Re: [Patch v5 06/18] x86: pmu: Add asserts to warn inconsistent fixed events and counters

Mi, Dapeng
2024-08-27T00:41:25Z

On 8/27/2024 2:36 AM, Jim Mattson wrote:
> On Sun, Aug 25, 2024 at 11:56 PM Mi, Dapeng <dapeng1.mi@linux.intel.com> wrote:
>>
>> On 8/23/2024 2:22 AM, Jim Mattson wrote:
>>> On Tue, Jul 2, 2024 at 7:12 PM Dapeng Mi <dapeng1.mi@linux.intel.com> wrote:
>>>> Current PMU code deosn't check whether PMU fixed counter number is
>>>> larger than pre-defined fixed events. If so, it would cause memory
>>>> access out of range.
>>>>
>>>> So add assert to warn this invalid case.
>>>>
>>>> Reviewed-by: Mingwei Zhang <mizhang@google.com>
>>>> Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
>>>> ---
>>>> x86/pmu.c | 10 ++++++++--
>>>> 1 file changed, 8 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/x86/pmu.c b/x86/pmu.c
>>>> index b4de2680..3e0bf3a2 100644
>>>> --- a/x86/pmu.c
>>>> +++ b/x86/pmu.c
>>>> @@ -113,8 +113,12 @@ static struct pmu_event* get_counter_event(pmu_counter_t *cnt)
>>>> for (i = 0; i < gp_events_size; i++)
>>>> if (gp_events[i].unit_sel == (cnt->config & 0xffff))
>>>> return &gp_events[i];
>>>> - } else
>>>> - return &fixed_events[cnt->ctr - MSR_CORE_PERF_FIXED_CTR0];
>>>> + } else {
>>>> + unsigned int idx = cnt->ctr - MSR_CORE_PERF_FIXED_CTR0;
>>>> +
>>>> + assert(idx < ARRAY_SIZE(fixed_events));
>>> Won't this assertion result in a failure on bare metal, for CPUs
>>> supporting fixed counter 3?
>> Yes, this is intended use. Currently KVM vPMU still doesn't support fixed
>> counter 3. If it's supported in KVM vPMU one day but forget to add
>> corresponding support in this pmu test, this assert would remind this.
> These tests are supposed to run (and pass) on bare metal. Hence, they
> should not be dependent on a non-architectural quirk of the KVM
> implementation.
>
> Perhaps a warning would serve as a reminder?

Sounds reasonable. Would change to a warning. Thanks.

>
>>>> + return &fixed_events[idx];
>>>> + }
>>>>
>>>> return (void*)0;
>>>> }
>>>> @@ -740,6 +744,8 @@ int main(int ac, char **av)
>>>> printf("Fixed counters: %d\n", pmu.nr_fixed_counters);
>>>> printf("Fixed counter width: %d\n", pmu.fixed_counter_width);
>>>>
>>>> + assert(pmu.nr_fixed_counters <= ARRAY_SIZE(fixed_events));
>>>> +
>>> And this one as well?
>>>
>>>> apic_write(APIC_LVTPC, PMI_VECTOR);
>>>>
>>>> check_counters();
>>>> --
>>>> 2.40.1
>>>>