[PATCH v3 6/6] selftests: prctl: introduce tests for disabling THPs except for madvise

[Usama Arif <usamaarif642@gmail.com>]

The test will set the global system THP setting to never, madvise
or always depending on the fixture variant and the 2M setting to
inherit before it starts (and reset to original at teardown)

This tests if the process can:
- successfully set and get the policy to disable THPs expect for madvise.
- get hugepages only on MADV_HUGE and MADV_COLLAPSE if the global policy
  is madvise/always and only with MADV_COLLAPSE if the global policy is
  never.
- successfully reset the policy of the process.
- after reset, only get hugepages with:
  - MADV_COLLAPSE when policy is set to never.
  - MADV_HUGE and MADV_COLLAPSE when policy is set to madvise.
  - always when policy is set to "always".
- repeat the above tests in a forked process to make sure  the policy is
  carried across forks.

Signed-off-by: Usama Arif <usamaarif642@gmail.com>
---
 .../testing/selftests/mm/prctl_thp_disable.c  | 107 ++++++++++++++++++
 1 file changed, 107 insertions(+)

diff --git a/tools/testing/selftests/mm/prctl_thp_disable.c b/tools/testing/selftests/mm/prctl_thp_disable.c
index ef150180daf4..93cedaa59854 100644
--- a/tools/testing/selftests/mm/prctl_thp_disable.c
+++ b/tools/testing/selftests/mm/prctl_thp_disable.c
@@ -16,6 +16,10 @@
 #include "thp_settings.h"
 #include "vm_util.h"
 
+#ifndef PR_THP_DISABLE_EXCEPT_ADVISED
+#define PR_THP_DISABLE_EXCEPT_ADVISED (1 << 1)
+#endif
+
 static int sz2ord(size_t size, size_t pagesize)
 {
 	return __builtin_ctzll(size / pagesize);
@@ -170,4 +174,107 @@ TEST_F(prctl_thp_disable_completely, fork)
 	ASSERT_EQ(ret, 0);
 }
 
+static void prctl_thp_disable_except_madvise_test(struct __test_metadata *const _metadata,
+						  size_t pmdsize,
+						  enum thp_enabled thp_policy)
+{
+	ASSERT_EQ(prctl(PR_GET_THP_DISABLE, NULL, NULL, NULL, NULL), 3);
+
+	/* tests after prctl overrides global policy */
+	ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_NONE, pmdsize), 0);
+
+	ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_MADV_HUGEPAGE, pmdsize),
+		  thp_policy == THP_NEVER ? 0 : 1);
+
+	ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_MADV_COLLAPSE, pmdsize), 1);
+
+	/* Reset to global policy */
+	ASSERT_EQ(prctl(PR_SET_THP_DISABLE, 0, NULL, NULL, NULL), 0);
+
+	/* tests after prctl is cleared, and only global policy is effective */
+	ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_NONE, pmdsize),
+		  thp_policy == THP_ALWAYS ? 1 : 0);
+
+	ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_MADV_HUGEPAGE, pmdsize),
+		  thp_policy == THP_NEVER ? 0 : 1);
+
+	ASSERT_EQ(test_mmap_thp(THP_COLLAPSE_MADV_COLLAPSE, pmdsize), 1);
+}
+
+FIXTURE(prctl_thp_disable_except_madvise)
+{
+	struct thp_settings settings;
+	size_t pmdsize;
+};
+
+FIXTURE_VARIANT(prctl_thp_disable_except_madvise)
+{
+	enum thp_enabled thp_policy;
+};
+
+FIXTURE_VARIANT_ADD(prctl_thp_disable_except_madvise, never)
+{
+	.thp_policy = THP_NEVER,
+};
+
+FIXTURE_VARIANT_ADD(prctl_thp_disable_except_madvise, madvise)
+{
+	.thp_policy = THP_MADVISE,
+};
+
+FIXTURE_VARIANT_ADD(prctl_thp_disable_except_madvise, always)
+{
+	.thp_policy = THP_ALWAYS,
+};
+
+FIXTURE_SETUP(prctl_thp_disable_except_madvise)
+{
+	if (!thp_available())
+		SKIP(return, "Transparent Hugepages not available\n");
+
+	self->pmdsize = read_pmd_pagesize();
+	if (!self->pmdsize)
+		SKIP(return, "Unable to read PMD size\n");
+
+	thp_save_settings();
+	thp_read_settings(&self->settings);
+	self->settings.thp_enabled = variant->thp_policy;
+	self->settings.hugepages[sz2ord(self->pmdsize, getpagesize())].enabled = THP_INHERIT;
+	thp_write_settings(&self->settings);
+}
+
+FIXTURE_TEARDOWN(prctl_thp_disable_except_madvise)
+{
+	thp_restore_settings();
+}
+
+TEST_F(prctl_thp_disable_except_madvise, nofork)
+{
+	ASSERT_EQ(prctl(PR_SET_THP_DISABLE, 1, PR_THP_DISABLE_EXCEPT_ADVISED, NULL, NULL), 0);
+	prctl_thp_disable_except_madvise_test(_metadata, self->pmdsize, variant->thp_policy);
+}
+
+TEST_F(prctl_thp_disable_except_madvise, fork)
+{
+	int ret = 0;
+	pid_t pid;
+
+	ASSERT_EQ(prctl(PR_SET_THP_DISABLE, 1, PR_THP_DISABLE_EXCEPT_ADVISED, NULL, NULL), 0);
+
+	/* Make sure prctl changes are carried across fork */
+	pid = fork();
+	ASSERT_GE(pid, 0);
+
+	if (!pid)
+		prctl_thp_disable_except_madvise_test(_metadata, self->pmdsize,
+						      variant->thp_policy);
+
+	wait(&ret);
+	if (WIFEXITED(ret))
+		ret = WEXITSTATUS(ret);
+	else
+		ret = -EINVAL;
+	ASSERT_EQ(ret, 0);
+}
+
 TEST_HARNESS_MAIN
-- 
2.47.3