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Date: Tue, 16 Jul 2013 21:24:30 +0200
From: Paolo Bonzini <pbonzini@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>, qemu-devel@nongnu.org, Gleb Natapov <gleb@redhat.com>, qemu-stable@nongnu.org

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?

>     } else {
>         abort();
>     }
>     if (supported_host_physical_size() < physical_size) {
>         abort();
>     }
>     *eax |= physical_size;
> 
> (Of course, the abort() calls should be replaced with proper error
> reporting)

This makes sense too.  Though the best would be of course to use CPUID
values coming from the real processors, and only using 40 for backwards
compatibility.

Paolo