Cross-device and cross-driver HMM support

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

Hi!

With our SVM mirror work we'll soon start looking at HMM cross-device
support. The identified needs are

1) Instead of migrating foreign device memory to system when the
current device is faulting, leave it in place...
1a) for access using internal interconnect,
1b) for access using PCIE p2p (probably mostly as a reference)

2) Request a foreign device to migrate memory range a..b of a CPU
mm_struct to local shareable device memory on that foreign device.

and we plan to add an infrastructure for this. Probably this can be
done initially without too much (or any) changes to the hmm code
itself.

So the question is basically whether anybody is interested in a 
drm-wide solution for this and in that case also whether anybody sees
the need for cross-driver support?

Otherwise any objections against us starting out with an xe driver
helper implementation that could be lifted to drm-level when needed?

Finally any suggestions or pointers to existing solutions for this?

Any comments / suggestions greatly appreciated.

Thanks,
Thomas