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Thu, 27 Jul 2023 00:30:25 -0700 Date: Thu, 27 Jul 2023 00:30:24 -0700 From: Nicolin Chen To: Jason Gunthorpe CC: , , , , , , , , , , , , Subject: Re: [PATCH v8 2/4] iommufd: Add iommufd_access_replace() API Message-ID: References: <5dfe3e9a9d511919cb105459ca9d96f013daadb4.1690226015.git.nicolinc@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: BN8NAM11FT031:EE_|SJ2PR12MB9114:EE_ X-MS-Office365-Filtering-Correlation-Id: 6c66ba6d-8ab9-4e37-022b-08db8e7362ec X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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:(13230028)(4636009)(396003)(39860400002)(346002)(136003)(376002)(451199021)(82310400008)(36840700001)(46966006)(40470700004)(82740400003)(7636003)(356005)(47076005)(186003)(336012)(83380400001)(2906002)(36860700001)(26005)(426003)(55016003)(54906003)(40460700003)(8676002)(8936002)(7416002)(41300700001)(5660300002)(86362001)(6862004)(478600001)(70206006)(9686003)(70586007)(4326008)(33716001)(40480700001)(316002)(6636002);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Jul 2023 07:30:43.3199 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 6c66ba6d-8ab9-4e37-022b-08db8e7362ec 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: BN8NAM11FT031.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ2PR12MB9114 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, Jul 26, 2023 at 07:59:17PM -0700, Nicolin Chen wrote: > > > > + if (new_ioas) { > > > > + rc = iopt_add_access(&new_ioas->iopt, access); > > > > + if (rc) { > > > > + iommufd_put_object(&new_ioas->obj); > > > > + access->ioas = cur_ioas; > > > > + return rc; > > > > + } > > > > + iommufd_ref_to_users(&new_ioas->obj); > > > > + } > > > > + > > > > + access->ioas = new_ioas; > > > > + access->ioas_unpin = new_ioas; > > > > iopt_remove_access(&cur_ioas->iopt, access); > > > > > > There was a bug in my earlier version, having the same flow by > > > calling iopt_add_access() prior to iopt_remove_access(). But, > > > doing that would override the access->iopt_access_list_id and > > > it would then get unset by the following iopt_remove_access(). > > > > Ah, I was wondering about that order but didn't check it. > > > > Maybe we just need to pass the ID into iopt_remove_access and keep the > > right version on the stack. > > > > > So, I came up with this version calling an iopt_remove_access() > > > prior to iopt_add_access(), which requires an add-back the old > > > ioas upon an failure at iopt_add_access(new_ioas). > > > > That is also sort of reasonable if the refcounting is organized like > > this does. > > I just realized that either my v8 or your version calls unmap() > first at the entire cur_ioas. So, there seems to be no point in > doing that fallback re-add routine since the cur_ioas isn't the > same, which I don't feel quite right... > > Perhaps we should pass the ID into iopt_add/remove_access like > you said above. And then we attach the new_ioas, piror to the > detach the cur_ioas? I sent v9 having the iopt_remove_access trick, so we can do an iopt_remove_access only upon success. Let's continue there. Thanks Nic