Re: [PATCH v3 7/7] selftest/mm: ksm_functional_tests: Add PROT_NONE test

[David Hildenbrand]

On 03.08.23 21:06, Peter Xu wrote:
> On Thu, Aug 03, 2023 at 04:32:08PM +0200, David Hildenbrand wrote:
> > Let's test whether merging and unmerging in PROT_NONE areas works as
> > expected.
> >
> > Pass a page protection to mmap_and_merge_range(), which will trigger
> > an mprotect() after writing to the pages, but before enabling merging.
> >
> > Make sure that unsharing works as expected, by performing a ptrace write
> > (using /proc/self/mem) and by setting MADV_UNMERGEABLE.
> >
> > Note that this implicitly tests that ptrace writes in an inaccessible
> > (PROT_NONE) mapping work as expected.
> >
> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
>
> [...]
>
> > +static void test_prot_none(void)
> > +{
> > +	const unsigned int size = 2 * MiB;
> > +	char *map;
> > +	int i;
> > +
> > +	ksft_print_msg("[RUN] %s\n", __func__);
> > +
> > +	map = mmap_and_merge_range(0x11, size, PROT_NONE, false);
> > +	if (map == MAP_FAILED)
> > +		goto unmap;
> > +
> > +	/* Store a unique value in each page on one half using ptrace */
> > +	for (i = 0; i < size / 2; i += pagesize) {
> > +		lseek(mem_fd, (uintptr_t) map + i, SEEK_SET);
> > +		if (write(mem_fd, &i, sizeof(size)) != sizeof(size)) {
>
> sizeof(i)?  May not matter a huge lot, though..

Oh, indeed, thanks!

> > +			ksft_test_result_fail("ptrace write failed\n");
> > +			goto unmap;
> > +		}
> > +	}
>
> Acked-by: Peter Xu <peterx@xxxxxxxxxx>

Thanks!

--
Cheers,

David / dhildenb