On 30/04/2024 18:57, 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. Thanks Catalin! I'm guessing this will turn up in today's linux-next, so if I send the tests today and Andrew puts them straight in mm-unstable (which will goto linux-next) there is no risk that the tests are there without the fix? Or do I need to hold off until the fix is in v6.9-rc7? > > [1/1] arm64/mm: pmd_mkinvalid() must handle swap pmds > https://git.kernel.org/arm64/c/e783331c7720 >
