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

From: Ingo Molnar <mingo@kernel.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>,
	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>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	Jason Gunthorpe <jgg@ziepe.ca>,
	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>,
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	Martin Schwidefsky <schwidefsky@de.ibm.com>,
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	Vineet Gupta <vgupta@synopsys.com>,
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	Paul Burton <paul.burton@mips.com>,
	Ralf Baechle <ralf@linux-mips.org>,
	Gerald Schaefer <gerald.schaefer@de.ibm.com>,
	Christophe Leroy <christophe.leroy@c-s.fr>,
	linux-snps-arc@lists.infradead.org, linux-mips@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org,
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	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH V4 2/2] mm/pgtable/debug: Add test validating architecture page table helpers
Date: Mon, 7 Oct 2019 15:51:58 +0200	[thread overview]
Message-ID: <20191007135158.GA36360@gmail.com> (raw)
In-Reply-To: <20191007132607.4q537nauwfn5thol@box>

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

> On Mon, Oct 07, 2019 at 03:06:17PM +0200, Ingo Molnar wrote:
> > 
> > * Anshuman Khandual <anshuman.khandual@arm.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