From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755578AbbITW6F (ORCPT ); Sun, 20 Sep 2015 18:58:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53537 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753537AbbITW6B (ORCPT ); Sun, 20 Sep 2015 18:58:01 -0400 Date: Sun, 20 Sep 2015 19:57:42 -0300 From: Marcelo Tosatti To: Radim =?utf-8?B?S3LEjW3DocWZ?= Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini , Luiz Capitulino Subject: Re: [RFC PATCH 0/2] kvmclock: fix ABI breakage from PVCLOCK_COUNTS_FROM_ZERO. Message-ID: <20150920225742.GA27666@amt.cnet> References: <1442591670-5216-1-git-send-email-rkrcmar@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1442591670-5216-1-git-send-email-rkrcmar@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 Fri, Sep 18, 2015 at 05:54:28PM +0200, Radim Krčmář wrote: > This patch series will be disabling PVCLOCK_COUNTS_FROM_ZERO flag and is > RFC because I haven't explored many potential problems or tested it. The justification to disable PVCLOCK_COUNTS_FROM_ZERO is because you haven't explored potential problems or tested it? Sorry can't parse it. > > [1/2] uses a different algorithm in the guest to start counting from 0. > [2/2] stops exposing PVCLOCK_COUNTS_FROM_ZERO in the hypervisor. > > A viable alternative would be to implement opt-in features in kvm clock. > > And because we probably only broke one old user (the infamous SLES 10), a > workaround like this is also possible: (but I'd rather not do that) Please describe why SLES 10 breaks in detail: the state of the guest and the host before the patch, the state of the guest and host after the patch. What does SLES10 expect? Is it counting from zero that breaks SLES10? > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index a60bdbccff51..ae9049248aaf 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -2007,7 +2007,8 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > > ka->boot_vcpu_runs_old_kvmclock = tmp; > > - ka->kvmclock_offset = -get_kernel_ns(); > + if (!ka->boot_vcpu_runs_old_kvmclock) > + ka->kvmclock_offset = -get_kernel_ns(); > } > > vcpu->arch.time = data; > > > Radim Krčmář (2): > x86: kvmclock: abolish PVCLOCK_COUNTS_FROM_ZERO > Revert "KVM: x86: zero kvmclock_offset when vcpu0 initializes kvmclock > system MSR" > > arch/x86/include/asm/pvclock-abi.h | 1 + > arch/x86/kernel/kvmclock.c | 46 +++++++++++++++++++++++++++++--------- > arch/x86/kvm/x86.c | 4 ---- > 3 files changed, 36 insertions(+), 15 deletions(-) > > -- > 2.5.2