Re: [PATCH V8] mm/debug: Add tests validating architecture page table helpers

[Anshuman Khandual <anshuman.khandual@xxxxxxx>]

On 10/29/2019 04:01 PM, Qian Cai wrote:
> 
> 
>> On Oct 28, 2019, at 1:29 AM, Anshuman Khandual <Anshuman.Khandual@xxxxxxx> wrote:
>>
>> This adds tests which will validate architecture page table helpers and
>> other accessors in their compliance with expected generic MM semantics.
>> This will help various architectures in validating changes to existing
>> page table helpers or addition of new ones.
>>
>> This test covers basic page table entry transformations including but not
>> limited to old, young, dirty, clean, write, write protect etc at various
>> level along with populating intermediate entries with next page table page
>> and validating them.
>>
>> Test page table pages are allocated from system memory with required size
>> and alignments. The mapped pfns at page table levels are derived from a
>> real pfn representing a valid kernel text symbol. This test gets called
>> right after page_alloc_init_late().
>>
>> This gets build and run when CONFIG_DEBUG_VM_PGTABLE is selected along with
>> CONFIG_VM_DEBUG. Architectures willing to subscribe this test also need to
>> select CONFIG_ARCH_HAS_DEBUG_VM_PGTABLE which for now is limited to x86 and
>> arm64. Going forward, other architectures too can enable this after fixing
>> build or runtime problems (if any) with their page table helpers.
>>
>> Folks interested in making sure that a given platform's page table helpers
>> conform to expected generic MM semantics should enable the above config
>> which will just trigger this test during boot. Any non conformity here will
>> be reported as an warning which would need to be fixed. This test will help
>> catch any changes to the agreed upon semantics expected from generic MM and
>> enable platforms to accommodate it thereafter.
> 
> This looks like a perfect candidate to streamline with the new kunit framework, no?

I have not been following the kunit test framework. But being highly dependent on
existing MM accessors (generic or platform) and very much page table modification
centric, mm/ is the best place for this test IMHO. It is now also part of DEBUG_VM
set of tests. Probably in future all existing MM tests (mm/ or lib/) might move to
kunit framework but for now it should remain with DEBUG_VM set of tests.