Re: [PATCH 1/8] perf/x86/intel: Fix memory corruption

[Thomas Gleixner <tglx@linutronix.de>]

On Thu, 21 Mar 2019, Peter Zijlstra wrote:
> Subject: perf/x86/intel: Initialize TFA MSR
> 
> Stephane reported that we don't initialize the TFA MSR, which could lead
> to trouble if the RESET value is not 0 or on kexec.

That sentence doesn't parse.

  Stephane reported that the TFA MSR is not initialized by the kernel, but
  the TFA bit could set by firmware or as a leftover from a kexec, which
  makes the state inconsistent.

> Reported-by: Stephane Eranian <eranian@google.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  arch/x86/events/intel/core.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 8baa441d8000..2d3caf2d1384 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -3575,6 +3575,12 @@ static void intel_pmu_cpu_starting(int cpu)
>  
>  	cpuc->lbr_sel = NULL;
>  
> +	if (x86_pmu.flags & PMU_FL_TFA) {
> +		WARN_ON_ONCE(cpuc->tfa_shadow);

Hmm. I wouldn't warn here as this is a legit state for kexec/kdump and I
don't think we can figure out whether this comes directly from the
firmware.

Thanks,

	tglx