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Sat, 9 May 2026 00:57:01 -0700 Date: Sat, 9 May 2026 00:56:57 -0700 From: Nicolin Chen To: Robin Murphy CC: Pranjal Shrivastava , Jason Gunthorpe , Will Deacon , Joerg Roedel , "Jean-Philippe Brucker" , Catalin Marinas , =?utf-8?Q?Miko=C5=82aj?= Lenczewski , , , Subject: Re: [PATCH] iommu/arm-smmu-v3-sva: Enable Hardware Access and Hardware Dirty bits Message-ID: References: <20260503135413.1108138-1-nicolinc@nvidia.com> <20260508123550.GB9254@nvidia.com> <4e129891-2f52-4bac-8e33-1fdde42fd29a@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <4e129891-2f52-4bac-8e33-1fdde42fd29a@arm.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ5PEPF000001F1:EE_|MN2PR12MB4064:EE_ X-MS-Office365-Filtering-Correlation-Id: 323196f9-3706-4de0-6b79-08deada08f2e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|7416014|82310400026|36860700016|18002099003|22082099003|56012099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: Ic8fvssMyVnfYIulZp6ccENlBGL0HNFvRaGLxqA2PxlCPBhQdMa8RK82JKpQ2uizYGI9N+lBKxnpjw7sRlOaJ+9sjsHhPf8mStDiBhjq/w6fjn75S0BCmtEH556SOgxM9vGf8DQM7DefgU8JGpMsLfKvXkCb+rPcrBTt5oLYm+t5/6ec4C1BtMWKBEbn2L4BwJ1mnvno+qHAfEp+1mnNhyzWXCre4a4TsklGvZJ234hqQpHepblJ0puMdCw3FobzbH26Cj2JKX15jB08Le9FNuoSkUdF9ySG7m2PW9ydR36br2O0wDafKbsbJ6UDC5y2zbCmH0H4ogXiLu5Dy6RcSEg+XJtBwKqfXy3OCZlcCeQo+cepCHY4U8m4yHz2R8jznvWJ1EjvvTWXhWsU8sykaRoWlapVE4/ghQ6czsi09ZFQxNqBg+h83DvOxZzkCEmy X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 May 2026 07:57:04.1537 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 323196f9-3706-4de0-6b79-08deada08f2e 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: SJ5PEPF000001F1.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR12MB4064 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260509_005714_116707_1E57171A X-CRM114-Status: GOOD ( 17.50 ) 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 Fri, May 08, 2026 at 03:24:32PM +0100, Robin Murphy wrote: > On 2026-05-08 2:57 pm, Pranjal Shrivastava wrote: > > I see, so IIUC, you mean if IS_ENABLED(CONFIG_ARM64_HW_AFDBM) but CPU > > doesn't enable HTTU, it is perfectly safe to let the SMMU do HTT updates, > > Since the fault handlers are already expecting HW-triggered updates? > > > > Which means our check would be something like: > > > > if (IS_ENABLED(CONFIG_ARM64_HW_AFDBM) { > > if (smmu->features & FEAT_HA) > > ... > > } > > > > instead of cpu_has_hw_af()? > > Hmm, looking closer, cpu_has_hw_af() is the thing which actually influences > mm behaviour (via arch_has_hw_pte_young and arch_wants_old_prefaulted_pte), > and that can still be false at runtime if ARM64_HW_AFDBM is enabled but any > CPU doesn't support HAFDBS, so perhaps you were right the first time :) IIUIC, v2 should be: + /* + * Enable Hardware Access and Dirty updates (DBM) if supported by + * both the SMMU and the CPU. It is unsafe to enable SMMU's HTTU, + * if the CPU does not support it as it bypasses mm page aging. + */ + if (cpu_has_hw_af()) { + if (master->smmu->features & ARM_SMMU_FEAT_HA) + target->data[0] |= cpu_to_le64(CTXDESC_CD_0_TCR_HA); + if (master->smmu->features & ARM_SMMU_FEAT_HD) + target->data[0] |= cpu_to_le64(CTXDESC_CD_0_TCR_HD); + } Thanks Nicolin