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

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Date:	Tue, 28 May 2013 15:07:06 +0100
From:	Will Deacon <will.deacon@....com>
To:	Sricharan R <r.sricharan@...com>
Cc:	Po-Yu Chuang <ratbert.chuang@...il.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"nico@...aro.org" <nico@...aro.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM: map_init_section flushes incorrect pmd

On Tue, May 28, 2013 at 03:03:36PM +0100, Sricharan R wrote:
> On Tuesday 28 May 2013 06:35 PM, 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.
>    I think in LPAE this loop iterates once and non LPAE twice.
>    So both the entries should be contained in same cache line right ?

Dunno, are there any guarantees about alignment of the starting pmd? Even
so, the function takes the range as parameters, so I don't think we
should tailor it to the caller. It may explain why this hasn't come up
sooner though.

Will
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