KVM: SVM: Adjust tsc_offset only if tsc_unstable

The tsc_offset adjustment in svm_vcpu_load is executed
unconditionally even if Linux considers the host tsc as
stable. This causes a Linux guest detecting an unstable tsc
in any case.
This patch removes the tsc_offset adjustment if the host tsc
is stable. The guest will now get the benefit of a stable
tsc too.
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/svm.c

@@ -765,6 +765,7 @@ static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	if (unlikely(cpu != vcpu->cpu)) {
 		u64 delta;
 
+		if (check_tsc_unstable()) {
 			/*
 			 * Make sure that the guest sees a monotonically
 			 * increasing TSC.
@@ -773,6 +774,7 @@ static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 			svm->vmcb->control.tsc_offset += delta;
 			if (is_nested(svm))
 				svm->nested.hsave->control.tsc_offset += delta;
+		}
 		vcpu->cpu = cpu;
 		kvm_migrate_timers(vcpu);
 		svm->asid_generation = 0;