tools: testing: add simple __mmap_region() userland test

Introduce demonstrative, basic, __mmap_region() test upon which we can
base further work upon moving forwards.

This simply asserts that mappings can be made and merges occur as
expected.

As part of this change, fix the security_vm_enough_memory_mm() stub which
was previously incorrectly implemented.

Link: https://lkml.kernel.org/r/20241213162409.41498-1-lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/vma/vma.c

@@ -1574,6 +1574,57 @@ static bool test_expand_only_mode(void)
 	return true;
 }
 
+static bool test_mmap_region_basic(void)
+{
+	struct mm_struct mm = {};
+	unsigned long addr;
+	struct vm_area_struct *vma;
+	VMA_ITERATOR(vmi, &mm, 0);
+
+	current->mm = &mm;
+
+	/* Map at 0x300000, length 0x3000. */
+	addr = __mmap_region(NULL, 0x300000, 0x3000,
+			     VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE,
+			     0x300, NULL);
+	ASSERT_EQ(addr, 0x300000);
+
+	/* Map at 0x250000, length 0x3000. */
+	addr = __mmap_region(NULL, 0x250000, 0x3000,
+			     VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE,
+			     0x250, NULL);
+	ASSERT_EQ(addr, 0x250000);
+
+	/* Map at 0x303000, merging to 0x300000 of length 0x6000. */
+	addr = __mmap_region(NULL, 0x303000, 0x3000,
+			     VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE,
+			     0x303, NULL);
+	ASSERT_EQ(addr, 0x303000);
+
+	/* Map at 0x24d000, merging to 0x250000 of length 0x6000. */
+	addr = __mmap_region(NULL, 0x24d000, 0x3000,
+			     VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE,
+			     0x24d, NULL);
+	ASSERT_EQ(addr, 0x24d000);
+
+	ASSERT_EQ(mm.map_count, 2);
+
+	for_each_vma(vmi, vma) {
+		if (vma->vm_start == 0x300000) {
+			ASSERT_EQ(vma->vm_end, 0x306000);
+			ASSERT_EQ(vma->vm_pgoff, 0x300);
+		} else if (vma->vm_start == 0x24d000) {
+			ASSERT_EQ(vma->vm_end, 0x253000);
+			ASSERT_EQ(vma->vm_pgoff, 0x24d);
+		} else {
+			ASSERT_FALSE(true);
+		}
+	}
+
+	cleanup_mm(&mm, &vmi);
+	return true;
+}
+
 int main(void)
 {
 	int num_tests = 0, num_fail = 0;
@@ -1607,6 +1658,8 @@ int main(void)
 	TEST(copy_vma);
 	TEST(expand_only_mode);
 
+	TEST(mmap_region_basic);
+
 #undef TEST
 
 	printf("%d tests run, %d passed, %d failed.\n",

tools/testing/vma/vma_internal.h

@@ -996,7 +996,7 @@ static inline bool is_file_hugepages(struct file *)
 
 static inline int security_vm_enough_memory_mm(struct mm_struct *, long)
 {
-	return true;
+	return 0;
 }
 
 static inline bool may_expand_vm(struct mm_struct *, vm_flags_t, unsigned long)