Re: [Qemu-devel] [PATCH v4 5/5] x86: Set physical address bits based on host

[Eduardo Habkost]

On Mon, Jul 11, 2016 at 04:39:22PM +0100, Dr. David Alan Gilbert wrote:
> * Eduardo Habkost (address@hidden) wrote:
[...]
> > > +            cpu->phys_bits = TCG_PHYS_ADDR_BITS;
> > > +        }
> > >      } else {
> > >          /* For 32 bit systems don't use the user set value, but keep
> > >           * phys_bits consistent with what we tell the guest.
> > 
> > Shouldn't we return error if host-phys-bits is set in 32-bit
> > mode?
> 
> I've just realised there's a reason that erroring in this case is a problem.
> Imagine a future (or downstream) machine type that made host-phys-bits the 
> default;
> how would it run with a 32bit CPU?

Oh, that's right. Ignoring it when explicitly set isn't
intuitive, but we need to be able to ignore it when set by a
machine compat_props (or if it's enabled by default). And
creating two separate properties sounds like overkill...

I'm reluctant, but I think it's OK to ignore it if LM is not set.
But we need to make sure it's documented somewhere.

-- 
Eduardo