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Wed, 27 Aug 2025 10:19:19 -0700 Date: Wed, 27 Aug 2025 10:19:18 -0700 From: Nicolin Chen To: Jason Gunthorpe CC: , , , , , , , , , , , , , , Subject: Re: [PATCH rfcv1 4/8] iommu/arm-smmu-v3: Introduce a per-domain arm_smmu_invs array Message-ID: References: <20250827164804.GA2206304@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20250827164804.GA2206304@nvidia.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN2PEPF000044A5:EE_|IA0PR12MB7507:EE_ X-MS-Office365-Filtering-Correlation-Id: 806d3b85-90f9-4530-81d8-08dde58decf3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|7416014|376014|1800799024|36860700013; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?BlhgLRH57j2Fak5wm5aOGhMIedse47lG982ZiaB6WHNhPQ404UakZ9wjJXkD?= =?us-ascii?Q?Bq8dZow0RLfjv7nLG5R3PwiSuSEnpDXyhe+Bu5EAS7lGMCrqtl58VVhrs4ed?= =?us-ascii?Q?ESbKsifQfyJ64321F+HjHPrFc8XE0J2Hlc00EjxpxEIVlFNjDhaxDW7o96d4?= =?us-ascii?Q?CF/1EE9U00XyE7t4mewl0grt9qx9rXSkyKgHOCHzykYFvtioEDpBjcGPuXQh?= =?us-ascii?Q?Fw4jN0Hc98/Xi9nxInH14rQm1yxoxIgWo+cyWsRm8GQZw6QeTjcWnXyKG1tD?= =?us-ascii?Q?5+MrDxqnxhk1UcvvWgFibsmmoVJBZotXL8Lvv5Of8+zhExH5xEtOGhGgyQMd?= =?us-ascii?Q?mcOy2RLXnh6U4qDTFV/xuGMbpQn3zKqEDseODH9QBbUwOMLJTKbMpkR0CwZR?= =?us-ascii?Q?tIXo9yAPVzGgSPFrQMWwHh1E9sv2pBkP+/FPlhB60ibE9oplnLUP3Rja3eCq?= =?us-ascii?Q?PxZ2U+p/Bo/GSc6tkkL0hLiLg//5ZA+LUHZp/qJOegKFwHADuQX5YC1t0ySs?= =?us-ascii?Q?wRlepkT1RmDhpOfOOe1tfDCmChUVi9QrrvNqDRO6RL/nX5G7u5Jd/ZLz2+W3?= =?us-ascii?Q?Kpf8Caid8r7FuIQBZPliECRjc9Bc5KeDKKOzLuC2t+lJkgSyHO7/xp5/ksta?= =?us-ascii?Q?LUmcP+v/xCM+DUXVzzO1dJQ9NJnf0/wcB55YDpm4aMrlpDB1HRzCEET19ucs?= =?us-ascii?Q?+nJSw8DCb0elFTwmCU6fMx7PS/E/KisxwdS3eMgub0NLbwVFg2x2IVLJm+/4?= =?us-ascii?Q?t7Kgnc7ymtdHYEJwkaeASAGOU2G05p7gp50GQG1z245T2d5yC46J6xJOttqe?= =?us-ascii?Q?FGvcY71buZShpPRhCBh/SswId8yAJl0vzLUoZ3F61eSpcLVZ/O6q5SZtrj8K?= =?us-ascii?Q?hpICin4VRHeKQj6xIUBwx/Qq0c7iKV3yyXRtbXOWK1CZwljfVSjfJ0jtED8t?= =?us-ascii?Q?Max9Tlk3xHSeH2dgIorR+YFmH6GjJ0HWYUhOrc2rfkCPYX6K8zSofosbKmzi?= =?us-ascii?Q?DBflKIz0yEIaVEt3l1pMqRwjFuDQvamlytxPinUpMPFNVWMBDg6kSpz2UYnN?= =?us-ascii?Q?xFfqLJVh+0be+8DZhhvik/3FhNpkL5DSba2rLfegAEpEiHJjr5wXKYD5oDKc?= =?us-ascii?Q?hVDm+0QcS7Sp0Uk4xlg0l/MDq5sqN2cHpx3oK6vluVLOxivbYCYTh8FeayUk?= =?us-ascii?Q?9/m1XaRE0rnLI8IniN9b1wUCgd5bpiJfNiRHZ+6uS+03Dul/8NepL0tUaQHD?= =?us-ascii?Q?bpOOxwzFCdtrE72seF8nvbpT784vs75Jy6eETNoW1nEPD1HWsWjmtMSOLyKr?= =?us-ascii?Q?55kejS8pge2dNsd9YrewnRGmGkwvxt4WJLWFEMxAhb2VmwGYuNvUgvfaRsv0?= =?us-ascii?Q?iwUWSDbLYw4h6p97R92GIUKt7qV4D+6VFpc89jXbzwsZXFqVurUduV51gPKf?= =?us-ascii?Q?dBqOOq7fJ4zsyDyzEvnYovKdvUwR8SQ+02incdSF+7FrKK1DThFDQZQNWoCW?= =?us-ascii?Q?R9+YcKO2v89y+sXsT7PPiJLzs4HAx9ddoz2P?= X-Forefront-Antispam-Report: CIP:216.228.117.161;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge2.nvidia.com;CAT:NONE;SFS:(13230040)(82310400026)(7416014)(376014)(1800799024)(36860700013);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Aug 2025 17:19:48.1667 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 806d3b85-90f9-4530-81d8-08dde58decf3 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: BN2PEPF000044A5.