From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932460AbeEHUty (ORCPT ); Tue, 8 May 2018 16:49:54 -0400 Received: from ale.deltatee.com ([207.54.116.67]:32932 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932283AbeEHUtv (ORCPT ); Tue, 8 May 2018 16:49:51 -0400 To: Alex Williamson Cc: =?UTF-8?Q?Christian_K=c3=b6nig?= , Bjorn Helgaas , linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org, linux-nvdimm@lists.01.org, linux-block@vger.kernel.org, Stephen Bates , Christoph Hellwig , Jens Axboe , Keith Busch , Sagi Grimberg , Bjorn Helgaas , Jason Gunthorpe , Max Gurtovoy , Dan Williams , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Benjamin Herrenschmidt References: <20180423233046.21476-1-logang@deltatee.com> <20180423233046.21476-5-logang@deltatee.com> <20180507231306.GG161390@bhelgaas-glaptop.roam.corp.google.com> <0b4183ef-e720-204b-9e85-b9eaf7a4136a@deltatee.com> <3584a6ac-95c7-5d23-1859-aee30605776e@deltatee.com> <20180508133407.57a46902@w520.home> <5fc9b1c1-9208-06cc-0ec5-1f54c2520494@deltatee.com> <20180508141331.7cd737cb@w520.home> <20180508144341.0441b676@w520.home> From: Logan Gunthorpe Message-ID: Date: Tue, 8 May 2018 14:49:23 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180508144341.0441b676@w520.home> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.162 X-SA-Exim-Rcpt-To: benh@kernel.crashing.org, jglisse@redhat.com, dan.j.williams@intel.com, maxg@mellanox.com, jgg@mellanox.com, bhelgaas@google.com, sagi@grimberg.me, keith.busch@intel.com, axboe@kernel.dk, hch@lst.de, sbates@raithlin.com, linux-block@vger.kernel.org, linux-nvdimm@lists.01.org, linux-rdma@vger.kernel.org, linux-nvme@lists.infradead.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, helgaas@kernel.org, christian.koenig@amd.com, alex.williamson@redhat.com X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH v4 04/14] PCI/P2PDMA: Clear ACS P2P flags for all devices behind switches X-SA-Exim-Version: 4.2.1 (built Tue, 02 Aug 2016 21:08:31 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/05/18 02:43 PM, Alex Williamson wrote: > Yes, GPUs seem to be leading the pack in implementing ATS. So now the > dumb question, why not simply turn off the IOMMU and thus ACS? The > argument of using the IOMMU for security is rather diminished if we're > specifically enabling devices to poke one another directly and clearly > this isn't favorable for device assignment either. Are there target > systems where this is not a simple kernel commandline option? Thanks, Well, turning off the IOMMU doesn't necessarily turn off ACS. We've run into some bios's that set the bits on boot (which is annoying). I also don't expect people will respond well to making the IOMMU and P2P exclusive. The IOMMU is often used for more than just security and on many platforms it's enabled by default. I'd much rather allow IOMMU use but have fewer isolation groups in much the same way as if you had PCI bridges that didn't support ACS. Logan