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

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Message-ID: <20170112171720.GA12257@obsidianresearch.com>
Date:   Thu, 12 Jan 2017 10:17:20 -0700
From:   Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:     Jerome Glisse <jglisse@...hat.com>
Cc:     Stephen Bates <sbates@...thlin.com>,
        Logan Gunthorpe <logang@...tatee.com>, david1.zhou@....com,
        qiang.yu@....com,
        "'linux-rdma@...r.kernel.org'" <linux-rdma@...r.kernel.org>,
        "'linux-nvdimm@...ts.01.org'" <linux-nvdimm@...1.01.org>,
        "Kuehling, Felix" <felix.kuehling@....com>,
        Serguei Sagalovitch <serguei.sagalovitch@....com>,
        "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
        "'dri-devel@...ts.freedesktop.org'" <dri-devel@...ts.freedesktop.org>,
        "Koenig, Christian" <christian.koenig@....com>, hch@...radead.org,
        "Deucher, Alexander" <alexander.deucher@....com>,
        "Sander, Ben" <ben.sander@....com>,
        "Suthikulpanit, Suravee" <suravee.suthikulpanit@....com>,
        "'linux-pci@...r.kernel.org'" <linux-pci@...r.kernel.org>,
        Jerome Glisse <j.glisse@...il.com>,
        "Blinzer, Paul" <paul.blinzer@....com>,
        "'Linux-media@...r.kernel.org'" <linux-media@...r.kernel.org>
Subject: Re: Enabling peer to peer device transactions for PCIe devices

On Thu, Jan 12, 2017 at 10:11:29AM -0500, Jerome Glisse wrote:
> On Wed, Jan 11, 2017 at 10:54:39PM -0600, Stephen Bates wrote:
> > > What we want is for RDMA, O_DIRECT, etc to just work with special VMAs
> > > (ie. at least those backed with ZONE_DEVICE memory). Then
> > > GPU/NVME/DAX/whatever drivers can just hand these VMAs to userspace
> > > (using whatever interface is most appropriate) and userspace can do what
> > > it pleases with them. This makes _so_ much sense and actually largely
> > > already works today (as demonstrated by iopmem).

> So i say let solve the IOMMU issue first and let everyone use it in their
> own way with their device. I do not think we can share much more than
> that.

Solve it for the easy ZONE_DIRECT/etc case then.

Jason