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA0PR12MB7507 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250827_101952_516069_A6690EB8 X-CRM114-Status: GOOD ( 24.97 ) 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 Wed, Aug 27, 2025 at 01:48:04PM -0300, Jason Gunthorpe wrote: > On Wed, Aug 13, 2025 at 06:25:35PM -0700, Nicolin Chen wrote: > > +/** > > + * arm_smmu_invs_del() - Remove @del_invs from @old_invs > > + * @old_invs: the old invalidation array > > + * @del_invs: an array of invlidations to delete > > + * > > + * Return: a newly allocated and sorted invalidation array on success, or an > > + * ERR_PTR. > > + * > > + * This function must be locked and serialized with arm_smmu_invs_add/dec(), > > + * but do not lockdep on any lock for KUNIT test. > > + * > > + * Caller is resposible for freeing the @old_invs and the returned one. > > + * > > + * Entries marked as trash will be completely removed in the returned array. > > + */ > > +VISIBLE_IF_KUNIT > > +struct arm_smmu_invs *arm_smmu_invs_del(struct arm_smmu_invs *old_invs, > > + struct arm_smmu_invs *del_invs) > > +{ > > Having looked at this more completely, I think we should drop this > function. > > Just always do decr, then have a simple function to compact the list > after the decr: But the _dec function will always take the write lock, which seems to lose the benefit of using an RCU array? The complexity of the _dec function wouldn't release the lock very quickly. The current version only invokes it upon kmalloc failure, which can be seem as a very rare case having a very minimal impact. > struct arm_smmu_invs *arm_smmu_invs_cleanup(struct arm_smmu_invs *invs, > size_t to_del) > { > struct arm_smmu_invs *new_invs; > size_t i, j; > > if (WARN_ON(invs->num_invs < to_del)) > return NULL; > > new_invs = arm_smmu_invs_alloc(invs->num_invs - to_del); > if (IS_ERR(new_invs)) > return NULL; > > for (i = 0, j = 0; i != invs->num_invs; i++) { > if (!refcount_read(&invs->inv[i].users)) > continue; > new_invs->inv[j] = invs->inv[i]; > j++; > } > return new_invs; > } > > If this returns NULL then just leave the list alone, it is OK to sit > there with the 0 users left behind. Yea, it's better than waiting for the next _add function to compact the list. > No need for the complex _del function and the _decr function.. > > This also means the memory doesn't need to be preallocated and it > significantly simplifies alot of the logic. By "preallocated" you mean "master->scratch_invs"? I think it will be still needed for the "dec_invs" argument in: size_t arm_smmu_invs_dec(struct arm_smmu_invs *invs, struct arm_smmu_invs *dec_invs); ? Or you mean the allocation in arm_smmu_invs_del()? Yes, this drops the kmalloc in the detach path. Thanks Nicolin