Fence wait in mmu_interval_notifier_ops::invalidate

[Jason Gunthorpe]

On Fri, Dec 11, 2020 at 08:50:53AM +0100, Thomas Hellström (Intel) wrote:

> My understanding of this particular case is that hardware would continue to
> DMA to orphaned pages that are pinned until the driver is done with
> DMA,

mmu notifier replaces pinning as the locking mechanism. Drivers using
mmu notifier should not be taking pins.

Keep in mind this was all built for HW with real shadow page tables
that can do fine grained manipulation.

The GPU version of this to instead manipulate a command queue is a big
aberration from what was intended.

Jason