linux-kernel - [PATCH v3 1/5] iommu: Lock group->mutex in iommu_deferred

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Message-ID: <44783ca52e17a9ca0ce7acfe8daae3edc3d7b45b.1754952762.git.nicolinc@nvidia.com>
Date: Mon, 11 Aug 2025 15:59:08 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: <robin.murphy@....com>, <joro@...tes.org>, <bhelgaas@...gle.com>,
	<jgg@...dia.com>
CC: <will@...nel.org>, <robin.clark@....qualcomm.com>, <yong.wu@...iatek.com>,
	<matthias.bgg@...il.com>, <angelogioacchino.delregno@...labora.com>,
	<thierry.reding@...il.com>, <vdumpa@...dia.com>, <jonathanh@...dia.com>,
	<rafael@...nel.org>, <lenb@...nel.org>, <kevin.tian@...el.com>,
	<yi.l.liu@...el.com>, <baolu.lu@...ux.intel.com>,
	<linux-arm-kernel@...ts.infradead.org>, <iommu@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
	<linux-mediatek@...ts.infradead.org>, <linux-tegra@...r.kernel.org>,
	<linux-acpi@...r.kernel.org>, <linux-pci@...r.kernel.org>,
	<patches@...ts.linux.dev>, <pjaroszynski@...dia.com>, <vsethi@...dia.com>,
	<helgaas@...nel.org>, <etzhao1900@...il.com>
Subject: [PATCH v3 1/5] iommu: Lock group->mutex in iommu_deferred_attach

The iommu_deferred_attach() is a runtime asynchronous function called by
iommu-dma function, which could race against other attach functions if it
accesses something in the dev->iommu_group.

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

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
---
 drivers/iommu/iommu.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 060ebe330ee16..1e0116bce0762 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -2144,10 +2144,17 @@ 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);
+	/*
+	 * 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;
 
-	return 0;
+	guard(mutex)(&dev->iommu_group->mutex);
+
+	return __iommu_attach_device(domain, dev);
 }
 
 void iommu_detach_device(struct iommu_domain *domain, struct device *dev)
-- 
2.43.0