On Mon, May 18, 2026 at 10:48:08AM -0700, Andrew Morton wrote: > On Wed, 13 May 2026 02:40:11 +0000 Stanislav Kinsburskii > <[email protected]> wrote: > > > This series extends the HMM framework to support userfaultfd-backed memory > > by allowing the mmap read lock to be dropped during hmm_range_fault(). > > > > Some page fault handlers — most notably userfaultfd — require the mmap lock > > to be released so that userspace can resolve the fault. The current HMM > > interface never sets FAULT_FLAG_ALLOW_RETRY, making it impossible to fault > > in pages from userfaultfd-registered regions. > > > > This series follows the established int *locked pattern from > > get_user_pages_remote() in mm/gup.c. A new entry point, > > hmm_range_fault_unlockable(), accepts an int *locked parameter. When the > > mmap lock is dropped during fault resolution (VM_FAULT_RETRY or > > VM_FAULT_COMPLETED), the function returns 0 with *locked = 0, signalling > > the caller to restart its walk. The existing hmm_range_fault() is > > refactored into a thin wrapper that passes NULL, preserving current > > behavior for all existing callers. > > > > Faulting hugetlb pages on the unlockable path is not supported because > > walk_hugetlb_range() unconditionally holds and releases > > hugetlb_vma_lock_read across the callback; if the mmap lock is dropped > > inside the callback, the VMA may be freed before the walk framework's > > unlock. Hugetlb pages already present in page tables are handled normally. > > Possible approaches to lift this limitation are documented in > > Documentation/mm/hmm.rst. > > Thanks. AI review asked some questions: > > https://sashiko.dev/#/patchset/177863991557.82528.15288076059759579141.st...@skinsburskii-cloud-desktop.internal.cloudapp.net > > I'd ignore the fist one: don't write buggy fault handlers! > >
Thank you for the review. I addressed the issues found in the new self test in v3 of this series. Please, take a look. Thanks, Stanislav
