From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: KVM: x86: workaround SuSE's 2.6.16 pvclock vs masterclock issue Date: Wed, 21 Jan 2015 12:16:34 -0200 Message-ID: <20150121141634.GB718@amt.cnet> References: <20150120175452.GA32680@amt.cnet> <20150121140926.GA9085@potion.brq.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: kvm-devel , Paolo Bonzini To: Radim =?utf-8?B?S3LEjW3DocWZ?= Return-path: Received: from mx1.redhat.com ([209.132.183.28]:45539 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752595AbbAUOQs (ORCPT ); Wed, 21 Jan 2015 09:16:48 -0500 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id t0LEGmKO003217 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL) for ; Wed, 21 Jan 2015 09:16:48 -0500 Content-Disposition: inline In-Reply-To: <20150121140926.GA9085@potion.brq.redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, Jan 21, 2015 at 03:09:27PM +0100, Radim Kr=C4=8Dm=C3=A1=C5=99 w= rote: > 2015-01-20 15:54-0200, Marcelo Tosatti: > > SuSE's 2.6.16 kernel fails to boot if the delta between tsc_timesta= mp > > and rdtsc is larger than a given threshold: > [...] > > Disable masterclock support (which increases said delta) in case th= e > > boot vcpu does not use MSR_KVM_SYSTEM_TIME_NEW. >=20 > Why do we care about 2.6.16 bugs in upstream KVM? Because people do use 2.6.16 guests. > The code to benefit tradeoff of this patch seems bad to me ... Can you state the tradeoff and then explain why it is bad ? > MSR_KVM_SYSTEM_TIME is deprecated -- we could remove it now, with > MSR_KVM_WALL_CLOCK (after hiding KVM_FEATURE_CLOCKSOURCE) if we want > to support old guests. What is the benefit of removing support for MSR_KVM_SYSTEM_TIME ? Supporting old guests is important.