From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753253Ab3GXViM (ORCPT ); Wed, 24 Jul 2013 17:38:12 -0400 Received: from terminus.zytor.com ([198.137.202.10]:50719 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752444Ab3GXViK (ORCPT ); Wed, 24 Jul 2013 17:38:10 -0400 User-Agent: K-9 Mail for Android In-Reply-To: References: <1374572465-15278-1-git-send-email-jasowang@redhat.com> <1374572465-15278-4-git-send-email-jasowang@redhat.com> <51EE97BD.4050402@zytor.com> <51EF59FB.8040207@redhat.com> <51EF5C9C.6070403@zytor.com> <51EF7A2A.6040003@redhat.com> <51EF7CFB.8030104@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: RE: [PATCH 4/4] x86: properly handle kvm emulation of hyperv From: "H. Peter Anvin" Date: Wed, 24 Jul 2013 14:37:43 -0700 To: KY Srinivasan , Paolo Bonzini , Jason Wang CC: "tglx@linutronix.de" , "mingo@redhat.com" , "x86@kernel.org" , "gleb@redhat.com" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" Message-ID: <889e20ee-7655-4fdc-b30a-150b8604ca0f@email.android.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org What I'm suggesting is exactly that except that the native hypervisor is later in CPUID space. KY Srinivasan wrote: > > >> -----Original Message----- >> From: H. Peter Anvin [mailto:hpa@zytor.com] >> Sent: Wednesday, July 24, 2013 11:14 AM >> To: KY Srinivasan; Paolo Bonzini; Jason Wang >> Cc: tglx@linutronix.de; mingo@redhat.com; x86@kernel.org; >gleb@redhat.com; >> kvm@vger.kernel.org; linux-kernel@vger.kernel.org >> Subject: RE: [PATCH 4/4] x86: properly handle kvm emulation of hyperv >> >> I don't see how this solves the A emulates B, B emulates A problem? > >As Paolo suggested if there were some priority encoded, the guest could >make an >informed decision. If the guest under question can run on both >hypervisors A and B, >we would rather the guest discover hypervisor A when running on A and >hypervisor B >when running on B. The priority encoding could be as simple as >surfacing the native hypervisor >signature earlier in the CPUID space. > >K. Y >> >> KY Srinivasan wrote: >> > >> > >> >> -----Original Message----- >> >> From: Paolo Bonzini [mailto:paolo.bonzini@gmail.com] On Behalf Of >> >Paolo >> >> Bonzini >> >> Sent: Wednesday, July 24, 2013 3:07 AM >> >> To: Jason Wang >> >> Cc: H. Peter Anvin; KY Srinivasan; tglx@linutronix.de; >> >mingo@redhat.com; >> >> x86@kernel.org; gleb@redhat.com; kvm@vger.kernel.org; linux- >> >> kernel@vger.kernel.org >> >> Subject: Re: [PATCH 4/4] x86: properly handle kvm emulation of >hyperv >> >> >> >> Il 24/07/2013 08:54, Jason Wang ha scritto: >> >> > On 07/24/2013 12:48 PM, H. Peter Anvin wrote: >> >> >> On 07/23/2013 09:37 PM, Jason Wang wrote: >> >> >>> On 07/23/2013 10:48 PM, H. Peter Anvin wrote: >> >> >>>> On 07/23/2013 06:55 AM, KY Srinivasan wrote: >> >> >>>>> This strategy of hypervisor detection based on some >detection >> >order >> >> IMHO is not >> >> >>>>> a robust detection strategy. The current scheme works since >the >> >only >> >> hypervisor emulated >> >> >>>>> (by other hypervisors happens to be Hyper-V). What if this >were >> >to >> >> change. >> >> >>>>> >> >> >>>> One strategy would be to pick the *last* one in the CPUID >list, >> >since >> >> >>>> the ones before it are logically the one(s) being emulated... >> >> >>>> >> >> >>>> -hpa >> >> >>>> >> >> >>> How about simply does a reverse loop from 0x40010000 to >> >0x40010000? >> >> >>> >> >> >> Not all systems like being poked too far into hyperspace. Just >> >remember >> >> >> the last match and walk the list. >> >> >> >> >> >> -hpa >> >> >> >> >> > >> >> > Ok, but it raises a question - how to know it was the 'last' >match >> >> > without knowing all signatures of other hyper-visor? >> >> >> >> You can return a "priority" value from the .detect function. The >> >> priority value can simply be the CPUID leaf where the signature >was >> >> found (or a low value such as 1 if detection was done with DMI). >> >> >> >> Then you can pick the hypervisor with the highest priority instead >of >> >> hard-coding the order. >> > >> >I like this idea; this allows some guest level control that is what >we >> >want >> >when we have hypervisors emulating each other. >> > >> > >> >Regards, >> > >> >K. Y >> >> >> >> Paolo >> >> >> >> >> >> -- >> Sent from my mobile phone. Please excuse brevity and lack of >formatting. >> >> -- Sent from my mobile phone. Please excuse brevity and lack of formatting.