Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754848Ab0FOHeg (ORCPT ); Tue, 15 Jun 2010 03:34:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42135 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754680Ab0FOHed (ORCPT ); Tue, 15 Jun 2010 03:34:33 -0400 From: Zachary Amsden To: avi@redhat.com, mtosatti@redhat.com, glommer@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Zachary Amsden Subject: [PATCH 04/17] Fix deep C-state TSC desynchronization Date: Mon, 14 Jun 2010 21:34:06 -1000 Message-Id: <1276587259-32319-5-git-send-email-zamsden@redhat.com> In-Reply-To: <1276587259-32319-1-git-send-email-zamsden@redhat.com> References: <1276587259-32319-1-git-send-email-zamsden@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1389 Lines: 42 When CPUs with unstable TSCs enter deep C-state, TSC may stop running. This causes us to require resynchronization. Since we can't tell when this may potentially happen, we assume the worst by forcing re-compensation for it at every point the VCPU task is descheduled. Signed-off-by: Zachary Amsden --- arch/x86/kvm/x86.c | 11 +++++++++++ 1 files changed, 11 insertions(+), 0 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c8289d0..618c435 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -1822,7 +1822,18 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) { kvm_x86_ops->vcpu_put(vcpu); kvm_put_guest_fpu(vcpu); + vcpu->arch.last_host_tsc = native_read_tsc(); + + /* + * When potentially leaving a CPU with unstable TSCs, we risk + * that the CPU enters deep C-state. If it does, the TSC may + * go out of sync but we will not recalibrate because the test + * vcpu->cpu != cpu can not detect this condition. So set + * vcpu->cpu = -1 to force the recalibration above. + */ + if (check_tsc_unstable()) + vcpu->cpu = -1; } static int is_efer_nx(void) -- 1.7.1 -- 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/