Re: [PATCH] arm64: perf: Count EL2 events if either of kernel and hyp are not excluded

[Ganapatrao Kulkarni]

Hi Will,

On Tue, Apr 4, 2017 at 4:48 PM, Will Deacon <will.deacon@xxxxxxx> wrote:
> On Tue, Apr 04, 2017 at 04:10:55PM +0530, Ganapatrao Kulkarni wrote:
>> commit d98ecda (arm64: perf: Count EL2 events if the kernel is running in HYP)
>> is returning error for perf syscall with mixed attribute set for exclude_kernel
>> and exlude_hv.
>>
>> This change is breaking some applications (observed with hhvm) when
>> ran with VHE enabled. Adding change to enable EL2 event counting,
>> if either of or both of exclude_kernel and exlude_hv are not set.
>>
>> Signed-off-by: Ganapatrao Kulkarni <ganapatrao.kulkarni@xxxxxxxxxx>
>> ---
>>  arch/arm64/kernel/perf_event.c | 19 ++++++++++++-------
>>  1 file changed, 12 insertions(+), 7 deletions(-)
>
> Hmm. When we have VHE, we can't distinguish between hypervisor and kernel,
> so this patch doesn't seem right to me. The code currently requires
> both exclude_kernel and exclude_hv to be clear before we enable profiling
> EL2, otherwise we're failing to exclude samples that were asked to be
> excluded.

The application cant differentiate that kernel is running in EL2/VHE or in EL1
when VHE=1, is it makes sense to enable EL2 event counting when there
is request from application to either include kernel or hypervisor
event count, since both are same.

IMO, it is not appropriate to have different application behaviour
when kernel booted with VHE=0/1

>
> Will
>
>> diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
>> index daf95919..ea5848a 100644
>> --- a/arch/arm64/kernel/perf_event.c
>> +++ b/arch/arm64/kernel/perf_event.c
>> @@ -871,15 +871,20 @@ static int armv8pmu_set_event_filter(struct hw_perf_event *event,
>>
>>       if (attr->exclude_idle)
>>               return -EPERM;
>> -     if (is_kernel_in_hyp_mode() &&
>> -         attr->exclude_kernel != attr->exclude_hv)
>> -             return -EINVAL;
>> +     if (is_kernel_in_hyp_mode()) {
>> +             /* include EL2 events, if either of not excluded */
>> +             if ((attr->exclude_kernel != attr->exclude_hv) ||
>> +                             !attr->exclude_kernel ||
>> +                             !attr->exclude_hv)
>> +                     config_base |= ARMV8_PMU_INCLUDE_EL2;
>> +     } else {
>> +             if (attr->exclude_kernel)
>> +                     config_base |= ARMV8_PMU_EXCLUDE_EL1;
>> +             if (!attr->exclude_hv)
>> +                     config_base |= ARMV8_PMU_INCLUDE_EL2;
>> +     }
>>       if (attr->exclude_user)
>>               config_base |= ARMV8_PMU_EXCLUDE_EL0;
>> -     if (!is_kernel_in_hyp_mode() && attr->exclude_kernel)
>> -             config_base |= ARMV8_PMU_EXCLUDE_EL1;
>> -     if (!attr->exclude_hv)
>> -             config_base |= ARMV8_PMU_INCLUDE_EL2;
>>
>>       /*
>>        * Install the filter into config_base as this is used to
>> --
>> 1.8.1.4
>>

thanks
Ganapat