linux-kernel - Re: [PATCH v3 05/19] x86/mce: WARN once if IA32_FEATURE

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Date:   Thu, 21 Nov 2019 12:45:38 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Tony Luck <tony.luck@...el.com>,
        Tony W Wang-oc <TonyWWang-oc@...oxin.com>,
        Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-edac@...r.kernel.org,
        linux-kselftest@...r.kernel.org, Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH v3 05/19] x86/mce: WARN once if IA32_FEATURE_CONTROL MSR
 is left unlocked

On Mon, Nov 18, 2019 at 07:12:26PM -0800, Sean Christopherson wrote:
> WARN if the IA32_FEATURE_CONTROL MSR is somehow left unlocked now that
> CPU initialization unconditionally locks the MSR.
> 
> Reviewed-by: Borislav Petkov <bp@...e.de>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kernel/cpu/mce/intel.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/mce/intel.c b/arch/x86/kernel/cpu/mce/intel.c
> index 3e5b29acd301..5abc55a67fce 100644
> --- a/arch/x86/kernel/cpu/mce/intel.c
> +++ b/arch/x86/kernel/cpu/mce/intel.c
> @@ -119,11 +119,10 @@ static bool lmce_supported(void)
>  	 * generate a #GP fault.
>  	 */
>  	rdmsrl(MSR_IA32_FEATURE_CONTROL, tmp);
> -	if ((tmp & (FEAT_CTL_LOCKED | FEAT_CTL_LMCE_ENABLED)) ==
> -		   (FEAT_CTL_LOCKED | FEAT_CTL_LMCE_ENABLED))
> -		return true;

I'd add a prepending comment:

/*
 * FEAT_CTL_LOCKED should have been always set either by
 * BIOS before handover to the kernel or init_feature_control_msr().
 */

> +	if (WARN_ON_ONCE(!(tmp & FEAT_CTL_LOCKED)))
> +		return false;
>  
> -	return false;
> +	return tmp & FEAT_CTL_LMCE_ENABLED;
>  }
>  
>  bool mce_intel_cmci_poll(void)
> -- 
> 2.24.0
> 

/Jarkko