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Mon, 4 May 2026 13:55:01 -0700 Date: Mon, 4 May 2026 13:54:59 -0700 From: Nicolin Chen To: Pranjal Shrivastava CC: , Will Deacon , Joerg Roedel , Robin Murphy , Jason Gunthorpe , Mostafa Saleh , Samiullah Khawaja , Daniel Mentz , Pasha Tatashin , David Matlack Subject: Re: [PATCH rc v2] iommu/arm-smmu-v3: Fix inconsistent ATS state tracking Message-ID: References: <20260504163842.2692314-1-praan@google.com> Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: 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: SA2PEPF000015CA:EE_|BN7PPFD91879A44:EE_ X-MS-Office365-Filtering-Correlation-Id: 71c3f29b-d1f0-4262-cc05-08deaa1f7888 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|82310400026|36860700016|7416014|18002099003|22082099003|56012099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: Thoggmhv8lKgZfoTAlK7LGmw9VRZfVFMgiYBlsXk9FRInjXKAN8ZTPybEnpluSb5lcxOgKcDA5ToAlG/psbMJibredflMofv0En6BY9dGErNGTdt+mwAjuk7UzqwOcyR6RrLC9h+oXcp4LjHu0p9LNtkRBZY9KPGSwIDOJlMdDX0BgKe0asRP/3uPB3HGWIH6uEkm8bKyIQ1z6AYCibOxyqwxkxqiVhCacby29YXd7c0I6PhX5qGDXfX3mTXiMnIKVf2o0z64obuPn+GKnqIJk8FAuilmJnUGb8W0+myhk+AJhc/VTakPpWLAhuJSprM8+LKdhxJ/tHWNAMKbZvN06SOGu9Ujs8mrUMK/qb7VPY/+IEhACQUNEnVdw8j024Ncl4Pfc2vt1SzfbF+odrlErGyeW1wsbglzU2LAP2oEK1Drt5x/nmjRjPVtO4MwAZu X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 May 2026 20:55:27.4735 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 71c3f29b-d1f0-4262-cc05-08deaa1f7888 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: SA2PEPF000015CA.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN7PPFD91879A44 On Mon, May 04, 2026 at 08:40:33PM +0000, Pranjal Shrivastava wrote: > On Mon, May 04, 2026 at 01:23:06PM -0700, Nicolin Chen wrote: > > On Mon, May 04, 2026 at 07:33:07PM +0000, Pranjal Shrivastava wrote: > > > On Mon, May 04, 2026 at 11:01:42AM -0700, Nicolin Chen wrote: > > > > On Mon, May 04, 2026 at 04:38:42PM +0000, Pranjal Shrivastava wrote: > > > and then in attach_prepare we can add the ats check for safety: > > > > > > if (!state->ats_enabled && master->ats_enabled) { > > > pci_disable_ats(to_pci_dev(master->dev)); > > > > > > + if (pdev->ats_enabled) > > > + pci_disable_ats(to_pci_dev(master->dev)); > > > > master->ats_enabled is redundant if we check pdev->ats_enabled. > > > > BTW, is it really redundant? I assume it represents the driver's state > machine? I believe the condition: > > if (!state->ats_enabled && master->ats_enabled) > > translates to: The current state has ATS active, but the new target > state is to have them inactive. Isn't that the case? That's fair enough. We would need an dev_is_pci(), so having master->ats_enabled makes sense. > > If we add a gate here, should add to pci_enable_ats() too? > > > > I see that pci_enable_ats already checks for it: > > if (WARN_ON(dev->ats_enabled)) > return -EBUSY; I see, then we could probably leave that so future corner case can warn us. IOW, yea, I think gating pci_disable_ats() only is fine. Thanks Nicolin