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Subject: Re: [perf] fuzzer triggers unchecked MSR access error: WRMSR to 0x318
To:     Peter Zijlstra <peterz@infradead.org>,
        "Liang, Kan" <kan.liang@linux.intel.com>
Cc:     Vince Weaver <vincent.weaver@maine.edu>,
        linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        "Liang, Kan" <kan.liang@intel.com>
References: <37881148-a43e-5fd4-817c-a875adc7a15f@maine.edu>
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 <45bee582-0f89-5125-82e7-92caf8b741ea@linux.intel.com>
 <YQLJhAiYQKtvvhjJ@hirez.programming.kicks-ass.net>
From:   Like Xu <like.xu.linux@gmail.com>
Organization: Tencent
Message-ID: <e3fd66b0-778a-21c5-5f01-e91db0099cc3@gmail.com>
Date:   Mon, 2 Aug 2021 19:40:54 +0800
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On 29/7/2021 11:30 pm, Peter Zijlstra wrote:
> On Thu, Jul 29, 2021 at 09:21:01AM -0400, Liang, Kan wrote:
>>
>>
>> On 7/29/2021 5:14 AM, Peter Zijlstra wrote:
>>> On Wed, Jul 28, 2021 at 12:49:43PM -0400, Vince Weaver wrote:
>>>> [32694.087403] unchecked MSR access error: WRMSR to 0x318 (tried to write 0x0000000000000000) at rIP: 0xffffffff8106f854 (native_write_msr+0x4/0x20)
>>>> [32694.101374] Call Trace:
>>>> [32694.103974]  perf_clear_dirty_counters+0x86/0x100
>>>
>>> Hmm.. if I read this right that's MSR_ARCH_PERFMON_FIXED_CTR0 + i, given
>>> that FIXED_CTR0 is 0x309 that gives i == 15, which is FIXED_BTS.
>>>
>>> I'm thinking something like this ought to cure things.
>>>
>>> ---
>>>    arch/x86/events/core.c | 12 +++++++-----
>>>    1 file changed, 7 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
>>> index 1eb45139fcc6..04edf8017961 100644
>>> --- a/arch/x86/events/core.c
>>> +++ b/arch/x86/events/core.c
>>> @@ -2489,13 +2489,15 @@ void perf_clear_dirty_counters(void)
>>>    		return;
>>>    	for_each_set_bit(i, cpuc->dirty, X86_PMC_IDX_MAX) {
>>> -		/* Metrics and fake events don't have corresponding HW counters. */
>>> -		if (is_metric_idx(i) || (i == INTEL_PMC_IDX_FIXED_VLBR))
>>> -			continue;
>>> -		else if (i >= INTEL_PMC_IDX_FIXED)
>>> +		if (i >= INTEL_PMC_IDX_FIXED) {
>>> +			/* Metrics and fake events don't have corresponding HW counters. */
>>> +			if ((i - INTEL_PMC_IDX_FIXED) >= x86_pmu.num_counters_fixed)
>>
>> Yes, the fix is better. My previous implementation tries to pick up all the
>> special cases. It's very likely to miss some special cases like FIXED_BTS
>> and probably any new fake events added later if there are.
>> Thanks for the fix.
>>
>> The x86_pmu.num_counters_fixed should work well on HSW. But we have hybrid
>> machines now. I think we can use
>> hybrid(cpuc->pmu, num_counters_fixed) instead, which should be more
>> accurate.
> 
> Yes, good point. I guess I still need to adjust to the hybrid world.

I recently enabled guest BTS and encountered the same call trace.

For the proposal hybrid(cpuc->pmu, num_counters_fixed),
Tested-by: Like Xu <likexu@tencent.com>