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Date: Wed, 17 Jul 2013 18:19:28 +0300
From: Gleb Natapov <gleb@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] fix guest physical bits to match host,
 to go beyond 1TB guests
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To: Eduardo Habkost <ehabkost@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org, qemu-stable@nongnu.org

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.

--
			Gleb.