KVM: arm64: Hide CNTHV_*_EL2 from userspace for nVHE guests

Although we correctly UNDEF any CNTHV_*_EL2 access from the guest
when E2H==0, we still expose these registers to userspace, which
is a bad idea.

Drop the ad-hoc UNDEF injection and switch to a .visibility()
callback which will also hide the register from userspace.

Fixes: 0e45981 ("KVM: arm64: timer: Don't adjust the EL2 virtual timer offset")
Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: Marc Zyngier

arch/arm64/kvm/sys_regs.c

@@ -1594,16 +1594,6 @@ static bool access_arch_timer(struct kvm_vcpu *vcpu,
 	return true;
 }
 
-static bool access_hv_timer(struct kvm_vcpu *vcpu,
-			    struct sys_reg_params *p,
-			    const struct sys_reg_desc *r)
-{
-	if (!vcpu_el2_e2h_is_set(vcpu))
-		return undef_access(vcpu, p, r);
-
-	return access_arch_timer(vcpu, p, r);
-}
-
 static s64 kvm_arm64_ftr_safe_value(u32 id, const struct arm64_ftr_bits *ftrp,
 				    s64 new, s64 cur)
 {
@@ -2831,6 +2821,16 @@ static unsigned int s1pie_el2_visibility(const struct kvm_vcpu *vcpu,
 	return __el2_visibility(vcpu, rd, s1pie_visibility);
 }
 
+static unsigned int cnthv_visibility(const struct kvm_vcpu *vcpu,
+				     const struct sys_reg_desc *rd)
+{
+	if (vcpu_has_nv(vcpu) &&
+	    !vcpu_has_feature(vcpu, KVM_ARM_VCPU_HAS_EL2_E2H0))
+		return 0;
+
+	return REG_HIDDEN;
+}
+
 static bool access_mdcr(struct kvm_vcpu *vcpu,
 			struct sys_reg_params *p,
 			const struct sys_reg_desc *r)
@@ -3691,9 +3691,9 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	EL2_REG(CNTHP_CTL_EL2, access_arch_timer, reset_val, 0),
 	EL2_REG(CNTHP_CVAL_EL2, access_arch_timer, reset_val, 0),
 
-	{ SYS_DESC(SYS_CNTHV_TVAL_EL2), access_hv_timer },
-	EL2_REG(CNTHV_CTL_EL2, access_hv_timer, reset_val, 0),
-	EL2_REG(CNTHV_CVAL_EL2, access_hv_timer, reset_val, 0),
+	{ SYS_DESC(SYS_CNTHV_TVAL_EL2), access_arch_timer, .visibility = cnthv_visibility },
+	EL2_REG_FILTERED(CNTHV_CTL_EL2, access_arch_timer, reset_val, 0, cnthv_visibility),
+	EL2_REG_FILTERED(CNTHV_CVAL_EL2, access_arch_timer, reset_val, 0, cnthv_visibility),
 
 	{ SYS_DESC(SYS_CNTKCTL_EL12), access_cntkctl_el12 },