Re: [PATCH v4 20/23] arm64: perf: Count EL2 events if the kernel is running in HYP

[Marc Zyngier]

On 15/02/16 17:22, Will Deacon wrote:
> On Thu, Feb 11, 2016 at 06:40:01PM +0000, Marc Zyngier wrote:
>> When the kernel is running in HYP (with VHE), it is necessary to
>> include EL2 events if the user requests counting kernel or
>> hypervisor events.
>>
>> Reviewed-by: Christoffer Dall <christoffer.d...@linaro.org>
>> Acked-by: Catalin Marinas <catalin.mari...@arm.com>
>> Signed-off-by: Marc Zyngier <marc.zyng...@arm.com>
>> ---
>>  arch/arm64/kernel/perf_event.c | 14 ++++++++++----
>>  1 file changed, 10 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
>> index f7ab14c..6013a38 100644
>> --- a/arch/arm64/kernel/perf_event.c
>> +++ b/arch/arm64/kernel/perf_event.c
>> @@ -20,6 +20,7 @@
>>   */
>>  
>>  #include <asm/irq_regs.h>
>> +#include <asm/virt.h>
>>  
>>  #include <linux/of.h>
>>  #include <linux/perf/arm_pmu.h>
>> @@ -693,10 +694,15 @@ static int armv8pmu_set_event_filter(struct 
>> hw_perf_event *event,
>>              return -EPERM;
>>      if (attr->exclude_user)
>>              config_base |= ARMV8_EXCLUDE_EL0;
>> -    if (attr->exclude_kernel)
>> -            config_base |= ARMV8_EXCLUDE_EL1;
>> -    if (!attr->exclude_hv)
>> -            config_base |= ARMV8_INCLUDE_EL2;
>> +    if (is_kernel_in_hyp_mode()) {
>> +            if (!attr->exclude_kernel || !attr->exclude_hv)
>> +                    config_base |= ARMV8_INCLUDE_EL2;
> 
> Hmm, so if userspace sets exclude_kernel but not exclude_user and
> exclude_hv, what should we do? I'm slightly tempted to reject the
> filter with -EINVAL...

I was angling for the minimum level of surprise for the user, but
I guess that the results are going to be troubling anyway.

How about something like this on top:

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index 6013a38..8c00ed4 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -695,7 +695,10 @@ static int armv8pmu_set_event_filter(struct hw_perf_event 
*event,
        if (attr->exclude_user)
                config_base |= ARMV8_EXCLUDE_EL0;
        if (is_kernel_in_hyp_mode()) {
-               if (!attr->exclude_kernel || !attr->exclude_hv)
+               /* Demand that kernel and hv are consistent */
+               if (attr->exclude_kernel != attr->exclude_hv)
+                       return -EINVAL;
+               if (!attr->exclude_hv)
                        config_base |= ARMV8_INCLUDE_EL2;
        } else {
                if (attr->exclude_kernel)

Thanks,

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