KVM: PPC: Graciously fail broken LE hypercalls

There are LE Linux guests out there that don't handle hypercalls correctly.
Instead of interpreting the instruction stream from device tree as big endian
they assume it's a little endian instruction stream and fail.

When we see an illegal instruction from such a byte reversed instruction stream,
bail out graciously and just declare every hcall as error.
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/kvm/book3s_emulate.c

@@ -94,8 +94,25 @@ int kvmppc_core_emulate_op_pr(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	int rs = get_rs(inst);
 	int ra = get_ra(inst);
 	int rb = get_rb(inst);
+	u32 inst_sc = 0x44000002;
 
 	switch (get_op(inst)) {
+	case 0:
+		emulated = EMULATE_FAIL;
+		if ((kvmppc_get_msr(vcpu) & MSR_LE) &&
+		    (inst == swab32(inst_sc))) {
+			/*
+			 * This is the byte reversed syscall instruction of our
+			 * hypercall handler. Early versions of LE Linux didn't
+			 * swap the instructions correctly and ended up in
+			 * illegal instructions.
+			 * Just always fail hypercalls on these broken systems.
+			 */
+			kvmppc_set_gpr(vcpu, 3, EV_UNIMPLEMENTED);
+			kvmppc_set_pc(vcpu, kvmppc_get_pc(vcpu) + 4);
+			emulated = EMULATE_DONE;
+		}
+		break;
 	case 19:
 		switch (get_xop(inst)) {
 		case OP_19_XOP_RFID: