KVM: PPC: Add AGAIN type for emulation return

Emulation of an instruction can have different outcomes. It can succeed,
fail, require MMIO, do funky BookE stuff - or it can just realize something's
odd and will be fixed the next time around.

Exactly that is what EMULATE_AGAIN means. Using that flag we can now tell
the caller that nothing happened, but we still want to go back to the
guest and see what happens next time we come around.

Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/powerpc/include/asm/kvm_ppc.h

@@ -37,6 +37,7 @@ enum emulation_result {
 	EMULATE_DO_MMIO,      /* kvm_run filled with MMIO request */
 	EMULATE_DO_DCR,       /* kvm_run filled with DCR request */
 	EMULATE_FAIL,         /* can't emulate this instruction */
+	EMULATE_AGAIN,        /* something went wrong. go again */
 };
 
 extern int __kvmppc_vcpu_run(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu);

arch/powerpc/kvm/book3s.c

@@ -789,6 +789,9 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
 		case EMULATE_DONE:
 			r = RESUME_GUEST_NV;
 			break;
+		case EMULATE_AGAIN:
+			r = RESUME_GUEST;
+			break;
 		case EMULATE_FAIL:
 			printk(KERN_CRIT "%s: emulation at %lx failed (%08x)\n",
 			       __func__, vcpu->arch.pc, vcpu->arch.last_inst);

arch/powerpc/kvm/emulate.c

@@ -486,7 +486,9 @@ int kvmppc_emulate_instruction(struct kvm_run *run, struct kvm_vcpu *vcpu)
 
 	if (emulated == EMULATE_FAIL) {
 		emulated = kvmppc_core_emulate_op(run, vcpu, inst, &advance);
-		if (emulated == EMULATE_FAIL) {
+		if (emulated == EMULATE_AGAIN) {
+			advance = 0;
+		} else if (emulated == EMULATE_FAIL) {
 			advance = 0;
 			printk(KERN_ERR "Couldn't emulate instruction 0x%08x "
 			       "(op %d xop %d)\n", inst, get_op(inst), get_xop(inst));