ensure device private pages have an owner v2

[Christoph Hellwig]

On Wed, Mar 18, 2020 at 09:28:49PM -0300, Jason Gunthorpe wrote:
> > Changes since v1:
> >  - split out the pgmap->owner addition into a separate patch
> >  - check pgmap->owner is set for device private mappings
> >  - rename the dev_private_owner field in struct migrate_vma to src_owner
> >  - refuse to migrate private pages if src_owner is not set
> >  - keep the non-fault device private handling in hmm_range_fault
> 
> I'm happy enough to take this, did you have plans for a v3?

I think the only open question is if merging 3 and 4 might make sense.
It's up to you if you want it resent that way or not.