Re: [PATCH v5 05/15] mm/frame-vector: Use FOLL_LONGTERM

[Jason Gunthorpe]

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