Re: [PATCH] mm/hugetlb: avoid corrupting page->mapping in hugetlb_mcopy_atomic_pte

[Peter Xu]

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?

Thanks,

-- 
Peter Xu