Re: [Qemu-stable] [Qemu-devel] [PATCH] fix guest physical bits to match host, to go beyond 1TB guests

[Eduardo Habkost]

On Wed, Jul 17, 2013 at 06:19:28PM +0300, Gleb Natapov wrote:
> On Tue, Jul 16, 2013 at 04:42:38PM -0300, Eduardo Habkost wrote:
> > On Tue, Jul 16, 2013 at 09:24:30PM +0200, Paolo Bonzini wrote:
> > > Il 16/07/2013 20:11, Eduardo Habkost ha scritto:
> > > > For physical bit size, what about extending it in a backwards-compatible
> > > > way? Something like this:
> > > > 
> > > >     *eax = 0x0003000; /* 48 bits virtual */
> > > >     if (ram_size < 1TB) {
> > > >         physical_size = 40; /* Keeping backwards compatibility */
> > > >     } else if (ram_size < 4TB) {
> > > >         physical_size = 42;
> > > 
> > > Why not go straight up to 44?
> > 
> > I simply trusted the comment saying: "The physical address space is
> > limited to 42 bits in exec.c", and assumed we had a 42-bit limit
> > somewhere else.
> > 
> > We could also try something like this:
> > 
> >     if (ram_size < 1TB) {
> >         physical_size = 40; /* Keeping backwards compatibility */
> >     } else {
> >         physical_size = msb(ram_size);
> >     }
> >     if (supported_host_physical_size() < physical_size) {
> >         abort();
> >     }
> > 
> > 
> ram_size is the things we set with -m, right? Because if it is then
> using it here is incorrect since, due to PCI hole, max phys address is
> higher than ram_size.

Yeah, everywhere I used ram_size I actually meant "max phys address".

-- 
Eduardo