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

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Date:	Tue, 4 Aug 2015 18:11:28 +0000
From:	"Liang, Kan" <kan.liang@...el.com>
To:	Andy Lutomirski <luto@...capital.net>
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;

Yes, we check cfg here. So msr[cfg] should be always available.