linux-kernel - Re: [Patch V1] x86, mce: Ensure offline CPU's don't participate in mce rendezvous process.

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Date:	Sat, 5 Dec 2015 00:06:54 +0100
From:	Borislav Petkov <bp@...e.de>
To:	Ashok Raj <ashok.raj@...el.com>
Cc:	linux-kernel@...r.kernel.org, linux-edac@...r.kernel.org,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [Patch V1] x86, mce: Ensure offline CPU's don't participate in
 mce rendezvous process.

On Fri, Dec 04, 2015 at 06:57:31PM -0500, Ashok Raj wrote:
> Linux has logical cpu offline capability. That can be triggered by:
> 
> # echo 0 > /sys/devices/system/cpu/cpuX/online
> 
> In Intel Architecture, MCE's are broadcasted to all CPUs in the system.
> 
> This includes the CPUs marked offline by Linux. Unless the CPU's were removed
> via an ACPI notification, in which case the cpu's are removed from the
> cpu_present_map.
> 
> This patch ensures offline CPU's don't participate in MCE rendezvous, but
> simply perform clearing some status bits to ensure a second MCE wont cause
> automatic shutdown.
> 
> Without the patch, mce_start will increment mce_callin, but mce_start would
> only wait for all online_cpus. So offline cpu's should avoid participating
> in the rendezvous process.
> 
> Reviewed-by: Tony Luck <tony.luck@...el.com>
> Cc: stable@...r.kernel.org
> Signed-off-by: Ashok Raj <ashok.raj@...el.com>
> ---
>  arch/x86/kernel/cpu/mcheck/mce.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
> index c5b0d56..72ea044 100644
> --- a/arch/x86/kernel/cpu/mcheck/mce.c
> +++ b/arch/x86/kernel/cpu/mcheck/mce.c
> @@ -998,7 +998,20 @@ void do_machine_check(struct pt_regs *regs, long error_code)
>  	u64 recover_paddr = ~0ull;
>  	int flags = MF_ACTION_REQUIRED;
>  	int lmce = 0;
> +	unsigned int cpu = smp_processor_id();
>  
> +	/*
> +	 * if this cpu is offline, just bail out.
> +	 */
> +	if (cpu_is_offline(cpu)) {
> +		u64 mcgstatus;
> +
> +		mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS);
> +		if (mcgstatus & MCG_STATUS_RIPV) {
> +			mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
> +			return;
> +		}
> +	}
>  	ist_enter(regs);
>  
>  	this_cpu_inc(mce_exception_count);
> @@ -1142,8 +1155,8 @@ void do_machine_check(struct pt_regs *regs, long error_code)
>  
>  	if (worst > 0)
>  		mce_report_event(regs);
> -	mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
>  out:
> +	mce_wrmsrl(MSR_IA32_MCG_STATUS, 0);
>  	sync_core();
>  
>  	if (recover_paddr == ~0ull)
> -- 

With that hunk here you want to clear MSR_IA32_MCG_STATUS in the
!cfg->banks case, right?

If so, this should be a separate patch. Also, CC: stable with an
explanation why.

Thanks.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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