arm64: KVM: PMU: Inject UNDEF exception on illegal register access

Both pmu_*_el0_disabled() and pmu_counter_idx_valid() perform checks
on the validity of an access, but only return a boolean indicating
if the access is valid or not.

Let's allow these functions to also inject an UNDEF exception if
the access was illegal.
Reviewed-by: Christoffer Dall <cdall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm64/kvm/sys_regs.c

@@ -465,6 +465,9 @@ static bool check_pmu_access_disabled(struct kvm_vcpu *vcpu, u64 flags)
 	u64 reg = vcpu_sys_reg(vcpu, PMUSERENR_EL0);
 	bool enabled = (reg & flags) || vcpu_mode_priv(vcpu);
 
+	if (!enabled)
+		kvm_inject_undefined(vcpu);
+
 	return !enabled;
 }
 
@@ -564,8 +567,10 @@ static bool pmu_counter_idx_valid(struct kvm_vcpu *vcpu, u64 idx)
 
 	pmcr = vcpu_sys_reg(vcpu, PMCR_EL0);
 	val = (pmcr >> ARMV8_PMU_PMCR_N_SHIFT) & ARMV8_PMU_PMCR_N_MASK;
-	if (idx >= val && idx != ARMV8_PMU_CYCLE_IDX)
+	if (idx >= val && idx != ARMV8_PMU_CYCLE_IDX) {
+		kvm_inject_undefined(vcpu);
 		return false;
+	}
 
 	return true;
 }