[PATCH hmm 8/8] mm/hmm: add missing call to hmm_pte_need_fault in HMM_PFN_SPECIAL handling

[Christoph Hellwig]

On Mon, Mar 16, 2020 at 02:12:01PM +0100, Christoph Hellwig wrote:
> On Mon, Mar 16, 2020 at 10:04:58AM -0300, Jason Gunthorpe wrote:
> > > Ok.  I had some cleanups like this based of older trees, but if you are
> > > active in this area I think I'll let you handle it.
> > 
> > You once said you wanted to loose the weird pfn flags scheme, so
> > before putting hmm_range_fault in ODP I planned to do that.
> > 
> > If you have your series someplace send me a URL and I'll look on it
> 
> I have a local branch I just started hacking on, but it is rather broken
> based on various discussions we had.  But for a basic one I'd suggest
> something like:
> 
>  - kill HMM_PFN_SPECIAL as it serves no purpose
>  - split the ->pfns array into an input flags (optional) and an output
>    pfn (mandtory) one, using new flags for the input side
>  - replace the output flags/values indirection with a bunch of values
>    encoded in the high bits of a u64, with the rest used for the pfn

Thinking out loud a bit more:

 - do we really need HMM_PFN_ERROR, or is just a return value from
   hmm_range_fault enough?
 - because if it is we don't need output flags at all, and the output
   array could be struct pages, which would make for a much easier
   to use API