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Tue, 27 Jan 2026 10:07:10 -0800 Date: Tue, 27 Jan 2026 10:07:09 -0800 From: Nicolin Chen To: Jason Gunthorpe CC: Pranjal Shrivastava , , , , , , , , , , , Subject: Re: [PATCH v9 6/7] iommu/arm-smmu-v3: Add arm_smmu_invs based arm_smmu_domain_inv_range() Message-ID: References: <06999367d001283744fd98eb7c1823afd516ce84.1766174731.git.nicolinc@nvidia.com> <20260127170837.GM1134360@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20260127170837.GM1134360@nvidia.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PEPF00001CDC:EE_|DS4PR12MB9746:EE_ X-MS-Office365-Filtering-Correlation-Id: 0a9d55c0-5315-4007-755b-08de5dcef408 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|36860700013|82310400026|7416014|1800799024|3613699012; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?lZl4781RGRFDoSsKT4mVgbGJiGDXSCNIY33KzqoCD4+G+qqhQC/6yoG9zG/F?= =?us-ascii?Q?kL/XzqmoQsfCceUnGJs+K41zD2Fg07cjV4H9yV1FpzhIIrQ7m/w0x3QazGTE?= =?us-ascii?Q?kMBGFj3yBOh0VKLLeer4dWqryocBNgpBf42cmJMdoSOLm+gbi+OEPgPDWFvc?= =?us-ascii?Q?U7SEjTMQTNA7ia7VUb3rhiIbCj1mn+sp9MHWy2A/NX5ilpiQMxEdgmE+0qjM?= =?us-ascii?Q?TDGvreuU1Cf4kJW+ppkcSwPK9oSh7P+ll0d3fTpGx3X1cUDyAfHztjouua3T?= =?us-ascii?Q?JI07FXufwEDDeUUpoJNYx37LvMHWuwjaKE76FtQk+zGSWZ6alMtw5S9g8q2C?= =?us-ascii?Q?/mraDfRNPWFFk5rcqtPZmQo5my9VfZ2Eql2QTtZX4vNFkYhCAAGjlXvLXeQN?= =?us-ascii?Q?/Nu6aNd/pF5opnHvb0zR2Chi1p3DQSkRXWaeDSSb76I+ykmLcd/pZ1r9HVDB?= =?us-ascii?Q?jXqaKOABjqTTqiwciJRXXnVyFe6Xac7eMfeVRT0zD69CK1N7Iaw7yhLsihxj?= =?us-ascii?Q?nT6Stu/9gvNhNo/4DUqmWBYA1cztMY8sr4eVR7D5/ef0DhOO98+wcSSmxdDu?= =?us-ascii?Q?BiwCZ1SNzABTqjMM9HNAyvvXC26iZ80F4+pbr73bnQ+UrvqbeScjSCQ1ZcHc?= =?us-ascii?Q?1lHPTuutbBOfo6zGDiqMIlW5+g2JMGywH3gZ97OKXYIUqFhu8R+7xB6eYjJ2?= =?us-ascii?Q?Wcd9pjbD0mCDrp6ofqsq/xQ/gg6FwVeg0cOuIxHu5ed/jvNkVGQT2/+T/M5Z?= =?us-ascii?Q?AhscO1s7n3+2KubgPU8VDvh1gmGNfxTRe/8bnqgGJ2jA6m0fnfA6Pz3oiG3a?= =?us-ascii?Q?5h6TCI8M1fQ0VsWVP+2HX/WVh6T0HPhk5v7CSyqNd9XfajFuAEbQtUE3cI8s?= =?us-ascii?Q?AILYFAUPaFEccc9aFCcNkFzrHI4kjMuxWubj1qAarYSEo/qaaLR3rDsJPduj?= =?us-ascii?Q?dU8cyYm7VnKZAtsp3j9c0XKdpn+dI6mHbqRR6qfN6c+HZgTECvJSJSLl6Y4P?= =?us-ascii?Q?v9Wd0WNNDIy0dKjeJH20sA4+QdTE7JkZI2Ckgx7PmDtV1r9XEz2Ylo73bOSU?= =?us-ascii?Q?TpyyI4BfVUM842C/aPAdwRFIySnxCjBpleqPT+Jc0/elaT9TB2hBjom6FZwo?= =?us-ascii?Q?ALdV2BgOkxPyljqdT1l/urbESf6+FBu4INn1+00HlKSVfD32XjSqPdNGyHTC?= =?us-ascii?Q?rYtc4DcnD0UbL1L3/MnQ1now4yVJyqoO1o/hP59c56zcXpy2of3ZyI8bCpq7?= =?us-ascii?Q?ynuSo9WZjNq0a8OvwtFaTxkeNfBZnwSJZU7weAl+SgrJrYaAkUax/d8GwSNY?= =?us-ascii?Q?t9Qn0Wr21o3vjc2yyi4k/Ug60UOw+BPkVTbKmR5S44pYl4sa6ymaVxcZPTPj?= =?us-ascii?Q?PjhO2vC5LhABAl7z7BQOvzdhPG0pX+oOHlZhLQj2NlmC2eNddiHwQBB8oeyf?= =?us-ascii?Q?AlIENuxbR1BZIrpMD4c3E4JJndTCycT5JzF4qdL9k9YybJ3jgqCbTHaxa2+0?