From: Logan Gunthorpe <logang@deltatee.com>
To: Alex Williamson <alex.williamson@redhat.com>,
        Bjorn Helgaas <helgaas@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>, Keith Busch <keith.busch@intel.com>,
        linux-nvdimm@lists.01.org, linux-rdma@vger.kernel.org,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-nvme@lists.infradead.org, linux-block@vger.kernel.org,
        =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
        Jason Gunthorpe <jgg@mellanox.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Max Gurtovoy <maxg@mellanox.com>,
        Christoph Hellwig <hch@lst.de>
References: <20180104190137.7654-1-logang@deltatee.com>
 <20180104190137.7654-5-logang@deltatee.com>
 <20180104215721.GF189897@bhelgaas-glaptop.roam.corp.google.com>
 <20180104153551.3118f71b@t450s.home>
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Message-ID: <99420cc9-48fd-5692-8426-bd5c2ec0dcf7@deltatee.com>
Date: Thu, 4 Jan 2018 18:09:43 -0700
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Subject: Re: [PATCH 04/12] pci-p2p: Clear ACS P2P flags for all client devices
Sender: linux-kernel-owner@vger.kernel.org


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