Hi, Mike,
On Tue, Nov 25, 2025 at 08:38:38PM +0200, Mike Rapoport wrote:
From: "Mike Rapoport (Microsoft)" rppt@kernel.org
When a VMA is registered with userfaulfd in minor mode, its ->fault() method should check if a folio exists in the page cache and if yes ->fault() should call handle_userfault(VM_UFFD_MISSING).
s/MISSING/MINOR/
Instead of calling handle_userfault() directly from a specific ->fault() implementation introduce new fault reason VM_FAULT_UFFD_MINOR that will notify the core page fault handler that it should call handle_userfaultfd(VM_UFFD_MISSING) to complete a page fault.
Same.
Replace a call to handle_userfault(VM_UFFD_MISSING) in shmem and use the
Same.
new VM_FAULT_UFFD_MINOR there instead.
Personally I'd keep the fault path as simple as possible, because that's the more frequently used path (rather than when userfaultfd is armed). I also see it slightly a pity that even with flags introduced, it only solves the MINOR problem, not MISSING.
If it's me, I'd simply export handle_userfault().. I confess I still don't know why exporting it is a problem, but maybe I missed something.
Only my two cents. Feel free to go with whatever way you prefer.
Thanks,