From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965185Ab3FTIkx (ORCPT ); Thu, 20 Jun 2013 04:40:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:8243 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965175Ab3FTIks (ORCPT ); Thu, 20 Jun 2013 04:40:48 -0400 Date: Thu, 20 Jun 2013 10:30:04 +0200 From: Igor Mammedov To: Paolo Bonzini Cc: Batalov Eugene , Marcelo Tosatti , Eugene Batalov , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv1] kvm guest: fix uninitialized kvmclock read by KVM guest Message-ID: <20130620103004.4aa39c47@nial.usersys.redhat.com> In-Reply-To: <51C1B23B.7080703@redhat.com> References: <20130610201933.GA31409@amt.cnet> <1371319305-590-1-git-send-email-ebatalov@parallels.com> <20130618222114.GC13856@amt.cnet> <51C1AC93.6010001@redhat.com> <51C1B23B.7080703@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 19 Jun 2013 15:29:31 +0200 Paolo Bonzini wrote: > Il 19/06/2013 15:20, Batalov Eugene ha scritto: > > > > I've missed this detail. It looks like Igor's patch doesn't bring > > secondary cpus kvm_clocksource behavior back to one before the regression, > > Before the regression per_cpu variables are used to allocate > > kvm_pv_clock areas. > > To to usage of percpu variables bootstrap cpu kvm_clock area contents > > were copied to smp secondary cpus kvm_clock areas when they were started. > > Bootstrap cpu kvm_clock area was not zeroed at this time. > > So kvm_pv_clock for secondary cpus never returned "zero" clock before > > the regression. > > > > During the analysis of the bug I introduced idea to return zero before > > kvm clocksource is initialized for secondary cpus > > just like bootstrap cpu does on kernel boot. You can read that in BZ. > > Yes, this is why I prefer to invert the two function calls. But Igor's > patch fixes the hang (trivially because version is even) and is more > appropriate for -rc6. I'll post this swap shortly, but zeroing out hv_clock at init time, would be still needed to provide sane values there if ftrace enabled at that time. > > Paolo > -- > 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/