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Fri, 15 Nov 2024 13:46:24 -0800 Date: Fri, 15 Nov 2024 13:46:23 -0800 From: Nicolin Chen To: Pranjal Shrivastava CC: Joerg Roedel , Will Deacon , "Robin Murphy" , Mostafa Saleh , , Jason Gunthorpe , Daniel Mentz Subject: Re: [PATCH v5 3/3] iommu/arm-smmu-v3: Avoid redundant master lookup in events Message-ID: References: <20241112083018.1662104-1-praan@google.com> <20241112083018.1662104-4-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: CY4PEPF0000EE32:EE_|SA1PR12MB7245:EE_ X-MS-Office365-Filtering-Correlation-Id: 268209dc-f76a-4932-9b6b-08dd05bef667 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|36860700013|376014|82310400026; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?309TO/jPFnVdY5WNnJzCllIb6q8WSgsBoM6QFZ+MOp75RNEKnCGCrXGDlIKC?= =?us-ascii?Q?UFexikMpPy7aCSRDbsr30yH/OvpdxgSL/yeCvRYxrOUBoTnCUDlsG5o+bkoY?= =?us-ascii?Q?9cO78uLZGXzfqGCYpIainVdjn/1alnuqZzhqjny5TU2uxGhm6lRjHN8JR4K3?= =?us-ascii?Q?w4Eb/NI45VO6XtB3gy8DyoFgsbXQQoyFYEcSNX3HMs/EwDcpU3vwvSRBCdJa?= =?us-ascii?Q?Sa005tyVBgehfyYqhDYhSjgmcJkdqlNShxakVtYZ1yx6MsjUVVnqUH1C1osX?= =?us-ascii?Q?V/5++xX1DHi2GPHKOwfV7F/fJLNf+c8wsv6SLNFuViWU+S98vUGJ+ONwCTQS?= =?us-ascii?Q?nd//SpVSV5zQj1sgt3O3cUCN3+rrHlbCMgfphvomI4c27vn57t2kKUi7ZEsn?= =?us-ascii?Q?1KYifb3Dd7I5kQNhkArOIpccbLavc/EF/lpzy/AI6Bk5hU3rVTMdf582jK41?= =?us-ascii?Q?nCJAaAiJEnn6rQK1weDcXnzcI0eEgRditTA0S/IK7HlaFZa52L0QFkK4xmP3?= =?us-ascii?Q?55BsIjeLwSgUCAIujsmlFls7K3R9rL0LDRJvs36oVUuaYrOu+Cl5udViQEAR?= =?us-ascii?Q?ZePl4eaAFln5groggHJVfzKmOCzZjPGAhev6S0Dw16qonfxHuMPzfi6j9tCk?= =?us-ascii?Q?k4Gs+dLY9vDKBWKvo4CvlMpg8/fTXuAa9JyXeErLpHrVpRygikt+TH7OdNaq?= =?us-ascii?Q?krBeLP7s+0DOoGNYXDg0F08u35wuqgKkKQtJ2ZQ8TfJD5PVpUtem2YPm2bkx?= =?us-ascii?Q?dBvX3dZyEK2aW9xinDSVXK6/B5VUieHrU3Z9KP7zvbviqwLXKhwnEOWe7myh?= =?us-ascii?Q?e8Ko70VqYyYvoORVo0RR1S/CXt1aUg3nzCvApVhc9UZ+No+FqB41mDc71sXZ?= =?us-ascii?Q?XL+8OVAM7PzqP+VvXebmDw/YC+LxvRCwgEsiBUkYqAN7loYqklKRAn3ai0b0?= =?us-ascii?Q?oavzJg1TcPkvdYtsIEfWoMheD9WAonlPykwwOe6n/TCw7vC8C667fFK2i8Tf?= =?us-ascii?Q?EyGv+SKmGFyN4eGfV/xCKDaN8kVzjw8/P2n1zl3u+bCct0u9pn1IGgpENX2B?= =?us-ascii?Q?Srmfjj/iOhL4lCNvK6LK9FuzFwa3g/sq8UwMt0ZSyzw27yBXBuxL+5VnFYdN?= =?us-ascii?Q?XlfybXYas+qKuTzKfhqzmtnzv53bAN3yOMhXlb6kCnjqUSf1REo6p8IV9VY9?= =?us-ascii?Q?2L7fAUS+1MfZnNHk2ntmhcQgaIpkv2zPxrfvzbRzVTk1RRTlbjLAM5GyZ0f0?= =?us-ascii?Q?CB/nJGp5ipm/VA/oizeb6aQtqVSemeeN2q4yflKAMnIsdX3PPnLTiVUnBBCZ?= =?us-ascii?Q?695Shb/vcDFC3Tq9js5eFNMQ5Sinai1kYVHfThyLIkBt3du156zTKWE19Zt/?= =?us-ascii?Q?YrXNvDAD+h3stB6Nn14bE3nSVazmk7lj7dHmrIrbKsploC+Rvg=3D=3D?= 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)(1800799024)(36860700013)(376014)(82310400026);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 Nov 2024 21:46:29.1451 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 268209dc-f76a-4932-9b6b-08dd05bef667 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: CY4PEPF0000EE32.