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Tue, 18 Feb 2025 09:47:53 -0800 Received: from nvidia.com (10.127.8.13) by mail.nvidia.com (10.126.190.182) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.14 via Frontend Transport; Tue, 18 Feb 2025 09:47:51 -0800 Date: Tue, 18 Feb 2025 09:47:50 -0800 From: Nicolin Chen To: Jason Gunthorpe CC: , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v6 05/14] iommufd: Add IOMMUFD_OBJ_VEVENTQ and IOMMUFD_CMD_VEVENTQ_ALLOC Message-ID: References: <2fb8d9c7b01ad36b42849283cd33d931f11092cb.1737754129.git.nicolinc@nvidia.com> <20250218152959.GB4099685@nvidia.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20250218152959.GB4099685@nvidia.com> X-NV-OnPremToCloud: AnonymousSubmission X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PEPF0000231B:EE_|DS7PR12MB6310:EE_ X-MS-Office365-Filtering-Correlation-Id: 5a0f3359-2756-40b0-f4d6-08dd504464ee X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|36860700013|1800799024|82310400026; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Feb 2025 17:48:03.7545 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 5a0f3359-2756-40b0-f4d6-08dd504464ee 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: DS7PR12MB6310 On Tue, Feb 18, 2025 at 11:29:59AM -0400, Jason Gunthorpe wrote: > On Fri, Jan 24, 2025 at 04:30:34PM -0800, Nicolin Chen wrote: > > + list_add_tail(&vevent->node, &eventq->deliver); > > + vevent->on_list = true; > > + vevent->header.sequence = atomic_read(&veventq->sequence); > > + if (atomic_read(&veventq->sequence) == INT_MAX) > > + atomic_set(&veventq->sequence, 0); > > + else > > + atomic_inc(&veventq->sequence); > > + spin_unlock(&eventq->lock); > > This is all locked, we don't need veventq->sequence to be an atomic? > > The bounding can be done with some simple math: > > veventq->sequence = (veventq->sequence + 1) & INT_MAX; Ack. Perhaps we can reuse eventq->lock to fence @num_events too. > > +static struct iommufd_vevent * > > +iommufd_veventq_deliver_fetch(struct iommufd_veventq *veventq) > > +{ > > + struct iommufd_eventq *eventq = &veventq->common; > > + struct list_head *list = &eventq->deliver; > > + struct iommufd_vevent *vevent = NULL; > > + > > + spin_lock(&eventq->lock); > > + if (!list_empty(list)) { > > + vevent = list_first_entry(list, struct iommufd_vevent, node); > > + list_del(&vevent->node); > > + vevent->on_list = false; > > + } > > + /* Make a copy of the overflow node for copy_to_user */ > > + if (vevent == &veventq->overflow) { > > + vevent = kzalloc(sizeof(*vevent), GFP_ATOMIC); > > + if (vevent) > > + memcpy(vevent, &veventq->overflow, sizeof(*vevent)); > > + } > > This error handling is wonky, if we can't allocate then we shouldn't > have done the list_del. Just return NULL which will cause > iommufd_veventq_fops_read() to exist and userspace will try again. OK. We have two cases to support here: 1) Normal vevent node -- list_del and return the node. 2) Overflow node -- list_del and return a copy. I think we can do: if (!list_empty(list)) { struct iommufd_vevent *next; next = list_first_entry(list, struct iommufd_vevent, node); if (next == &veventq->overflow) { /* Make a copy of the overflow node for copy_to_user */ vevent = kzalloc(sizeof(*vevent), GFP_ATOMIC); if (!vevent) goto out_unlock; } list_del(&next->node); if (vevent) memcpy(vevent, next, sizeof(*vevent)); else vevent = next; } > > @@ -403,6 +531,10 @@ static int iommufd_eventq_fops_release(struct inode *inode, struct file *filep) > > { > > struct iommufd_eventq *eventq = filep->private_data; > > > > + if (eventq->obj.type == IOMMUFD_OBJ_VEVENTQ) { > > + atomic_set(&eventq_to_veventq(eventq)->sequence, 0); > > + atomic_set(&eventq_to_veventq(eventq)->num_events, 0); > > + } > > Why? We are about to free the memory? Ack. I thought about a re-entry of an open(). But release() does lose the event_fd completely, and user space wouldn't be able to open the same fd again. > > +int iommufd_veventq_alloc(struct iommufd_ucmd *ucmd) > > +{ > > + struct iommu_veventq_alloc *cmd = ucmd->cmd; > > + struct iommufd_veventq *veventq; > > + struct iommufd_viommu *viommu; > > + int fdno; > > + int rc; > > + > > + if (cmd->flags || cmd->type == IOMMU_VEVENTQ_TYPE_DEFAULT) > > + return -EOPNOTSUPP; > > + if (!cmd->veventq_depth) > > + return -EINVAL; > > Check __reserved for 0 too Kevin is suggesting a 32-bit flag field, so I think we can drop the __reserved in that case. Thanks Nicolin