iommu/io-pgtable-arm: Add self test for the last page in the IAS

Add a case in the selftests that can detect some bugs with concatenated
page tables, where it maps the biggest supported page size at the end of
the IAS, this test would fail without the previous fix.

Signed-off-by: Mostafa Saleh <smostafa@google.com>
Link: https://lore.kernel.org/r/20241024162516.2005652-3-smostafa@google.com
Signed-off-by: Will Deacon <will@kernel.org>

Author: misaleh

drivers/iommu/io-pgtable-arm.c

@@ -1394,6 +1394,23 @@ static int __init arm_lpae_run_tests(struct io_pgtable_cfg *cfg)
 			iova += SZ_1G;
 		}
 
+		/*
+		 * Map/unmap the last largest supported page of the IAS, this can
+		 * trigger corner cases in the concatednated page tables.
+		 */
+		mapped = 0;
+		size = 1UL << __fls(cfg->pgsize_bitmap);
+		iova = (1UL << cfg->ias) - size;
+		if (ops->map_pages(ops, iova, iova, size, 1,
+				   IOMMU_READ | IOMMU_WRITE |
+				   IOMMU_NOEXEC | IOMMU_CACHE,
+				   GFP_KERNEL, &mapped))
+			return __FAIL(ops, i);
+		if (mapped != size)
+			return __FAIL(ops, i);
+		if (ops->unmap_pages(ops, iova, size, 1, NULL) != size)
+			return __FAIL(ops, i);
+
 		free_io_pgtable_ops(ops);
 	}