From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [Xen-devel] [RFC] Hypervisor RNG and enumeration Date: Wed, 29 Oct 2014 14:45:41 +0100 Message-ID: <5450EF85.8090500@redhat.com> References: <5450C35D.1030907@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5450C35D.1030907@citrix.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Andrew Cooper , Andy Lutomirski , Linux Virtualization Cc: Mathew John , Theodore Ts'o , David Hepkin , kvm list , Gleb Natapov , Niels Ferguson , Doug Covelli , Jim Mattson , "H. Peter Anvin" , Jake Oshins , xen-devel@lists.xenproject.org, Alok Kataria , John Starks List-Id: virtualization@lists.linuxfoundation.org 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. Paolo