[PATCH 3/4] mm: simplify device private page handling in hmm_range_fault

[Christoph Hellwig]

On Tue, Mar 17, 2020 at 09:15:36AM -0300, Jason Gunthorpe wrote:
> > Getting rid of HMM_PFN_DEVICE_PRIVATE seems reasonable to me since a driver can
> > look at the struct page but what if a driver needs to fault in a page from
> > another device's private memory? Should it call handle_mm_fault()?
> 
> Isn't that what this series basically does?
>
> The dev_private_owner is set to the type of pgmap the device knows how
> to handle, and everything else is automatically faulted for the
> device.
> 
> If the device does not know how to handle device_private then it sets
> dev_private_owner to NULL and it never gets device_private pfns.
> 
> Since the device_private pfn cannot be dma mapped, drivers must have
> explicit support for them.

No, with this series (and all actual callers before this series)
we never fault in device private pages.