linux-kernel - Re: Enabling peer to peer device transactions for PCIe devices

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Message-ID: <20161124162620.GC20818@obsidianresearch.com>
Date:   Thu, 24 Nov 2016 09:26:20 -0700
From:   Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:     Christian König <christian.koenig@....com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Serguei Sagalovitch <serguei.sagalovitch@....com>,
        "Deucher, Alexander" <Alexander.Deucher@....com>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...1.01.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "Kuehling, Felix" <Felix.Kuehling@....com>,
        "Bridgman, John" <John.Bridgman@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "Sander, Ben" <ben.sander@....com>,
        "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>,
        "Blinzer, Paul" <Paul.Blinzer@....com>,
        "Linux-media@...r.kernel.org" <Linux-media@...r.kernel.org>,
        Haggai Eran <haggaie@...lanox.com>
Subject: Re: Enabling peer to peer device transactions for PCIe devices

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