Re: [PATCH v7 15/19] KVM: ARM64: Add access handler for PMUSERENR register

[Marc Zyngier <marc.zyngier@arm.com>]

On 15/12/15 15:59, Shannon Zhao wrote:
> 
> 
> On 2015/12/15 22:58, Marc Zyngier wrote:
>> On 15/12/15 08:49, Shannon Zhao wrote:
>>>> From: Shannon Zhao<shannon.zhao@linaro.org>
>>>>
>>>> The reset value of PMUSERENR_EL0 is UNKNOWN, use reset_unknown.
>>>>
>>>> PMUSERENR_EL0 holds some bits which decide whether PMU registers can be
>>>> accessed from EL0. Add some check helpers to handle the access from EL0.
>>>>
>>>> Signed-off-by: Shannon Zhao<shannon.zhao@linaro.org>
>>>> ---
>>>>  arch/arm64/kvm/sys_regs.c | 124 ++++++++++++++++++++++++++++++++++++++++++++--
>>>>  1 file changed, 119 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>>>> index b2ccc25..bad3dfd 100644
>>>> --- a/arch/arm64/kvm/sys_regs.c
>>>> +++ b/arch/arm64/kvm/sys_regs.c
>>>> @@ -452,12 +452,44 @@ static void reset_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
>>>>  	vcpu_sys_reg(vcpu, r->reg) = val;
>>>>  }
>>>>
>>>> +static inline bool pmu_access_el0_disabled(struct kvm_vcpu *vcpu)
>>>> +{
>>>> +	u64 reg = vcpu_sys_reg(vcpu, PMUSERENR_EL0);
>>>> +
>>>> +	return !((reg & 0x1) || vcpu_mode_priv(vcpu));
>>>> +}
>>>> +
>>>> +static inline bool pmu_write_swinc_el0_disabled(struct kvm_vcpu *vcpu)
>>>> +{
>>>> +	u64 reg = vcpu_sys_reg(vcpu, PMUSERENR_EL0);
>>>> +
>>>> +	return !((reg & 0x3) || vcpu_mode_priv(vcpu));
>>>> +}
>>>> +
>>>> +static inline bool pmu_access_cycle_counter_el0_disabled(struct kvm_vcpu *vcpu)
>>>> +{
>>>> +	u64 reg = vcpu_sys_reg(vcpu, PMUSERENR_EL0);
>>>> +
>>>> +	return !((reg & 0x5) || vcpu_mode_priv(vcpu));
>>>> +}
>>>> +
>>>> +static inline bool pmu_access_event_counter_el0_disabled(struct kvm_vcpu *vcpu)
>>>> +{
>>>> +	u64 reg = vcpu_sys_reg(vcpu, PMUSERENR_EL0);
>>>> +
>>>> +	return !((reg & 0x9) || vcpu_mode_priv(vcpu));
>>>> +}
>> Please add #defines for the PMUSERNR_EL0 bits.
>>
>>>> +
>>>>  static bool access_pmcr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
>>>>  			const struct sys_reg_desc *r)
>>>>  {
>>>>  	u64 val;
>>>> +	bool unaccessible = pmu_access_el0_disabled(vcpu);
>>>>
>>>>  	if (p->is_write) {
>>>> +		if (unaccessible)
>>>> +			return ignore_write(vcpu, p);
>>>> +
>> This is not how this is supposed to work. If EL0 is denied access to the
>> PMU, you must inject an exception into EL1 for it to handle the fault.
>> The code should reflect the flow described at D5.11.2 in the ARM ARM.
>>
> Does it need to add a helper to inject an exception into EL1 or is there 
> a existing one?

You can use some of the stuff in inject_fault.c as a starting point.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...