linux-kernel - Re: [PATCH] arm64: fix pud_huge() for 2-level pagetables

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Message-ID: <20140516162006.GJ5624@arm.com>
Date:	Fri, 16 May 2014 17:20:06 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Mark Salter <msalter@...hat.com>
Cc:	Will Deacon <Will.Deacon@....com>,
	Steve Capper <steve.capper@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: fix pud_huge() for 2-level pagetables

On Fri, May 16, 2014 at 04:54:11PM +0100, Mark Salter wrote:
> On Fri, 2014-05-16 at 11:04 +0100, Catalin Marinas wrote:
> > On Thu, May 15, 2014 at 03:19:22PM +0100, Mark Salter wrote:
> > > diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
> > > index 5e9aec3..9bed38f 100644
> > > --- a/arch/arm64/mm/hugetlbpage.c
> > > +++ b/arch/arm64/mm/hugetlbpage.c
> > > @@ -51,7 +51,11 @@ int pmd_huge(pmd_t pmd)
> > >  
> > >  int pud_huge(pud_t pud)
> > >  {
> > > +#ifndef __PAGETABLE_PMD_FOLDED
> > >  	return !(pud_val(pud) & PUD_TABLE_BIT);
> > > +#else
> > > +	return 0;
> > > +#endif
> > >  }
> > >  
> > >  int pmd_huge_support(void)
> > > @@ -64,8 +68,10 @@ static __init int setup_hugepagesz(char *opt)
> > >  	unsigned long ps = memparse(opt, &opt);
> > >  	if (ps == PMD_SIZE) {
> > >  		hugetlb_add_hstate(PMD_SHIFT - PAGE_SHIFT);
> > > +#ifndef __PAGETABLE_PMD_FOLDED
> > >  	} else if (ps == PUD_SIZE) {
> > >  		hugetlb_add_hstate(PUD_SHIFT - PAGE_SHIFT);
> > > +#endif
> > 
> > Since PMD_SIZE == PUD_SIZE when __PAGETABLE_PMD_FOLDED, do we need the
> > #ifndef here? Maybe the compiler is smart enough to remove it but it's
> > not on a critical path anyway, so I wouldn't bother.
> 
> Yes, I think it would remove it. In any case, one less ifdef would be
> a good thing.

I merged this patch and dropped the last #ifndef.

I still have doubts about the kvm code calling put_page more than
necessary, especially since pud == pmd and the loop continues after
pud_huge() returns true, but your patch looks harmless.

Unless Steve has any objection, I'll push it to mainline. I also added
Cc: stable # v3.11+

Thanks.

-- 
Catalin
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