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA1PR12MB7245 On Fri, Nov 15, 2024 at 01:26:22PM +0000, Pranjal Shrivastava wrote: > On Tue, Nov 12, 2024 at 03:52:36PM -0800, Nicolin Chen wrote: > > On Tue, Nov 12, 2024 at 08:30:18AM +0000, Pranjal Shrivastava wrote: > > > Remove the call to `arm_smmu_find_master` in `arm_smmu_handle_evt`. > > > > > > The call was primarily to retrieve `master->dev` ptr for reporting iommu > > > device faults. Since this info is already available in the `event->dev` > > > field, we no longer need to lookup the master to fetch the dev pointer. > > > > We only protected the "dev" for dev_name() while the streams_mutex > > is still required against arm_smmu_remove_master? > > > > Umm.. as per the code upstream, we were just finding master because we > wanted to pass the master->dev in "iommu_report_device_fault", thus even > if the master is free'd by arm_smmu_remove_master, the struct dev > wouldn't be free'd as we still hold a reference to it here due to the > call to get_device in arm_smmu_decode_event. The iommu_report_device_fault() needs to dereference dev->iommu and dev->iommu_group, both of which might be NULL if the master gets freed? > > > @@ -1857,17 +1855,14 @@ static int arm_smmu_handle_evt(struct arm_smmu_device *smmu, > > > flt->prm.pasid = event->ssid; > > > } > > > > > > - mutex_lock(&smmu->streams_mutex); > > > - master = arm_smmu_find_master(smmu, event->sid); > > > - if (!master) { > > > - ret = -EINVAL; > > > - goto out_unlock; > > > - } > > > + /* > > > + * If the master wasn't found while reading the event or > > > + * get_device() returned NULL, we shouldn't report a fault. > > > + */ > > > + if (!event->dev) > > > + return -EINVAL; > > > > > > - ret = iommu_report_device_fault(master->dev, &fault_evt); > > > -out_unlock: > > > - mutex_unlock(&smmu->streams_mutex); > > > - return ret; > > > + return iommu_report_device_fault(event->dev, &fault_evt); > > > > Apart from the question that I asked above, it'd be convenient for > > my vIRQ series to add on top if we can keep the master here: > > > > Given that your flow is: > > arm_smmu_decode_event(...); // get event->dev > > if (arm_smmu_handle_evt(...)) // validate event->dev > > arm_smmu_dump_event(...); // use event->dev > > > > Could we just keep the driver as it is, so your flow will be: > > arm_smmu_decode_event(...); // no event->dev > > if (arm_smmu_handle_evt(...)) // get event->dev > > arm_smmu_dump_event(...); // use event->dev > > ? > > Hmm.. looking at the vIRQ series it seems like we'd anyways need to call > arm_smmu_find_master here as you're adding more fields to that struct > and plan to use them here. > > In that case, I don't think we need this patch [Patch 3/3] ? > We can keep the code as is and simply populate the event->dev ptr in > arm_smmu_handle_evt when we lock the streams_mutex as you suggested. Yea, that works the best for me. Thanks Nicolin