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Thu, 6 Feb 2025 12:33:22 -0800 Received: from rnnvmail201.nvidia.com (10.129.68.8) by rnnvmail205.nvidia.com (10.129.68.10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.14; Thu, 6 Feb 2025 12:33:22 -0800 Received: from Asurada-Nvidia (10.127.8.12) by mail.nvidia.com (10.129.68.8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.14 via Frontend Transport; Thu, 6 Feb 2025 12:33:21 -0800 Date: Thu, 6 Feb 2025 12:33:19 -0800 From: Nicolin Chen To: Shameerali Kolothum Thodi , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Jason Gunthorpe CC: "qemu-arm@nongnu.org" , "qemu-devel@nongnu.org" , "eric.auger@redhat.com" , "peter.maydell@linaro.org" , "ddutile@redhat.com" , Linuxarm , "Wangzhou (B)" , jiangkunkun , "Jonathan Cameron" , "zhangfei.gao@linaro.org" , "nathanc@nvidia.com" Subject: Re: [RFC PATCH 0/5] hw/arm/virt: Add support for user-creatable nested SMMUv3 Message-ID: References: <71116749d1234ab48a205fd2588151ec@huawei.com> <20250206170238.GG2960738@nvidia.com> <20250206174647.GA3480821@nvidia.com> <20250206175843.GI2960738@nvidia.com> <13b1d8b97a314cb28b87563fa9b45299@huawei.com> <20250206181306.GK2960738@nvidia.com> <02a0080a4a1642d69b7f5dd4707a5b3d@huawei.com> <20250206182201.GL2960738@nvidia.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:dc6edge2.nvidia.com; CAT:NONE; SFS:(13230040)(36860700013)(1800799024)(376014)(7416014)(82310400026); DIR:OUT; SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 Feb 2025 20:33:40.8948 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 60659fb1-e119-483c-7246-08dd46ed8b13 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a; Ip=[216.228.117.161]; Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BL02EPF0001A0FA.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA0PR12MB9046 Received-SPF: softfail client-ip=2a01:111:f403:2009::621; envelope-from=nicolinc@nvidia.com; helo=NAM10-BN7-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 Thu, Feb 06, 2025 at 02:22:01PM -0400, Jason Gunthorpe wrote: > On Thu, Feb 06, 2025 at 06:18:14PM +0000, Shameerali Kolothum Thodi wrote: > > > > So even if you invent an iommu ID we cannot accept it as a handle to > > > create viommu in iommufd. > > > > Creating the vIOMMU only happens when the user does a cold/hot plug of > > a VFIO device. At that time Qemu checks whether the assigned id matches > > with whatever the kernel tell it. > > This is not hard up until the guest is started. If you boot a guest > without a backing viommu iommufd object then there will be some more > complexities. Yea, I imagined that things would be complicated with hotplugs.. On one hand, I got the part that we need some fixed link forehand to ease migration/hotplugs. On the other hand, all IOMMUFD ioctls need a VFIO device FD, which brings the immediate attention that we cannot even decide vSMMU's capabilities being reflected in its IDR/IIDR registers, without a coldplug device -- if we boot a VM (one vSMMU<->pSMMU) with only a hotplug device, the IOMMU_GET_HW_INFO cannot be done during guest kernel probing vSMMU instance. So we would have to reset the vSMMU "HW" after the device hotplug? Nicolin