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Mon, 21 Sep 2026 12:24:15 -0700 Date: Mon, 21 Sep 2026 12:24:13 -0700 From: Nicolin Chen To: "Peng Fan (OSS)" CC: Will Deacon , Robin Murphy , "Joerg Roedel (AMD)" , Jean-Philippe Brucker , Jason Gunthorpe , , , , Peng Fan Subject: Re: [PATCH RFC v2 1/4] iommu/arm-smmu-v3: Convert streams from RB tree to XArray Message-ID: References: <20260921-smmu-shared-sid-v2-0-4b656ce68178@nxp.com> <20260921-smmu-shared-sid-v2-1-4b656ce68178@nxp.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20260921-smmu-shared-sid-v2-1-4b656ce68178@nxp.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH1PEPF0000AD79:EE_|CH1PR12MB9621:EE_ X-MS-Office365-Filtering-Correlation-Id: fb7a92ec-eb73-4511-d6a6-08df1815fc58 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700016|82310400026|1800799024|23010399003|376014|7416014|10067099003|11063799006|22082099003|18002099003|56012099006|4143699003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: hwFa0QDooMgL9GgP+1Ec3/xMijoYUWoTOwAyEmQe1lhMeTQ6b/6WuQ4PBQKD7gEH7Xhk3CX9JiLDzxbcHVMj054M1rXDOHExi34Wr51P0cUnXKY+egVAbAj2M0O/BfbF+LgN+epAwzVuk88Cob7mldljewvyPrkyQER2WNpaHIOp/+TskeW7Gk/ZzaKqlxQQY7mhkNwaXd+OWlzPzGXg2LeOGYt0WId3YbRvIpXfA0OQ2NNdLJEOMMLPZXQe3R0CaqzMhCqxEi0nPdjMXansDmEbaPmT/LcZFuIVbQB8LOmsRHTWToFwIiwtL/9v2i65s6o/CvS3Le/UNFAL+QjQcOtxF4P9TxCALp2zlININDaz873fHQ3qloGGYjVospHBeNqXCfn59RqcA/wNjpm7wGGsbQACVysu+4NBK1nc8q3c1TfRztyyiP7TOsUKeVdr X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 21 Sep 2026 19:24:41.5502 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: fb7a92ec-eb73-4511-d6a6-08df1815fc58 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: CH1PEPF0000AD79.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH1PR12MB9621 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260921_122451_756272_67D8410A X-CRM114-Status: GOOD ( 10.95 ) 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, Sep 21, 2026 at 07:35:00PM +0800, Peng Fan (OSS) wrote: > From: Peng Fan > > Replace the smmu->streams RB tree with an XArray for SID -> > arm_smmu_stream lookups. The existing streams_mutex serialises all > accesses (both xa_store/xa_erase and xa_load), protecting the lifetime > of returned pointers against concurrent arm_smmu_remove_master() > without requiring RCU grace periods. A mutex (rather than xa_lock) is > needed because several paths sleep while the lock is held: > dmam_alloc_coherent(GFP_KERNEL) in arm_smmu_init_sid_strtab(), and > down_read() inside iommu_report_device_fault(). The commit message reads very unconvincing. The first paragraph starts with an action "replace" without giving a clear reason for the action. > This removes the RB tree comparators, the rb_node from Then the second paragraph repeats the action... > arm_smmu_stream, and simplifies duplicate-SID handling for bridged PCI > devices. ... and slightly mentions "simplifies". Maybe it should write about why this is necessary and how xarray would simplify vs RB tree? Nicolin