KVM: PPC: booke: add GS documentation for program interrupt

The comment for program interrupts triggered when using bookehv was
misleading. Update it to mention why MSR_GS indicates that we have
to inject an interrupt into the guest again, not emulate it.
Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/powerpc/kvm/booke.c

@@ -685,8 +685,14 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
 
 	case BOOKE_INTERRUPT_PROGRAM:
 		if (vcpu->arch.shared->msr & (MSR_PR | MSR_GS)) {
-			/* Program traps generated by user-level software must be handled
-			 * by the guest kernel. */
+			/*
+			 * Program traps generated by user-level software must
+			 * be handled by the guest kernel.
+			 *
+			 * In GS mode, hypervisor privileged instructions trap
+			 * on BOOKE_INTERRUPT_HV_PRIV, not here, so these are
+			 * actual program interrupts, handled by the guest.
+			 */
 			kvmppc_core_queue_program(vcpu, vcpu->arch.fault_esr);
 			r = RESUME_GUEST;
 			kvmppc_account_exit(vcpu, USR_PR_INST);