[PATCH 3/3] selftests/mm: add PAGEMAP_SCAN guard region test

[Andrei Vagin <avagin@google.com>]

From: Andrei Vagin <avagin@gmail.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@gmail.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