Re: [PATCH v1] mm/userfaultfd: enable writenotify while userfaultfd-wp is enabled for a VMA

[David Hildenbrand]

On 08.12.22 21:21, Peter Xu wrote:
> On Thu, Dec 08, 2022 at 03:06:06PM -0500, Peter Xu wrote:
> > On Thu, Dec 08, 2022 at 05:44:35PM +0100, David Hildenbrand wrote:
> > > I'll wait for some more (+retest) before I resend tomorrow.
> >
> > One more thing just to double check:
> >
> > It's 6a56ccbcf6c6 ("mm/autonuma: use can_change_(pte|pmd)_writable() to
> > replace savedwrite", 2022-11-30) that just started to break uffd-wp on
> > numa, am I right?
> >
> > With the old code, pte_modify() will persist uffd-wp bit, afaict, and we
> > used to do savedwrite for numa hints.  That all look correct to me until
> > the savedwrite removal patchset with/without vm_page_prot changes.
> >
> > If that's the case, we'd better also mention that in the commit message and
> > has another Fixes: for that one to be clear.
>
> Nah, never mind.  I think the savedwrite will not guarantee pte write
> protected just like the migration path.  The commit message is correct.

Right, the problem is not the uffd-wp bit getting lost, but the write 
bit getting set, which is independent of 6a56ccbcf6c6. Thanks for 
double-checking 6a56ccbcf6c6.

--
Thanks,

David / dhildenb