linux-kernel - Re: [PATCH v3 01/11] PCI/P2PDMA: Support peer-to-peer memory

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Date:   Tue, 13 Mar 2018 14:46:31 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Sinan Kaya <okaya@...eaurora.org>, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-rdma@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-block@...r.kernel.org
Cc:     Stephen Bates <sbates@...thlin.com>,
        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>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH v3 01/11] PCI/P2PDMA: Support peer-to-peer memory



On 13/03/18 01:53 PM, Sinan Kaya wrote:
> I agree disabling globally would be bad. Somebody can always say I have
> ten switches on my system. I want to do peer-to-peer on one switch only. Now,
> this change weakened security for the other switches that I had no intention
> with doing P2P.
> 
> Isn't this a problem?

Well, if it's a problem for someone they'll have to solve it. We're
targeting JBOFs that have no use for ACS / IOMMU groups at all.

> Can we specify the BDF of the downstream device we want P2P with during boot via
> kernel command line?

That's a painful configuration burden. And then things might stop
working if you change your topology at all and now have to change boot
parameters.

Logan