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Date:   Thu, 5 Nov 2020 08:49:50 -0400
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     John Hubbard <jhubbard@nvidia.com>,
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        Linux MM <linux-mm@kvack.org>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        Daniel Vetter <daniel.vetter@intel.com>,
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Subject: Re: [PATCH v5 05/15] mm/frame-vector: Use FOLL_LONGTERM
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On Thu, Nov 05, 2020 at 10:25:24AM +0100, Daniel Vetter wrote:
> > /*
> >  * If we can't determine whether or not a pte is special, then fail immediately
> >  * for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
> >  * to be special.
> >  *
> >  * For a futex to be placed on a THP tail page, get_futex_key requires a
> >  * get_user_pages_fast_only implementation that can pin pages. Thus it's still
> >  * useful to have gup_huge_pmd even if we can't operate on ptes.
> >  */
> 
> We support hugepage faults in gpu drivers since recently, and I'm not
> seeing a pud_mkhugespecial anywhere. So not sure this works, but probably
> just me missing something again.

It means ioremap can't create an IO page PUD, it has to be broken up.

Does ioremap even create anything larger than PTEs?

Jason