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

[Jason Gunthorpe]

On Wed, Feb 16, 2022 at 12:23:44PM +1100, Alistair Popple wrote:

> Device private and device coherent pages are not marked with pte_devmap and they
> are backed by a struct page. The only way of inserting them is via migrate_vma.
> The refcount is decremented in zap_pte_range() on munmap() with special handling
> for device private pages. Looking at it again though I wonder if there is any
> special treatment required in zap_pte_range() for device coherent pages given
> they count as present pages.

This is what I guessed, but we shouldn't be able to just drop
pte_devmap on these pages without any other work?? Granted it does
very little already..

I thought at least gup_fast needed to be touched or did this get
handled by scanning the page list after the fact?

Jason