] arm64/mm: pmd_mkinvalid() must handle swap pmds
https://git.kernel.org/arm64/c/e783331c7720
--
Catalin
