Re: [PATCH 2/2] kselftest: mm: replace usage of /proc/self/smaps for check_huge_xxx() helper

[Yeoreum Yun <yeoreum.yun@arm.com>]

On Thu, Aug 20, 2026 at 08:40:16PM +0100, Yeoreum Yun wrote:
> Since glibc commit 321e1fc73f (“malloc: Enable 2MB THP by default on AArch64”),
> glibc may call madvise(MADV_HUGEPAGE) for sufficiently large allocations
> made by memalign().
> 
> The underlying VMA may start at a different address from the aligned
> address returned by memalign(). Furthermore, a subsequent
> madvise(MADV_HUGEPAGE) call does not split the VMA because the flag is
> already set.
> 
> This causes split_huge_page_test to fail because the check_huge_xxx()
> helpers incorrectly require the address returned by memalign() to
> match the VMA start address reported in /proc/self/smaps.
> 
> Fix this by using /proc/self/pagemap and /proc/kpageflags instead of
> /proc/self/smaps to detect huge pages and change the meaning of
> check_huge_xxx()'s nr_hpages argument:
> 
>   - nr_hpages > 0: check all of pages in the range are huge page.
>   - nr_hpages < 0: check all of pages in the range are not huge page.
>   - nr_hpages == 0: invalid.
> 
> Reported-by: David Hildenbrand (Arm) <david@kernel.org>
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---
>  tools/testing/selftests/mm/khugepaged.c           |  26 ++---
>  tools/testing/selftests/mm/split_huge_page_test.c |   6 +-
>  tools/testing/selftests/mm/vm_util.c              | 135 ++++++++++++++++++----
>  tools/testing/selftests/mm/vm_util.h              |   1 +
>  4 files changed, 131 insertions(+), 37 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/khugepaged.c b/tools/testing/selftests/mm/khugepaged.c
> index 10e8dedcb087d..2e4665e6d5852 100644
> --- a/tools/testing/selftests/mm/khugepaged.c
> +++ b/tools/testing/selftests/mm/khugepaged.c
> @@ -533,7 +533,7 @@ static void __madvise_collapse(const char *msg, char *p, int nr_hpages,
>  	ret = madvise_collapse_retry(p, nr_hpages * hpage_pmd_size);
>  	if (((bool)ret) == expect)
>  		fail("Fail: Bad return value");
> -	else if (!ops->check_huge(p, expect ? nr_hpages : 0))
> +	else if (!ops->check_huge(p, expect ? nr_hpages : -nr_hpages))
>  		fail("Fail: check_huge()");
>  	else
>  		success("OK");
> @@ -545,7 +545,7 @@ static void madvise_collapse(const char *msg, char *p, int nr_hpages,
>  			     struct mem_ops *ops, bool expect)
>  {
>  	/* Sanity check */
> -	if (!ops->check_huge(p, 0))
> +	if (!ops->check_huge(p, -nr_hpages))
>  		ksft_exit_fail_msg("Unexpected huge page\n");
>  	__madvise_collapse(msg, p, nr_hpages, ops, expect);
>  }
> @@ -558,7 +558,7 @@ static bool wait_for_scan(const char *msg, char *p, int nr_hpages,
>  	int timeout = 6; /* 3 seconds */
>  
>  	/* Sanity check */
> -	if (!ops->check_huge(p, 0))
> +	if (!ops->check_huge(p, -nr_hpages))
>  		ksft_exit_fail_msg("Unexpected huge page\n");
>  
>  	madvise(p, nr_hpages * hpage_pmd_size, MADV_HUGEPAGE);
> @@ -605,7 +605,7 @@ static void khugepaged_collapse(const char *msg, char *p, int nr_hpages,
>  	if (ops != &__anon_ops)
>  		ops->fault(p, 0, nr_hpages * hpage_pmd_size);
>  
> -	if (ops->check_huge(p, expect ? nr_hpages : 0))
> +	if (ops->check_huge(p, expect ? nr_hpages : -nr_hpages))
>  		success("OK");
>  	else
>  		fail("Fail");
> @@ -643,7 +643,7 @@ static void alloc_at_fault(void)
>  
>  	madvise(p, page_size, MADV_DONTNEED);
>  	ksft_print_msg("Split huge PMD on MADV_DONTNEED...");
> -	if (check_huge_anon(p, 0, hpage_pmd_size))
> +	if (check_huge_anon(p, -1, hpage_pmd_size))
>  		success("OK");
>  	else
>  		fail("Fail");
> @@ -815,7 +815,7 @@ static void collapse_single_pte_entry_compound(struct collapse_context *c, struc
>  	madvise(p, hpage_pmd_size, MADV_NOHUGEPAGE);
>  	ksft_print_msg("Split huge page leaving single PTE mapping compound page...");
>  	madvise(p + page_size, hpage_pmd_size - page_size, MADV_DONTNEED);
> -	if (ops->check_huge(p, 0))
