KVM/PPC: update the comment of memory barrier in the kvmppc_prepare_to_enter()

The barrier also orders the write to mode from any reads
to the page tables done and so update the comment.
Signed-off-by: Lan Tianyu <tianyu.lan@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/powerpc/kvm/powerpc.c

@@ -96,6 +96,9 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
 		 * so we don't miss a request because the requester sees
 		 * OUTSIDE_GUEST_MODE and assumes we'll be checking requests
 		 * before next entering the guest (and thus doesn't IPI).
+		 * This also orders the write to mode from any reads
+		 * to the page tables done while the VCPU is running.
+		 * Please see the comment in kvm_flush_remote_tlbs.
 		 */
 		smp_mb();