linux-kernel - Re: [PATCH 4/6] export new cpuid KVM

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Message-ID: <4BD73914.8040209@redhat.com>
Date:	Tue, 27 Apr 2010 22:20:52 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Glauber Costa <glommer@...hat.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/6] export new cpuid KVM_CAP

On 04/27/2010 10:09 PM, Glauber Costa wrote:
>
>> Hmm.  We already have an API to get cpuid bits:
>> KVM_GET_SUPPORTED_CPUID2.  The nice thing about it is that it will
>> mean -cpu host will work out of the box.
>>      
> Ok, from what I understand, KVM_GET_CPUID2 gets a set of features, and tells
> userspace which of them are available. Right?
>    

No.  KVM_GET_CPUID2 reads what was set by KVM_SET_CPUID, as modified by 
the guest executing the cpuid instruction.  KVM_GET_SUPPORTED_CPUID 
tells userspace which bits are supported by the host cpu and kvm.

> If this is the case, userspace could ask for 0xffffffff, and then we tell them
> which of them are present.
>
> Does that make sense?
>    

The API for KVM_GET_SUPPORTED_CPUID returns all cpuid leaves supported 
in one go, IIRC.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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