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Fri, 21 Aug 2026 19:07:40 -0700 Date: Fri, 21 Aug 2026 19:07:40 -0700 From: Nicolin Chen To: Jason Gunthorpe CC: , , , , , , , , , Subject: Re: [PATCH v9 07/12] iommu/arm-smmu-v3-kexec: Add ASID/VMID reservation helpers Message-ID: References: <9f9d227c0adf472e93293008e7083973688d015e.1784663184.git.nicolinc@nvidia.com> <178735412602.18212.13622444378152698190.b4-review@b4> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <178735412602.18212.13622444378152698190.b4-review@b4> X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ5PEPF000001F0:EE_|LV3PR12MB9215:EE_ X-MS-Office365-Filtering-Correlation-Id: 48fa04ad-124a-4bb9-b60c-08defff2298d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700016|1800799024|376014|23010399003|82310400026|11063799006|10067099003|4143699003|56012099006|18002099003|22082099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: zxW01dBIzZYNd9masFMbtHYzVhWSHTeCol2MjaA7iP7zCWeUKGdIcvXABI0dsZYLmtGOBcdst1fbzkRA0hablIZ3wCdSK0PRD6W7rNTvC1gyfyL1fNPJrCw8lcBEzFhAaBHDCnkz+S7PrhFF9jbau1IZsu5xBcgftWMxdovdfY+Xt0YeP+aIK5ElrKn7yWmJ0Po7XiAhlsr9kwPSlHQNPoETgQL0hZyXfZlQLRGD+3jKBx/HqLBfsnfh6d++qL0zwD8lXyoHoJxVIXUEurqOciHeih4Kc7A82EwjhpvZPIW2RaGhUMyA0yv0kmlV425RF10ZVYm3a+G0bwF/D1ROZsTth4mZq85mIMr8SQNl9m2kFCikC3TjSoFKpyzDrfPRhKxjEcS7yIFFH/ZdAFJjwglIvAObH5tYHo6KXq4+X23nGgZef+UEqXvy3OrmL39H X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Aug 2026 02:07:47.6732 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 48fa04ad-124a-4bb9-b60c-08defff2298d 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: SJ5PEPF000001F0.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: LV3PR12MB9215 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260821_190759_972646_82D631B2 X-CRM114-Status: GOOD ( 15.46 ) 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, Aug 21, 2026 at 08:15:26PM -0300, Jason Gunthorpe wrote: > > +static int arm_smmu_kexec_resv_asid(struct arm_smmu_device *smmu, u32 asid) > > +{ > > + int ret; > > + > > + /* A valid CD never has ASID 0; both kernels share the same HW limit */ > > + if (!asid || asid >= 1UL << smmu->asid_bits) > > + return -EINVAL; > > + > > + guard(mutex)(&arm_smmu_asid_lock); > > + > > + /* The value entry marks the ASID as in-use and identifies its scan */ > > + ret = xa_insert(&arm_smmu_asid_xa, asid, > > + xa_mk_value(arm_smmu_kexec_scan_id), GFP_KERNEL); > > + /* > > + * An -EBUSY against a value entry safely shares a permanent reservation > > + * made by another scan. A pointer entry means a live domain that will > > + * free its ASID for reuse eventually: keep -EBUSY to fail the scan. > > + */ > > + if (ret == -EBUSY && xa_is_value(xa_load(&arm_smmu_asid_xa, asid))) > > + ret = 0; > > Huh. Somewhere I had a patch to make ASID per smmu instance, just like vmid. > I think you might actually need it here? Is it possible that one instance > could probe, the core code could start changing domains and end up with an > unintended ASID conflict on a later instance? Then things go sideways? Yes. I've noticed a problem: SMMU-A allocates ASIDx from the global space for a default domain, later SMMU-B wants to reserve ASIDx. So my local v10 adds a new patch making ASID per smmu. If you would like your version, I can swap that. > > If you have that you can also drop the arm_smmu_kexec_resv_lock? Yes. The entire thing ended up cleaner actually. Thanks Nicolin