[PATCH v6 01/10] mm: add zone device coherent type memory support

[Jason Gunthorpe]

On Tue, Feb 15, 2022 at 07:32:09PM +0100, Christoph Hellwig wrote:
> On Tue, Feb 15, 2022 at 10:45:24AM -0400, Jason Gunthorpe wrote:
> > > Do you know if DEVICE_GENERIC pages would end up as PageAnon()? My
> > > assumption was that they would be part of a special mapping.
> > 
> > We need to stop using the special PTEs and VMAs for things that have a
> > struct page. This is a mistake DAX created that must be undone.
> 
> Yes, we'll get to it.  Maybe we can do it for the non-DAX devmap
> ptes first given that DAX is more complicated.

Probably, I think we can check the page->pgmap type to tell the
difference.

I'm not sure how the DEVICE_GENERIC can work without this, as DAX was
made safe by using the unmap_mapping_range(), which won't work
here. Is there some other trick being used to keep track of references
inside the AMD driver?

Jason