KVM: x86: Fix deep C-state TSC desynchronization

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 <zamsden@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 468fafaed1ae..9396b3f2c594 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1866,7 +1866,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
         }
 
         kvm_x86_ops->vcpu_load(vcpu, cpu);
-        if (unlikely(vcpu->cpu != cpu)) {
+        if (unlikely(vcpu->cpu != cpu) || check_tsc_unstable()) {
                 /* Make sure TSC doesn't go backwards */
                 s64 tsc_delta = !vcpu->arch.last_host_tsc ? 0 :
                                 native_read_tsc() - vcpu->arch.last_host_tsc;