iommufd: Add alloc_domain_nested op to iommufd_viommu_ops

Allow IOMMU driver to use a vIOMMU object that holds a nesting parent
hwpt/domain to allocate a nested domain.

Link: https://patch.msgid.link/r/2dcdb5e405dc0deb68230564530d989d285d959c.1730836219.git.nicolinc@nvidia.com
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Author: nicolinc

include/linux/iommufd.h

@@ -14,6 +14,7 @@
 struct device;
 struct file;
 struct iommu_group;
+struct iommu_user_data;
 struct iommufd_access;
 struct iommufd_ctx;
 struct iommufd_device;
@@ -95,9 +96,17 @@ struct iommufd_viommu {
  * struct iommufd_viommu_ops - vIOMMU specific operations
  * @destroy: Clean up all driver-specific parts of an iommufd_viommu. The memory
  *           of the vIOMMU will be free-ed by iommufd core after calling this op
+ * @alloc_domain_nested: Allocate a IOMMU_DOMAIN_NESTED on a vIOMMU that holds a
+ *                       nesting parent domain (IOMMU_DOMAIN_PAGING). @user_data
+ *                       must be defined in include/uapi/linux/iommufd.h.
+ *                       It must fully initialize the new iommu_domain before
+ *                       returning. Upon failure, ERR_PTR must be returned.
  */
 struct iommufd_viommu_ops {
 	void (*destroy)(struct iommufd_viommu *viommu);
+	struct iommu_domain *(*alloc_domain_nested)(
+		struct iommufd_viommu *viommu, u32 flags,
+		const struct iommu_user_data *user_data);
 };
 
 #if IS_ENABLED(CONFIG_IOMMUFD)