[PATCH v6 14/14] mm: Add basic tests for lazy_mmu

[Kevin Brodsky <kevin.brodsky@xxxxxxx>]

Add basic KUnit tests for the generic aspects of the lazy MMU mode:
ensure that it appears active when it should, depending on how
enable/disable and pause/resume pairs are nested.

Signed-off-by: Kevin Brodsky <kevin.brodsky@xxxxxxx>
---
 mm/Kconfig                     | 12 ++++++
 mm/Makefile                    |  1 +
 mm/tests/lazy_mmu_mode_kunit.c | 71 ++++++++++++++++++++++++++++++++++
 3 files changed, 84 insertions(+)
 create mode 100644 mm/tests/lazy_mmu_mode_kunit.c

diff --git a/mm/Kconfig b/mm/Kconfig
index 62073bd61544..ac48deb44884 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1471,6 +1471,18 @@ config ARCH_HAS_LAZY_MMU_MODE
          MMU-related architectural state to be deferred until the mode is
          exited. See <linux/pgtable.h> for details.
 
+config LAZY_MMU_MODE_KUNIT_TEST
+       tristate "KUnit tests for the lazy MMU mode" if !KUNIT_ALL_TESTS
+       depends on ARCH_HAS_LAZY_MMU_MODE
+       depends on KUNIT
+       default KUNIT_ALL_TESTS
+       help
+         Enable this option to check that the lazy MMU mode interface behaves
+         as expected. Only tests for the generic interface are included (not
+         architecture-specific behaviours).
+
+         If unsure, say N.
+
 source "mm/damon/Kconfig"
 
 endmenu
diff --git a/mm/Makefile b/mm/Makefile
index 2d0570a16e5b..9175f8cc6565 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -147,3 +147,4 @@ obj-$(CONFIG_SHRINKER_DEBUG) += shrinker_debug.o
 obj-$(CONFIG_EXECMEM) += execmem.o
 obj-$(CONFIG_TMPFS_QUOTA) += shmem_quota.o
 obj-$(CONFIG_PT_RECLAIM) += pt_reclaim.o
+obj-$(CONFIG_LAZY_MMU_MODE_KUNIT_TEST) += tests/lazy_mmu_mode_kunit.o
diff --git a/mm/tests/lazy_mmu_mode_kunit.c b/mm/tests/lazy_mmu_mode_kunit.c
new file mode 100644
index 000000000000..2720eb995714
--- /dev/null
+++ b/mm/tests/lazy_mmu_mode_kunit.c
@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <kunit/test.h>
+#include <linux/pgtable.h>
+
+static void expect_not_active(struct kunit *test)
+{
+       KUNIT_EXPECT_FALSE(test, is_lazy_mmu_mode_active());
+}
+
+static void expect_active(struct kunit *test)
+{
+       KUNIT_EXPECT_TRUE(test, is_lazy_mmu_mode_active());
+}
+
+static void lazy_mmu_mode_active(struct kunit *test)
+{
+       expect_not_active(test);
+
+       lazy_mmu_mode_enable();
+       expect_active(test);
+
+       {
+               /* Nested section */
+               lazy_mmu_mode_enable();
+               expect_active(test);
+
+               lazy_mmu_mode_disable();
+               expect_active(test);
+       }
+
+       {
+               /* Paused section */
+               lazy_mmu_mode_pause();
+               expect_not_active(test);
+
+               {
+                       /* No effect (paused) */
+                       lazy_mmu_mode_enable();
+                       expect_not_active(test);
+
+                       lazy_mmu_mode_disable();
+                       expect_not_active(test);
+
+                       lazy_mmu_mode_pause();
+                       expect_not_active(test);
+
+                       lazy_mmu_mode_resume();
+                       expect_not_active(test);
+               }
+
+               lazy_mmu_mode_resume();
+               expect_active(test);
+       }
+
+       lazy_mmu_mode_disable();
+       expect_not_active(test);
+}
+
+static struct kunit_case lazy_mmu_mode_test_cases[] = {
+       KUNIT_CASE(lazy_mmu_mode_active),
+       {}
+};
+
+static struct kunit_suite lazy_mmu_mode_test_suite = {
+       .name = "lazy_mmu_mode",
+       .test_cases = lazy_mmu_mode_test_cases,
+};
+kunit_test_suite(lazy_mmu_mode_test_suite);
+
+MODULE_DESCRIPTION("Tests for the lazy MMU mode");
+MODULE_LICENSE("GPL");
-- 
2.51.2