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Fri, 10 Jan 2025 11:27:55 -0800 Date: Fri, 10 Jan 2025 11:27:53 -0800 From: Nicolin Chen To: Jason Gunthorpe CC: , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v5 06/14] iommufd: Add IOMMUFD_OBJ_VEVENTQ and IOMMUFD_CMD_VEVENTQ_ALLOC Message-ID: References: <86e78625c48d0c8fb815496dbc57708b98a46ec7.1736237481.git.nicolinc@nvidia.com> <20250110174842.GI396083@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20250110174842.GI396083@nvidia.com> X-NV-OnPremToCloud: AnonymousSubmission X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PEPF000023DA:EE_|PH8PR12MB6844:EE_ X-MS-Office365-Filtering-Correlation-Id: 31ecec42-1d1f-4517-6728-08dd31ace432 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|1800799024|376014|36860700013|82310400026; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?6owmVDVMGTFZ12uErqMcIOCytB5F03qLNVcVCSqxcXK5B4PP2Vp8xh73NpLu?= =?us-ascii?Q?gWgXgkAvkJzW9R8a+EeF+5wEMcpjd7ZFUtqrCvafhLsWma/fxqORVlxYdjYc?= =?us-ascii?Q?E6UHAkHdWLjvN+ExblCUhrmxNlTpND/GjIYWeNCSv+KjB28LpWNUtBUBn9S4?= =?us-ascii?Q?N24B3tAkYv7fi2wrrgAB107+qwkry2G5D/Oek/Jz4McBl/Zak47i1a0213ym?= =?us-ascii?Q?YjbkuEhsiVfd3BR/U3bimaWbFRYcUFGTJh95vTMFHVzPo1HvyKd8kYRVVBL8?= =?us-ascii?Q?7T0vmYfILMWYA54u7DvY7Yty1y3nGDHUBL9kDWze0+MyUeWf6JbGsz+uKw01?= =?us-ascii?Q?TfiPBgg1oIoEliu/KZHIq/g46ezJgDgwzmvWh3NsGR4EqpdFC+VhTAkEJljq?= =?us-ascii?Q?zXdD52yZGdUSpAV10+eajbRhkkjtccClqJ4UhMCrcNyv4Hhuu/Vm+5Yl3nNS?= =?us-ascii?Q?qo14qZ1JDE2iCvI0ajLA8ZgEw0SrOvPnkcjlZM6fQ5Hs/AQ0x+PdAL4d2vFt?= =?us-ascii?Q?fikEWbLmoIUfePVqPnqLGlDsHv35P7Hcf+vHjR/8/ZPyfUlGpfDqJcBModh0?= =?us-ascii?Q?hFcDMZE0Tcw6w4Ngnkn0NOwUM9vkspb53mM6TBJ5oRBskAvGkWvlLSJpDEix?= =?us-ascii?Q?X/OFz42e/57ewPSGqLKcm7iFgm/TRTJsZtKpQh/ZwkJmiyOLGMdCRZT0vKtj?= =?us-ascii?Q?UtTXfRiyvo+3RG7Aqco/TUUnOKlQZYysCqSQivqhO3UlVzViuoWbDVLy5seu?= =?us-ascii?Q?Ag8zgie9MciixEz8iItWaC3gqg99hKXdGWaUockUodDo81OII3UXSdtCJxS9?= =?us-ascii?Q?R+iPhGjBo13vXiaBb52pkxTSFX3tkc+IJEelDB+ugInwnR+AjtpjGSGB0VbF?= =?us-ascii?Q?xbp8NRj7odp698TGllHLNC5IP7kaczK2mmRCrXPSs96ydSx9mtvE6MkmIHuz?= =?us-ascii?Q?UOMO5MbFhuGhb/DKLtmGTtz6WRr6qu5Y2+pajvIUzhPb58NACYqhwMXLzXOX?= =?us-ascii?Q?Q0ZNI+aZMJGQkTDAxK5icBwiE+xn6nFc/mfcm2buHkg94JpTga4iZspSMi6f?= =?us-ascii?Q?lFatPMK5SHnvh6W0Q+3fd+lIj5287yfqki3lNR0TaLEy84ueOVDP/WWVY3aG?= =?us-ascii?Q?fMl7vT4xQw0/zoB8KimnUqL3Okgs46F1Bi+T7LFzHG3uJzV9N99JWBKPeOL5?= =?us-ascii?Q?jt8I1r0+z1uxwGtmzSFGIxQHh6HsTW5oM+YlFJneSGE0R3KDVAEWNKZ9uVZy?= =?us-ascii?Q?FLNaw/LX3O5mDB+nCaJGeTH+QUVheuU8l2KSRx1Y28e8CaFMH3wPePo4geRa?= =?us-ascii?Q?8GqUIBIPdVElPCwjLzU5PQhQukcIA22TnnDP330esQubomy6bp0vs6NO6FYZ?= =?us-ascii?Q?f11aDgZUwCnTCL+CYwubZEuZ1wnxs+gghDKDGv73xx3+PR1S0bPP+hH7V6FP?= =?us-ascii?Q?VDsL3m4h2rPGWTV7fqNQ/AitC5GW/ZKD?= X-Forefront-Antispam-Report: CIP:216.228.118.233;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc7edge2.nvidia.com;CAT:NONE;SFS:(13230040)(7416014)(1800799024)(376014)(36860700013)(82310400026);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Jan 2025 19:27:58.8810 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 31ecec42-1d1f-4517-6728-08dd31ace432 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: SJ1PEPF000023DA.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH8PR12MB6844 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250110_112806_308883_7045CCBF X-CRM114-Status: GOOD ( 21.09 ) 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, Jan 10, 2025 at 01:48:42PM -0400, Jason Gunthorpe wrote: > On Tue, Jan 07, 2025 at 09:10:09AM -0800, Nicolin Chen wrote: > > > +static ssize_t iommufd_veventq_fops_read(struct iommufd_eventq *eventq, > > + char __user *buf, size_t count, > > + loff_t *ppos) > > +{ > > + size_t done = 0; > > + int rc = 0; > > + > > + if (*ppos) > > + return -ESPIPE; > > + > > + mutex_lock(&eventq->mutex); > > + while (!list_empty(&eventq->deliver) && count > done) { > > + struct iommufd_vevent *cur = list_first_entry( > > + &eventq->deliver, struct iommufd_vevent, node); > > + > > + if (cur->data_len > count - done) > > + break; > > + > > + if (copy_to_user(buf + done, cur->event_data, cur->data_len)) { > > + rc = -EFAULT; > > + break; > > + } > > Now that I look at this more closely, the fault path this is copied > from is not great. > > This copy_to_user() can block while waiting on a page fault, possibily > for a long time. While blocked the mutex is held and we can't add more > entries to the list. > > That will cause the shared IRQ handler in the iommu driver to back up, > which would cause a global DOS. > > This probably wants to be organized to look more like > > while (itm = eventq_get_next_item(eventq)) { > if (..) { > eventq_restore_failed_item(eventq); > return -1; > } > } > > Where the next_item would just be a simple spinlock across the linked > list manipulation. Would it be simpler by just limiting one node per read(), i.e. no "while (!list_empty)" and no block? The report() adds one node at a time, and wakes up the poll() each time of adding a node. And user space could read one event at a time too? Thanks Nicolin