selftests/mm: pagemap_scan ioctl: add PFN ZERO test cases

Add test cases to test the correctness of PFN ZERO flag of pagemap_scan
ioctl.  Test with normal pages backed memory and huge pages backed memory.

Link: https://lkml.kernel.org/r/20250707073321.106431-1-usama.anjum@collabora.com
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/mm/cow.c

@@ -72,31 +72,6 @@ static int detect_thp_sizes(size_t sizes[], int max)
 	return count;
 }
 
-static void detect_huge_zeropage(void)
-{
-	int fd = open("/sys/kernel/mm/transparent_hugepage/use_zero_page",
-		      O_RDONLY);
-	size_t enabled = 0;
-	char buf[15];
-	int ret;
-
-	if (fd < 0)
-		return;
-
-	ret = pread(fd, buf, sizeof(buf), 0);
-	if (ret > 0 && ret < sizeof(buf)) {
-		buf[ret] = 0;
-
-		enabled = strtoul(buf, NULL, 10);
-		if (enabled == 1) {
-			has_huge_zeropage = true;
-			ksft_print_msg("[INFO] huge zeropage is enabled\n");
-		}
-	}
-
-	close(fd);
-}
-
 static bool range_is_swapped(void *addr, size_t size)
 {
 	for (; size; addr += pagesize, size -= pagesize)
@@ -1903,7 +1878,7 @@ int main(int argc, char **argv)
 	}
 	nr_hugetlbsizes = detect_hugetlb_page_sizes(hugetlbsizes,
 						    ARRAY_SIZE(hugetlbsizes));
-	detect_huge_zeropage();
+	has_huge_zeropage = detect_huge_zeropage();
 
 	ksft_set_plan(ARRAY_SIZE(anon_test_cases) * tests_per_anon_test_case() +
 		      ARRAY_SIZE(anon_thp_test_cases) * tests_per_anon_thp_test_case() +

tools/testing/selftests/mm/pagemap_ioctl.c

@@ -1,4 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
+
 #define _GNU_SOURCE
 #include <stdio.h>
 #include <fcntl.h>
@@ -34,8 +35,8 @@
 #define PAGEMAP "/proc/self/pagemap"
 int pagemap_fd;
 int uffd;
-unsigned long page_size;
-unsigned int hpage_size;
+size_t page_size;
+size_t hpage_size;
 const char *progname;
 
 #define LEN(region)	((region.end - region.start)/page_size)
@@ -1480,6 +1481,68 @@ static void transact_test(int page_size)
 			      extra_thread_faults);
 }
 
+void zeropfn_tests(void)
+{
+	unsigned long long mem_size;
+	struct page_region vec;
+	int i, ret;
+	char *mmap_mem, *mem;
+
+	/* Test with normal memory */
+	mem_size = 10 * page_size;
+	mem = mmap(NULL, mem_size, PROT_READ, MAP_PRIVATE | MAP_ANON, -1, 0);
+	if (mem == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem\n");
+
+	/* Touch each page to ensure it's mapped */
+	for (i = 0; i < mem_size; i += page_size)
+		(void)((volatile char *)mem)[i];
+
+	ret = pagemap_ioctl(mem, mem_size, &vec, 1, 0,
+			    (mem_size / page_size), PAGE_IS_PFNZERO, 0, 0, PAGE_IS_PFNZERO);
+	if (ret < 0)
+		ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+	ksft_test_result(ret == 1 && LEN(vec) == (mem_size / page_size),
+			 "%s all pages must have PFNZERO set\n", __func__);
+
+	munmap(mem, mem_size);
+
+	/* Test with huge page if user_zero_page is set to 1 */
+	if (!detect_huge_zeropage()) {
+		ksft_test_result_skip("%s use_zero_page not supported or set to 1\n", __func__);
+		return;
+	}
+
+	mem_size = 2 * hpage_size;
+	mmap_mem = mmap(NULL, mem_size, PROT_READ | PROT_WRITE,
+			MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	if (mmap_mem == MAP_FAILED)
+		ksft_exit_fail_msg("error nomem\n");
+
+	/* We need a THP-aligned memory area. */
+	mem = (char *)(((uintptr_t)mmap_mem + hpage_size) & ~(hpage_size - 1));
+
+	ret = madvise(mem, hpage_size, MADV_HUGEPAGE);
+	if (!ret) {
+		char tmp = *mem;
+
+		asm volatile("" : "+r" (tmp));
+
+		ret = pagemap_ioctl(mem, hpage_size, &vec, 1, 0,
+				    0, PAGE_IS_PFNZERO, 0, 0, PAGE_IS_PFNZERO);
+		if (ret < 0)
+			ksft_exit_fail_msg("error %d %d %s\n", ret, errno, strerror(errno));
+
+		ksft_test_result(ret == 1 && LEN(vec) == (hpage_size / page_size),
+				 "%s all huge pages must have PFNZERO set\n", __func__);
+	} else {
+		ksft_test_result_skip("%s huge page not supported\n", __func__);
+	}
+
+	munmap(mmap_mem, mem_size);
+}
+
 int main(int __attribute__((unused)) argc, char *argv[])
 {
 	int shmid, buf_size, fd, i, ret;
@@ -1494,7 +1557,7 @@ int main(int __attribute__((unused)) argc, char *argv[])
 	if (init_uffd())
 		ksft_exit_pass();
 
-	ksft_set_plan(115);
+	ksft_set_plan(117);
 
 	page_size = getpagesize();
 	hpage_size = read_pmd_pagesize();
@@ -1669,6 +1732,9 @@ int main(int __attribute__((unused)) argc, char *argv[])
 	/* 16. Userfaultfd tests */
 	userfaultfd_tests();
 
+	/* 17. ZEROPFN tests */
+	zeropfn_tests();
+
 	close(pagemap_fd);
 	ksft_exit_pass();
 }

tools/testing/selftests/mm/vm_util.c

@@ -532,3 +532,26 @@ void *sys_mremap(void *old_address, unsigned long old_size,
 			       old_size, new_size, flags,
 			       (unsigned long)new_address);
 }
+
+bool detect_huge_zeropage(void)
+{
+	int fd = open("/sys/kernel/mm/transparent_hugepage/use_zero_page",
+		      O_RDONLY);
+	bool enabled = 0;
+	char buf[15];
+	int ret;
+
+	if (fd < 0)
+		return 0;
+
+	ret = pread(fd, buf, sizeof(buf), 0);
+	if (ret > 0 && ret < sizeof(buf)) {
+		buf[ret] = 0;
+
+		if (strtoul(buf, NULL, 10) == 1)
+			enabled = 1;
+	}
+
+	close(fd);
+	return enabled;
+}

tools/testing/selftests/mm/vm_util.h

@@ -44,6 +44,8 @@ static inline unsigned int pshift(void)
 	return __page_shift;
 }
 
+bool detect_huge_zeropage(void);
+
 /*
  * Plan 9 FS has bugs (at least on QEMU) where certain operations fail with
  * ENOENT on unlinked files. See