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Mon, 13 Jan 2025 12:44:39 -0800 Date: Mon, 13 Jan 2025 12:44:37 -0800 From: Nicolin Chen To: Jason Gunthorpe CC: , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v5 08/14] iommufd/viommu: Add iommufd_viommu_report_event helper Message-ID: References: <20250110174132.GH396083@nvidia.com> <20250110195114.GJ5556@nvidia.com> <20250113192144.GT5556@nvidia.com> <20250113195433.GV5556@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20250113195433.GV5556@nvidia.com> X-NV-OnPremToCloud: AnonymousSubmission X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SN1PEPF000397B0:EE_|DM6PR12MB4283:EE_ X-MS-Office365-Filtering-Correlation-Id: ac85281a-37a4-4838-6c83-08dd3413242d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700013|82310400026|1800799024|7416014|376014; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?FlPLho091fwMX08/BwjJzhAoWn+KQD8ej7xopkQzmoKrcyX4ZLOFn1N1/VYc?= =?us-ascii?Q?dE1Hin/bJPjpZmOfcTWcpsGUrGg8tybn1rqB9+OCq+nKwpSyRs8BIGuF855J?= =?us-ascii?Q?nNMmqbZxgGprighbhed8HSqijhg7xQdBp4lSjppoOnjG+3/brBPm+bU1gAFv?= =?us-ascii?Q?yhx0ZCz8J+6c+F/m2AlHYEmUp9I/UOGeFfTbnwfl4blNOnptl+N4p+8oexdm?= =?us-ascii?Q?PO1vqOJT/ot+cQb9PJVIGi8Ffsq7YlC4Sh0CQiVsXQYa0oasJLyGUbfmt36c?= =?us-ascii?Q?T77EJeJ4UvrzxN4ssmveBBznhTflyJiEb++WB38rdDt5eaHDi+CUh5KfYRS1?= =?us-ascii?Q?AgoiUWvc0vD39evqAi6WeebVbQMp+5hM/ZbuZp2Se7jr/T6ist2Ps+AKGPPn?= =?us-ascii?Q?OdOUkr5HyStG7Waf05x6z9ti3AHdm6ozVSa0N2aw2wh7zpreNWNJO3gsOJAn?= =?us-ascii?Q?FaX45mfakCYSWCaEdhCYsC53LxcesQFrprxRBSvcpy2bWa+I68EkM+TjFLYq?= =?us-ascii?Q?nYCSFxeCk54EZlG3J5v9DJhVqdZCIQRk3/3jPuKKMa+Vn2kLkN2xAtJUYTV7?= =?us-ascii?Q?JBFsY8iIiEYVW3dPIuo5QXGq1T5e6VG9nYnNT3+FLWqenaOuDmkBQvmvozld?= =?us-ascii?Q?FaAUAbEyEdvDVDd1jpvtu3pYoNYpGojVKdIVl/8g//zGWbW6FmnMILuNPT8c?= =?us-ascii?Q?Z0UC3X21x6a7k+qATZqpKGjH+lIhM5IbRN1OKoedzcVsYz/dgJwYcbu00kdp?= =?us-ascii?Q?UqGHUDxYC2xA4Hi2kQ2ch5U+8ZmcenWwM7oM/U/j6gh1d7A+prq+0kVXLusQ?= =?us-ascii?Q?D97TP8QxHyZKRCeucZZaW+LyTkTkgVZFTXcxc1okChn1FzqfbL0/xaRJ9v6O?= =?us-ascii?Q?RWSVds9Z07Zrek3BMgkdeKJRIKP8XbPEYoiNmuizbRz6N29qQUsBMMWtnL8Q?= =?us-ascii?Q?S+kN7LYvlzzuOD5J6V4RBA8/8vDo/WoyemGkIrA6GIpEpHZqxmki2ppC+4sp?= =?us-ascii?Q?8g9sXSoe6rtkkqB0IszyuXIBCL5KFgTztbNt6Djy83ecHcLR23oaN+VOAvLs?= =?us-ascii?Q?FK1I7JOQlR+gbxL2Xgk8T7BoPgJHEIcf8yiKjrAwY7/7w6XLbyOOZDpNBHMF?= =?us-ascii?Q?qmDA1RWAO8KK/EhVLITOnw1UbTtrzvMrXl17Gk8mruDkBf5DdV/fLyD+hfE0?= =?us-ascii?Q?WAUouEnUfz0N3nhfaPsA+XY8F48ph1Htms/143Err1rivgQknaaFkmQPbXi6?= =?us-ascii?Q?YLfyoe4XKLQNNCRGESQqeH4qBlJYgODWTxdMel7N/hjDpBxmC5Svi+2yqq1/?= =?us-ascii?Q?8R/7sUtalDzjW85uvOlvRGiNwC5P4kP6TKQNacPGAPVwwJFYTcvb3SHFXJsr?= =?us-ascii?Q?JLdgg0VyOVtsa16kQQObAJFsBIJ79Tqnu+TCuRVY1vTFA8ZnMjajnGVAhB0v?= =?us-ascii?Q?3b1Ks3w0Od4So9emlB+F+X1Zu5FUxzkaMqsliGex30P/xyIE5X/1CqOXAy2u?= =?us-ascii?Q?87x35+1htXktY2g=3D?