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Tue, 3 Feb 2026 11:24:26 -0800 Date: Tue, 3 Feb 2026 11:24:25 -0800 From: Nicolin Chen To: Robin Murphy CC: Jason Gunthorpe , , "Tian, Kevin" , Jonathan Cameron , "will@kernel.org" , "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" , "linux-cxl@vger.kernel.org" Subject: Re: [PATCH RFCv1 1/3] PCI: Allow ATS to be always on for CXL.cache capable devices Message-ID: References: <69727e7ded712_3095100ab@dwillia2-mobl4.notmuch> <20260127150440.GF1134360@nvidia.com> <69795d0366a9_1d33100d3@dwillia2-mobl4.notmuch> <20260128130520.GV1134360@nvidia.com> <20260203143348.GA3931454@nvidia.com> <20260203175540.GC3931454@nvidia.com> <0472f0f6-2f13-459e-857d-d5003f2f0ac4@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <0472f0f6-2f13-459e-857d-d5003f2f0ac4@arm.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH1PEPF0000AD81:EE_|MW3PR12MB4442:EE_ X-MS-Office365-Filtering-Correlation-Id: c38b9ca7-939e-4a54-2645-08de6359e6b8 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|376014|7416014|36860700013|1800799024; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: gJiz4pWh5QKwVbvRDRCqY0udoPNHXsaC4lAgIO92ADiaIj0YkV50qY+yUQfNO0WZtVJRn54kk9/NjNzZXp+60AZk3saNGC6Imu6r07mW7GtF4obY/DEkNQI2f3aD42yhd2Shl82c8sgmI8D62/S8TqCbxCUznkiLzvUx04ppkbfNXejidhiGXNQBWm5SskRKKtUleyK1KyyR41PZPIIzMlazAJ7MY9nVAPN+pkSQa6hYgTsXWQi5lmUvqatPlVPVUF++jAQhqiy8PZwSZQ/bnN0oDrV/gN7z2mTKF3UsWTKwC6XTb+Wn5x2MIvjvsDzLhrMvcF1Z3YsY8wLRP/9j/b4fylmBfL/KCgWrkzJ5Sm3QNPY8meRtBl+Z9VSyuwNMRQODQtsQvv/TEg17dRsPlE9LoUlhmjeO9KKeiKJmbQTd1gYYw1b1wQHs5LSRtZNO X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 03 Feb 2026 19:24:50.5640 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: c38b9ca7-939e-4a54-2645-08de6359e6b8 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: CH1PEPF0000AD81.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW3PR12MB4442 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260203_112458_483580_2FBA8D1B X-CRM114-Status: GOOD ( 15.80 ) 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, Feb 03, 2026 at 06:59:35PM +0000, Robin Murphy wrote: > On 2026-02-03 5:55 pm, Jason Gunthorpe wrote: > > On Tue, Feb 03, 2026 at 09:45:17AM -0800, Nicolin Chen wrote: > > > Btw, attaching to IOMMU_DOMAIN_BLOCKED/group->blocking_domain is not > > > allowed in general if require_direct=true. I assume this case can be > > > an exception since there's no point in allowing a device that has no > > > driver yet to access any reserved region? > > No, the point of RMRs in general is that the device can be assumed to > already be accessing them, and that access must be preserved, regardless of > whether an OS driver may or may not take over the device later. I see. Thanks for the input. > In fact RMRs > with the "Remapping Permitted" flag are only strictly needed *until* an OS > driver has taken control over whatever it was that firmware left them doing. Yes. I see that doesn't set require_direct. Nicolin