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 <mtosatti@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8b8fc0b..84a2d41 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -106,6 +106,8 @@
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 @@
&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 @@
*/
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;