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Date: Tue, 8 Sep 2015 16:57:55 +0200
From: "Edgar E. Iglesias" <edgar.iglesias@xilinx.com>
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Subject: Re: [Qemu-devel] [PATCH v1 07/10] target-arm: Supress the use of
 TTBR1 for S2 translations
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: "Edgar E. Iglesias" <edgar.iglesias@gmail.com>, Sergey Fedorov <serge.fdrv@gmail.com>, Alex =?iso-8859-1?Q?Benn=E9e?= <alex.bennee@linaro.org>, QEMU Developers <qemu-devel@nongnu.org>, Alexander Graf <agraf@suse.de>

On Tue, Sep 08, 2015 at 03:50:34PM +0100, Peter Maydell wrote:
> On 8 September 2015 at 15:42, Edgar E. Iglesias
> <edgar.iglesias@xilinx.com> wrote:
> > On Tue, Sep 08, 2015 at 03:32:36PM +0100, Peter Maydell wrote:
> >> On 3 September 2015 at 21:14, Edgar E. Iglesias
> >> <edgar.iglesias@gmail.com> wrote:
> >> > From: "Edgar E. Iglesias" <edgar.iglesias@xilinx.com>
> >> >
> >> > Stage-2 MMU translations do not use TTBR1.
> >> >
> >> > Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
> >> > ---
> >> >  target-arm/helper.c | 5 +++++
> >> >  1 file changed, 5 insertions(+)
> >> >
> >> > diff --git a/target-arm/helper.c b/target-arm/helper.c
> >> > index 9ea9719..66b3fed 100644
> >> > --- a/target-arm/helper.c
> >> > +++ b/target-arm/helper.c
> >> > @@ -6372,6 +6372,11 @@ static bool get_phys_addr_lpae(CPUARMState *env, target_ulong address,
> >> >          }
> >> >      }
> >> >
> >> > +    /* Stage2 translations do not use TTBR1.  */
> >> > +    if (mmu_idx == ARMMMUIdx_S2NS) {
> >> > +        ttbr1_valid = false;
> >> > +    }
> >> > +
> >>
> >> I think this is unnecessary, because we've already set ttbr1_valid
> >> to false in the previous chunk of code for the case where el == 2
> >> (as it is for stage 2 translations).
> >
> > I think we may be confused here.
> >
> > Note S2NS translations are controlled by EL2 but apply to NS EL0 and EL1.
> 
> Yep. el is the result of regime_el(), which returns what the ARM ARM
> calls "the EL that the translation regime is controlled from".
> In particular, we do things this way because it's the register width
> of the controlling EL that determines whether the translation
> regime is 64 bit, whether the TCR/TTBR/etc registers are the 64-bit
> forms or not, etc.

OK, I see. I'll have another look at this...

Thanks!
Edgar