linux-kernel - Re: [PATCH V12] mm/debug: Add tests validating architecture page table helpers

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Date:   Sun, 2 Feb 2020 09:31:18 +0100
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Dan Williams <dan.j.williams@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mark Brown <broonie@...nel.org>,
        Steven Price <Steven.Price@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Kees Cook <keescook@...omium.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Matthew Wilcox <willy@...radead.org>,
        Sri Krishna chowdary <schowdary@...dia.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        "David S. Miller" <davem@...emloft.net>,
        Vineet Gupta <vgupta@...opsys.com>,
        James Hogan <jhogan@...nel.org>,
        Paul Burton <paul.burton@...s.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        linux-snps-arc@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V12] mm/debug: Add tests validating architecture page
 table helpers



Le 02/02/2020 à 08:18, Anshuman Khandual a écrit :
> On 01/30/2020 07:43 PM, Christophe Leroy wrote:
>>
>>
>> Le 30/01/2020 à 14:04, Anshuman Khandual a écrit :
>>>
>>> On 01/28/2020 10:35 PM, Christophe Leroy wrote:
>>
>>>
>>>> I think we could make it standalone and 'default y if DEBUG_VM' instead.
>>>
>>> Which will yield the same result like before but in a different way. But
>>> yes, this test could go about either way but unless there is a good enough
>>> reason why change the current one.
>>
>> I think if we want people to really use it on other architectures it must be possible to activate it without having to modify Kconfig. Otherwise people won't even know the test exists and the architecture fails the test.
>>
>> The purpose of a test suite is to detect bugs. If you can't run the test until you have fixed the bugs, I guess nobody will ever detect the bugs and they will never be fixed.
>>
>> So I think:
>> - the test should be 'default y' when ARCH_HAS_DEBUG_VM_PGTABLE is selected
>> - the test should be 'default n' when ARCH_HAS_DEBUG_VM_PGTABLE is not selected, and it should be user selectable if EXPERT is selected.
>>
>> Something like:
>>
>> config DEBUG_VM_PGTABLE
>>      bool "Debug arch page table for semantics compliance" if ARCH_HAS_DEBUG_VM_PGTABLE || EXPERT
>>      depends on MMU
> 
> (ARCH_HAS_DEBUG_VM_PGTABLE || EXPERT) be moved along side MMU on the same line ?

Yes could also go along side MMU, or could be a depend by itself:
	depends on ARCH_HAS_DEBUG_VM_PGTABLE || EXPERT

> 
>>      default 'n' if !ARCH_HAS_DEBUG_VM_PGTABLE
>>      default 'y' if DEBUG_VM
> 
> This looks good, at least until we get all platforms enabled. Will do all these
> changes along with s390 enablement and re-spin.

Christophe