vfio/iommu_type1: initialize pgsize_bitmap in ->open

Ensure pgsize_bitmap is always valid by initializing it to PAGE_MASK
in vfio_iommu_type1_open and remove the now pointless update for
the external domain case in vfio_iommu_type1_attach_group, which was
just setting pgsize_bitmap to PAGE_MASK when only external domains
were attached.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20210924155705.4258-14-hch@lst.de
[aw: s/ULONG_MAX/PAGE_MASK/ per discussion in link]
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/vfio_iommu_type1.c

@@ -2196,7 +2196,6 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
 		if (!iommu->external_domain) {
 			INIT_LIST_HEAD(&domain->group_list);
 			iommu->external_domain = domain;
-			vfio_update_pgsize_bitmap(iommu);
 		} else {
 			kfree(domain);
 		}
@@ -2582,6 +2581,7 @@ static void *vfio_iommu_type1_open(unsigned long arg)
 	mutex_init(&iommu->lock);
 	BLOCKING_INIT_NOTIFIER_HEAD(&iommu->notifier);
 	init_waitqueue_head(&iommu->vaddr_wait);
+	iommu->pgsize_bitmap = PAGE_MASK;
 
 	return iommu;
 }