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

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Date:   Fri, 11 May 2018 22:24:59 +0000
From:   "Stephen  Bates" <sbates@...thlin.com>
To:     Logan Gunthorpe <logang@...tatee.com>,
        Christian König <christian.koenig@....com>,
        Jerome Glisse <jglisse@...hat.com>
CC:     Jens Axboe <axboe@...nel.dk>, Keith Busch <keith.busch@...el.com>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        "Bjorn Helgaas" <helgaas@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v4 04/14] PCI/P2PDMA: Clear ACS P2P flags for all devices
 behind switches

All

> Alex (or anyone else) can you point to where IOVA addresses are generated?

A case of RTFM perhaps (though a pointer to the code would still be appreciated).

https://www.kernel.org/doc/Documentation/Intel-IOMMU.txt

Some exceptions to IOVA
-----------------------
Interrupt ranges are not address translated, (0xfee00000 - 0xfeefffff).
The same is true for peer to peer transactions. Hence we reserve the
address from PCI MMIO ranges so they are not allocated for IOVA addresses.

Cheers

Stephen