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

David Hildenbrand (Red Hat)
2026-01-09T15:08:10Z

On 12/15/25 16:03, Kevin Brodsky wrote:
> 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@arm.com>
> ---
> 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");

Very nice test :)

I think I prefer the EXPORT_SYMBOL_IF_KUNIT over disabling the test for
PPC and over making lazy_mmu_mode_enable() non-inlined functions with an
exported symbol.

With the EXPORT_SYMBOL_IF_KUNIT stuff added

Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>

--
Cheers

David