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 Date: Wed, 14 May 2014 04:26:38 -0300 Message-ID: <20140514072638.GA9285@amt.cnet> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Paolo Bonzini , Alexander Graf To: kvm-devel Return-path: Received: from mx1.redhat.com ([209.132.183.28]:60448 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751004AbaENHls (ORCPT ); Wed, 14 May 2014 03:41:48 -0400 Content-Disposition: inline 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..9f5dd40 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 suspend_backwards_tsc = false; + #define KVM_NR_SHARED_MSRS 16 struct kvm_shared_msrs_global { @@ -1472,6 +1474,8 @@ static void pvclock_update_vm_gtod_copy(struct kvm *kvm) &ka->master_cycle_now); ka->use_master_clock = host_tsc_clocksource & vcpus_matched; + if (suspend_backwards_tsc) + ka->use_master_clock = 0; if (ka->use_master_clock) atomic_set(&kvm_guest_has_master_clock, 1); @@ -6939,6 +6943,7 @@ int kvm_arch_hardware_enable(void *garbage) */ if (backwards_tsc) { u64 delta_cyc = max_tsc - local_tsc; + suspend_backwards_tsc = true; list_for_each_entry(kvm, &vm_list, vm_list) { kvm_for_each_vcpu(i, vcpu, kvm) { vcpu->arch.tsc_offset_adjustment += delta_cyc;