From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [RFC PATCH 0/2] kvmclock: fix ABI breakage from PVCLOCK_COUNTS_FROM_ZERO. Date: Sun, 20 Sep 2015 19:57:42 -0300 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-Transfer-Encoding: QUOTED-PRINTABLE Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini , Luiz Capitulino To: Radim =?utf-8?B?S3LEjW3DocWZ?= Return-path: 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 Content-Disposition: inline In-Reply-To: <1442591670-5216-1-git-send-email-rkrcmar@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Fri, Sep 18, 2015 at 05:54:28PM +0200, Radim Kr=C4=8Dm=C3=A1=C5=99 w= rote: > 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. >=20 > [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. >=20 > A viable alternative would be to implement opt-in features in kvm clo= ck. >=20 > 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 an= d 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?=20 > 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, s= truct msr_data *msr_info) > =20 > ka->boot_vcpu_runs_old_kvmclock =3D tmp; > =20 > - ka->kvmclock_offset =3D -get_kernel_ns(); > + if (!ka->boot_vcpu_runs_old_kvmclock) > + ka->kvmclock_offset =3D -get_kernel_ns(); > } > =20 > vcpu->arch.time =3D data; >=20 >=20 > Radim Kr=C4=8Dm=C3=A1=C5=99 (2): > x86: kvmclock: abolish PVCLOCK_COUNTS_FROM_ZERO > Revert "KVM: x86: zero kvmclock_offset when vcpu0 initializes kvmcl= ock > system MSR" >=20 > 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(-) >=20 > --=20 > 2.5.2