On Fri, Jul 15, 2022 at 10:28:44AM -0700, Axel Rasmussen wrote: > On Fri, Jul 15, 2022 at 10:07 AM Peter Xu <peterx@xxxxxxxxxx> wrote: > > > > On Fri, Jul 15, 2022 at 09:45:37AM -0700, Axel Rasmussen wrote: > > > I agree we should either: > > > - Update the UFFD selftest to exercise this case > > > - Or, don't allow it, update vma_can_userfault() to also require VM_SHARED > > > for VM_UFFD_MINOR registration. > > > > > > The first one is unfortunately not completely straightforward as Peter > > > described. I would say it's probably not worth holding up this fix while we > > > wait for it to happen? > > > > Agreed, Andrew has already queued it. It actually is a real fix since we > > never forbid the user running private mappings upon minor faults, so > > it's literally a bug in kernel irrelevant of the kselftest. > > > > > > > > I don't really have a strong preference between the two. The second option > > > is what I originally proposed in the first version of the minor fault > > > series, so going back to that isn't a problem at least from my perspective. > > > If in the future we find a real use case for this, we could always easily > > > re-enable it and add selftests for it at that point. > > > > I'd go for fixing the test case if possible. Mike, would it be fine if we > > go back to /dev/hugepages path based approach in the test case? > > One possible alternative, can we use memfd_create() with MFD_HUGE_*? > This afaict lets us have an fd so we can create two mappings, > without having to mount hugetlbfs, pass in a path to the test, ... Sounds good. :) We can also rework the shared hugetlb too. Wanna post a patch? I can do that too, let me know otherwise. Thanks! -- Peter Xu
