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

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Message-ID: <alpine.DEB.2.21.1903211741120.1784@nanos.tec.linutronix.de>
Date:   Thu, 21 Mar 2019 17:45:41 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Stephane Eranian <eranian@...gle.com>,
        Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, tonyj@...e.com,
        nelson.dsouza@...el.com
Subject: Re: [PATCH 1/8] perf/x86/intel: Fix memory corruption

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@...gle.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.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