Re: [Qemu-devel] [PATCH v4 2/5] x86: Allow physical address bits to be set

[Eduardo Habkost]

On Fri, Jul 08, 2016 at 05:59:16PM -0700, Richard Henderson wrote:
> On 07/08/2016 04:36 PM, Eduardo Habkost wrote:
> >   -#elif defined(TARGET_X86_64)
> >   -#define TARGET_PHYS_ADDR_SPACE_BITS 42
> >   -#elif defined(TARGET_I386)
> >   -#define TARGET_PHYS_ADDR_SPACE_BITS 36
> > [...]
> >   --- a/target-i386/cpu.h
> >   +++ b/target-i386/cpu.h
> > [...]
> >   +#ifdef TARGET_X86_64
> >   +#define TARGET_PHYS_ADDR_SPACE_BITS 52
> >   +/* ??? This is really 48 bits, sign-extended, but the only thing
> >   +   accessible to userland with bit 48 set is the VSYSCALL, and that
> >   +   is handled via other mechanisms.  */
> >   +#define TARGET_VIRT_ADDR_SPACE_BITS 47
> >   +#else
> >   +#define TARGET_PHYS_ADDR_SPACE_BITS 36
> >   +#define TARGET_VIRT_ADDR_SPACE_BITS 32
> >   +#endif
> >   +
> > 
> > But I really don't understand why it was changed to 52 when the
> > macros were moved. A (fortunate) typo?
> 
> It was 6 years ago, but I assume that I looked up 52 as a theoretical
> maximum. I'm not going to look it up again to verify though.

Probably that's the case. David Gilbert also found 52 to be the
maximum.

-- 
Eduardo