[PATCH 5/6] tools/testing/vma: add test to assert MAP_PRIVATE-/dev/zero is anon

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

Now we've made MAP_PRIVATE-mapped /dev/zero mappings truly anonymous, add a
VMA userland test to assert that this is the case and everything is as we
would expect for an anonymous mapping.

Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 tools/testing/vma/tests/mmap.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/tools/testing/vma/tests/mmap.c b/tools/testing/vma/tests/mmap.c
index c85bc000d1cb..fa73faff2262 100644
--- a/tools/testing/vma/tests/mmap.c
+++ b/tools/testing/vma/tests/mmap.c
@@ -45,7 +45,44 @@ static bool test_mmap_region_basic(void)
 	return true;
 }
 
+static bool test_pure_anon_dev_zero(void)
+{
+	const vma_flags_t vma_flags = mk_vma_flags(VMA_READ_BIT, VMA_WRITE_BIT,
+			VMA_MAYREAD_BIT, VMA_MAYWRITE_BIT);
+	struct file file = {
+		.f_op = &zero_fops,
+	};
+	struct mm_struct mm = {};
+	struct vm_area_struct *vma;
+	unsigned long addr;
+	VMA_ITERATOR(vmi, &mm, 0);
+
+	current->mm = &mm;
+
+	/*
+	 * Map a MAP_PRIVATE-/dev/zero mapping at address 0x300000 with a page
+	 * offset of 0x10, which we expect to be reset to the anonymous page
+	 * offset.
+	 */
+	addr = __mmap_region(&file, 0x300000, 0x3000, vma_flags, 0x10, NULL);
+	ASSERT_EQ(addr, 0x300000);
+
+	/* Assert that it truly is an anonymous mapping. */
+	vma = vma_lookup(&mm, addr);
+	ASSERT_NE(vma, NULL);
+	ASSERT_TRUE(vma_is_anonymous(vma));
+	ASSERT_EQ(vma->vm_file, NULL);
+	ASSERT_EQ(vma->vm_private_data, NULL);
+	/* Expect anonymous page offsets. */
+	ASSERT_EQ(vma->vm_pgoff, 0x300);
+	ASSERT_EQ(vma_start_anon_pgoff(vma), 0x300);
+
+	cleanup_mm(&mm, &vmi);
+	return true;
+}
+
 static void run_mmap_tests(int *num_tests, int *num_fail)
 {
 	TEST(mmap_region_basic);
+	TEST(pure_anon_dev_zero);
 }

-- 
2.55.0