vfio: Do not manipulate iommu dma_owner for fake iommu groups

Since asserting dma ownership now causes the group to have its DMA blocked
the iommu layer requires a working iommu. This means the dma_owner APIs
cannot be used on the fake groups that VFIO creates. Test for this and
avoid calling them.

Otherwise asserting dma ownership will fail for VFIO mdev devices as a
BLOCKING iommu_domain cannot be allocated due to the NULL iommu ops.

Fixes: 0286300 ("iommu: iommu_group_claim_dma_owner() must always assign a domain")
Reported-by: Eric Farman <farman@linux.ibm.com>
Tested-by: Eric Farman <farman@linux.ibm.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/0-v1-9cfc47edbcd4+13546-vfio_dma_owner_fix_jgg@nvidia.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/vfio.c

@@ -927,7 +927,8 @@ static void __vfio_group_unset_container(struct vfio_group *group)
 		driver->ops->detach_group(container->iommu_data,
 					  group->iommu_group);
 
-	iommu_group_release_dma_owner(group->iommu_group);
+	if (group->type == VFIO_IOMMU)
+		iommu_group_release_dma_owner(group->iommu_group);
 
 	group->container = NULL;
 	group->container_users = 0;
@@ -1001,17 +1002,21 @@ static int vfio_group_set_container(struct vfio_group *group, int container_fd)
 		goto unlock_out;
 	}
 
-	ret = iommu_group_claim_dma_owner(group->iommu_group, f.file);
-	if (ret)
-		goto unlock_out;
+	if (group->type == VFIO_IOMMU) {
+		ret = iommu_group_claim_dma_owner(group->iommu_group, f.file);
+		if (ret)
+			goto unlock_out;
+	}
 
 	driver = container->iommu_driver;
 	if (driver) {
 		ret = driver->ops->attach_group(container->iommu_data,
 						group->iommu_group,
 						group->type);
 		if (ret) {
-			iommu_group_release_dma_owner(group->iommu_group);
+			if (group->type == VFIO_IOMMU)
+				iommu_group_release_dma_owner(
+					group->iommu_group);
 			goto unlock_out;
 		}
 	}