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

From: Paolo Bonzini <pbonzini@redhat.com>
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
Subject: Re: [Qemu-devel] [PATCH] fix guest physical bits to match host, to go beyond 1TB guests
Date: Tue, 16 Jul 2013 21:24:30 +0200	[thread overview]
Message-ID: <51E59DEE.5030603@redhat.com> (raw)
In-Reply-To: <20130716181136.GD19826@otherpad.lan.raisama.net>

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