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Fri, 30 May 2025 11:39:32 -0700 Date: Fri, 30 May 2025 11:39:31 -0700 From: Nicolin Chen To: Jason Gunthorpe CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v5 14/29] iommufd/viommu: Add IOMMUFD_CMD_HW_QUEUE_ALLOC ioctl Message-ID: References: <5c509f092ba61d4c0852ba57b530888ffb864ccb.1747537752.git.nicolinc@nvidia.com> <20250530161455.GE233377@nvidia.com> <20250530174037.GR233377@nvidia.com> <20250530182519.GV233377@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20250530182519.GV233377@nvidia.com> X-NV-OnPremToCloud: AnonymousSubmission X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SN1PEPF0002BA4E:EE_|PH7PR12MB5735:EE_ X-MS-Office365-Filtering-Correlation-Id: 986f4635-9a84-4005-325b-08dd9fa95f77 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|36860700013|7416014|376014|82310400026; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 May 2025 18:39:55.4955 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 986f4635-9a84-4005-325b-08dd9fa95f77 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: SN1PEPF0002BA4E.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB5735 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250530_114003_334007_B866592B X-CRM114-Status: GOOD ( 18.36 ) 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, May 30, 2025 at 03:25:19PM -0300, Jason Gunthorpe wrote: > On Fri, May 30, 2025 at 11:23:02AM -0700, Nicolin Chen wrote: > > On Fri, May 30, 2025 at 02:40:37PM -0300, Jason Gunthorpe wrote: > > > On Fri, May 30, 2025 at 10:38:24AM -0700, Nicolin Chen wrote: > > > > On Fri, May 30, 2025 at 01:14:55PM -0300, Jason Gunthorpe wrote: > > > > > On Sat, May 17, 2025 at 08:21:31PM -0700, Nicolin Chen wrote: > > > > > > + offset = > > > > > > + cmd->nesting_parent_iova - PAGE_ALIGN(cmd->nesting_parent_iova); > > > > > > + max_npages = DIV_ROUND_UP(offset + cmd->length, PAGE_SIZE); > > > > > > > > > > This should probably be capped to PAGE_SIZE/sizeof(void *), return > > > > > EINVAL if not > > > > > > > > Hmm, mind elaborating where this PAGE_SIZE/sizeof comes from? > > > > > > We can usually allocate up to a PAGE_SIZE without too much > > > trouble. Beyond that it gets more likely to fail. > > > > If PAGE_SIZE=4096, the upper limit for max_npages is 512, i.e. the > > max size of a guest queue is 2MB? It seems to be too small, as the > > VMM can use a larger huge page size to back the guest queue? > > May need to make a new API that returns a bio_vec or something else > more efficient then :\ Hmm, that sounds like a rabbit hole :-\ Let me leave a FIXME at this max_npages calculation instead.. Thanks Nicolin