Xen devel - Jun 2013 - [PATCH] xen/arm: Update VTCR to use region size of 2^40 bytes instead of 2^39

According to the ARM manual, T0SZ is a 4-bit signed integer.
The current value of T0SZ = b1000 which is equal to -7. This is result
to a size of 2^39 bytes instead of the desired value 2^40.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
---
 xen/arch/arm/mm.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index d1290cd..7d4e186 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -315,9 +315,9 @@ void __cpuinit setup_virt_paging(void)
     /* Setup Stage 2 address translation */
     /* SH0=00, ORGN0=IRGN0=01
      * SL0=01 (Level-1)
-     * T0SZ=(1)1000 = -8 (40 bit physical addresses)
+     * T0SZ=(1)1111 = -8 (40 bit physical addresses)
      */
-    WRITE_SYSREG32(0x80002558, VTCR_EL2); isb();
+    WRITE_SYSREG32(0x8000255f, VTCR_EL2); isb();
 }
 
 /* This needs to be a macro to stop the compiler spilling to the stack
-- 
1.7.10.4

At 13:06 +0100 on 06 Jun (1370524015), Julien Grall
wrote:
> According to the ARM manual, T0SZ is a 4-bit signed integer.
> The current value of T0SZ = b1000 which is equal to -7. This is result
Really?  By my count, 4-bit -7 is b1001 and b1000 is indeed -8.
> to a size of 2^39 bytes instead of the desired value 2^40.
> 
> Signed-off-by: Julien Grall <julien.grall@linaro.org>
> ---
>  xen/arch/arm/mm.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index d1290cd..7d4e186 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -315,9 +315,9 @@ void __cpuinit setup_virt_paging(void)
>      /* Setup Stage 2 address translation */
>      /* SH0=00, ORGN0=IRGN0=01
>       * SL0=01 (Level-1)
> -     * T0SZ=(1)1000 = -8 (40 bit physical addresses)
> +     * T0SZ=(1)1111 = -8 (40 bit physical addresses)
That''s certainly wrong: b1111 must be -1.

Tim.
>       */
> -    WRITE_SYSREG32(0x80002558, VTCR_EL2); isb();
> +    WRITE_SYSREG32(0x8000255f, VTCR_EL2); isb();
>  }
>  
>  /* This needs to be a macro to stop the compiler spilling to the stack
> -- 
> 1.7.10.4
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel

On Thu, 6 Jun 2013, Tim Deegan wrote:
> At 13:06 +0100 on 06 Jun (1370524015), Julien Grall wrote:
> > According to the ARM manual, T0SZ is a 4-bit signed integer.
> > The current value of T0SZ = b1000 which is equal to -7. This is result
> 
> Really?  By my count, 4-bit -7 is b1001 and b1000 is indeed -8.
Tim is right on this one:

https://en.wikipedia.org/wiki/Two%27s_complement

> > to a size of 2^39 bytes instead of the desired value 2^40.
> > 
> > Signed-off-by: Julien Grall <julien.grall@linaro.org>
> > ---
> >  xen/arch/arm/mm.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> > index d1290cd..7d4e186 100644
> > --- a/xen/arch/arm/mm.c
> > +++ b/xen/arch/arm/mm.c
> > @@ -315,9 +315,9 @@ void __cpuinit setup_virt_paging(void)
> >      /* Setup Stage 2 address translation */
> >      /* SH0=00, ORGN0=IRGN0=01
> >       * SL0=01 (Level-1)
> > -     * T0SZ=(1)1000 = -8 (40 bit physical addresses)
> > +     * T0SZ=(1)1111 = -8 (40 bit physical addresses)
> 
> That''s certainly wrong: b1111 must be -1.
right

 
> >       */
> > -    WRITE_SYSREG32(0x80002558, VTCR_EL2); isb();
> > +    WRITE_SYSREG32(0x8000255f, VTCR_EL2); isb();
> >  }
> >  
> >  /* This needs to be a macro to stop the compiler spilling to the
stack
> > -- 
> > 1.7.10.4
> > 
> > 
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xen.org
> > http://lists.xen.org/xen-devel
>

On 06/06/2013 02:17 PM, Tim Deegan wrote:
> At 13:06 +0100 on 06 Jun (1370524015), Julien Grall wrote:
>> According to the ARM manual, T0SZ is a 4-bit signed integer.
>> The current value of T0SZ = b1000 which is equal to -7. This is result
> 
> Really?  By my count, 4-bit -7 is b1001 and b1000 is indeed -8.

Indeed :/. I don''t know why I find this value by hand.

-- 
Julien