linux-kernel - Re: [PATCH 04/12] pci-p2p: Clear ACS P2P flags for all client devices

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Date:   Thu, 4 Jan 2018 18:09:43 -0700
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <helgaas@...nel.org>
Cc:     Jens Axboe <axboe@...nel.dk>, Keith Busch <keith.busch@...el.com>,
        linux-nvdimm@...ts.01.org, linux-rdma@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-block@...r.kernel.org,
        Jérôme Glisse <jglisse@...hat.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 04/12] pci-p2p: Clear ACS P2P flags for all client devices



On 04/01/18 05:00 PM, Logan Gunthorpe wrote:
> 
> 
> On 04/01/18 03:35 PM, Alex Williamson wrote:
>> Yep, flipping these ACS bits invalidates any IOMMU groups that depend
>> on the isolation of that downstream port and I suspect also any peers
>> within the same PCI slot of that port and their downstream devices.  The
>> entire sub-hierarchy grouping needs to be re-evaluated.  This
>> potentially affects running devices that depend on that isolation, so
>> I'm not sure how that happens dynamically.  A boot option might be
>> easier.  Thanks,
> 

Also, considering this further: if you can point me to a way to tell if
a device is in an IOMMU group it should be pretty easy to disallow a
device that has been assigned to a group from being used in P2P
transactions.

Logan