linux-kernel - Re: [PATCH v4 04/14] PCI/P2PDMA: Clear ACS P2P flags for all devices behind switches

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Message-ID: <20180510131015.4ad59477@w520.home>
Date:   Thu, 10 May 2018 13:10:15 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     "Stephen  Bates" <sbates@...thlin.com>
Cc:     Jerome Glisse <jglisse@...hat.com>,
        Christian König <christian.koenig@....com>,
        "Logan Gunthorpe" <logang@...tatee.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "Christoph Hellwig" <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        Keith Busch <keith.busch@...el.com>,
        Sagi Grimberg <sagi@...mberg.me>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "Benjamin Herrenschmidt" <benh@...nel.crashing.org>
Subject: Re: [PATCH v4 04/14] PCI/P2PDMA: Clear ACS P2P flags for all
 devices behind switches

On Thu, 10 May 2018 18:41:09 +0000
"Stephen  Bates" <sbates@...thlin.com> wrote:    
> >    Reasons is that GPU are giving up on PCIe (see all specialize link like
> >    NVlink that are popping up in GPU space). So for fast GPU inter-connect
> >    we have this new links.   
> 
> I look forward to Nvidia open-licensing NVLink to anyone who wants to use it ;-).

No doubt, the marketing for it is quick to point out the mesh topology
of NVLink, but I haven't seen any technical documents that describe the
isolation capabilities or IOMMU interaction.  Whether this is included
or an afterthought, I have no idea.

> >    Also the IOMMU isolation do matter a lot to us. Think someone using this
> >    peer to peer to gain control of a server in the cloud.  

>From that perspective, do we have any idea what NVLink means for
topology and IOMMU provided isolation and translation?  I've seen a
device assignment user report that seems to suggest it might pretend to
be PCIe compatible, but the assigned GPU ultimately doesn't work
correctly in a VM, so perhaps the software compatibility is only so
deep. Thanks,

Alex