linux-kernel - Re: [PATCH 1/2] ARM: LPAE: load upper bits of early TTBR0/TTBR1

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Date:	Mon, 28 Jul 2014 19:47:41 +0100
From:	Will Deacon <will.deacon@....com>
To:	Konstantin Khlebnikov <koct9i@...il.com>
Cc:	Konstantin Khlebnikov <k.khlebnikov@...sung.com>,
	Vitaly Andrianov <vitalya@...com>,
	Russell King <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Cyril Chemparathy <cyril@...com>
Subject: Re: [PATCH 1/2] ARM: LPAE: load upper bits of early TTBR0/TTBR1

On Mon, Jul 28, 2014 at 07:40:58PM +0100, Konstantin Khlebnikov wrote:
> On Mon, Jul 28, 2014 at 10:12 PM, Will Deacon <will.deacon@....com> wrote:
> > On Tue, Jul 22, 2014 at 04:36:23PM +0100, Konstantin Khlebnikov wrote:
> >> This patch fixes booting when idmap pgd lays above 4gb. Commit
> >> 4756dcbfd37 mostly had fixed this, but it'd failed to load upper bits.
> >>
> >> Also this fixes adding TTBR1_OFFSET to TTRR1: if lower part overflows
> >> carry flag must be added to the upper part.
> >>
> >> Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@...sung.com>
> >> Cc: Cyril Chemparathy <cyril@...com>
> >> Cc: Vitaly Andrianov <vitalya@...com>
> >> ---
> >>  arch/arm/mm/proc-v7-3level.S |    7 +++----
> >>  1 file changed, 3 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/arch/arm/mm/proc-v7-3level.S b/arch/arm/mm/proc-v7-3level.S
> >> index 22e3ad6..f0481dd 100644
> >> --- a/arch/arm/mm/proc-v7-3level.S
> >> +++ b/arch/arm/mm/proc-v7-3level.S
> >> @@ -140,12 +140,11 @@ ENDPROC(cpu_v7_set_pte_ext)
> >>       mov     \tmp, \ttbr1, lsr #(32 - ARCH_PGD_SHIFT)        @ upper bits
> >>       mov     \ttbr1, \ttbr1, lsl #ARCH_PGD_SHIFT             @ lower bits
> >>       addls   \ttbr1, \ttbr1, #TTBR1_OFFSET
> >> -     mcrr    p15, 1, \ttbr1, \zero, c2                       @ load TTBR1
> >> +     adcls   \tmp, \tmp, #0
> >> +     mcrr    p15, 1, \ttbr1, \tmp, c2                        @ load TTBR1
> >>       mov     \tmp, \ttbr0, lsr #(32 - ARCH_PGD_SHIFT)        @ upper bits
> >>       mov     \ttbr0, \ttbr0, lsl #ARCH_PGD_SHIFT             @ lower bits
> >> -     mcrr    p15, 0, \ttbr0, \zero, c2                       @ load TTBR0
> >> -     mcrr    p15, 1, \ttbr1, \zero, c2                       @ load TTBR1
> >> -     mcrr    p15, 0, \ttbr0, \zero, c2                       @ load TTBR0
> >> +     mcrr    p15, 0, \ttbr0, \tmp, c2                        @ load TTBR0
> >
> > I must admit, the code you are removing here looks really strange. Was there
> > a badly resolved conflict somewhere along the way? It would be nice to see
> > if your fix (which seems ok to me) was actually present in the mailing list
> > posting of the patch that ended in the above mess.
> 
> Nope, no merge conflicts, source in original patch
> https://lkml.org/lkml/2012/9/11/346
> 
> That mess completely harmless, this code is used only once on boot.
> I don't have that email, so replying isn't trivial for me.

How bizarre. Also, Cyril doesn't work for TI anymore (his email is
bouncing), so it's tricky to know what he meant here.

Your patch looks better than what we currently have though. Have you managed
to test it on a keystone platform (I don't have one)?

Will
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