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

[Dr. David Alan Gilbert]

* Eduardo Habkost (address@hidden) wrote:
> 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.

OK, I'll add a comment and a note in the commit message.

Dave

> 
> -- 
> Eduardo
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK