1 files changed, 80 insertions, 3 deletions

diff --git a/tools/testing/selftests/mm/guard-pages.c b/tools/testing/selftests/mm/guard-pages.c
index 7cdf815d0d63..ece37212a8a2 100644
--- a/tools/testing/selftests/mm/guard-pages.c
+++ b/tools/testing/selftests/mm/guard-pages.c
@@ -55,6 +55,12 @@ static int pidfd_open(pid_t pid, unsigned int flags)
 	return syscall(SYS_pidfd_open, pid, flags);
 }
 
+static ssize_t sys_process_madvise(int pidfd, const struct iovec *iovec,
+				   size_t n, int advice, unsigned int flags)
+{
+	return syscall(__NR_process_madvise, pidfd, iovec, n, advice, flags);
+}
+
 /*
  * Enable our signal catcher and try to read/write the specified buffer. The
  * return value indicates whether the read/write succeeds without a fatal
@@ -419,7 +425,7 @@ TEST_F(guard_pages, process_madvise)
 	ASSERT_EQ(munmap(&ptr_region[99 * page_size], page_size), 0);
 
 	/* Now guard in one step. */
-	count = process_madvise(pidfd, vec, 6, MADV_GUARD_INSTALL, 0);
+	count = sys_process_madvise(pidfd, vec, 6, MADV_GUARD_INSTALL, 0);
 
 	/* OK we don't have permission to do this, skip. */
 	if (count == -1 && errno == EPERM)
@@ -440,7 +446,7 @@ TEST_F(guard_pages, process_madvise)
 	ASSERT_FALSE(try_read_write_buf(&ptr3[19 * page_size]));
 
 	/* Now do the same with unguard... */
-	count = process_madvise(pidfd, vec, 6, MADV_GUARD_REMOVE, 0);
+	count = sys_process_madvise(pidfd, vec, 6, MADV_GUARD_REMOVE, 0);
 
 	/* ...and everything should now succeed. */
 
@@ -990,7 +996,7 @@ TEST_F(guard_pages, fork)
 		   MAP_ANON | MAP_PRIVATE, -1, 0);
 	ASSERT_NE(ptr, MAP_FAILED);
 
-	/* Establish guard apges in the first 5 pages. */
+	/* Establish guard pages in the first 5 pages. */
 	ASSERT_EQ(madvise(ptr, 5 * page_size, MADV_GUARD_INSTALL), 0);
 
 	pid = fork();
@@ -1030,6 +1036,77 @@ TEST_F(guard_pages, fork)
 }
 
 /*
+ * Assert expected behaviour after we fork populated ranges of anonymous memory
+ * and then guard and unguard the range.
+ */
+TEST_F(guard_pages, fork_cow)
+{
+	const unsigned long page_size = self->page_size;
+	char *ptr;
+	pid_t pid;
+	int i;
+
+	/* Map 10 pages. */
+	ptr = mmap(NULL, 10 * page_size, PROT_READ | PROT_WRITE,
+		   MAP_ANON | MAP_PRIVATE, -1, 0);
+	ASSERT_NE(ptr, MAP_FAILED);
+
+	/* Populate range. */
+	for (i = 0; i < 10 * page_size; i++) {
+		char chr = 'a' + (i % 26);
+
+		ptr[i] = chr;
+	}
+
+	pid = fork();
+	ASSERT_NE(pid, -1);
+	if (!pid) {
+		/* This is the child process now. */
+
+		/* Ensure the range is as expected. */
+		for (i = 0; i < 10 * page_size; i++) {
+			char expected = 'a' + (i % 26);
+			char actual = ptr[i];
+
+			ASSERT_EQ(actual, expected);
+		}
+
+		/* Establish guard pages across the whole range. */
+		ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_INSTALL), 0);
+		/* Remove it. */
+		ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_REMOVE), 0);
+
+		/*
+		 * By removing the guard pages, the page tables will be
+		 * cleared. Assert that we are looking at the zero page now.
+		 */
+		for (i = 0; i < 10 * page_size; i++) {
+			char actual = ptr[i];
+
+			ASSERT_EQ(actual, '\0');
+		}
+
+		exit(0);
+	}
+
+	/* Parent process. */
+
+	/* Parent simply waits on child. */
+	waitpid(pid, NULL, 0);
+
+	/* Ensure the range is unchanged in parent anon range. */
+	for (i = 0; i < 10 * page_size; i++) {
+		char expected = 'a' + (i % 26);
+		char actual = ptr[i];
+
+		ASSERT_EQ(actual, expected);
+	}
+
+	/* Cleanup. */
+	ASSERT_EQ(munmap(ptr, 10 * page_size), 0);
+}
+
+/*
  * Assert that forking a process with VMAs that do have VM_WIPEONFORK set
  * behave as expected.
  */