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>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 468fafaed1ae0b9ebb7b10c86edc35ef97525595..9396b3f2c5943581c5d9ac7e72f2f9f64cd7ffa7 100644 (file)
--- 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;