ensure device private pages have an owner v2

[Bharata B Rao]

On Mon, Mar 16, 2020 at 08:32:12PM +0100, Christoph Hellwig wrote:
> When acting on device private mappings a driver needs to know if the
> device (or other entity in case of kvmppc) actually owns this private
> mapping.  This series adds an owner field and converts the migrate_vma
> code over to check it.  I looked into doing the same for
> hmm_range_fault, but as far as I can tell that code has never been
> wired up to actually work for device private memory, so instead of
> trying to fix some unused code the second patch just remove the code.
> We can add it back once we have a working and fully tested code, and
> then should pass the expected owner in the hmm_range structure.

Boot-tested a pseries secure guest with this change (1/4 and 2/4 only)

So Tested-by: Bharata B Rao <bharata at linux.ibm.com> for the above
two patches.

Regards,
Bharata.