From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751181AbaHAJCd (ORCPT ); Fri, 1 Aug 2014 05:02:33 -0400 Received: from mail.skyhub.de ([78.46.96.112]:45742 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750708AbaHAJCb (ORCPT ); Fri, 1 Aug 2014 05:02:31 -0400 Date: Fri, 1 Aug 2014 11:02:28 +0200 From: Borislav Petkov To: Igor Mammedov Cc: linux-kernel@vger.kernel.org, x86@kernel.org, hpa@zytor.com, mingo@redhat.com, tglx@linutronix.de, pbonzini@redhat.com, kvm@vger.kernel.org, mtosatti@redhat.com Subject: Re: [PATCH 1/2] x86: AMD: mark TSC unstable on APU family 15h models 10h-1fh Message-ID: <20140801090228.GA3924@nazgul.tnic> References: <1406800033-13404-1-git-send-email-imammedo@redhat.com> <1406800033-13404-2-git-send-email-imammedo@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1406800033-13404-2-git-send-email-imammedo@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 31, 2014 at 09:47:12AM +0000, Igor Mammedov wrote: > Due to erratum #778 from > "Revision Guide for AMD Family 15h Models 10h-1Fh Processors, > Publication # 48931, Issue Date: May 2013, Revision: 3.10" > > TSC on affected processor, a core may drift under certain conditions, > which makes initially synchronized TSCs to become unsynchronized. > > As result TSC clocksource becomes unsuitable for using as wallclock > and it brakes pvclock when it's running with PVCLOCK_TSC_STABLE_BIT > flag set. > That causes backwards clock jumps when pvclock is first read on > CPU with drifted TSC and then on CPU where TSC was stable or had > a lower drift rate. > > To fix issue mark TSC as unstable on affected CPU, so it won't > be used as clocksource. Which in turn disables master_clock > mechanism in KVM and force pvclock using global clock counter > that can't go backwards. > > Signed-off-by: Igor Mammedov Acked-by: Borislav Petkov