KVM: x86: Tell the guest we'll warn it about tsc stability

This patch puts up the flag that tells the guest that we'll warn it
about the tsc being trustworthy or not. By now, we also say
it is not.

Signed-off-by: Glauber Costa <glommer@redhat.com>
Acked-by: Zachary Amsden <zamsden@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/x86.c

@@ -857,6 +857,8 @@ static void kvm_write_guest_time(struct kvm_vcpu *v)
 	vcpu->hv_clock.system_time = ts.tv_nsec +
 				     (NSEC_PER_SEC * (u64)ts.tv_sec) + v->kvm->arch.kvmclock_offset;
 
+	vcpu->hv_clock.flags = 0;
+
 	/*
 	 * The interface expects us to write an even number signaling that the
 	 * update is finished. Since the guest won't see the intermediate
@@ -1984,7 +1986,8 @@ static void do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
 	case KVM_CPUID_FEATURES:
 		entry->eax = (1 << KVM_FEATURE_CLOCKSOURCE) |
 			     (1 << KVM_FEATURE_NOP_IO_DELAY) |
-			     (1 << KVM_FEATURE_CLOCKSOURCE2);
+			     (1 << KVM_FEATURE_CLOCKSOURCE2) |
+			     (1 << KVM_FEATURE_CLOCKSOURCE_STABLE_BIT);
 		entry->ebx = 0;
 		entry->ecx = 0;
 		entry->edx = 0;