linux-kernel - [PATCH v2 3/4] iommu: Keep dev->iommu state consistent

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Message-Id: <d219663a3f23001f23d520a883ac622d70b4e642.1740753261.git.robin.murphy@arm.com>
Date: Fri, 28 Feb 2025 15:46:32 +0000
From: Robin Murphy <robin.murphy@....com>
To: Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Hanjun Guo <guohanjun@...wei.com>,
	Sudeep Holla <sudeep.holla@....com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>,
	Russell King <linux@...linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Stuart Yoder <stuyoder@...il.com>,
	Laurentiu Tudor <laurentiu.tudor@....com>,
	Nipun Gupta <nipun.gupta@....com>,
	Nikhil Agarwal <nikhil.agarwal@....com>,
	Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>
Cc: linux-acpi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev,
	devicetree@...r.kernel.org,
	linux-pci@...r.kernel.org,
	Charan Teja Kalla <quic_charante@...cinc.com>
Subject: [PATCH v2 3/4] iommu: Keep dev->iommu state consistent

At the moment, if of_iommu_configure() allocates dev->iommu itself via
iommu_fwspec_init(), then suffers a DT parsing failure, it cleans up the
fwspec but leaves the empty dev_iommu hanging around. So far this is
benign (if a tiny bit wasteful), but we'd like to be able to reason
about dev->iommu having a consistent and unambiguous lifecycle. Thus
make sure that the of_iommu cleanup undoes precisely whatever it did.

Signed-off-by: Robin Murphy <robin.murphy@....com>
---

v2: New

 drivers/iommu/iommu-priv.h | 2 ++
 drivers/iommu/iommu.c      | 2 +-
 drivers/iommu/of_iommu.c   | 6 +++++-
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/iommu/iommu-priv.h b/drivers/iommu/iommu-priv.h
index 17e245cf17bb..6574c1f97e14 100644
--- a/drivers/iommu/iommu-priv.h
+++ b/drivers/iommu/iommu-priv.h
@@ -17,6 +17,8 @@ static inline const struct iommu_ops *dev_iommu_ops(struct device *dev)
 	return dev->iommu->iommu_dev->ops;
 }
 
+void dev_iommu_free(struct device *dev);
+
 const struct iommu_ops *iommu_ops_from_fwnode(const struct fwnode_handle *fwnode);
 
 static inline const struct iommu_ops *iommu_fwspec_ops(struct iommu_fwspec *fwspec)
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 37b7088e129a..a3b45b84f42b 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -352,7 +352,7 @@ static struct dev_iommu *dev_iommu_get(struct device *dev)
 	return param;
 }
 
-static void dev_iommu_free(struct device *dev)
+void dev_iommu_free(struct device *dev)
 {
 	struct dev_iommu *param = dev->iommu;
 
diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
index 97987cd78da9..e10a68b5ffde 100644
--- a/drivers/iommu/of_iommu.c
+++ b/drivers/iommu/of_iommu.c
@@ -116,6 +116,7 @@ static void of_pci_check_device_ats(struct device *dev, struct device_node *np)
 int of_iommu_configure(struct device *dev, struct device_node *master_np,
 		       const u32 *id)
 {
+	bool dev_iommu_present;
 	int err;
 
 	if (!master_np)
@@ -127,6 +128,7 @@ int of_iommu_configure(struct device *dev, struct device_node *master_np,
 		mutex_unlock(&iommu_probe_device_lock);
 		return 0;
 	}
+	dev_iommu_present = dev->iommu;
 
 	/*
 	 * We don't currently walk up the tree looking for a parent IOMMU.
@@ -147,8 +149,10 @@ int of_iommu_configure(struct device *dev, struct device_node *master_np,
 		err = of_iommu_configure_device(master_np, dev, id);
 	}
 
-	if (err)
+	if (err && dev_iommu_present)
 		iommu_fwspec_free(dev);
+	else if (err && dev->iommu)
+		dev_iommu_free(dev);
 	mutex_unlock(&iommu_probe_device_lock);
 
 	if (!err && dev->bus)
-- 
2.39.2.101.g768bb238c484.dirty