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Wed, 7 May 2025 13:49:57 -0700 Date: Wed, 7 May 2025 13:49:55 -0700 From: Nicolin Chen To: Jason Gunthorpe CC: Baolu Lu , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v2 13/22] iommufd: Add mmap interface Message-ID: References: <7be26560c604b0cbc2fd218997b97a47e4ed11ff.1745646960.git.nicolinc@nvidia.com> <20250505165019.GM2260709@nvidia.com> <20250505172813.GS2260709@nvidia.com> <20250506125425.GX2260709@nvidia.com> <20250507123648.GE90261@nvidia.com> Precedence: bulk X-Mailing-List: patches@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: <20250507123648.GE90261@nvidia.com> X-NV-OnPremToCloud: AnonymousSubmission X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN3PEPF0000B071:EE_|CH0PR12MB8464:EE_ X-MS-Office365-Filtering-Correlation-Id: fcb38684-c7bc-4f1b-53cd-08dd8da8c5b7 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|7416014|376014|1800799024|36860700013; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 May 2025 20:50:16.5569 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: fcb38684-c7bc-4f1b-53cd-08dd8da8c5b7 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: BN3PEPF0000B071.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH0PR12MB8464 On Wed, May 07, 2025 at 09:36:48AM -0300, Jason Gunthorpe wrote: > On Tue, May 06, 2025 at 01:54:10PM -0700, Nicolin Chen wrote: > > > Now I start to think about the FD situation: either a fault queue or > > an eventq returns an FD and holds a refcount on the event object. So > > the event object can't be destroyed unless the FD is released first. > > Are we doing it incorrectly here? > > Not necessarily, and maybe that is a good point that we are already > doing these cross dependencies. But we could fix the FDs with some > work too. Noted it down. Similar to unmap_mapping_range() in the mmap case, is close_fd() or file_close_fd() the one that we should use in the event object destroy()? Either of which is holding a spinlock, so likely it's safe from a close racing, v.s. the mmap situation? > > I see! It just needs to call that function when we remove the mmap > > for a vIOMMU destroy(). > > It is a little fussy to setup the inode as well, but yes. > > The other small advantage is you don't need to setup a special VMA ops > and do VMA tracking to hold the refcount on the vqueue object. > > But there is also any annoying race with unmap in setting up the mmap > PFNs which is why vfio is doing it from a fault handler.. I see. That's why VFIO is doing vmf_insert_pfn() in the fault op, instead of calling remap_pfn_range() in mmap(). > So maybe refcount is the simplest option for now. We could fix it > later and it won't prevent close() from working right. Ack. I will keep the one that I posted in v3. Thanks Nicolin