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Sun, 5 Jul 2026 22:36:34 -0700 From: Nicolin Chen To: Will Deacon , Jason Gunthorpe CC: Robin Murphy , , Kevin Tian , , , Subject: [PATCH v2 2/3] iommufd/viommu: Publish a vDEVICE only after vdevice_init() succeeds Date: Sun, 5 Jul 2026 22:36:10 -0700 Message-ID: <1e05999347f4bf583edbc6a1312c857d5548708c.1783311134.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: CH3PEPF0000000B:EE_|DS0PR12MB9275:EE_ X-MS-Office365-Filtering-Correlation-Id: 420fa9f5-25ca-456b-1a06-08dedb209436 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|82310400026|36860700016|1800799024|376014|23010399003|11063799006|56012099006|18002099003|22082099003; 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That op is where a driver validates the device and may reject it, but the xarray entry is already live by then: a concurrent IOMMU_HWPT_INVALIDATE can look it up with iommufd_viommu_find_dev() and run the driver invalidation path against a device that vdevice_init() would have refused. Reserve the index with xa_insert(): it stores a zero entry that reads back as NULL, and returns -EBUSY on a duplicate virt_id. Run vdevice_init() and store the vDEVICE pointer only once it succeeds. A failed vdevice_init() releases the reservation, so lookups observe the vDEVICE only after it is fully initialized and accepted. Fixes: ed42eee797ff3 ("iommufd/viommu: Add driver-defined vDEVICE support") Cc: stable@vger.kernel.org Reviewed-by: Kevin Tian Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Nicolin Chen --- drivers/iommu/iommufd/viommu.c | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-) diff --git a/drivers/iommu/iommufd/viommu.c b/drivers/iommu/iommufd/viommu.c index 0c12c7e352a14..fc13cf4737ea3 100644 --- a/drivers/iommu/iommufd/viommu.c +++ b/drivers/iommu/iommufd/viommu.c @@ -143,7 +143,7 @@ void iommufd_vdevice_destroy(struct iommufd_object *obj) int iommufd_vdevice_alloc_ioctl(struct iommufd_ucmd *ucmd) { struct iommu_vdevice_alloc *cmd = ucmd->cmd; - struct iommufd_vdevice *vdev, *curr; + struct iommufd_vdevice *vdev; size_t vdev_size = sizeof(*vdev); struct iommufd_viommu *viommu; struct iommufd_device *idev; @@ -218,18 +218,28 @@ int iommufd_vdevice_alloc_ioctl(struct iommufd_ucmd *ucmd) */ idev->vdev = vdev; - curr = xa_cmpxchg(&viommu->vdevs, virt_id, NULL, vdev, GFP_KERNEL); - if (curr) { - rc = xa_err(curr) ?: -EEXIST; + /* + * Reserve the slot with a zero entry (reads back as NULL) until the + * vdevice_init() op accepts the vDEVICE. Only the xa_* helpers hide a + * reserved entry, so never use a raw xas_* iterator on this xarray. + */ + rc = xa_insert(&viommu->vdevs, virt_id, NULL, GFP_KERNEL); + if (rc) { + if (rc == -EBUSY) + rc = -EEXIST; goto out_abort; } if (viommu->ops && viommu->ops->vdevice_init) { rc = viommu->ops->vdevice_init(vdev); - if (rc) + if (rc) { + xa_release(&viommu->vdevs, virt_id); goto out_abort; + } } + xa_store(&viommu->vdevs, virt_id, vdev, GFP_KERNEL); + cmd->out_vdevice_id = vdev->obj.id; rc = iommufd_ucmd_respond(ucmd, sizeof(*cmd)); if (rc) -- 2.43.0