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Sun, 17 May 2026 19:28:57 -0700 From: Nicolin Chen To: , CC: , , Subject: [PATCH rc v1 1/4] iommufd: Move vevent memory allocation outside spinlock Date: Sun, 17 May 2026 19:28:46 -0700 Message-ID: <446bc952846ad0c98e5226e73cd29b560d70ceb7.1779070992.git.nicolinc@nvidia.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PEPF0000231B:EE_|DM4PR12MB5913:EE_ X-MS-Office365-Filtering-Correlation-Id: 02d69e00-af9f-4a44-0a7d-08deb48537f4 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|36860700016|376014|1800799024|11063799003|18002099003|56012099003|22082099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:216.228.118.232;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc7edge1.nvidia.com;CAT:NONE;SFS:(13230040)(82310400026)(36860700016)(376014)(1800799024)(11063799003)(18002099003)(56012099003)(22082099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: yzH5c4Z/CK84/XsAIvw334ESJGoajkGYJJkgQ517N592Ck5BJujzFbl8sOJPmiAgXtMgbv8Sk9dNpZyQlfbha579lqTTUPMsHkDSTt9ocQJCJvReM2+qWxc6ax4aU0XdWLOI2OoKYtD8/9cRFaiydn2ut934tFdBgfExSUMhtsIN2E2YSrtyAoODYT7Jk0+mhhN9QgBWA3evE3AxZFqbbEc9cpYp+/F6vJbhEX3IYKm420T9/E0n8bGrQYTi6oXuAhpN49RwRVd0cnLkVjAHSnqL6e8V4cgat4o1zMrZi9THRz60c/oi+yo7p8DN7OBfmIdrjldYvVqrDjrTjwreWwXzjm5Fx/xHnw2fws0W+VztuTqPUt/tGw1ckPJ1HYc95GyQkZ2KPUnO2PPwPknaqdLtZrwbSXr6/K2QDsepknuIZwina3OwruiHPVNGAd7Y X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 May 2026 02:28:59.5276 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 02d69e00-af9f-4a44-0a7d-08deb48537f4 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.118.232];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: SJ1PEPF0000231B.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR12MB5913 The veventq memory allocation happens inside the spinlock. Given its depth is decided by the user space, this leaves a vulnerability, where userspace can allocate large queues to exhaust atomic memory reserves. Move the allocation outside the spinlock and use GFP_NOWAIT, which can fail fast under memory pressure without dipping into the GFP_ATOMIC reserves or direct-reclaiming from the threaded IRQ handler. Treat the failure the same as a queue-overflow and return -ENOMEM to notify the caller. A subsequent change will cap the upper bound of the veventq_depth. Fixes: e36ba5ab808e ("iommufd: Add IOMMUFD_OBJ_VEVENTQ and IOMMUFD_CMD_VEVENTQ_ALLOC") Cc: stable@vger.kernel.org Signed-off-by: Nicolin Chen --- drivers/iommu/iommufd/driver.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-) diff --git a/drivers/iommu/iommufd/driver.c b/drivers/iommu/iommufd/driver.c index 61e6b02601d1a..b0dec089aeee1 100644 --- a/drivers/iommu/iommufd/driver.c +++ b/drivers/iommu/iommufd/driver.c @@ -149,15 +149,28 @@ int iommufd_viommu_report_event(struct iommufd_viommu *viommu, goto out_unlock_veventqs; } - spin_lock(&veventq->common.lock); - if (veventq->num_events == veventq->depth) { + /* + * Optimistic skip when clearly full. A concurrent reader may free a slot + * before the spinlock; the cost is recording one extra event as lost. + */ + if (READ_ONCE(veventq->num_events) >= veventq->depth) { + spin_lock(&veventq->common.lock); vevent = &veventq->lost_events_header; goto out_set_header; } - vevent = kzalloc_flex(*vevent, event_data, data_len, GFP_ATOMIC); + /* Pre-allocate to avoid GFP_ATOMIC; use GFP_NOWAIT to avoid sleeping */ + vevent = kzalloc_flex(*vevent, event_data, data_len, GFP_NOWAIT); if (!vevent) { + spin_lock(&veventq->common.lock); + vevent = &veventq->lost_events_header; rc = -ENOMEM; + goto out_set_header; + } + + spin_lock(&veventq->common.lock); + if (veventq->num_events == veventq->depth) { + kfree(vevent); vevent = &veventq->lost_events_header; goto out_set_header; } -- 2.43.0