[PATCH v1 5/8] iommu: Let a driver mark an IOMMU as confidential

[Nicolin Chen <nicolinc@nvidia.com>]

An IOMMU inside a confidential VM needs private memory for its queues and
tables. Later changes also need to identify it when handling TDISP devices.

Add a confidential marker and a helper for IOMMU drivers. The helper also
marks the IOMMU device as able to access private memory. Drivers must call
it before iommu_device_register().

Assisted-by: Claude:claude-opus-5
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
 include/linux/iommu.h | 10 ++++++++++
 drivers/iommu/iommu.c | 20 ++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index ac43b8b93f14a..bd68532e7f3be 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -822,6 +822,8 @@ struct iommu_domain_ops {
  * @singleton_group: Used internally for drivers that have only one group
  * @max_pasids: number of supported PASIDs
  * @ready: set once iommu_device_register() has completed successfully
+ * @confidential: this instance runs inside a confidential VM. Set by the driver
+ *                before any dma allocation.
  */
 struct iommu_device {
 	struct list_head list;
@@ -831,6 +833,7 @@ struct iommu_device {
 	struct iommu_group *singleton_group;
 	u32 max_pasids;
 	bool ready;
+	bool confidential;
 };
 
 /**
@@ -890,6 +893,8 @@ struct dev_iommu {
 int iommu_device_register(struct iommu_device *iommu,
 			  const struct iommu_ops *ops,
 			  struct device *hwdev);
+void iommu_device_set_confidential(struct iommu_device *iommu,
+				   struct device *hwdev);
 void iommu_device_unregister(struct iommu_device *iommu);
 int  iommu_device_sysfs_add(struct iommu_device *iommu,
 			    struct device *parent,
@@ -1423,6 +1428,11 @@ static inline int iommu_device_register(struct iommu_device *iommu,
 	return -ENODEV;
 }
 
+static inline void iommu_device_set_confidential(struct iommu_device *iommu,
+						 struct device *hwdev)
+{
+}
+
 static inline struct iommu_device *dev_to_iommu_device(struct device *dev)
 {
 	return NULL;
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index cd1bca7ede9af..feff390727d13 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -17,6 +17,7 @@
 #include <linux/slab.h>
 #include <linux/errno.h>
 #include <linux/host1x_context_bus.h>
+#include <linux/dma-mapping.h>
 #include <linux/iommu.h>
 #include <linux/iommufd.h>
 #include <linux/idr.h>
@@ -313,6 +314,25 @@ int iommu_device_register(struct iommu_device *iommu,
 }
 EXPORT_SYMBOL_GPL(iommu_device_register);
 
+/**
+ * iommu_device_set_confidential - Mark an IOMMU instance as confidential
+ * @iommu: the IOMMU instance
+ * @hwdev: the struct device of @iommu, whose own DMA reaches private memory
+ *
+ * Declare that @iommu runs inside a confidential VM
+ *
+ * Call this before @iommu makes any DMA allocation of its own, and not merely
+ * before iommu_device_register(). Queues and tables allocated any earlier land
+ * in shared memory that the hypervisor can read.
+ */
+void iommu_device_set_confidential(struct iommu_device *iommu,
+				   struct device *hwdev)
+{
+	iommu->confidential = true;
+	dma_set_cc_private(hwdev, true);
+}
+EXPORT_SYMBOL_GPL(iommu_device_set_confidential);
+
 void iommu_device_unregister(struct iommu_device *iommu)
 {
 	for (int i = 0; i < ARRAY_SIZE(iommu_buses); i++)
-- 
2.43.0