selftests/mm: add new selftests for KSM

This adds three new tests to the selftests for KSM.  These tests use the
new prctl API's to enable and disable KSM.

1) add new prctl flags to prctl header file in tools dir

   This adds the new prctl flags to the include file prct.h in the
   tools directory.  This makes sure they are available for testing.

2) add KSM prctl merge test to ksm_tests

   This adds the -t option to the ksm_tests program.  The -t flag
   allows to specify if it should use madvise or prctl ksm merging.

3) add two functions for debugging merge outcome for ksm_tests

   This adds two functions to report the metrics in /proc/self/ksm_stat
   and /sys/kernel/debug/mm/ksm. The debug output is enabled with the
   -d option.

4) add KSM prctl test to ksm_functional_tests

   This adds a test to the ksm_functional_test that verifies that the
   prctl system call to enable / disable KSM works.

5) add KSM fork test to ksm_functional_test

   Add fork test to verify that the MMF_VM_MERGE_ANY flag is inherited
   by the child process.

Link: https://lkml.kernel.org/r/20230418051342.1919757-4-shr@devkernel.io
Signed-off-by: Stefan Roesch <shr@devkernel.io>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Bagas Sanjaya <bagasdotme@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/include/uapi/linux/prctl.h

@@ -290,4 +290,6 @@ struct prctl_mm_map {
 #define PR_SET_VMA		0x53564d41
 # define PR_SET_VMA_ANON_NAME		0
 
+#define PR_SET_MEMORY_MERGE		67
+#define PR_GET_MEMORY_MERGE		68
 #endif /* _LINUX_PRCTL_H */

tools/testing/selftests/mm/Makefile

@@ -29,7 +29,7 @@ MACHINE ?= $(shell echo $(uname_M) | sed -e 's/aarch64.*/arm64/' -e 's/ppc64.*/p
 # LDLIBS.
 MAKEFLAGS += --no-builtin-rules
 
-CFLAGS = -Wall -I $(top_srcdir) $(EXTRA_CFLAGS) $(KHDR_INCLUDES)
+CFLAGS = -Wall -I $(top_srcdir) -I $(top_srcdir)/tools/include/uapi $(EXTRA_CFLAGS) $(KHDR_INCLUDES)
 LDLIBS = -lrt -lpthread
 
 TEST_GEN_PROGS = cow

tools/testing/selftests/mm/ksm_functional_tests.c

@@ -15,8 +15,10 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <sys/mman.h>
+#include <sys/prctl.h>
 #include <sys/syscall.h>
 #include <sys/ioctl.h>
+#include <sys/wait.h>
 #include <linux/userfaultfd.h>
 
 #include "../kselftest.h"
@@ -237,9 +239,93 @@ static void test_unmerge_uffd_wp(void)
 }
 #endif
 
+/* Verify that KSM can be enabled / queried with prctl. */
+static void test_prctl(void)
+{
+	int ret;
+
+	ksft_print_msg("[RUN] %s\n", __func__);
+
+	ret = prctl(PR_SET_MEMORY_MERGE, 1, 0, 0, 0);
+	if (ret < 0 && errno == EINVAL) {
+		ksft_test_result_skip("PR_SET_MEMORY_MERGE not supported\n");
+		return;
+	} else if (ret) {
+		ksft_test_result_fail("PR_SET_MEMORY_MERGE=1 failed\n");
+		return;
+	}
+
+	ret = prctl(PR_GET_MEMORY_MERGE, 0, 0, 0, 0);
+	if (ret < 0) {
+		ksft_test_result_fail("PR_GET_MEMORY_MERGE failed\n");
+		return;
+	} else if (ret != 1) {
+		ksft_test_result_fail("PR_SET_MEMORY_MERGE=1 not effective\n");
+		return;
+	}
+
+	ret = prctl(PR_SET_MEMORY_MERGE, 0, 0, 0, 0);
+	if (ret) {
+		ksft_test_result_fail("PR_SET_MEMORY_MERGE=0 failed\n");
+		return;
+	}
+
+	ret = prctl(PR_GET_MEMORY_MERGE, 0, 0, 0, 0);
+	if (ret < 0) {
+		ksft_test_result_fail("PR_GET_MEMORY_MERGE failed\n");
+		return;
+	} else if (ret != 0) {
+		ksft_test_result_fail("PR_SET_MEMORY_MERGE=0 not effective\n");
+		return;
+	}
+
+	ksft_test_result_pass("Setting/clearing PR_SET_MEMORY_MERGE works\n");
+}
+
+/* Verify that prctl ksm flag is inherited. */
+static void test_prctl_fork(void)
+{
+	int ret, status;
+	pid_t child_pid;
+
+	ksft_print_msg("[RUN] %s\n", __func__);
+
+	ret = prctl(PR_SET_MEMORY_MERGE, 1, 0, 0, 0);
+	if (ret < 0 && errno == EINVAL) {
+		ksft_test_result_skip("PR_SET_MEMORY_MERGE not supported\n");
+		return;
+	} else if (ret) {
+		ksft_test_result_fail("PR_SET_MEMORY_MERGE=1 failed\n");
+		return;
+	}
+
+	child_pid = fork();
+	if (!child_pid) {
+		exit(prctl(PR_GET_MEMORY_MERGE, 0, 0, 0, 0));
+	} else if (child_pid < 0) {
+		ksft_test_result_fail("fork() failed\n");
+		return;
+	}
+
+	if (waitpid(child_pid, &status, 0) < 0) {
+		ksft_test_result_fail("waitpid() failed\n");
+		return;
+	} else if (WEXITSTATUS(status) != 1) {
+		ksft_test_result_fail("unexpected PR_GET_MEMORY_MERGE result in child\n");
+		return;
+	}
+
+	if (prctl(PR_SET_MEMORY_MERGE, 0, 0, 0, 0)) {
+		ksft_test_result_fail("PR_SET_MEMORY_MERGE=0 failed\n");
+		return;
+	}
+
+	ksft_test_result_pass("PR_SET_MEMORY_MERGE value is inherited\n");
+}
+
 int main(int argc, char **argv)
 {
-	unsigned int tests = 2;
+	unsigned int tests = 4;
 	int err;
 
 #ifdef __NR_userfaultfd
@@ -267,6 +353,9 @@ int main(int argc, char **argv)
 	test_unmerge_uffd_wp();
 #endif
 
+	test_prctl();
+	test_prctl_fork();
+
 	err = ksft_get_fail_cnt();
 	if (err)
 		ksft_exit_fail_msg("%d out of %d tests failed\n",