linux-kernel - Re: [PATCH V4 2/2] mm/pgtable/debug: Add test validating architecture page table helpers

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Message-ID: <20191007135158.GA36360@gmail.com>
Date:   Mon, 7 Oct 2019 15:51:58 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org,
        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>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        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 V4 2/2] mm/pgtable/debug: Add test validating
 architecture page table helpers


* Kirill A. Shutemov <kirill@...temov.name> wrote:

> On Mon, Oct 07, 2019 at 03:06:17PM +0200, Ingo Molnar wrote:
> > 
> > * Anshuman Khandual <anshuman.khandual@....com> wrote:
> > 
> > > This adds a test module which will validate architecture page table helpers
> > > and accessors regarding compliance with generic MM semantics expectations.
> > > This will help various architectures in validating changes to the existing
> > > page table helpers or addition of new ones.
> > > 
> > > Test page table and memory pages creating it's entries at various level are
> > > all allocated from system memory with required alignments. If memory pages
> > > with required size and alignment could not be allocated, then all depending
> > > individual tests are skipped.
> > 
> > > diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
> > > index 52e5f5f2240d..b882792a3999 100644
> > > --- a/arch/x86/include/asm/pgtable_64_types.h
> > > +++ b/arch/x86/include/asm/pgtable_64_types.h
> > > @@ -40,6 +40,8 @@ static inline bool pgtable_l5_enabled(void)
> > >  #define pgtable_l5_enabled() 0
> > >  #endif /* CONFIG_X86_5LEVEL */
> > >  
> > > +#define mm_p4d_folded(mm) (!pgtable_l5_enabled())
> > > +
> > >  extern unsigned int pgdir_shift;
> > >  extern unsigned int ptrs_per_p4d;
> > 
> > Any deep reason this has to be a macro instead of proper C?
> 
> It's a way to override the generic mm_p4d_folded(). It can be rewritten
> as inline function + define. Something like:
> 
> #define mm_p4d_folded mm_p4d_folded
> static inline bool mm_p4d_folded(struct mm_struct *mm)
> {
> 	return !pgtable_l5_enabled();
> }
> 
> But I don't see much reason to be more verbose here than needed.

C type checking? Documentation? Yeah, I know it's just a one-liner, but 
the principle of the death by a thousand cuts applies here.

BTW., any reason this must be in the low level pgtable_64_types.h type 
header, instead of one of the API level header files?

Thanks,

	Ingo