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Thu, 23 Jun 2022 00:47:01 -0700 Date: Thu, 23 Jun 2022 00:47:00 -0700 From: Nicolin Chen To: Robin Murphy , "Tian, Kevin" CC: "joro@8bytes.org" , "will@kernel.org" , "marcan@marcan.st" , "sven@svenpeter.dev" , "robdclark@gmail.com" , "baolu.lu@linux.intel.com" , "matthias.bgg@gmail.com" , "orsonzhai@gmail.com" , "baolin.wang7@gmail.com" , "zhang.lyra@gmail.com" , "jean-philippe@linaro.org" , "alex.williamson@redhat.com" , "jgg@nvidia.com" , "suravee.suthikulpanit@amd.com" , "alyssa@rosenzweig.io" , "dwmw2@infradead.org" , "yong.wu@mediatek.com" , "mjrosato@linux.ibm.com" , "gerald.schaefer@linux.ibm.com" , "thierry.reding@gmail.com" , "vdumpa@nvidia.com" , "jonathanh@nvidia.com" , "cohuck@redhat.com" , "thunder.leizhen@huawei.com" , "tglx@linutronix.de" , "christophe.jaillet@wanadoo.fr" , "john.garry@huawei.com" , "chenxiang66@hisilicon.com" , "saiprakash.ranjan@codeaurora.org" , "isaacm@codeaurora.org" , "yangyingliang@huawei.com" , "jordan@cosmicpenguin.net" , "iommu@lists.linux-foundation.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-arm-msm@vger.kernel.org" , "linux-mediatek@lists.infradead.org" , "linux-s390@vger.kernel.org" , "linux-tegra@vger.kernel.org" , "virtualization@lists.linux-foundation.org" , "kvm@vger.kernel.org" Subject: Re: [PATCH v2 3/5] vfio/iommu_type1: Remove the domain->ops comparison Message-ID: References: <20220616000304.23890-1-nicolinc@nvidia.com> <20220616000304.23890-4-nicolinc@nvidia.com> <6e1280c5-4b22-ebb3-3912-6c72bc169982@arm.com> MIME-Version: 1.0 Content-Type: text/plain; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Jun 2022 07:47:12.3754 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 26759e5c-e47f-44c0-434d-08da54ec959d X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[12.22.5.236];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN8NAM11FT024.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW3PR12MB4554 Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On Thu, Jun 23, 2022 at 03:50:22AM +0000, Tian, Kevin wrote: > External email: Use caution opening links or attachments > > > > From: Robin Murphy > > Sent: Wednesday, June 22, 2022 3:55 PM > > > > On 2022-06-16 23:23, Nicolin Chen wrote: > > > On Thu, Jun 16, 2022 at 06:40:14AM +0000, Tian, Kevin wrote: > > > > > >>> The domain->ops validation was added, as a precaution, for mixed- > > driver > > >>> systems. However, at this moment only one iommu driver is possible. So > > >>> remove it. > > >> > > >> It's true on a physical platform. But I'm not sure whether a virtual > > platform > > >> is allowed to include multiple e.g. one virtio-iommu alongside a virtual VT- > > d > > >> or a virtual smmu. It might be clearer to claim that (as Robin pointed out) > > >> there is plenty more significant problems than this to solve instead of > > simply > > >> saying that only one iommu driver is possible if we don't have explicit > > code > > >> to reject such configuration. 😊 > > > > > > Will edit this part. Thanks! > > > > Oh, physical platforms with mixed IOMMUs definitely exist already. The > > main point is that while bus_set_iommu still exists, the core code > > effectively *does* prevent multiple drivers from registering - even in > > emulated cases like the example above, virtio-iommu and VT-d would both > > try to bus_set_iommu(&pci_bus_type), and one of them will lose. The > > aspect which might warrant clarification is that there's no combination > > of supported drivers which claim non-overlapping buses *and* could > > appear in the same system - even if you tried to contrive something by > > emulating, say, VT-d (PCI) alongside rockchip-iommu (platform), you > > could still only describe one or the other due to ACPI vs. Devicetree. > > > > This explanation is much clearer! thanks. Thanks +1 I've also updated the commit log.