Re: GUP guarantees wrt to userspace mappings

From: Andrea Arcangeli
Date: Mon May 02 2016 - 15:14:16 EST

On Mon, May 02, 2016 at 07:12:52PM +0300, Kirill A. Shutemov wrote:
> Any reason why mmu_notifier is not an option?

No way to trigger an hardware re-tried secondary MMU fault as result
of PCI DMA memory access, and expensive to do an MMU notifier
invalidate if it requires waiting for the DMA to complete (but since
MMU notifier is now sleepable the latter is a secondary concern).