Re: [PATCH v1] mm/userfaultfd: propagate uffd-wp bit when PTE-mapping the huge zeropage

Peter Xu
2023-03-02T22:30:44Z

On Thu, Mar 02, 2023 at 06:54:23PM +0100, David Hildenbrand wrote:
> Currently, we'd lose the userfaultfd-wp marker when PTE-mapping a huge
> zeropage, resulting in the next write faults in the PMD range
> not triggering uffd-wp events.
>
> Various actions (partial MADV_DONTNEED, partial mremap, partial munmap,
> partial mprotect) could trigger this. However, most importantly,
> un-protecting a single sub-page from the userfaultfd-wp handler when
> processing a uffd-wp event will PTE-map the shared huge zeropage and
> lose the uffd-wp bit for the remainder of the PMD.
>
> Let's properly propagate the uffd-wp bit to the PMDs.

Ouch.. I thought this was reported once, probably it fell through the
cracks.

Acked-by: Peter Xu <peterx@redhat.com>

Thanks,

--
Peter Xu