KVM: arm64: Reorder handling of invariant sysregs from userspace

In order to allow some further refactor of the sysreg helpers,
move the handling of invariant sysreg to occur before we handle
all the other ones.
Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/kvm/sys_regs.c

@@ -2849,6 +2849,7 @@ int kvm_arm_sys_reg_get_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg
 {
 	const struct sys_reg_desc *r;
 	void __user *uaddr = (void __user *)(unsigned long)reg->addr;
+	int err;
 
 	if ((reg->id & KVM_REG_ARM_COPROC_MASK) == KVM_REG_ARM_DEMUX)
 		return demux_c15_get(reg->id, uaddr);
@@ -2856,12 +2857,14 @@ int kvm_arm_sys_reg_get_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg
 	if (KVM_REG_SIZE(reg->id) != sizeof(__u64))
 		return -ENOENT;
 
+	err = get_invariant_sys_reg(reg->id, uaddr);
+	if (err != -ENOENT)
+		return err;
+
 	r = index_to_sys_reg_desc(vcpu, reg->id);
-	if (!r)
-		return get_invariant_sys_reg(reg->id, uaddr);
 
 	/* Check for regs disabled by runtime config */
-	if (sysreg_hidden(vcpu, r))
+	if (!r || sysreg_hidden(vcpu, r))
 		return -ENOENT;
 
 	if (r->get_user)
@@ -2874,6 +2877,7 @@ int kvm_arm_sys_reg_set_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg
 {
 	const struct sys_reg_desc *r;
 	void __user *uaddr = (void __user *)(unsigned long)reg->addr;
+	int err;
 
 	if ((reg->id & KVM_REG_ARM_COPROC_MASK) == KVM_REG_ARM_DEMUX)
 		return demux_c15_set(reg->id, uaddr);
@@ -2881,12 +2885,14 @@ int kvm_arm_sys_reg_set_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg
 	if (KVM_REG_SIZE(reg->id) != sizeof(__u64))
 		return -ENOENT;
 
+	err = set_invariant_sys_reg(reg->id, uaddr);
+	if (err != -ENOENT)
+		return err;
+
 	r = index_to_sys_reg_desc(vcpu, reg->id);
-	if (!r)
-		return set_invariant_sys_reg(reg->id, uaddr);
 
 	/* Check for regs disabled by runtime config */
-	if (sysreg_hidden(vcpu, r))
+	if (!r || sysreg_hidden(vcpu, r))
 		return -ENOENT;
 
 	if (r->set_user)