Re: Buffered I/O broken on s390x with page faults disabled (gfs2)

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On Tue, 8 Mar 2022 14:32:25 +0100
David Hildenbrand <david@xxxxxxxxxx> wrote:

[...]
> 
> > - using set_pte_at() here seems a bit dangerous, as I'm not sure if this will
> >   always only operate on invalid PTEs. Using it on active valid PTEs could
> >   result in TLB issues because of missing flush. Also not sure about kvm impact.
> >   Using ptep_set_access_flags() seems safer, again similar to touch_pmd() and
> >   also cow_user_page().
> 
> Yeah, I sticked to what follow_pfn_pte() does for simplicity for now.

Uh oh, that set_pte_at() in follow_pfn_pte() also looks dangerous, at least
I do not spontaneously see that it would only be used for invalid / pte_none()
PTEs. But that is a totally different story, and maybe (hopefully) not
affecting s390 until we have proper DAX support...



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