KVM: x86: Hypercall handling does not considers opsize correctly

Currently, the hypercall handling routine only considers LME as an indication
to whether the guest uses 32/64-bit mode. This is incosistent with hyperv
hypercalls handling and against the common sense of considering cs.l as well.
This patch uses is_64_bit_mode instead of is_long_mode for that matter. In
addition, the result is masked in respect to the guest execution mode. Last, it
changes kvm_hv_hypercall to use is_64_bit_mode as well to simplify the code.
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/x86.c

@@ -5669,7 +5669,6 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
 	u64 param, ingpa, outgpa, ret;
 	uint16_t code, rep_idx, rep_cnt, res = HV_STATUS_SUCCESS, rep_done = 0;
 	bool fast, longmode;
-	int cs_db, cs_l;
 
 	/*
 	 * hypercall generates UD from non zero cpl and real mode
@@ -5680,8 +5679,7 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
 		return 0;
 	}
 
-	kvm_x86_ops->get_cs_db_l_bits(vcpu, &cs_db, &cs_l);
-	longmode = is_long_mode(vcpu) && cs_l == 1;
+	longmode = is_64_bit_mode(vcpu);
 
 	if (!longmode) {
 		param = ((u64)kvm_register_read(vcpu, VCPU_REGS_RDX) << 32) |
@@ -5746,7 +5744,7 @@ static void kvm_pv_kick_cpu_op(struct kvm *kvm, unsigned long flags, int apicid)
 int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 {
 	unsigned long nr, a0, a1, a2, a3, ret;
-	int r = 1;
+	int op_64_bit, r = 1;
 
 	if (kvm_hv_hypercall_enabled(vcpu->kvm))
 		return kvm_hv_hypercall(vcpu);
@@ -5759,7 +5757,8 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 
 	trace_kvm_hypercall(nr, a0, a1, a2, a3);
 
-	if (!is_long_mode(vcpu)) {
+	op_64_bit = is_64_bit_mode(vcpu);
+	if (!op_64_bit) {
 		nr &= 0xFFFFFFFF;
 		a0 &= 0xFFFFFFFF;
 		a1 &= 0xFFFFFFFF;
@@ -5785,6 +5784,8 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 		break;
 	}
 out:
+	if (!op_64_bit)
+		ret = (u32)ret;
 	kvm_register_write(vcpu, VCPU_REGS_RAX, ret);
 	++vcpu->stat.hypercalls;
 	return r;