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Mon, 6 Jul 2026 11:05:52 -0700 Date: Mon, 6 Jul 2026 11:05:51 -0700 From: Nicolin Chen To: Jason Gunthorpe CC: Will Deacon , Robin Murphy , , Kevin Tian , , , Subject: Re: [PATCH v2 2/3] iommufd/viommu: Publish a vDEVICE only after vdevice_init() succeeds Message-ID: References: <1e05999347f4bf583edbc6a1312c857d5548708c.1783311134.git.nicolinc@nvidia.com> <20260706172356.GB118313@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20260706172356.GB118313@nvidia.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PEPF000023CD:EE_|SA5PPF8ECEC29A9:EE_ X-MS-Office365-Filtering-Correlation-Id: b4a7bf3d-53df-4d98-1c1c-08dedb8942d6 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|36860700016|1800799024|23010399003|82310400026|5023799004|11063799006|22082099003|18002099003|56012099006|4143699003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: rz+UPThzitpisBHq61O1mJqW5vrS0NOFfQRL14BBjhVBmfy3GDv69A3wHpUROCQyqowxsmkVRFOwf4qgxLj8mKYjWXGerb6BpMgAgw30Q2wycEuOre/449J/SoJwKdDfPQd8fZGURyNqjTCk38VD2XB5GFt6G7IlvwHLhGXOXQarcbHTumvD4q3ZgUN40oDFwZX9wNzBhL53NARJUbuRvh5YVQjosNHG43vBG5Xs2Fjr7farZuHMm9Ofn6GhQ7tFbJKT2meNAuvyvTynUlpo15JQfRV1yEIePdVOrF9G4clxhgYOvVXF+M7MTd+Ap5OvkpNSKcIIeqGJD8fmrxqX7m/D90ny+7r9zdqEtwH842Hpy9XJrLwXr5Kphbgo/e7DB145YJciiParpKkx/luhSdbuyB1WKUet/yFtptekXIsPqR7/2dctaFi2ySFeaCtH X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 Jul 2026 18:06:11.1351 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: b4a7bf3d-53df-4d98-1c1c-08dedb8942d6 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.118.232];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: SJ1PEPF000023CD.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA5PPF8ECEC29A9 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260706_110621_905438_9EBCBA01 X-CRM114-Status: GOOD ( 12.56 ) 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 Mon, Jul 06, 2026 at 02:23:56PM -0300, Jason Gunthorpe wrote: > On Sun, Jul 05, 2026 at 10:36:10PM -0700, Nicolin Chen wrote: > > @@ -218,18 +218,28 @@ int iommufd_vdevice_alloc_ioctl(struct iommufd_ucmd *ucmd) > > */ > > idev->vdev = vdev; > > > > - curr = xa_cmpxchg(&viommu->vdevs, virt_id, NULL, vdev, GFP_KERNEL); > > - if (curr) { > > - rc = xa_err(curr) ?: -EEXIST; > > + /* > > + * Reserve the slot with a zero entry (reads back as NULL) until the > > + * vdevice_init() op accepts the vDEVICE. Only the xa_* helpers hide a > > + * reserved entry, so never use a raw xas_* iterator on this xarray. > > + */ > > + rc = xa_insert(&viommu->vdevs, virt_id, NULL, GFP_KERNEL); > > + if (rc) { > > Why xa_insert() not xa_reserve() ? xa_reserve's kdoc says: "* If there is already something stored at @index, this function does * nothing" By its implementation, it wouldn't return an error on duplication? Nicolin