From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Vrabel <david.vrabel@citrix.com>
Subject: Re: [Xen-devel] [RFC] Hypervisor RNG and enumeration
Date: Wed, 29 Oct 2014 13:57:08 +0000
Message-ID: <5450F234.6040302@citrix.com>
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To: Paolo Bonzini <pbonzini@redhat.com>, Andrew Cooper <andrew.cooper3@citrix.com>, Andy Lutomirski <luto@amacapital.net>, Linux Virtualization <virtualization@lists.linux-foundation.org>
Cc: Mathew John <mathewj@microsoft.com>, Theodore Ts'o <tytso@mit.edu>, Jim Mattson <jmattson@vmware.com>, kvm list <kvm@vger.kernel.org>, Gleb Natapov <gleb@kernel.org>, Niels Ferguson <niels@microsoft.com>, Doug Covelli <dcovelli@vmware.com>, David Hepkin <davidhep@microsoft.com>, "H. Peter Anvin" <hpa@zytor.com>, Jake Oshins <jakeo@microsoft.com>, xen-devel@lists.xenproject.org, Alok Kataria <akataria@vmware.com>, John Starks <John.Starks@microsoft.com>
List-Id: virtualization@lists.linuxfoundation.org

On 29/10/14 13:45, Paolo Bonzini wrote:
> 
> 
> On 10/29/2014 11:37 AM, Andrew Cooper wrote:
>> While testing various nested combinations, XenServer has found that
>> modern Windows Server versions must have the hypervisor bit hidden from
>> them for them to be happy running HyperV, despite the fact that they
>> will make use of the Viridian virtual extensions also provided.
> 
> Right.
> 
>> As a result, while it is certainly advisable for the hypervisor bit to
>> be set, CommonHV should be available to be found by paravirtualised
>> drivers inside an OS which can't cope with the hypervisor bit set.
> 
> Microsoft should just stop putting arbitrary limitations on their
> software; or pay the price which, in this case, is not being able to use
> the features from the common specification.  I guess what they'd do is
> reinvent the RNG as a Viridian extension (if they need it).
> 
> You can certainly do CPUID(0x4F000000) even if HYPERVISOR=0.  What you
> get back is undefined, but in all likelihood it won't be the
> "CommonHVIntf" string.

Microsoft already has a specification to obtain a random number via an
ACPI device.  The VM Generation ID.

http://www.microsoft.com/en-us/download/details.aspx?id=30707

David