= =?us-ascii?Q?xgFwdlMQ1Iz48ANMDimOZmH9x38lNx/Bb598ad3jbphRCk8Z6FPYp06DluqN?= =?us-ascii?Q?+B8ymCPHY/Jmt+uVQZGJyRIGLRtBXJBRvMIDQ177s5xo+5Fjj5xLoLJHB3q3?= =?us-ascii?Q?QqazsM5ne0krAmcHCY5pDBvT2lgWBn1Lx7eLMP8c1zV17cbc1bIIbbIAVjZp?= =?us-ascii?Q?EZHsMkwTMegKpRqb3aijFidmJfE=3D?= 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)(376014)(36860700013)(82310400026)(7416014)(1800799024)(3613699012);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Jan 2026 18:07:37.0730 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 0a9d55c0-5315-4007-755b-08de5dcef408 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: SJ1PEPF00001CDC.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS4PR12MB9746 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260127_100743_532737_74551028 X-CRM114-Status: GOOD ( 24.30 ) 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 Tue, Jan 27, 2026 at 01:08:37PM -0400, Jason Gunthorpe wrote: > On Tue, Jan 27, 2026 at 08:38:31AM -0800, Nicolin Chen wrote: > > Hi Pranjal, > > > > Sorry, I missed this! > > > > On Fri, Jan 23, 2026 at 09:48:37AM +0000, Pranjal Shrivastava wrote: > > > On Fri, Dec 19, 2025 at 12:11:28PM -0800, Nicolin Chen wrote: > > > > + /* > > > > + * Avoid locking unless ATS is being used. No ATC invalidation can be > > > > + * going on after a domain is detached. > > > > + */ > > > > + if (invs->has_ats) { > > > > + read_lock(&invs->rwlock); > > > > > > Shouldn't these be read_lock_irqsave for all rwlock variants here? > > > Invalidations might happen in IRQ context as well.. > > > > > > > + __arm_smmu_domain_inv_range(invs, iova, size, granule, leaf); > > > > + read_unlock(&invs->rwlock); > > > > It was kept from the older versions where we had a trylock. Jason > > had an insight about this, mainly for less latency on invalidation > > threads. > > > > Yet, now we have a plain locking. TBH, I can't find a good reason > > justifying this. And it does look a bit unsafe to me. So, I think > > I will just change to the _irqsave version. (Jason?) > > My understanding has been that this invalidation can run from an IRQ > context - we permit the use of the DMA API from an interrupt handler? > > I though that for rwsem the read side does not require the _irqsave, > even if it is in an irq context, unless the write side runs from an > IRQ. Hmm, is "rwsem" a typo? Because it's rwlock_t, which is spinlock :-/ > Here the write side always runs from a process context. > > So the write side will block the IRQ which ensures we don't spin > during read in an IRQ. And, does write_lock_irqsave() disable global IRQ or local IRQ only? Documentation/locking/locktypes.rst mentions "local_irq_disable()".. Thanks Nicolin