KVM: x86: reading DR cannot fail

kvm_get_dr and emulator_get_dr except an in-range value for the register
number so they cannot fail.  Change the return type to void.
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -1562,7 +1562,7 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3);
 int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
 int kvm_set_cr8(struct kvm_vcpu *vcpu, unsigned long cr8);
 int kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val);
-int kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val);
+void kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val);
 unsigned long kvm_get_cr8(struct kvm_vcpu *vcpu);
 void kvm_lmsw(struct kvm_vcpu *vcpu, unsigned long msw);
 void kvm_get_cs_db_l_bits(struct kvm_vcpu *vcpu, int *db, int *l);

arch/x86/kvm/kvm_emulate.h

@@ -205,7 +205,7 @@ struct x86_emulate_ops {
 	ulong (*get_cr)(struct x86_emulate_ctxt *ctxt, int cr);
 	int (*set_cr)(struct x86_emulate_ctxt *ctxt, int cr, ulong val);
 	int (*cpl)(struct x86_emulate_ctxt *ctxt);
-	int (*get_dr)(struct x86_emulate_ctxt *ctxt, int dr, ulong *dest);
+	void (*get_dr)(struct x86_emulate_ctxt *ctxt, int dr, ulong *dest);
 	int (*set_dr)(struct x86_emulate_ctxt *ctxt, int dr, ulong value);
 	u64 (*get_smbase)(struct x86_emulate_ctxt *ctxt);
 	void (*set_smbase)(struct x86_emulate_ctxt *ctxt, u64 smbase);

arch/x86/kvm/vmx/vmx.c

@@ -5142,8 +5142,7 @@ static int handle_dr(struct kvm_vcpu *vcpu)
 	if (exit_qualification & TYPE_MOV_FROM_DR) {
 		unsigned long val;
 
-		if (kvm_get_dr(vcpu, dr, &val))
-			return 1;
+		kvm_get_dr(vcpu, dr, &val);
 		kvm_register_write(vcpu, reg, val);
 	} else
 		if (kvm_set_dr(vcpu, dr, kvm_register_readl(vcpu, reg)))

arch/x86/kvm/x86.c

@@ -1181,7 +1181,7 @@ int kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
 }
 EXPORT_SYMBOL_GPL(kvm_set_dr);
 
-int kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val)
+void kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val)
 {
 	size_t size = ARRAY_SIZE(vcpu->arch.db);
 
@@ -1198,7 +1198,6 @@ int kvm_get_dr(struct kvm_vcpu *vcpu, int dr, unsigned long *val)
 		*val = vcpu->arch.dr7;
 		break;
 	}
-	return 0;
 }
 EXPORT_SYMBOL_GPL(kvm_get_dr);
 
@@ -6610,10 +6609,10 @@ static void emulator_wbinvd(struct x86_emulate_ctxt *ctxt)
 	kvm_emulate_wbinvd_noskip(emul_to_vcpu(ctxt));
 }
 
-static int emulator_get_dr(struct x86_emulate_ctxt *ctxt, int dr,
-			   unsigned long *dest)
+static void emulator_get_dr(struct x86_emulate_ctxt *ctxt, int dr,
+			    unsigned long *dest)
 {
-	return kvm_get_dr(emul_to_vcpu(ctxt), dr, dest);
+	kvm_get_dr(emul_to_vcpu(ctxt), dr, dest);
 }
 
 static int emulator_set_dr(struct x86_emulate_ctxt *ctxt, int dr,