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Date: Tue, 25 May 2010 08:26:08 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [PATCH] resent: x86/cpuid: propagate further CPUID
	leafs when -cpu host
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To: Andre Przywara <andre.przywara@amd.com>
Cc: "avi@redhat.com" <avi@redhat.com>, "aurelien@aurel32.net" <aurelien@aurel32.net>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

On 05/25/2010 08:21 AM, Andre Przywara wrote:
>> What's the benefit of exposing this information to the guest?
>
> That is mostly to propagate the cache size and organization parameters 
> to the guest:
> >> +/* safe CPUID leafs to propagate to guest if -cpu host is specified
> >> + * Intel defined leafs:
> >> + * Cache descriptors (0x02)
> >> + * Deterministic cache parameters (0x04)
> >> + * Monitor/MWAIT parameters (0x05)
> >> + *
> >> + * AMD defined leafs:
> >> + * L1 Cache and TLB (0x05)
> >> + * L2+L3 TLB (0x06)
> >> + * LongMode address size (0x08)
> >> + * 1GB page TLB (0x19)
> >> + * Performance optimization (0x1A)
> >> + */
> Since at least L1 and L2 caches are mostly private to vCPUs, I see no 
> reason to disguise them.

But in practice, what is it useful for?  Just because we can expose it 
doesn't mean we should.

Regards,

Anthony Liguori

> Regards,
> Andre.
>