Re: [PATCH v4 19/20] tools/testing/vma: add test to assert MAP_PRIVATE-/dev/zero is anon

On Wed, Aug 12, 2026 at 07:17:39PM +0200, David Hildenbrand (Arm) wrote:
> > +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);
> > +
>
> When we go with a zero_vm_ops this gets a bit simpler (see schloppedi-schlop).

Obviously will have to replace this with something else that just sets anon in
an mmap_prepare callback once I drop 17/20.

>
> > +	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);
>
> Yes, that looks good to me.
>
> Acked-by: David Hildenbrand (Arm) <[email protected]>

Thanks

>
> --
> Cheers,
>
> David

--
Cheers, Lorenzo