linux-kernel - Re: [tip:perf/core] perf/x86: Add an MSR PMU driver

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Date:	Tue, 4 Aug 2015 11:00:54 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"Liang, Kan" <kan.liang@...el.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Lutomirski <luto@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:perf/core] perf/x86: Add an MSR PMU driver

On Tue, Aug 4, 2015 at 8:03 AM, Liang, Kan <kan.liang@...el.com> wrote:
>
>> > +
>> > +enum perf_msr_id {
>> > +       PERF_MSR_TSC                    = 0,
>> > +       PERF_MSR_APERF                  = 1,
>> > +       PERF_MSR_MPERF                  = 2,
>> > +       PERF_MSR_PPERF                  = 3,
>> > +       PERF_MSR_SMI                    = 4,
>> > +
>> > +       PERF_MSR_EVENT_MAX,
>> > +};
>> > +
>> > +struct perf_msr {
>> > +       int     id;
>> > +       u64     msr;
>> > +};
>> > +
>> > +static struct perf_msr msr[] = {
>> > +       { PERF_MSR_TSC, 0 },
>> > +       { PERF_MSR_APERF, MSR_IA32_APERF },
>> > +       { PERF_MSR_MPERF, MSR_IA32_MPERF },
>> > +       { PERF_MSR_PPERF, MSR_PPERF },
>> > +       { PERF_MSR_SMI, MSR_SMI_COUNT }, };
>>
>> I think this could be easier to work with if it were [PERF_MSR_TSC] = {...},
>> etc.  No big deal, though, until the list gets long.  However, it might make
>> fixing the apparent issue below easier...
>>
>> > +static int msr_event_init(struct perf_event *event) {
>> > +       u64 cfg = event->attr.config;
>>
>> ...
>>
>> > +       event->hw.event_base = msr[cfg].msr;
>>
>> Shouldn't this verify that the fancy enumeration code actually believes that
>> msr[cfg] exists on this system? Otherwise we might have a very short wait
>> until the perf fuzzer oopses this thing :)
>>
>
> I think we already did the check before using msr[cfg].

Where?  All I see is:

+       if (cfg >= PERF_MSR_EVENT_MAX)
+               return -EINVAL;

--Andy
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