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Sun, 1 Sep 2024 22:27:10 -0700 Date: Sun, 1 Sep 2024 22:27:09 -0700 From: Nicolin Chen To: Baolu Lu CC: , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v2 02/19] iommufd/viommu: Add IOMMUFD_OBJ_VIOMMU and IOMMU_VIOMMU_ALLOC ioctl Message-ID: References: <55918c41-65c4-435c-860b-b2a177b0d364@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <55918c41-65c4-435c-860b-b2a177b0d364@linux.intel.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SN1PEPF000397B1:EE_|SN7PR12MB7980:EE_ X-MS-Office365-Filtering-Correlation-Id: d31ca81a-f9f9-4c69-2f17-08dccb0fef6b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|82310400026|376014|36860700013|1800799024; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?g+kneiUg2KHJWXMQfrvIfJLB5u9WJdndcJK6hoUK9gC07O8Yte/2P3Esqsz9?= =?us-ascii?Q?ewhJN+7VS9kxoeLtPezyIM6lHNuaeEysrf8ZmptWOOB+A/aJcY4k//Q06bZq?= =?us-ascii?Q?iOK8MelokMkt51CrGEe2eg4AT0vLsrZKIMqmZbHXaKn2vq4u/sA4NQuAJ9AE?= =?us-ascii?Q?OZThpzRMzFbKPSeorZITQQZ3Uql/wcslwkUYV4HDSIUIPDdr0ut4vzcD1RPi?= =?us-ascii?Q?L71OGFCrPqQrCEDmiVvpjdtuNMOLra38MIgNfkqd1bnwjhchQZcDwNw3pDw6?= =?us-ascii?Q?Nm1/iTSIoM6zfqRA5gt8i5utAFDTMEzEcfMmwmFxKmLuHCzEgEDVq/rnm3UH?= =?us-ascii?Q?s2y7ly93+J05L8UqNKhwTgv46sCPkqHPDZzxEDHHY53dsBvVbpup+iCDDTc8?= =?us-ascii?Q?QSe5l5KrruWmwQL8kAyV6UtxefHzmCvy+qCmOZDFXY7mCuK6Bhq9AlI9jL5p?= =?us-ascii?Q?VEhwVMq4AQOYizo/wWE3YChQyCtaQm3GMl2MA6xJxI+eMdoMP4qHaQSfIKqV?= =?us-ascii?Q?Ai5XfwsgwxQX7bI7Mt2HU/JbDJBBn1m0LFfM5YyasOevX67M4QoLFvdzMx45?= =?us-ascii?Q?EKnYKzf6P4GPbiQxBYX6/7guS3GsLXnhoK8ZUwYKhguGgwzCRLnJjDayfP17?= =?us-ascii?Q?NqTJMTUS2sa63sU8krSmW3+VaGzFIgF9mSMaFc6GheLn7Rtxy0ZwEprJMjEX?= =?us-ascii?Q?HhzckuZYQe8ZG5mcxMkSCRWbdYFIn4pJJt2yQ0+oN0VFEWnkCXZlGdkO9ifk?= =?us-ascii?Q?gtDDAJZf5u2HZZkbTjk+rQXEEFlWARvJSuyythETvhDHa0unWQIc/irfWMZ8?= =?us-ascii?Q?b52b9MjC3/+mcrmkNyAAaGwrFPvnKmag3JUNmtKiNIJiYrxDz6ghCzRL+PIr?= =?us-ascii?Q?BwZIbEt5pJZ2KM0UzRwojiu+wJsICdT4axh9yAqCp9Sbks7jKwm3299WEleA?= =?us-ascii?Q?g/CO+HH7AGDFGICNMo4HMNFClVVCHEIECrd4iKCq2SOMiWFGOXJxkXd6o9qK?= =?us-ascii?Q?xVRS0B2Ut+OD6b1yqSTqpD9sfmupiYNVZaig5zxOYn64RJ2fbaOtp7H6FBUr?= =?us-ascii?Q?oP1X1M5i1pL/SOzrGgVoElKIWHzBaoSve7ZY4w3Z5i2mucESzzYwcbLfK0r/?= =?us-ascii?Q?tC+hnS/xKoDxpRtACme4spBK0iMBZkJcfaoudbc/8+GpaFU8LrmbM4O+t3PF?= =?us-ascii?Q?rKlwmWlBKvuNYlu4Ca8eZPIxVqP+W+NXN4R8Xv5VQezSgQHh/pdpXTI17W/K?= =?us-ascii?Q?N/agyPSA6VYZdj+8bGhPwc2KliZmBzqdHdnyG/tgxeyLU74GaQ2AtJ4YWAaP?= =?us-ascii?Q?QxHueISsXbU7DmnGtTsNFL/XwaPLdPqKWaW2vtIGWFCCLuPo8ZSOR6LWEdpo?= =?us-ascii?Q?XJUP3KMN4ZE19qrEliRkUmXg7gvaRJCqlgtP2HetIG7gUrJvaJdLp1DE6+6F?= =?us-ascii?Q?LiNa8F8PZgN5FW1uGXfaWHbcKzqpHHnV?= X-Forefront-Antispam-Report: CIP:216.228.117.160;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge1.nvidia.com;CAT:NONE;SFS:(13230040)(7416014)(82310400026)(376014)(36860700013)(1800799024);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 02 Sep 2024 05:27:28.0088 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: d31ca81a-f9f9-4c69-2f17-08dccb0fef6b 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: SN1PEPF000397B1.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR12MB7980 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240901_222737_162123_21CAD786 X-CRM114-Status: GOOD ( 13.57 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Sun, Sep 01, 2024 at 10:39:17AM +0800, Baolu Lu wrote: > On 2024/8/28 0:59, Nicolin Chen wrote: > > +int iommufd_viommu_alloc_ioctl(struct iommufd_ucmd *ucmd) > > +{ > > + struct iommu_viommu_alloc *cmd = ucmd->cmd; > > + struct iommufd_hwpt_paging *hwpt_paging; > > + struct iommufd_viommu *viommu; > > + struct iommufd_device *idev; > > + int rc; > > + > > + if (cmd->flags) > > + return -EOPNOTSUPP; > > + > > + idev = iommufd_get_device(ucmd, cmd->dev_id); > > Why does a device reference count is needed here? When is this reference > count released after the VIOMMU is allocated? Hmm, it was used to get dev->iommu->iommu_dev to pin the VIOMMU to a physical IOMMU instance (in v1). Jason suggested to remove that, yet I didn't realize that this idev is now completely useless. With that being said, a parent HWPT could be shared across VIOMUs allocated for the same VM. So, I think we do need a dev pointer to know which physical instance the VIOMMU allocates for, especially for a driver-managed VIOMMU. Perhaps we should add back the iommu_dev and properly refcount it. Thanks Nicolin