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Subject: Re: [PATCH V8] mm/debug: Add tests validating architecture page table
 helpers
To:     Qian Cai <cai@lca.pw>
Cc:     linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Dan Williams <dan.j.williams@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Michal Hocko <mhocko@kernel.org>,
        Mark Rutland <Mark.Rutland@arm.com>,
        Mark Brown <broonie@kernel.org>,
        Steven Price <Steven.Price@arm.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Kees Cook <keescook@chromium.org>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        Matthew Wilcox <willy@infradead.org>,
        Sri Krishna chowdary <schowdary@nvidia.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Russell King - ARM Linux <linux@armlinux.org.uk>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Paul Mackerras <paulus@samba.org>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
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        Christophe Leroy <christophe.leroy@c-s.fr>,
        Ingo Molnar <mingo@kernel.org>,
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References: <1572240562-23630-1-git-send-email-anshuman.khandual@arm.com>
 <B6AAFA3F-745D-48E2-98CC-CFB30934CE39@lca.pw>
From:   Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <fdb72ac1-5f21-bcf1-ebab-411f56e67b56@arm.com>
Date:   Mon, 4 Nov 2019 07:45:56 +0530
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On 10/29/2019 04:01 PM, Qian Cai wrote:
> 
> 
>> On Oct 28, 2019, at 1:29 AM, Anshuman Khandual <Anshuman.Khandual@arm.com> 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.