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SubjectRe: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift
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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().


> + 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.


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