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Mon, 28 Apr 2025 10:41:47 -0700 Date: Mon, 28 Apr 2025 10:41:45 -0700 From: Nicolin Chen To: Baolu Lu CC: , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v2 08/22] iommufd: Abstract iopt_pin_pages and iopt_unpin_pages helpers Message-ID: References: <376566b4-6c13-45ad-b1e5-8cfe2de437bc@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <376566b4-6c13-45ad-b1e5-8cfe2de437bc@linux.intel.com> X-NV-OnPremToCloud: AnonymousSubmission X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CO1PEPF000044FB:EE_|MW4PR12MB7144:EE_ X-MS-Office365-Filtering-Correlation-Id: f6baf04d-40d2-40b1-7958-08dd867c0060 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700013|7416014|82310400026|376014|1800799024; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?ayzFFx1RvndeLeN5zBNomAIjkcAc7t0sfwLqedwCTp2/O3B13Vnp9eXKoyi6?= =?us-ascii?Q?y6xYdB4N2zC08m4Q1+U/EVm1E76PJWRSwMc6DuEMATz5/odLL4Kf1s77Nxiv?= =?us-ascii?Q?H8aSsUG2sGRqb+kmAC0ZLuRgbfYZXkBYy6a+KZKwhz+mNoqS5icbBJ+NLlSb?= =?us-ascii?Q?jqWxu/nagHWq12wtYGW/lIzh++dfcD1xwo601lp2pR28Os57Q70rrQI1SbqM?= =?us-ascii?Q?aJzdpyJsEQK6v/LUAc48GDS7KqxRN+8ETSHYnqqAhn/lgSaKka6QfRRFHRGz?= =?us-ascii?Q?T0GNmG4frAh/+jjZ5FpUMqnuhi82J049xf5EZYfRA9lPt7MMBbO4aqosx0o3?= =?us-ascii?Q?E2w18P+NIBSN63PnyUaUkbwOPmJ/3JPTk3xGQP0ZiTewqCSpCcQ0XTyqNxeU?= =?us-ascii?Q?1RCyZrqW4OdIkCvqZ/0tqzL6iCHLbo0cQ1ahmiGrzojNNyGMqTeR2ULv0AYM?= =?us-ascii?Q?UfO78gdjP0ZZnd5RjjICset2OHqJKYkeK1j3zWeqcxsSn4/ewg6kKDWdZAJB?= =?us-ascii?Q?Gv8PvJdUN72a4Is59hDkAmi6B1pmErsRK4U8GPoE2VpZ6t7xXpHmHawT4ewA?= =?us-ascii?Q?X5ZzxmbDPszUmBk6ioI5heJjr1AnhNZDbQ8pdxpCFAeZ13GoHWQYS8PgGQqR?= =?us-ascii?Q?kJnHbtcu/vLVoIFKKIdbGSU3x5f8SAgsGVz6psf8hZ1QH8BzhGqmNMlDvNJR?= =?us-ascii?Q?hZSW7RBdX1Aobw1lAO3RGMi1MGlsWN7tE5eIA8WXdfXDI4g06UlohwwNtmxO?= =?us-ascii?Q?qfw3XmySCAsqC7S86JSaIsq2UoMSV8sWyLu8B4Toz1/uR2HUDVtRNMifQYdN?= =?us-ascii?Q?luZXLbL0Rx63kI+WD2peNxDBhb7/g2/kdVZUau7V5d09FUVVu3mBclzGtapw?= =?us-ascii?Q?eoPM8UHq78LNVjCrXk7IDuyZ/VYffynn4z34nikCCuDXiW08WCE+Z9zhSHWf?= =?us-ascii?Q?D8y1fs4WuRScnYByCQQNobnmo5NqMKj2NoFQ7aDl1bBqar9ZkiTEK3Kq8Goh?= =?us-ascii?Q?49VpII4wWYsschttkMnlQtiOi4R64aFbo4Fd0znvZSSZ06RUVY5fdPDgqFui?= =?us-ascii?Q?s/LMnnBx6cZ37gLNBQIyLq95DZOZ9FVOrX4kktsGTybBwhAYiZrd94vXVc0T?= =?us-ascii?Q?G3MfonaHXtxoMbcSYsyZ2lV/gXiOw4gn3m4momMAxk38RcI5uCuZ5BP2bEX7?= =?us-ascii?Q?nvapuaQ5sj6EdYiqiJXWiNV5y2ZmLjDsORp+ZjrP8ijVZGSub+ZNDluwYhsw?= =?us-ascii?Q?xksJey4tDCzD61tmSlGrFdHbNFxe7C28+1LbtUIuSATzMXajgWjram5+zLSn?= =?us-ascii?Q?p2fVBgg/8Nj8vaOf5ydZiEVEfEXHs/KBlT9CenurJO8+TdSjkEJuyh2YjoBn?= =?us-ascii?Q?4CbHV1fzUiOeH1GcJ5hg5JOUQSWUIGFedIqH9wSnP+u/zKQWBM1kMY7R6jRT?= =?us-ascii?Q?cEYqdTaB/4ae2jp2q+SDYlSI3e+2kEFOF9RIrSHtfoE4otIdkitHh0tB8/VB?= =?us-ascii?Q?NshTLxN73gr4T1BzKE2tbPC19P13rq2TPCsp?= X-Forefront-Antispam-Report: CIP:216.228.117.160;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge1.nvidia.com;CAT:NONE;SFS:(13230040)(36860700013)(7416014)(82310400026)(376014)(1800799024);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Apr 2025 17:42:09.5265 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: f6baf04d-40d2-40b1-7958-08dd867c0060 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.160];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CO1PEPF000044FB.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW4PR12MB7144 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250428_104218_656118_025CE6A7 X-CRM114-Status: GOOD ( 21.44 ) 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 Sun, Apr 27, 2025 at 03:22:13PM +0800, Baolu Lu wrote: > On 4/26/25 13:58, Nicolin Chen wrote: > > The new vCMDQ object will be added for HW to access the guest memory for a > > HW-accelerated virtualization feature. It needs to ensure the guest memory > > pages are pinned when HW accesses them and they are contiguous in physical > > address space. > > > > This is very like the existing iommufd_access_pin_pages() that outputs the > > pinned page list for the caller to test its contiguity. > > > > Move those code from iommufd_access_pin/unpin_pages() and related function > > for a pair of iopt helpers that can be shared with the vCMDQ allocator. As > > the vCMDQ allocator will be a user-space triggered ioctl function, WARN_ON > > would not be a good fit in the new iopt_unpin_pages(), thus change them to > > use WARN_ON_ONCE instead. > > I'm uncertain, but perhaps pr_warn_ratelimited() would be a better > alternative to WARN_ON() here? WARN_ON_ONCE() generates warning messages > with kernel call traces in the kernel messages, which might lead users > to believe that something serious has happened in the kernel. We already have similar practice, e.g. iommufd_hwpt_nested_alloc. In my review, a WARN_ON/WARN_ON_ONCE means there is a kernel bug, which shouldn't occur in the first place and isn't something that user space should concern. In case that it is hit, a WARN_ON_ONCE only spits one piece of traces that is enough for kernel folks to identify what's wrong, while pr_warn_ratelimited would likely end up with periodical warnings (more lines) that are neither related to user space nor useful for kernel. Thanks Nicolin