linux-kernel - Re: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift

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Date:	Mon, 22 Nov 2010 09:22:12 -0500
From:	Don Zickus <dzickus@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jason Wessel <jason.wessel@...driver.com>,
	Ingo Molnar <mingo@...e.hu>,
	Robert Richter <robert.richter@....com>, ying.huang@...el.com,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift

On Sat, Nov 20, 2010 at 12:09:39AM +0100, Peter Zijlstra wrote:
> On Fri, 2010-11-19 at 17:59 -0500, Don Zickus wrote:
> > +++ b/arch/x86/kernel/cpu/perf_event.c
> > @@ -381,6 +381,19 @@ static void release_pmc_hardware(void) {}
> >  
> >  #endif
> >  
> > +static bool check_hw_exists(void)
> > +{
> > +       u64 val, val_new;
> > +
> > +       val = 0xabcdUL;
> > +       (void) checking_wrmsrl(x86_pmu.perfctr, val);
> > +       rdmsrl(x86_pmu.perfctr, val_new);
> 
> 
> Yeah, this looks about right, although for extreme prudence I'd also use
> a checking_rdmsrl().

I didn't realize such a function existed, I'll look into it.

> 
> 
> > +       if (val != val_new)
> > +               return false;
> > +
> > +       return true;
> > +}
> > +
> >  static void reserve_ds_buffers(void);
> >  static void release_ds_buffers(void);
> >  
> > @@ -1371,6 +1385,12 @@ void __init init_hw_perf_events(void)
> >  
> >         pmu_check_apic();
> >  
> > +       /* sanity check that the hardware exists or is emulated */
> > +       if (!check_hw_exists()) {
> > +               pr_cont("no PMU driver, software events only.\n");
> > +               return;
> > +       } 
> 
> Maybe report something like this: 
>   "Broken PMU hardware detected, software events only."
> 
> Because this is really not something that's supposed to happen.

Ok.  Thanks.  I'll respin a cleaner patch today.

Thanks,
Don

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