KVM: PPC: Teach MMIO Signedness

The guest I was trying to get to run uses the LHA and LHAU instructions.
Those instructions basically do a load, but also sign extend the result.

Since we need to fill our registers by hand when doing MMIO, we also need
to sign extend manually.

This patch implements sign extended MMIO and the LHA(U) instructions.
Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/powerpc/include/asm/kvm_host.h

@@ -270,6 +270,7 @@ struct kvm_vcpu_arch {
 
 	u8 io_gpr; /* GPR used as IO source/target */
 	u8 mmio_is_bigendian;
+	u8 mmio_sign_extend;
 	u8 dcr_needed;
 	u8 dcr_is_write;
 

arch/powerpc/include/asm/kvm_ppc.h

@@ -48,6 +48,9 @@ extern void kvmppc_dump_vcpu(struct kvm_vcpu *vcpu);
 extern int kvmppc_handle_load(struct kvm_run *run, struct kvm_vcpu *vcpu,
                               unsigned int rt, unsigned int bytes,
                               int is_bigendian);
+extern int kvmppc_handle_loads(struct kvm_run *run, struct kvm_vcpu *vcpu,
+                               unsigned int rt, unsigned int bytes,
+                               int is_bigendian);
 extern int kvmppc_handle_store(struct kvm_run *run, struct kvm_vcpu *vcpu,
                                u64 val, unsigned int bytes, int is_bigendian);
 

arch/powerpc/kvm/emulate.c

@@ -62,6 +62,8 @@
 #define OP_STBU 39
 #define OP_LHZ  40
 #define OP_LHZU 41
+#define OP_LHA  42
+#define OP_LHAU 43
 #define OP_STH  44
 #define OP_STHU 45
 
@@ -450,6 +452,18 @@ int kvmppc_emulate_instruction(struct kvm_run *run, struct kvm_vcpu *vcpu)
 		kvmppc_set_gpr(vcpu, ra, vcpu->arch.paddr_accessed);
 		break;
 
+	case OP_LHA:
+		rt = get_rt(inst);
+		emulated = kvmppc_handle_loads(run, vcpu, rt, 2, 1);
+		break;
+
+	case OP_LHAU:
+		ra = get_ra(inst);
+		rt = get_rt(inst);
+		emulated = kvmppc_handle_loads(run, vcpu, rt, 2, 1);
+		kvmppc_set_gpr(vcpu, ra, vcpu->arch.paddr_accessed);
+		break;
+
 	case OP_STH:
 		rs = get_rs(inst);
 		emulated = kvmppc_handle_store(run, vcpu,

arch/powerpc/kvm/powerpc.c

@@ -301,6 +301,22 @@ static void kvmppc_complete_mmio_load(struct kvm_vcpu *vcpu,
 		}
 	}
 
+	if (vcpu->arch.mmio_sign_extend) {
+		switch (run->mmio.len) {
+#ifdef CONFIG_PPC64
+		case 4:
+			gpr = (s64)(s32)gpr;
+			break;
+#endif
+		case 2:
+			gpr = (s64)(s16)gpr;
+			break;
+		case 1:
+			gpr = (s64)(s8)gpr;
+			break;
+		}
+	}
+
 	kvmppc_set_gpr(vcpu, vcpu->arch.io_gpr, gpr);
 
 	switch (vcpu->arch.io_gpr & KVM_REG_EXT_MASK) {
@@ -338,10 +354,23 @@ int kvmppc_handle_load(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	vcpu->arch.mmio_is_bigendian = is_bigendian;
 	vcpu->mmio_needed = 1;
 	vcpu->mmio_is_write = 0;
+	vcpu->arch.mmio_sign_extend = 0;
 
 	return EMULATE_DO_MMIO;
 }
 
+/* Same as above, but sign extends */
+int kvmppc_handle_loads(struct kvm_run *run, struct kvm_vcpu *vcpu,
+                        unsigned int rt, unsigned int bytes, int is_bigendian)
+{
+	int r;
+
+	r = kvmppc_handle_load(run, vcpu, rt, bytes, is_bigendian);
+	vcpu->arch.mmio_sign_extend = 1;
+
+	return r;
+}
+
 int kvmppc_handle_store(struct kvm_run *run, struct kvm_vcpu *vcpu,
                         u64 val, unsigned int bytes, int is_bigendian)
 {