iommufd: Use the domain_alloc_user() op for domain allocation

Make IOMMUFD use iommu_domain_alloc_user() by default for iommu_domain
creation. IOMMUFD needs to support iommu_domain allocation with parameters
from userspace in nested support, and a driver is expected to implement
everything under this op.

If the iommu driver doesn't provide domain_alloc_user callback then
IOMMUFD falls back to use iommu_domain_alloc() with an UNMANAGED type if
possible.

Link: https://lore.kernel.org/r/20230928071528.26258-3-yi.l.liu@intel.comSuggested-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Co-developed-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Yi Liu <yi.l.liu@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/iommu/iommufd/hw_pagetable.c

@@ -5,6 +5,7 @@
 #include <linux/iommu.h>
 #include <uapi/linux/iommufd.h>
 
+#include "../iommu-priv.h"
 #include "iommufd_private.h"
 
 void iommufd_hw_pagetable_destroy(struct iommufd_object *obj)
@@ -74,6 +75,7 @@ struct iommufd_hw_pagetable *
 iommufd_hw_pagetable_alloc(struct iommufd_ctx *ictx, struct iommufd_ioas *ioas,
 			   struct iommufd_device *idev, bool immediate_attach)
 {
+	const struct iommu_ops *ops = dev_iommu_ops(idev->dev);
 	struct iommufd_hw_pagetable *hwpt;
 	int rc;
 
@@ -88,10 +90,19 @@ iommufd_hw_pagetable_alloc(struct iommufd_ctx *ictx, struct iommufd_ioas *ioas,
 	refcount_inc(&ioas->obj.users);
 	hwpt->ioas = ioas;
 
-	hwpt->domain = iommu_domain_alloc(idev->dev->bus);
-	if (!hwpt->domain) {
-		rc = -ENOMEM;
-		goto out_abort;
+	if (ops->domain_alloc_user) {
+		hwpt->domain = ops->domain_alloc_user(idev->dev, 0);
+		if (IS_ERR(hwpt->domain)) {
+			rc = PTR_ERR(hwpt->domain);
+			hwpt->domain = NULL;
+			goto out_abort;
+		}
+	} else {
+		hwpt->domain = iommu_domain_alloc(idev->dev->bus);
+		if (!hwpt->domain) {
+			rc = -ENOMEM;
+			goto out_abort;
+		}
 	}
 
 	/*