linux-kernel - Re: [PATCH 3/3] selftests/mm: add PAGEMAP

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Message-ID: <52bbf098-46df-4227-8429-befd1e250b17@lucifer.local>
Date: Mon, 31 Mar 2025 12:27:27 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrei Vagin <avagin@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-doc@...r.kernel.org, David Hildenbrand <david@...hat.com>,
        Shuah Khan <shuah@...nel.org>, Jonathan Corbet <corbet@....net>,
        criu@...ts.linux.dev, Andrei Vagin <avagin@...il.com>
Subject: Re: [PATCH 3/3] selftests/mm: add PAGEMAP_SCAN guard region test

On Mon, Mar 24, 2025 at 06:53:28AM +0000, Andrei Vagin wrote:
> From: Andrei Vagin <avagin@...il.com>
>
> Add a selftest to verify the PAGEMAP_SCAN ioctl correctly reports guard
> regions using the newly introduced PAGE_IS_GUARD flag.
>
> Signed-off-by: Andrei Vagin <avagin@...il.com>

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
>  tools/testing/selftests/mm/guard-regions.c | 57 ++++++++++++++++++++++
>  1 file changed, 57 insertions(+)
>
> diff --git a/tools/testing/selftests/mm/guard-regions.c b/tools/testing/selftests/mm/guard-regions.c
> index 0c7183e8b661..c99f3da8bfb7 100644
> --- a/tools/testing/selftests/mm/guard-regions.c
> +++ b/tools/testing/selftests/mm/guard-regions.c
> @@ -8,6 +8,7 @@
>  #include <fcntl.h>
>  #include <linux/limits.h>
>  #include <linux/userfaultfd.h>
> +#include <linux/fs.h>
>  #include <setjmp.h>
>  #include <signal.h>
>  #include <stdbool.h>
> @@ -2079,4 +2080,60 @@ TEST_F(guard_regions, pagemap)
>  	ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
>  }
>
> +/*
> + * Assert that PAGEMAP_SCAN correctly reports guard region ranges.
> + */
> +TEST_F(guard_regions, pagemap_scan)
> +{
> +	const unsigned long page_size = self->page_size;
> +	struct page_region pm_regs[10];
> +	struct pm_scan_arg pm_scan_args = {
> +		.size = sizeof(struct pm_scan_arg),
> +		.category_anyof_mask = PAGE_IS_GUARD,
> +		.return_mask = PAGE_IS_GUARD,
> +		.vec = (long)&pm_regs,
> +		.vec_len = ARRAY_SIZE(pm_regs),
> +	};
> +	int proc_fd, i;
> +	char *ptr;
> +
> +	proc_fd = open("/proc/self/pagemap", O_RDONLY);
> +	ASSERT_NE(proc_fd, -1);
> +
> +	ptr = mmap_(self, variant, NULL, 10 * page_size,
> +		    PROT_READ | PROT_WRITE, 0, 0);
> +	ASSERT_NE(ptr, MAP_FAILED);
> +
> +	pm_scan_args.start = (long)ptr;
> +	pm_scan_args.end = (long)ptr + 10 * page_size;
> +	ASSERT_EQ(ioctl(proc_fd, PAGEMAP_SCAN, &pm_scan_args), 0);
> +	ASSERT_EQ(pm_scan_args.walk_end, (long)ptr + 10 * page_size);
> +
> +	/* Install a guard region in every other page. */
> +	for (i = 0; i < 10; i += 2) {
> +		char *ptr_p = &ptr[i * page_size];
> +
> +		ASSERT_EQ(syscall(__NR_madvise, ptr_p, page_size, MADV_GUARD_INSTALL), 0);
> +	}
> +
> +	/*
> +	 * Assert ioctl() returns the count of located regions, where each
> +	 * region spans every other page within the range of 10 pages.
> +	 */
> +	ASSERT_EQ(ioctl(proc_fd, PAGEMAP_SCAN, &pm_scan_args), 5);
> +	ASSERT_EQ(pm_scan_args.walk_end, (long)ptr + 10 * page_size);
> +
> +	/* Re-read from pagemap, and assert guard regions are detected. */
> +	for (i = 0; i < 5; i++) {
> +		long ptr_p = (long)&ptr[2 * i * page_size];
> +
> +		ASSERT_EQ(pm_regs[i].start, ptr_p);
> +		ASSERT_EQ(pm_regs[i].end, ptr_p + page_size);
> +		ASSERT_EQ(pm_regs[i].categories, PAGE_IS_GUARD);
> +	}
> +
> +	ASSERT_EQ(close(proc_fd), 0);
> +	ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
> +}
> +
>  TEST_HARNESS_MAIN
> --
> 2.49.0.395.g12beb8f557-goog
>