iommu: Improve map/unmap sanity checks

The current checks for the __IOMMU_DOMAIN_PAGING capability seem a
bit stifled, since it is quite likely now that a non-paging domain
won't have a pgsize_bitmap and/or mapping ops, and thus get caught
by the earlier condition anyway. Swap them around to test the more
fundamental condition first, then we can reasonably also upgrade
the other to a WARN_ON, since if a driver does ever expose a paging
domain without the means to actually page, it's clearly very broken.
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/524db1ec0139c964d26928a6a264945aa66d010c.1694525662.git.robin.murphy@arm.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/iommu.c

@@ -2519,12 +2519,12 @@ static int __iommu_map(struct iommu_domain *domain, unsigned long iova,
 	phys_addr_t orig_paddr = paddr;
 	int ret = 0;
 
-	if (unlikely(!ops->map_pages || domain->pgsize_bitmap == 0UL))
-		return -ENODEV;
-
 	if (unlikely(!(domain->type & __IOMMU_DOMAIN_PAGING)))
 		return -EINVAL;
 
+	if (WARN_ON(!ops->map_pages || domain->pgsize_bitmap == 0UL))
+		return -ENODEV;
+
 	/* find out the minimum page size supported */
 	min_pagesz = 1 << __ffs(domain->pgsize_bitmap);
 
@@ -2602,10 +2602,10 @@ static size_t __iommu_unmap(struct iommu_domain *domain,
 	unsigned long orig_iova = iova;
 	unsigned int min_pagesz;
 
-	if (unlikely(!ops->unmap_pages || domain->pgsize_bitmap == 0UL))
+	if (unlikely(!(domain->type & __IOMMU_DOMAIN_PAGING)))
 		return 0;
 
-	if (unlikely(!(domain->type & __IOMMU_DOMAIN_PAGING)))
+	if (WARN_ON(!ops->unmap_pages || domain->pgsize_bitmap == 0UL))
 		return 0;
 
 	/* find out the minimum page size supported */