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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

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@xxxxxxxxxx>
> > ---
> >  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@xxxxxxxxxxxxx
> > http://lists.xen.org/xen-devel
> 

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