KVM: Emulate hlt on real mode for Intel

This has two use cases: the bios can't boot from disk, and guest smp
bootstrap.

Signed-off-by: Avi Kivity <avi@qumranet.com>

drivers/kvm/kvm.h

@@ -347,6 +347,7 @@ struct kvm_vcpu {
 			u32 ar;
 		} tr, es, ds, fs, gs;
 	} rmode;
+	int halt_request; /* real mode on Intel only */
 
 	int cpuid_nent;
 	struct kvm_cpuid_entry cpuid_entries[KVM_MAX_CPUID_ENTRIES];

drivers/kvm/vmx.c

@@ -1608,8 +1608,13 @@ static int handle_exception(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 
 	if (vcpu->rmode.active &&
 	    handle_rmode_exception(vcpu, intr_info & INTR_INFO_VECTOR_MASK,
-								error_code))
+								error_code)) {
+		if (vcpu->halt_request) {
+			vcpu->halt_request = 0;
+			return kvm_emulate_halt(vcpu);
+		}
 		return 1;
+	}
 
 	if ((intr_info & (INTR_INFO_INTR_TYPE_MASK | INTR_INFO_VECTOR_MASK)) == (INTR_TYPE_EXCEPTION | 1)) {
 		kvm_run->exit_reason = KVM_EXIT_DEBUG;

drivers/kvm/x86_emulate.c

@@ -143,7 +143,8 @@ static u8 opcode_table[256] = {
 	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
 	/* 0xF0 - 0xF7 */
 	0, 0, 0, 0,
-	0, 0, ByteOp | DstMem | SrcNone | ModRM, DstMem | SrcNone | ModRM,
+	ImplicitOps, 0,
+	ByteOp | DstMem | SrcNone | ModRM, DstMem | SrcNone | ModRM,
 	/* 0xF8 - 0xFF */
 	0, 0, 0, 0,
 	0, 0, ByteOp | DstMem | SrcNone | ModRM, DstMem | SrcNone | ModRM
@@ -1149,6 +1150,9 @@ special_insn:
 	case 0xae ... 0xaf:	/* scas */
 		DPRINTF("Urk! I don't handle SCAS.\n");
 		goto cannot_emulate;
+	case 0xf4:              /* hlt */
+		ctxt->vcpu->halt_request = 1;
+		goto done;
 	}
 	goto writeback;