On Tue, Apr 30, 2024 at 06:57:52PM +0100, Catalin Marinas wrote: > 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 Since Andrew merged the generic mm fix, I dropped this patch from the arm64 for-next/fixes branch. -- Catalin
