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

Kevin Brodsky
2025-12-17T16:10:53Z

On 17/12/2025 16:46, Ritesh Harjani (IBM) wrote:
> Ryan Roberts <ryan.roberts@arm.com> writes:
>
>> On 17/12/2025 09:26, Kevin Brodsky wrote:
>>> On 17/12/2025 05:14, Andrew Morton wrote:
>>>> On Mon, 15 Dec 2025 15:03:23 +0000 Kevin Brodsky <kevin.brodsky@arm.com> 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.
>>>> I needed this for powerpc allmodconfig;
>>>>
>>>> --- a/arch/powerpc/mm/book3s64/hash_tlb.c~mm-add-basic-tests-for-lazy_mmu-fix
>>>> +++ a/arch/powerpc/mm/book3s64/hash_tlb.c
>>>> @@ -30,6 +30,7 @@
>>>> #include <trace/events/thp.h>
>>>>
>>>> DEFINE_PER_CPU(struct ppc64_tlb_batch, ppc64_tlb_batch);
>>>> +EXPORT_SYMBOL_GPL(ppc64_tlb_batch);
>>>>
>>>> /*
>>>> * A linux PTE was changed and the corresponding hash table entry
>>>> @@ -154,6 +155,7 @@ void __flush_tlb_pending(struct ppc64_tl
>>>> flush_hash_range(i, local);
>>>> batch->index = 0;
>>>> }
>>>> +EXPORT_SYMBOL_GPL(__flush_tlb_pending);
>>>>
>>>> void hash__tlb_flush(struct mmu_gather *tlb)
>>>> {
>>>> _
>>> Oh indeed I hadn't considered that arch_{enter,leave}_lazy_mmu_mode()
>>> refer to those symbols on powerpc... Maybe a bit overkill to export
>>> those just for a test module, but I'm not sure there's a good
>>> alternative. Forcing LAZY_MMU_MODE_KUNIT_TEST=y is ugly as it would also
>>> force KUNIT=y. Alternatively we could depend on !PPC, not pretty either.
>> Does EXPORT_SYMBOL_IF_KUNIT() help?
>>
> yes, that make sense. Thanks for the suggestion!
> I guess we will need a diff like this in that case -
>
>
> diff --git a/arch/powerpc/mm/book3s64/hash_tlb.c b/arch/powerpc/mm/book3s64/hash_tlb.c
> index fbdeb8981ae7..ec2941cec815 100644
> --- a/arch/powerpc/mm/book3s64/hash_tlb.c
> +++ b/arch/powerpc/mm/book3s64/hash_tlb.c
> @@ -25,11 +25,12 @@
> #include <asm/tlb.h>
> #include <asm/bug.h>
> #include <asm/pte-walk.h>
> -
> +#include <kunit/visibility.h>
>
> #include <trace/events/thp.h>
>
> DEFINE_PER_CPU(struct ppc64_tlb_batch, ppc64_tlb_batch);
> +EXPORT_SYMBOL_IF_KUNIT(ppc64_tlb_batch);
>
> /*
> * A linux PTE was changed and the corresponding hash table entry
> @@ -154,6 +155,7 @@ void __flush_tlb_pending(struct ppc64_tlb_batch *batch)
> flush_hash_range(i, local);
> batch->index = 0;
> }
> +EXPORT_SYMBOL_IF_KUNIT(__flush_tlb_pending);
>
> void hash__tlb_flush(struct mmu_gather *tlb)
> {
> diff --git a/mm/tests/lazy_mmu_mode_kunit.c b/mm/tests/lazy_mmu_mode_kunit.c
> index 2720eb995714..340d7cda9096 100644
> --- a/mm/tests/lazy_mmu_mode_kunit.c
> +++ b/mm/tests/lazy_mmu_mode_kunit.c
> @@ -69,3 +69,4 @@ kunit_test_suite(lazy_mmu_mode_test_suite);
>
> MODULE_DESCRIPTION("Tests for the lazy MMU mode");
> MODULE_LICENSE("GPL");
> +MODULE_IMPORT_NS("EXPORTED_FOR_KUNIT_TESTING");

Indeed, that's pretty much what I was about to send :)

- Kevin