= 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)(82310400026)(1800799024)(7416014)(376014);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 Jan 2025 20:44:57.1051 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: ac85281a-37a4-4838-6c83-08dd3413242d 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: SN1PEPF000397B0.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB4283 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250113_124503_359977_80672577 X-CRM114-Status: GOOD ( 23.03 ) 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 Mon, Jan 13, 2025 at 03:54:33PM -0400, Jason Gunthorpe wrote: > On Mon, Jan 13, 2025 at 11:47:52AM -0800, Nicolin Chen wrote: > > > The other approach would be to add a sequence number to each event and > > > let userspace detect the non-montonicity. It would require adding a > > > header to the native ARM evt. > > > > Yea, I thought about that. The tricky thing is that the header will > > be a core-level header pairing with a driver-level vEVENTQ type and > > can never change its length, though we can define a 64-bit flag that > > can reserve the other 63 bits for future use? > > The header format could be revised by changing the driver specific > format tag. Yea, we need a header format (or "header type") when the vEVENTQ is allocated. > You'd want to push a special event when the first overflow happens and > probably also report a counter so userspace can know how many events > got lost. How about this: enum iommufd_veventq_header_type { IOMMU_VEVENTQ_HEADER_TYPE_V1, }; enum iommu_hwpt_pgfault_flags { IOMMU_VEVENT_HEADER_FLAGS_OVERFLOW = (1 << 0), }; struct iommufd_vevent_header_v1 { __u64 flags; __u32 num_events; __u32 num_overflows; // valid if flag_overflow is set }; > This seems most robust and simplest to implement.. > > I think I'd implement it by having a static overflow list entry so no > memory allocation is needed and just keep moving that entry to the > back of the list every time an event is lost. This way it will cover > lost events due to memory outages too Could double-adding the same static node to the list happen and corrupt the list? I think the vevent_header doesn't need to be exactly match with the driver event. So, maybe a vEVENTQ object could hold a header structure during iommu_veventq_alloc? struct iommufd_veventq { ... atomic_t num_events; atomic_t num_overflows; DECLARE_BITMAP(errors, 32); struct iommufd_vevent_header_v1 *header; }; The header is a bit redundant to its upper three members though. > For old formats like the fault queue you could return EOVERFLOW > whenever the sequence number becomes discontiguous or it sees the > overflow event.. So, IOMMU_OBJ_FAULT is safe to return EOVERFLOW via read(), as you mentioned that it is self-limited right? Thanks Nicolin