On 2016-11-24 11:26 AM, Jason Gunthorpe wrote: > On Thu, Nov 24, 2016 at 10:45:18AM +0100, Christian König wrote: >> Am 24.11.2016 um 00:25 schrieb Jason Gunthorpe: >>> There is certainly nothing about the hardware that cares >>> about ZONE_DEVICE vs System memory. >> Well that is clearly not so simple. When your ZONE_DEVICE pages describe a >> PCI BAR and another PCI device initiates a DMA to this address the DMA >> subsystem must be able to check if the interconnection really works. > I said the hardware doesn't care.. You are right, we still have an > outstanding problem in Linux of how to generically DMA map a P2P > address - which is a different issue from getting the P2P address from > a __user pointer... > > Jason I agreed but the problem is that one issue immediately introduce another one to solve and so on (if we do not want to cut corners). I would think that a lot of them interconnected because the way how one problem could be solved may impact solution for another.
btw: about "DMA map a p2p address": Right now to enable p2p between devices it is required/recommended to disable iommu support (e.g. intel iommu driver has special logic for graphics and comment "Reserve all PCI MMIO to avoid peer-to-peer access").
