From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= Subject: [RFC PATCH 0/2] kvmclock: fix ABI breakage from PVCLOCK_COUNTS_FROM_ZERO. Date: Fri, 18 Sep 2015 17:54:28 +0200 Message-ID: <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: kvm@vger.kernel.org, Paolo Bonzini , Marcelo Tosatti , Luiz Capitulino To: linux-kernel@vger.kernel.org Return-path: Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org This patch series will be disabling PVCLOCK_COUNTS_FROM_ZERO flag and i= s RFC because I haven't explored many potential problems or tested 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= =2E 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) 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, str= uct 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; 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 kvmcloc= k 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(-) --=20 2.5.2