[RFC PATCH v6 05/11] iommu: Add a helper to validate a vIOMMU parent

["Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org>]

Let a vIOMMU implementation ask the physical IOMMU driver whether a
device and nesting parent are compatible. Return EOPNOTSUPP when the
driver does not supply the validation callback.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
 drivers/iommu/iommu.c | 11 +++++++++++
 include/linux/iommu.h |  8 ++++++++
 2 files changed, 19 insertions(+)

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index e8f13dcebbde..04cd5a686e18 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -47,6 +47,17 @@ static unsigned int iommu_def_domain_type __read_mostly;
 static bool iommu_dma_strict __read_mostly = IS_ENABLED(CONFIG_IOMMU_DEFAULT_DMA_STRICT);
 static u32 iommu_cmd_line __read_mostly;
 
+int iommu_viommu_validate_parent(struct device *dev,
+		enum iommu_viommu_type type, struct iommu_domain *parent_domain)
+{
+	const struct iommu_ops *ops = dev_iommu_ops(dev);
+
+	if (!ops->viommu_validate_parent)
+		return -EOPNOTSUPP;
+	return ops->viommu_validate_parent(dev, type, parent_domain);
+}
+EXPORT_SYMBOL_GPL(iommu_viommu_validate_parent);
+
 /* Tags used with xa_tag_pointer() in group->pasid_array */
 enum { IOMMU_PASID_ARRAY_DOMAIN = 0, IOMMU_PASID_ARRAY_HANDLE = 1 };
 
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index d20aa6f6863a..ee016a7c7a41 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -435,6 +435,9 @@ struct iommu_user_data {
 	size_t len;
 };
 
+int iommu_viommu_validate_parent(struct device *dev,
+		enum iommu_viommu_type type, struct iommu_domain *parent_domain);
+
 /**
  * struct iommu_user_data_array - iommu driver specific user space data array
  * @type: The data type of all the entries in the user buffer array
@@ -679,6 +682,8 @@ __iommu_copy_struct_to_user(const struct iommu_user_data *dst_data,
  *               resources shared/passed to user space IOMMU instance. Associate
  *               it with a nesting @parent_domain. It is required for driver to
  *               set @viommu->ops pointing to its own viommu_ops
+ * @viommu_validate_parent: Validate that @parent_domain is compatible with
+ *                          @dev for @viommu_type.
  * @owner: Driver module providing these ops
  * @identity_domain: An always available, always attachable identity
  *                   translation.
@@ -734,6 +739,9 @@ struct iommu_ops {
 	int (*viommu_init)(struct iommufd_viommu *viommu,
 			   struct iommu_domain *parent_domain,
 			   const struct iommu_user_data *user_data);
+	int (*viommu_validate_parent)(struct device *dev,
+				      enum iommu_viommu_type viommu_type,
+				      struct iommu_domain *parent_domain);
 
 	const struct iommu_domain_ops *default_domain_ops;
 	struct module *owner;
-- 
2.43.0