From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757378AbcKXRAf (ORCPT ); Thu, 24 Nov 2016 12:00:35 -0500 Received: from mail-dm3nam03on0059.outbound.protection.outlook.com ([104.47.41.59]:31360 "EHLO NAM03-DM3-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756664AbcKXRAZ (ORCPT ); Thu, 24 Nov 2016 12:00:25 -0500 Authentication-Results: spf=none (sender IP is ) smtp.mailfrom=Serguei.Sagalovitch@amd.com; Subject: Re: Enabling peer to peer device transactions for PCIe devices To: Jason Gunthorpe , =?UTF-8?Q?Christian_K=c3=b6nig?= References: <20161123190515.GA12146@obsidianresearch.com> <7bc38037-b6ab-943f-59db-6280e16901ab@amd.com> <20161123193228.GC12146@obsidianresearch.com> <20161123203332.GA15062@obsidianresearch.com> <20161123215510.GA16311@obsidianresearch.com> <20161123232503.GA13965@obsidianresearch.com> <20161124162620.GC20818@obsidianresearch.com> CC: Dan Williams , Logan Gunthorpe , "Deucher, Alexander" , "linux-nvdimm@lists.01.org" , "linux-rdma@vger.kernel.org" , "linux-pci@vger.kernel.org" , "Kuehling, Felix" , "Bridgman, John" , "linux-kernel@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , "Sander, Ben" , "Suthikulpanit, Suravee" , "Blinzer, Paul" , "Linux-media@vger.kernel.org" , Haggai Eran From: Serguei Sagalovitch Message-ID: <87e6cfce-c65d-2d9f-a3c6-e4224cb94b2c@amd.com> Date: Thu, 24 Nov 2016 12:00:14 -0500 User-Agent: Mozilla/5.0 (X11; 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When your ZONE_DEVICE pages describe a >> PCI BAR and another PCI device initiates a DMA to this address the DMA >> subsystem must be able to check if the interconnection really works. > I said the hardware doesn't care.. You are right, we still have an > outstanding problem in Linux of how to generically DMA map a P2P > address - which is a different issue from getting the P2P address from > a __user pointer... > > Jason I agreed but the problem is that one issue immediately introduce another one to solve and so on (if we do not want to cut corners). I would think that a lot of them interconnected because the way how one problem could be solved may impact solution for another. btw: about "DMA map a p2p address": Right now to enable p2p between devices it is required/recommended to disable iommu support (e.g. intel iommu driver has special logic for graphics and comment "Reserve all PCI MMIO to avoid peer-to-peer access").