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Thu, 9 Apr 2026 15:45:27 -0700 Date: Thu, 9 Apr 2026 15:45:26 -0700 From: Nicolin Chen To: "Tian, Kevin" CC: "jgg@nvidia.com" , "will@kernel.org" , "robin.murphy@arm.com" , "bhelgaas@google.com" , "joro@8bytes.org" , "praan@google.com" , "baolu.lu@linux.intel.com" , "miko.lenczewski@arm.com" , "linux-arm-kernel@lists.infradead.org" , "iommu@lists.linux.dev" , "linux-kernel@vger.kernel.org" , "linux-pci@vger.kernel.org" , "Williams, Dan J" , "jonathan.cameron@huawei.com" , Vikram Sethi , "linux-cxl@vger.kernel.org" Subject: Re: [PATCH v3 1/3] PCI: Allow ATS to be always on for CXL.cache capable devices Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PEPF00000141:EE_|DS0PR12MB7851:EE_ X-MS-Office365-Filtering-Correlation-Id: 8540e8b5-2729-43e7-cd57-08de9689be31 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|1800799024|36860700016|376014|7416014|22082099003|18002099003|56012099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: +a99R+uzYKM4IVbwR89RVnLaRC5fNalNpBJpm/WVptFBREsaKk4OmAm3RGzd3JAuFu6BqVGkNgPjihjsn2Zy9GDJdsuvx50CXejJh9HaqT7+UB+czuSpFrIlGAcBrJMR48GSXNGUL3mEtBTh9I6NAMPb5ycDMXW+5v3YP8zu3HrJZiSsDLD2uVo2Nql7giDv/gHgiJR+zJkwWJkntyVtambYh81YUmM9YbT7/B4BVqXj1z0qqXZHhsHgDPY3tenxd2Yso4lPTY2oducY/1ROX0yXVp8HZOyh8FB3V86gYkQu8tuZ0xAJsnzvfR2yPyT4tRgDUzv99kK4XhvwtLeThE+9bZa2IOhXVtHcPv15hM/+7AYHWdX8Ca1b+eI0wiN9yR2gGFOUREe1h+tavLftcoLdY8q//jJqIPLQFsfYhxKzhQNptoxg4q8HtmDaYRr0 X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Apr 2026 22:45:47.7307 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 8540e8b5-2729-43e7-cd57-08de9689be31 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.118.233];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CH2PEPF00000141.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR12MB7851 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260409_154558_019301_AD69B12E X-CRM114-Status: GOOD ( 17.64 ) 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, Mar 31, 2026 at 08:19:19AM +0000, Tian, Kevin wrote: > > From: Nicolin Chen > > Sent: Saturday, March 7, 2026 7:41 AM > > > > Controlled by the IOMMU driver, ATS is usually enabled "on demand" when > > a > > device requests a translation service from its associated IOMMU HW running > > on the channel of a given PASID. This is working even when a device has no > > translation on its RID (i.e., the RID is IOMMU bypassed). > > ATS is usually enabled "on demand" when a given PASID on the device > is attached to an I/O page table. Above sounds like there will be a software > action to enable ATS upon a device translation request. > > +/* > > + * CXL r4.0, sec 3.2.5.13 Memory Type on CXL.cache notes: to source > > requests on > > + * CXL.cache, devices need to get the Host Physical Address (HPA) from the > > Host > > + * by means of an ATS request on CXL.io. > > + * > > + * In other world, CXL.cache devices cannot access host physical memory > > without > > + * ATS. > > + */ > > s/world/words/ I have updated commit messages and inline comments. Thanks all for the reviews! One question regarding VM case: if a device is ats_always_on, while VM somehow doesn't set nested_domain->enable_ats. Should the kernel at least spit a warning, given that it would surely fail the device? Nicolin