On 2022/7/16 1:51, Axel Rasmussen wrote: > On Fri, Jul 15, 2022 at 10:39 AM Peter Xu <peterx@xxxxxxxxxx> wrote: >> >> 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! > > Sure, I'll take a whack at it. Many thanks for all of your hard work. :) > >> >> -- >> Peter Xu >> > . >