> +	if (ops->check_huge(p, -1))
>  		success("OK");
>  	else
>  		fail("Fail");
> @@ -836,7 +836,7 @@ static void collapse_full_of_compound(struct collapse_context *c, struct mem_ops
>  	ksft_print_msg("Split huge page leaving single PTE page table full of compound pages...");
>  	madvise(p, page_size, MADV_NOHUGEPAGE);
>  	madvise(p, hpage_pmd_size, MADV_NOHUGEPAGE);
> -	if (ops->check_huge(p, 0))
> +	if (ops->check_huge(p, -1))
>  		success("OK");
>  	else
>  		fail("Fail");
> @@ -903,7 +903,7 @@ static void collapse_fork(struct collapse_context *c, struct mem_ops *ops)
>  
>  	ksft_print_msg("Allocate small page...");
>  	ops->fault(p, 0, page_size);
> -	if (ops->check_huge(p, 0))
> +	if (ops->check_huge(p, -1))
>  		success("OK");
>  	else
>  		fail("Fail");
> @@ -911,7 +911,7 @@ static void collapse_fork(struct collapse_context *c, struct mem_ops *ops)
>  	ksft_print_msg("Share small page over fork()...");
>  	if (!fork()) {
>  		/* Do not touch settings on child exit */
> -		if (ops->check_huge(p, 0))
> +		if (ops->check_huge(p, -1))
>  			success("OK");
>  		else
>  			fail("Fail");
> @@ -929,7 +929,7 @@ static void collapse_fork(struct collapse_context *c, struct mem_ops *ops)
>  	exit_status = WEXITSTATUS(wstatus);
>  
>  	ksft_print_msg("Check if parent still has small page...");
> -	if (ops->check_huge(p, 0))
> +	if (ops->check_huge(p, -1))
>  		success("OK");
>  	else
>  		fail("Fail");
> @@ -955,7 +955,7 @@ static void collapse_fork_compound(struct collapse_context *c, struct mem_ops *o
>  		ksft_print_msg("Split huge page PMD in child process...");
>  		madvise(p, page_size, MADV_NOHUGEPAGE);
>  		madvise(p, hpage_pmd_size, MADV_NOHUGEPAGE);
> -		if (ops->check_huge(p, 0))
> +		if (ops->check_huge(p, -1))
>  			success("OK");
>  		else
>  			fail("Fail");
> @@ -1003,7 +1003,7 @@ static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops
>  		ksft_print_msg("Trigger CoW on page %d of %d...",
>  				hpage_pmd_nr - max_ptes_shared - 1, hpage_pmd_nr);
>  		ops->fault(p, 0, (hpage_pmd_nr - max_ptes_shared - 1) * page_size);
> -		if (ops->check_huge(p, 0))
> +		if (ops->check_huge(p, -1))
>  			success("OK");
>  		else
>  			fail("Fail");
> @@ -1016,7 +1016,7 @@ static void collapse_max_ptes_shared(struct collapse_context *c, struct mem_ops
>  			       hpage_pmd_nr - max_ptes_shared, hpage_pmd_nr);
>  			ops->fault(p, 0, (hpage_pmd_nr - max_ptes_shared) *
>  				    page_size);
> -			if (ops->check_huge(p, 0))
> +			if (ops->check_huge(p, -1))
>  				success("OK");
>  			else
>  				fail("Fail");
> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
> index 99b45e5518199..4fcd330cf0726 100644
> --- a/tools/testing/selftests/mm/split_huge_page_test.c
> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
> @@ -314,7 +314,7 @@ static void verify_rss_anon_split_huge_page_all_zeroes(char *one_page, int nr_hp
>  		if (one_page[i] != (char)0)
>  			ksft_exit_fail_msg("%ld byte corrupted\n", i);
>  
> -	if (!check_huge_anon(one_page, 0, pmd_pagesize))
> +	if (!check_huge_anon(one_page, -nr_hpages, pmd_pagesize))
>  		ksft_exit_fail_msg("Still AnonHugePages not split\n");
>  
>  	rss_anon_after = rss_anon();
> @@ -372,7 +372,7 @@ static void split_pmd_thp_to_order(int order)
>  					   (pmd_order + 1)))
>  		ksft_exit_fail_msg("Unexpected THP split\n");
>  
> -	if (!check_huge_anon(one_page, 0, pmd_pagesize))
> +	if (!check_huge_anon(one_page, -4, pmd_pagesize))
>  		ksft_exit_fail_msg("Still AnonHugePages not split\n");
>  
>  	ksft_test_result_pass("Split huge pages to order %d successful\n", order);
> @@ -746,7 +746,7 @@ static void split_thp_in_pagecache_to_order_at(size_t fd_size,
>  		goto out;
>  	}
>  
> -	if (!check_huge_file(addr, 0, pmd_pagesize)) {
> +	if (!check_huge_file(addr, -(fd_size / pmd_pagesize), pmd_pagesize)) {
>  		ksft_print_msg("Still FilePmdMapped not split\n");
>  		err = EXIT_FAILURE;
>  		goto out;
> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> index 311fc5b4513eb..166d5d79289f3 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -14,6 +14,8 @@
>  #define PMD_SIZE_FILE_PATH "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size"
>  #define SMAP_FILE_PATH "/proc/self/smaps"
>  #define STATUS_FILE_PATH "/proc/self/status"
> +#define PAGEMAP_FILE_PATH "/proc/self/pagemap"
> +#define KPAGEFLAGS_FILE_PATH "/proc/kpageflags"
>  #define MAX_LINE_LENGTH 500
>  
>  unsigned int __page_size;
> @@ -229,37 +231,128 @@ char *__get_smap_entry(void *addr, const char *pattern, char *buf, size_t len)
>  	return entry;
>  }
>  
> -bool __check_huge(void *addr, char *pattern, int nr_hpages,
> -		  uint64_t hpage_size)
> -{
> -	char buffer[MAX_LINE_LENGTH];
> -	uint64_t thp = -1;
> -	char *entry;
> -
> -	entry = __get_smap_entry(addr, pattern, buffer, sizeof(buffer));
> -	if (!entry)
> -		goto err_out;
> -
> -	if (sscanf(entry, "%9" SCNu64 " kB", &thp) != 1)
> -		ksft_exit_fail_msg("Reading smap error\n");
> -
> -err_out:
> -	return thp == (nr_hpages * (hpage_size >> 10));
> -}
> -
>  bool check_huge_anon(void *addr, int nr_hpages, uint64_t hpage_size)
>  {
> -	return __check_huge(addr, "AnonHugePages: ", nr_hpages, hpage_size);
> +	int i, pagemap_fd, nr = 0;
> +	uint64_t categories;
> +	bool expect_huge;
> +
> +	if (nr_hpages == 0 || hpage_size == 0)
> +		return false;
> +
> +	if (nr_hpages < 0) {
> +		nr_hpages = -nr_hpages;
> +		expect_huge = false;
> +	} else
> +		expect_huge = true;
> +
> +	pagemap_fd = open(PAGEMAP_FILE_PATH, O_RDONLY);
> +	if (pagemap_fd < 0)
> +		ksft_exit_fail_msg("open pagemap: %s\n", strerror(errno));
> +
> +	for (i = 0; i < nr_hpages; i++, addr += hpage_size) {
> +		categories = pagemap_scan_get_categories(pagemap_fd, addr);
> +		if (!(categories & PAGE_IS_HUGE))
> +			continue;
> +		if (categories & PAGE_IS_FILE)
> +			continue;
> +		nr++;
> +	}
> +
> +	close(pagemap_fd);
> +	return expect_huge ? nr == nr_hpages : nr == 0;
>  }
>  
>  bool check_huge_file(void *addr, int nr_hpages, uint64_t hpage_size)
>  {
> -	return __check_huge(addr, "FilePmdMapped:", nr_hpages, hpage_size);
> +	int i, pagemap_fd, kpf_fd, nr = 0;
> +	unsigned long pfn;
> +	uint64_t categories, kpf;
> +	bool expect_huge;
> +
> +	if (nr_hpages == 0 || hpage_size == 0)
> +		return false;
> +
> +	if (nr_hpages < 0) {
> +		nr_hpages = -nr_hpages;
> +		expect_huge = false;
> +	} else
> +		expect_huge = true;
> +
> +	pagemap_fd = open(PAGEMAP_FILE_PATH, O_RDONLY);
> +	if (pagemap_fd < 0)
> +		ksft_exit_fail_msg("open pagemap: %s\n", strerror(errno));
> +
> +	kpf_fd = open(KPAGEFLAGS_FILE_PATH, O_RDONLY);
> +	if (kpf_fd < 0)
> +		ksft_exit_fail_msg("open kpageflags: %s\n", strerror(errno));
> +
> +	for (i = 0; i < nr_hpages; i++, addr += hpage_size) {
> +		categories = pagemap_scan_get_categories(pagemap_fd, addr);
> +		pfn = pagemap_get_pfn(pagemap_fd, addr);
> +		if (pfn == -1UL)
> +			continue;
> +		if (pageflags_get(pfn, kpf_fd, &kpf))
> +			ksft_exit_fail_msg("read kpageflags: %s\n", strerror(errno));
> +		if (!(categories & PAGE_IS_HUGE))
> +			continue;
> +		if (!(categories & PAGE_IS_FILE))
> +			continue;
> +		if (kpf & KPF_SWAPBACKED)
> +			continue;
> +		nr++;
> +	}
> +
> +	close(pagemap_fd);
> +	close(kpf_fd);
> +
> +	return expect_huge ? nr == nr_hpages : nr == 0;
>  }
>  
>  bool check_huge_shmem(void *addr, int nr_hpages, uint64_t hpage_size)
>  {
> -	return __check_huge(addr, "ShmemPmdMapped:", nr_hpages, hpage_size);
> +	int i, pagemap_fd, kpf_fd, nr = 0;
> +	unsigned long pfn;
> +	uint64_t categories, kpf;
> +	bool expect_huge;
> +
> +	if (nr_hpages == 0 || hpage_size == 0)
> +		return false;
> +
> +	if (nr_hpages < 0) {
> +		nr_hpages = -nr_hpages;
> +		expect_huge = true;
> +	} else
> +		expect_huge = false;
> +

Oops... this part has mistaked compared with other function...
I'll fix later...

-- 
Sincerely,
Yeoreum Yun