Commit 5d5388b0 authored Dec 15, 2025 by Nicolin Chen Committed by Joerg Roedel Jan 10, 2026

iommu: Lock group->mutex in iommu_deferred_attach()

The iommu_deferred_attach() function invokes __iommu_attach_device(), but
doesn't hold the group->mutex like other __iommu_attach_device() callers.

Though there is no pratical bug being triggered so far, it would be better
to apply the same locking to this __iommu_attach_device(), since the IOMMU
drivers nowaday are more aware of the group->mutex -- some of them use the
iommu_group_mutex_assert() function that could be potentially in the path
of an attach_dev callback function invoked by the __iommu_attach_device().

Worth mentioning that the iommu_deferred_attach() will soon need to check
group->resetting_domain that must be locked also.

Thus, grab the mutex to guard __iommu_attach_device() like other callers.

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Tested-by: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Samiullah Khawaja <skhawaja@google.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

parent 9ace4753

drivers/iommu/iommu.c

+10 −3

Original line number	Diff line number	Diff line
		@@ -2185,10 +2185,17 @@ EXPORT_SYMBOL_GPL(iommu_attach_device);

		int iommu_deferred_attach(struct device dev, struct iommu_domain domain)
		{
		if (dev->iommu && dev->iommu->attach_deferred)
		return __iommu_attach_device(domain, dev, NULL);

		/*
		* This is called on the dma mapping fast path so avoid locking. This is
		* racy, but we have an expectation that the driver will setup its DMAs
		* inside probe while being single threaded to avoid racing.
		*/
		if (!dev->iommu \|\| !dev->iommu->attach_deferred)
		return 0;

		guard(mutex)(&dev->iommu_group->mutex);

		return __iommu_attach_device(domain, dev, NULL);
		}

		void iommu_detach_device(struct iommu_domain domain, struct device dev)