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Mon, 1 Jun 2026 13:41:28 -0700 Date: Mon, 1 Jun 2026 13:41:26 -0700 From: Nicolin Chen To: Jason Gunthorpe CC: Will Deacon , Robin Murphy , "Joerg Roedel" , Bjorn Helgaas , "Rafael J . Wysocki" , Len Brown , "Pranjal Shrivastava" , Mostafa Saleh , Lu Baolu , Kevin Tian , , , , , , , Shuai Xue Subject: Re: [PATCH v4 18/24] iommu/arm-smmu-v3: Introduce master->ats_broken flag Message-ID: References: <49dde0a2e2dc88e421a3010956db33d47cc92aa8.1779161849.git.nicolinc@nvidia.com> <20260519120658.GB3477375@nvidia.com> <20260601123231.GG3195266@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20260601123231.GG3195266@nvidia.com> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS2PEPF000061C3:EE_|CH2PR12MB4070:EE_ X-MS-Office365-Filtering-Correlation-Id: 3df27cc5-5664-4047-3334-08dec01e3249 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|36860700016|1800799024|7416014|376014|22082099003|18002099003|6133799003|11063799006|4143699003|56012099006; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:216.228.118.233;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc7edge2.nvidia.com;CAT:NONE;SFS:(13230040)(82310400026)(36860700016)(1800799024)(7416014)(376014)(22082099003)(18002099003)(6133799003)(11063799006)(4143699003)(56012099006);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: icSMcEJOV7TMcyg+j+xK5572Pab56HU5ni5AAima9lGnAP4F+w0yF3rNOyagX/TGKzieCixngrA8rqrEqVJ4/0euMPSr6t9aUj87A/8FAE5OQiuq+srdU5HvQPLckx1Q6uGcikTl+Ec2Ls79zjBiIvN2ZV2gby2TIorwaiu0+wYBM7BZGM0og5ezZXFqqpuw28yXPSSVWy1foqt/Q5s3v3A5BC7jQMPZi4ri5WikkAHSeL2W5lTeblbkAsGBDlwfhGFPok/FjsVQNpxWDWYJOgrVgRsvCLo3XqkiIvrSidL5ijbTzTaL9Or+HTfEoSzera1/Zs0qx10yOoc7e80R/G3jGL0y1V+uGgipWGolHuyfKT9g3oSRs8OZuT7KO6MFY+L/mDgohldwdZeK2lWo0c/uBZMF9XM9Avqw0oHLbN6eFyle7m3F3mvDDmx0lW+l X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Jun 2026 20:41:45.6922 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 3df27cc5-5664-4047-3334-08dec01e3249 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: DS2PEPF000061C3.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH2PR12MB4070 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260601_134158_579210_DC2037D8 X-CRM114-Status: GOOD ( 26.39 ) 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, Jun 01, 2026 at 09:32:31AM -0300, Jason Gunthorpe wrote: > On Fri, May 29, 2026 at 06:27:40PM -0700, Nicolin Chen wrote: > > On Tue, May 19, 2026 at 09:06:58AM -0300, Jason Gunthorpe wrote: > > > On Mon, May 18, 2026 at 08:39:01PM -0700, Nicolin Chen wrote: > > So I've tried INV_TYPE_ATS_BROKEN: during per-domain invalidation, > > each batch is built from domain->invs so it can carry the "invs"; > > if the batch times out, we can immediately mutate its ATS entries. > > > > But I realized a limitation. E.g., if a device attaches to two SVA > > domains on two SSIDs. An invalidation timing out on one of the SVA > > domains could mark INV_TYPE_ATS_BROKEN in its own invs, but not in > > the other SVA domain's invs? > > You'd have to mark all the S1's sharing the STE. That would be a bit convoluted as we would have to go through all other domains' invs arrays. A master (that timed out an ATC_INV) might be attached to multiple domains (RID, SVA1, SVA2, ...). Also, we currently don't have any per-master reverse-tracking to its attached domains (master_domain is added to smmu_domain->devices list only for now). So, two things would be needed on top of what we currently have. Firstly, we would need another per-master list tracking all the attached smmu_domains. Maybe reuse master_domain? Let's call this master->master_domains for now. Secondly, locking. We have two paths that can trigger an ATC_INV timeout: __arm_smmu_domain_inv_range() that takes the rwlock read on the current smmu_domain->invs; arm_smmu_atc_inv_master() that doesn't take any rwlock. When these two paths walk through the master->master_domains, we would need to take different rwlocks for those domains. Also, the __arm_smmu_domain_inv_range() path should skip the invs on the current master_domain, as the rwlock is already held. I wonder what's your opinion about these? Given all this complexity, I started to wonder if we could have implemented the invs as an RCU-list than an RCU-array: all IOTLB tag nodes would be still allocated to add/delete/read locklessly; all ATS nodes would be fixed in the master structure to add/del/ read with the rwlock. Then, a timeout occurring to either path can simply mutate the ATS entries on the master directly without going through the list of domains. > > So, it seems that master->ats_broken is still a cleaner solution? > > I don't want the invs code touching master, that is against the entire > design. I think I can understand the idea here: we want the invs design to be in the common code, so anything that's driver-specific (smmu or master) shouldn't be touched. > Maybe a flag in the invs list itself is sufficient. I think we would have to use INV_TYPE_ATS_BROKEN than a per-invs flag: e.g., a nesting parent domain will have multiple ATS devices so it cannot use one flag on its big invs to separate the broken devices from all other healthy devices. Nicolin