Re: perf with precise attribute kills all KVM based VMs

[Peter Zijlstra <peterz@infradead.org>]

On Wed, 2012-07-11 at 10:10 +0300, Gleb Natapov wrote:

> Looks like Avi is right about the overshoot. Can you test something like this?
> 
> diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
> index 166546e..5fb371a 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel.c
> @@ -1374,8 +1374,11 @@ static struct perf_guest_switch_msr *intel_guest_get_msrs(int *nr)
>  	arr[0].msr = MSR_CORE_PERF_GLOBAL_CTRL;
>  	arr[0].host = x86_pmu.intel_ctrl & ~cpuc->intel_ctrl_guest_mask;
>  	arr[0].guest = x86_pmu.intel_ctrl & ~cpuc->intel_ctrl_host_mask;
> +	arr[1].msr = MSR_IA32_PEBS_ENABLE;
> +	arr[1].host = cpuc->pebs_enabled;
> +	arr[1].guest = 0;
> +	*nr = 2;
>  
> -	*nr = 1;
>  	return arr;
>  }


You also need to clear TR, BTS, BTINT from MSR_IA32_DEBUGCTLMSR and
ideally you'd also clear MSR_IA32_DS_AREA so that any write will be a
proper NULL deref or such.