From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: KVM: x86: disable master clock if TSC is reset during suspend (v3) Date: Wed, 14 May 2014 12:43:24 -0300 Message-ID: <20140514154324.GA29206@amt.cnet> References: <20140514072638.GA9285@amt.cnet> <537332D0.1090505@redhat.com> <20140514100636.GB20451@amt.cnet> <537343A7.3030805@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm-devel , Alexander Graf To: Paolo Bonzini Return-path: Received: from mx1.redhat.com ([209.132.183.28]:6959 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754508AbaENPno (ORCPT ); Wed, 14 May 2014 11:43:44 -0400 Content-Disposition: inline In-Reply-To: <537343A7.3030805@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Updating system_time from the kernel clock once master clock has been enabled can result in time backwards event, in case kernel clock frequency is lower than TSC frequency. Disable master clock in case its necessary to update it from the resume path. Signed-off-by: Marcelo Tosatti diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index de0931c..c098728 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -106,6 +106,8 @@ EXPORT_SYMBOL_GPL(kvm_max_guest_tsc_khz); static u32 tsc_tolerance_ppm = 250; module_param(tsc_tolerance_ppm, uint, S_IRUGO | S_IWUSR); +static bool backwards_tsc_observed = false; + #define KVM_NR_SHARED_MSRS 16 struct kvm_shared_msrs_global { @@ -1471,7 +1473,8 @@ static void pvclock_update_vm_gtod_copy(struct kvm *kvm) &ka->master_kernel_ns, &ka->master_cycle_now); - ka->use_master_clock = host_tsc_clocksource & vcpus_matched; + ka->use_master_clock = host_tsc_clocksource && vcpus_matched + && !backwards_tsc_observed; if (ka->use_master_clock) atomic_set(&kvm_guest_has_master_clock, 1); @@ -6939,6 +6942,7 @@ int kvm_arch_hardware_enable(void *garbage) */ if (backwards_tsc) { u64 delta_cyc = max_tsc - local_tsc; + backwards_tsc_observed = true; list_for_each_entry(kvm, &vm_list, vm_list) { kvm_for_each_vcpu(i, vcpu, kvm) { vcpu->arch.tsc_offset_adjustment += delta_cyc;