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Wed, 16 Jul 2025 11:21:45 -0700 Received: from rnnvmail202.nvidia.com (10.129.68.7) by rnnvmail204.nvidia.com (10.129.68.6) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.14; Wed, 16 Jul 2025 11:21:45 -0700 Received: from Asurada-Nvidia (10.127.8.10) by mail.nvidia.com (10.129.68.7) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.14 via Frontend Transport; Wed, 16 Jul 2025 11:21:44 -0700 Date: Wed, 16 Jul 2025 11:21:42 -0700 From: Nicolin Chen To: Shameerali Kolothum Thodi CC: "Duan, Zhenzhong" , "qemu-arm@nongnu.org" , "qemu-devel@nongnu.org" , "eric.auger@redhat.com" , "peter.maydell@linaro.org" , "jgg@nvidia.com" , "ddutile@redhat.com" , "berrange@redhat.com" , "nathanc@nvidia.com" , "mochs@nvidia.com" , "smostafa@google.com" , Linuxarm , "Wangzhou (B)" , jiangkunkun , "Jonathan Cameron" , "zhangfei.gao@linaro.org" , "shameerkolothum@gmail.com" Subject: Re: [RFC PATCH v3 06/15] hw/arm/smmuv3-accel: Restrict accelerated SMMUv3 to vfio-pci endpoints with iommufd Message-ID: References: <20250714155941.22176-1-shameerali.kolothum.thodi@huawei.com> <20250714155941.22176-7-shameerali.kolothum.thodi@huawei.com> <798f739303f74fbca49a09a623a0a118@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; 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CTRY:US; LANG:en; SCL:1; SRV:; IPV:NLI; SFV:NSPM; H:mail.nvidia.com; PTR:dc6edge1.nvidia.com; CAT:NONE; SFS:(13230040)(36860700013)(376014)(7416014)(82310400026)(1800799024); DIR:OUT; SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 Jul 2025 18:22:03.4064 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 806fa0eb-b8c2-4302-9341-08ddc495a9dc X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a; Ip=[216.228.117.160]; Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CO1PEPF000044FB.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR12MB6282 Received-SPF: permerror client-ip=2a01:111:f403:2417::62e; envelope-from=nicolinc@nvidia.com; helo=NAM12-DM6-obe.outbound.protection.outlook.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Jul 16, 2025 at 10:51:23AM -0700, Nicolin Chen wrote: > On Wed, Jul 16, 2025 at 09:34:04AM +0000, Shameerali Kolothum Thodi wrote: > > > >> Seems aggressive for a hotplug, could we fail hotplug instead of kill > > > QEMU? > > > > > > > >Hotplug will unlikely be supported well, as it would introduce > > > >too much complication. > > > > > > > >With iommufd, a vIOMMU object is allocated per device (vfio). If > > > >the device fd (cdev) is not yet given to the QEMU. It isn't able > > > >to allocate a vIOMMU object when creating a VM. > > > > > > > >While a vIOMMU object can be allocated at a later stage once the > > > >device is hotplugged. But things like IORT mappings aren't able > > > >to get refreshed since the OS is likely already booted. Even an > > > >IOMMU capability sync via the hw_info ioctl will be difficult to > > > >do at the runtime post the guest iommu driver's initialization. > > > > > > > >I am not 100% sure. But I think Intel model could have a similar > > > >problem if the guest boots with zero cold-plugged device and then > > > >hot-plugs a PASID-capable device at the runtime, when the guest- > > > >level IOMMU driver is already inited? > > > > > > For vtd we define a property for each capability we care about. > > > When hotplug a device, we get hw_info through ioctl and compare > > > host's capability with virtual vtd's property setting, if incompatible, > > > we fail the hotplug. > > > > > > In old implementation we sync host iommu caps into virtual vtd's cap, > > > but that's Naked by maintainer. The suggested way is to define property > > > for each capability we care and do compatibility check. > > > > > > There is a "pasid" property in virtual vtd, only when it's true, the PASID- > > > capable > > > device can work with pasid. > > > > Thanks for this information. I think probably we need to take a look at this as > > this doesn't have a dependency on cold-plug device to be present for SMMUv3. > > Will go through intel vtd implementation. > > I see. A compatibility test sounds promising. > > It still feels tricky when dealing with multi vSMMU instances, if > some instances don't have a cold-plug device to poll hw_info. We > would need to pre-define all the feature bits. Then, run the test > on every hotplug device attached later to the vSMMU instance. > > Maybe we could do something wise: > The sysfs node provides all the IOMMU nodes. So, we could compare > the node names to see if they are likely symmetric or not. Nodes > sharing the same naming pattern are more likely created by the > same IOMMU driver. So, as a speculation, a vSMMU instance with no > coldplug device could borrow the bits from a vSMMU instance with > a device? > > Sure, individual IOMMU instances could differ in specific fields > despite using the same node name. This would unfortunately lead > to hotplug failure upon the compatibility check. Hmm, forget what I said here. Each vSMMU instance should be pre defined with a list of parameters. So, we will need to run the compatibility test not only for hotplug devices, but coldplug ones too. Thanks Nicolin