[PATCH v2 14/15] tools/testing/vma: add test to assert MAP_PRIVATE-/dev/zero is anon

[Lorenzo Stoakes (ARM)]

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.

Signed-off-by: Lorenzo Stoakes (ARM) <l...@kernel.org>
---
 tools/testing/vma/include/dup.h |  1 +
 tools/testing/vma/tests/mmap.c  | 50 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index c5191b9718fd..47a91e35efe5 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h
@@ -20,6 +20,7 @@ struct task_struct *get_current(void);
 
 #define MAJOR(dev)     ((unsigned int) ((dev) >> MINORBITS))
 #define MINOR(dev)     ((unsigned int) ((dev) & MINORMASK))
+#define MKDEV(ma, mi)  (((ma) << MINORBITS) | (mi))
 
 #define S_IFMT  00170000
 #define S_IFCHR  0020000
diff --git a/tools/testing/vma/tests/mmap.c b/tools/testing/vma/tests/mmap.c
index c85bc000d1cb..b720deb4227d 100644
--- a/tools/testing/vma/tests/mmap.c
+++ b/tools/testing/vma/tests/mmap.c
@@ -45,7 +45,57 @@ static bool test_mmap_region_basic(void)
        return true;
 }
 
+static int dummy_mmap_prepare(struct vm_area_desc *desc)
+{
+       return 0;
+}
+
+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);
+       const struct file_operations f_op = {
+               .mmap_prepare = dummy_mmap_prepare,
+       };
+       struct inode inode = {
+               .i_mode = S_IFCHR,
+               .i_rdev = MKDEV(MEM_MAJOR, DEVZERO_MINOR),
+       };
+       struct file file = {
+               .f_inode = &inode,
+               .f_op = &f_op,
+       };
+       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 virtual 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 virtual page offsets. */
+       ASSERT_EQ(vma->vm_pgoff, 0x300);
+       ASSERT_EQ(vma_start_virt_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