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Date: Mon, 29 Sep 2008 10:58:41 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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Subject: Re: Use CPUID to communicate with the hypervisor.
References: <1222472815.29886.43.camel@alok-dev1>	 <48E090B6.2080809@redhat.com> <1222710924.30247.21.camel@alok-dev1>
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Alok Kataria wrote:
>> Shouldn't you check the hypervisor signature here?
> 
> Nope the whole idea of not checking the hypervisor signature is that we
> should keep this interface generic. 

Unfortunately, given current evidence this is entirely unrealistic.

> So for instance right now, VMware has defined 40000010 leaf, if either
> kvm/xen think it could be useful they could just define that leaf to
> return nonzero value and the kernel will start using it for them.
> Likewise, if in future either kvm/xen come up with a need to define a
> new CPUID leaf they can define the semantics for that leaf, and the
> corresponding kernel side stuff. If VMware, think that this new leaf is
> useful, we can then support that leaf in our hypervisor or return zero
> otherwise.

This is only true if you can also except M$ and other hypervisor vendors 
to stick to it.  So far, hypervisor vendors have hardly shown any 
inclination toward standardization.

Hence I really don't think it is sane.

	-hpa