linux-kernel - Re: [PATCH] ARM: map_init_section flushes incorrect pmd

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Date:	Tue, 28 May 2013 17:04:40 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Will Deacon <will.deacon@....com>
Cc:	Po-Yu Chuang <ratbert.chuang@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"nico@...aro.org" <nico@...aro.org>
Subject: Re: [PATCH] ARM: map_init_section flushes incorrect pmd

On Tue, May 28, 2013 at 02:05:02PM +0100, Will Deacon wrote:
> On Tue, May 28, 2013 at 11:48:20AM +0100, Po-Yu Chuang wrote:
> > This bug was introduced in commit e651eab0.
> > Some v4/v5 platforms failed to boot due to this.
> > 
> > Signed-off-by: Po-Yu Chuang <ratbert.chuang@...il.com>
> > ---
> >  arch/arm/mm/mmu.c |    4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> > index e0d8565..19a43f8 100644
> > --- a/arch/arm/mm/mmu.c
> > +++ b/arch/arm/mm/mmu.c
> > @@ -620,6 +620,8 @@ static void __init map_init_section(pmd_t *pmd, unsigned long addr,
> >  			unsigned long end, phys_addr_t phys,
> >  			const struct mem_type *type)
> >  {
> > +	pmd_t *p = pmd;
> > +
> >  #ifndef CONFIG_ARM_LPAE
> >  	/*
> >  	 * In classic MMU format, puds and pmds are folded in to
> > @@ -638,7 +640,7 @@ static void __init map_init_section(pmd_t *pmd, unsigned long addr,
> >  		phys += SECTION_SIZE;
> >  	} while (pmd++, addr += SECTION_SIZE, addr != end);
> >  
> > -	flush_pmd_entry(pmd);
> > +	flush_pmd_entry(p);
> 
> Wait, shouldn't this flush be *inside* the loop anyway? Otherwise we just
> flush the cacheline containing the first pmd. The flushing code could also
> flush to PoU instead of PoC for UP ARMv7, but that's an unrelated optimisation.

With LPAE, map_init_section() is called once per section from
alloc_init_pmd(). The loop is there for classic MMU to allow setting two
pmd entries (maximum) and flush_pmd_entry() takes care of both (it
flushes a full cache line anyway).

-- 
Catalin
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