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Mon, 26 Jan 2026 19:14:35 -0800 Received: from Asurada-Nvidia (10.127.8.14) by mail.nvidia.com (10.126.190.180) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.20 via Frontend Transport; Mon, 26 Jan 2026 19:14:35 -0800 Date: Mon, 26 Jan 2026 19:14:33 -0800 From: Nicolin Chen To: Will Deacon CC: Jason Gunthorpe , , , , , , , , , , , 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> <20260123200327.GF1134360@nvidia.com> <20260126152019.GK1134360@nvidia.com> <20260126160940.GM1134360@nvidia.com> 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: SN1PEPF0002636A:EE_|DS0PR12MB7827:EE_ X-MS-Office365-Filtering-Correlation-Id: d1713cb2-9e87-4e09-40f1-08de5d523a9b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|82310400026|7416014|36860700013|376014|3613699012; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Jan 2026 03:14:48.3840 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: d1713cb2-9e87-4e09-40f1-08de5d523a9b X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.118.232];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: SN1PEPF0002636A.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR12MB7827 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260126_191452_677978_9C03AF19 X-CRM114-Status: GOOD ( 18.20 ) 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 Mon, Jan 26, 2026 at 06:56:34PM +0000, Will Deacon wrote: > On Mon, Jan 26, 2026 at 12:09:40PM -0400, Jason Gunthorpe wrote: > > On Mon, Jan 26, 2026 at 04:02:19PM +0000, Will Deacon wrote: > > > If we do that, can we drop the smp_mb()s from > > > arm_smmu_install_{old,new}_domain_invs()? > > > > I suppose so, but domain attach isn't a performance path so it depends > > on your preference for strict pairing of barriers. Currently the two > > smp_mbs() are paired. Can we reliably pair smp_mb() with dma_wmb()? > > Are you happy with that clarity? > > Yeah, I think that's ok. > > > My view is attach isn't a performance path, so having extra barriers > > is fine if it helps understandability. > > I think that the more barriers we have, the harder the code is to > understand so I would prefer just to have the smp_mb() for the > write->read case in arm_smmu_domain_inv_range() along with a comment > explaining why it's needed. > > I think that also means that my concern about the old comments on the > other patch largely disappears. I sent v10. Thanks for the insightful reviews! Nicolin