Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966395Ab3DQNtW (ORCPT ); Wed, 17 Apr 2013 09:49:22 -0400 Received: from mail-la0-f50.google.com ([209.85.215.50]:56853 "EHLO mail-la0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966116Ab3DQNtV (ORCPT ); Wed, 17 Apr 2013 09:49:21 -0400 Message-ID: From: "Victor Miasnikov" To: , Subject: Re: KVM "Hyper-V emulation" -- this can be related "Linux on Hyper-V" ? Or "KVM emulates Hyper-V" as "Hyper-V emulates Hyper-V" ? Re: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V Date: Wed, 17 Apr 2013 16:49:16 +0300 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="utf-8"; reply-type=original Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.3790.4548 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.3790.4862 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4099 Lines: 144 Hi! 2013/4/17 Jan Beulich > > >>> On 17.04.13 at 12:16, "Michael S. Tsirkin" wrote: > > If the hypervisor says it's Hyper-V, that's because it wants > > guests to use Hyper-V. I don't see why is guest second-guessing > > this a good idea. > > There are two reasons here: For one, when the hypervisor is not > Hyper-V, but is providing some Hyper-V emulation, that's intended > for Windows guests to use, not e.g. Linux ones, especially when > such guests could use the native hypervisor interface with much > greater benefit. > > And second, there reportedly are features of (newer?) Hyper-V > that some emulation may not provide, but that are also not easily > detectable. > Yes + > On Wed, Apr 17, 2013 at 12:10:01PM +0300, Victor Miasnikov wrote: >> >> Question is very simple: Hyper-V users/sysadmins need wait patch a-la this: >> Or "KVM_and_or_XEN_or_other_Hypervisor_what_has_non-full-emulation_of_Hyper-V emulates Hyper-V" as "Hyper-V emulates >> Hyper-V" ? >> > > No. You are using Hyper-V, not the KVM_and_or_XEN_or_other_Hypervisor_what_has_non-full-emulation_of_Hyper-V > emulation of it. > No patches dealing with this emulation should have any effect on you. This is _positive_ variant of possible future, but on _practic_ very often we need prevent _negative_ variant of possible future >> == >> + /* >> + * KVM_and_or_XEN_or_other_Hypervisor_what_has_non-full-emulation_of_Hyper-V emulates Hyper-V to support >> enlightened Windows. >> + * Check to see first if we are on a KVM_and_or_XEN_or_other_Hypervisor_what_has_non-full-emulation_of_Hyper-V >> Hypervisor. >> + */ >> + >> + if (KVM_and_or_XEN_or_other_Hypervisor_what_has_non-full-emulation_of_Hyper-V_cpuid_base()) >> + return false; > > If the hypervisor says it's Hyper-V, that's because it wants guests to use Hyper-V. > Even if guest ( i.e. Virtual Computer) contain Linux OS ? >> == >> KVM_and_or_XEN_or_other_Hypervisor_what_has_non-full-emulation_of_Hyper-V emulates Hyper-V to host enlightened >> Windows. >> >> . . . >> >> [ hpa: the problem here is that >> KVM_and_or_XEN_or_other_Hypervisor_what_has_non-full-emulation_of_Hyper-V doesn't emulate Hyper-V well enough, . >> . ] > > What's emulated not well enough? > In case of XEN variant non-full-emulation_of_Hyper-V , IMHO : {{ ----- Original Message ----- From: "Victor Miasnikov" To: "Michael S. Tsirkin" Sent: Wednesday, April 17, 2013 12:41 PM Subject: IMHO, XEN emulation of Hyper-V not contain needed clocksource for Lunux guest Re: [PATCH 2/3] X86: Add a check to catch Xen emulation of Hyper-V Hi! > It seems that one might want to use hyper-v emulation e.g. to test > hyper-v code without using windows, so the functionality > that this patch disables is not completely useless, > so there should be a good reason for disabling it. As I undestand, XEN emulation of Hyper-V not contain needed clocksource for Lunux guest ( virtual computers) I.e. Linux VM "think" what is running on Hyper-V host call clocksource_register_hz(&hyperv_cs, NSEC_PER_SEC/100) and a-la BSOD or vice versa . . . > I went over the original discussion in > https://patchwork.kernel.org/patch/2064331/ > and that's still not clear to me. Is there a configuration > that is broken without this patch but starts working with > this patch? IMHO, this related to: - clocksource_register_hz(&hyperv_cs, NSEC_PER_SEC/100); + if (ms_hyperv.features & HV_X64_MSR_TIME_REF_COUNT_AVAILABLE) + clocksource_register_hz(&hyperv_cs, NSEC_PER_SEC/100); See https://lkml.org/lkml/2013/2/12/623 == Date Tue, 12 Feb 2013 16:56:07 -0800 From tip-bot for Olaf Hering Subject [tip:x86/hyperv] x86: Hyper-V: register clocksource only if its advertised . . . == Best regards, Victor Miasnikov }} Best regards, Victor Miasnikov Blog: http://vvm.blog.tut.by/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/