Re: [PATCH v6 10/21] KVM: ARM64: Add access handler for PMEVCNTRn and PMCCNTR register

[Shannon Zhao <zhaoshenglong@huawei.com>]

Hi Marc,

On 2015/12/9 0:30, Marc Zyngier wrote:
> On 08/12/15 12:47, Shannon Zhao wrote:
>> > From: Shannon Zhao <shannon.zhao@linaro.org>
>> > 
>> > Since the reset value of PMEVCNTRn or PMCCNTR is UNKNOWN, use
>> > reset_unknown for its reset handler. Add access handler which emulates
>> > writing and reading PMEVCNTRn or PMCCNTR register. When reading
>> > PMEVCNTRn or PMCCNTR, call perf_event_read_value to get the count value
>> > of the perf event.
>> > 
>> > Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
>> > ---
>> >  arch/arm64/kvm/sys_regs.c | 107 +++++++++++++++++++++++++++++++++++++++++++++-
>> >  1 file changed, 105 insertions(+), 2 deletions(-)
>> > 
>> > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> > index c116a1b..f7a73b5 100644
>> > --- a/arch/arm64/kvm/sys_regs.c
>> > +++ b/arch/arm64/kvm/sys_regs.c
>> > @@ -525,6 +525,12 @@ static bool access_pmu_regs(struct kvm_vcpu *vcpu,
>> >  
>> >  	if (p->is_write) {
>> >  		switch (r->reg) {
>> > +		case PMEVCNTR0_EL0 ... PMCCNTR_EL0: {
> Same problem as previously mentioned.
> 
>> > +			val = kvm_pmu_get_counter_value(vcpu,
>> > +							r->reg - PMEVCNTR0_EL0);
>> > +			vcpu_sys_reg(vcpu, r->reg) += (s64)p->regval - val;
>> > +			break;
>> > +		}

If I use a handler to handle these accesses to PMEVCNTRn and PMCCNTR
like below. It converts the register offset c14_PMEVCNTRn and c9_PMCCNTR
to PMEVCNTRn_EL0 and PMCCNTR_EL0, uniformly uses vcpu_sys_reg and
doesn't need to take care the big endian. What do you think about this?

static bool access_pmu_evcntr(struct kvm_vcpu *vcpu,
                              struct sys_reg_params *p,
                              const struct sys_reg_desc *r)
{
        u64 idx, reg, val;

        if (p->is_aarch32)
                reg = r->reg / 2;
        else
                reg = r->reg;

        switch (reg) {
        case PMEVCNTR0_EL0 ... PMEVCNTR30_EL0: {
                idx = reg - PMEVCNTR0_EL0;
                break;
        }
        case PMCCNTR_EL0: {
                idx = ARMV8_CYCLE_IDX;
                break;
        }
        default:
                idx = vcpu_sys_reg(vcpu, PMSELR_EL0) & ARMV8_COUNTER_MASK;
                if (!pmu_counter_idx_valid(vcpu, idx))
                        return true;
                reg = (idx == ARMV8_CYCLE_IDX) ? PMCCNTR_EL0 :
PMEVCNTR0_EL0 + idx;
                break;
        }

        val = kvm_pmu_get_counter_value(vcpu, idx);
        if (p->is_write)
                vcpu_sys_reg(vcpu, reg) = (s64)p->regval - val;
        else
                p->regval = val;

        return true;
}

Thanks,
-- 
Shannon