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

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Message-ID: <cea61aab-3feb-4008-adb9-2f2645589714@linux.intel.com>
Date: Mon, 26 Aug 2024 14:56:02 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Jim Mattson <jmattson@...gle.com>
Cc: Sean Christopherson <seanjc@...gle.com>,
 Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, Mingwei Zhang <mizhang@...gle.com>,
 Xiong Zhang <xiong.y.zhang@...el.com>, Zhenyu Wang
 <zhenyuw@...ux.intel.com>, Like Xu <like.xu.linux@...il.com>,
 Jinrong Liang <cloudliang@...cent.com>, Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [Patch v5 06/18] x86: pmu: Add asserts to warn inconsistent fixed
 events and counters


On 8/23/2024 2:22 AM, Jim Mattson wrote:
> On Tue, Jul 2, 2024 at 7:12 PM Dapeng Mi <dapeng1.mi@...ux.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@...gle.com>
>> Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.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.


>
>> +               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
>>