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Re: [Qemu-devel] [PATCH] resent: x86/cpuid: propagate further CPUID leaf

From: Avi Kivity
Subject: Re: [Qemu-devel] [PATCH] resent: x86/cpuid: propagate further CPUID leafs when -cpu host
Date: Tue, 25 May 2010 16:47:44 +0300
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100330 Fedora/3.0.4-1.fc12 Thunderbird/3.0.4

On 05/25/2010 04:26 PM, Anthony Liguori wrote:
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?

See my other mail.

Just because we can expose it doesn't mean we should.

What's the point of -cpu host then?

error compiling committee.c: too many arguments to function

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