[PATCH v2] tools/testing/vma: cover hole filling through __mmap_region()

[Tianyi Chen]

The mmap tests extend existing mappings one neighbor at a time, while
merge tests construct merge state directly. Neither exercises filling
a hole between compatible mappings through the mmap setup and completion
path.

Fill a gap through __mmap_region() and require both neighbors to merge
into one VMA. Repeat with only the new mapping's execute permission set
and require three separate VMAs. Check boundaries, permissions, page
offsets, map_count and cleanup.

Signed-off-by: Tianyi Chen <hi@xxxxxxxxx>
Assisted-by: Codex:GPT-6
---
Changes in v2:
- Rebase onto mm-unstable, preserving the new /dev/zero test.
- Rename hole_flags to middle_flags and describe each mapping's address
  and length in its comment.
- Remove the redundant hole, per-page and outer-boundary iterator checks.
- Use const bounds and named booleans for the middle VMA's expected execute
  permission, and separate assertion groups for readability.

Validation: all 29 VMA tests passed with ASan and UBSan enabled, built
with clang 20 using the existing VMA Makefile.

v1: https://lore.kernel.org/r/20260906144100.849288-1-hi@xxxxxxxxx
Review: https://lore.kernel.org/r/ap5pmX-RddQ-c90O@gremlin

 tools/testing/vma/tests/mmap.c | 68 ++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)

diff --git a/tools/testing/vma/tests/mmap.c b/tools/testing/vma/tests/mmap.c
index fa73faff226..53e4abe6a63 100644
--- a/tools/testing/vma/tests/mmap.c
+++ b/tools/testing/vma/tests/mmap.c
@@ -45,6 +45,72 @@ static bool test_mmap_region_basic(void)
 	return true;
 }
 
+static bool mmap_region_fill_hole(bool merge)
+{
+	const vma_flags_t vma_flags = mk_vma_flags(VMA_READ_BIT, VMA_WRITE_BIT,
+			VMA_MAYREAD_BIT, VMA_MAYWRITE_BIT, VMA_MAYEXEC_BIT);
+	vma_flags_t middle_flags = vma_flags;
+	struct mm_struct mm = {};
+	struct vm_area_struct *vma;
+	unsigned long addr;
+	int count = 0;
+	VMA_ITERATOR(vmi, &mm, 0);
+
+	current->mm = &mm;
+	if (!merge)
+		vma_flags_set(&middle_flags, VMA_EXEC_BIT);
+
+	/* Map at 0x300000, length 0x3000. */
+	addr = __mmap_region(NULL, 0x300000, 0x3000, vma_flags, 0x300, NULL);
+	ASSERT_EQ(addr, 0x300000);
+
+	/* Map at 0x306000, length 0x3000, leaving a hole. */
+	addr = __mmap_region(NULL, 0x306000, 0x3000, vma_flags, 0x306, NULL);
+	ASSERT_EQ(addr, 0x306000);
+	ASSERT_EQ(mm.map_count, 2);
+
+	/* Map at 0x303000, length 0x3000, filling the hole. */
+	addr = __mmap_region(NULL, 0x303000, 0x3000, middle_flags, 0x303, NULL);
+	ASSERT_EQ(addr, 0x303000);
+	ASSERT_EQ(mm.map_count, merge ? 1 : 3);
+
+	vma_iter_set(&vmi, 0);
+	for_each_vma(vmi, vma) {
+		const unsigned long start = 0x300000 + count * 0x3000;
+		const unsigned long end = merge ? 0x309000 : start + 0x3000;
+		/* Only the middle VMA in the non-merge case has VMA_EXEC. */
+		const bool is_middle_vma = count == 1;
+		const bool expect_exec_vma = is_middle_vma && !merge;
+
+		ASSERT_EQ(vma->vm_start, start);
+		ASSERT_EQ(vma->vm_end, end);
+		ASSERT_EQ(vma_start_pgoff(vma), start >> PAGE_SHIFT);
+		ASSERT_EQ(vma_start_anon_pgoff(vma), start >> PAGE_SHIFT);
+
+		ASSERT_TRUE(vma_test_all(vma, VMA_READ_BIT, VMA_WRITE_BIT,
+					 VMA_MAYREAD_BIT, VMA_MAYWRITE_BIT,
+					 VMA_MAYEXEC_BIT));
+		ASSERT_EQ(vma_test(vma, VMA_EXEC_BIT), expect_exec_vma);
+
+		count++;
+	}
+
+	ASSERT_EQ(count, mm.map_count);
+
+	ASSERT_EQ(cleanup_mm(&mm, &vmi), count);
+	return true;
+}
+
+static bool test_mmap_region_fill_hole_merge(void)
+{
+	return mmap_region_fill_hole(true);
+}
+
+static bool test_mmap_region_fill_hole_flags_mismatch(void)
+{
+	return mmap_region_fill_hole(false);
+}
+
 static bool test_pure_anon_dev_zero(void)
 {
 	const vma_flags_t vma_flags = mk_vma_flags(VMA_READ_BIT, VMA_WRITE_BIT,
@@ -84,5 +150,7 @@ static bool test_pure_anon_dev_zero(void)
 static void run_mmap_tests(int *num_tests, int *num_fail)
 {
 	TEST(mmap_region_basic);
+	TEST(mmap_region_fill_hole_merge);
+	TEST(mmap_region_fill_hole_flags_mismatch);
 	TEST(pure_anon_dev_zero);
 }
-- 
2.55.0