From 16a9602158861687c78b6de6dc6a79e6e8a9136f Mon Sep 17 00:00:00 2001 From: Marcelo Tosatti Date: Wed, 14 May 2014 12:43:24 -0300 Subject: [PATCH] KVM: x86: disable master clock if TSC is reset during suspend 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 it is necessary to update it from the resume path. Signed-off-by: Marcelo Tosatti Signed-off-by: Paolo Bonzini --- arch/x86/kvm/x86.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 8b8fc0b792ba..84a2d4152a63 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 { @@ -1486,7 +1488,8 @@ 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); @@ -6945,6 +6948,7 @@ 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; -- 2.20.1