Re: [v4.6-rc1 Regression] x86/topology: Create logical package id

From	Ingo Molnar <mingo@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [v4.6-rc1 Regression] x86/topology: Create logical package id
Date	2016-05-07 07:20 +0200
Message-ID	<rw2OL-3At-13@gated-at.bofh.it> (permalink)
References	<rvSw3-1EJ-39@gated-at.bofh.it> <rvT8K-20P-11@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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* Thomas Gleixner <tglx@linutronix.de> wrote:

> > I was hoping to get your feedback, since you are the patch author.  Do
> > you think gathering any additional data will help diagnose this issue,
> > or would it be best to submit a revert request?
> 
> Yuck. That dies with a divide error. And that looks like XEN is supplying crap
> data in the CPUID.
> 
> Does the patch below cure the issue?
> 
> Thanks,
> 
>         tglx
> 
> 8<---------------
> 
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -332,6 +332,11 @@ static void __init smp_init_package_map(
>  	 * primary cores.
>  	 */
>  	ncpus = boot_cpu_data.x86_max_cores;
> +	if (!ncpus) {
> +		pr_warn("x86_max_cores == zero !?!?");
> +		ncpus = 1;
> +	}
> +

Even if the underlying Xen bug is fixed, I think we should add this protective 
measure to defend against future CPUID mishaps.

Thanks,

	Ingo

Thread

[v4.6-rc1 Regression] x86/topology: Create logical package id Joseph Salisbury <joseph.salisbury@canonical.com> - 2016-05-06 20:20 +0200
  Re: [v4.6-rc1 Regression] x86/topology: Create logical package id Thomas Gleixner <tglx@linutronix.de> - 2016-05-06 21:00 +0200
    Re: [v4.6-rc1 Regression] x86/topology: Create logical package id Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-05-06 21:20 +0200
      Re: [v4.6-rc1 Regression] x86/topology: Create logical package id Joseph Salisbury <joseph.salisbury@canonical.com> - 2016-05-06 21:40 +0200
        Re: [v4.6-rc1 Regression] x86/topology: Create logical package id Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-05-06 22:50 +0200
          Re: [v4.6-rc1 Regression] x86/topology: Create logical package id Joseph Salisbury <joseph.salisbury@canonical.com> - 2016-05-06 23:00 +0200
            Re: [v4.6-rc1 Regression] x86/topology: Create logical package id Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2016-05-06 23:30 +0200
    Re: [v4.6-rc1 Regression] x86/topology: Create logical package id Joseph Salisbury <joseph.salisbury@canonical.com> - 2016-05-06 21:40 +0200
      Re: [v4.6-rc1 Regression] x86/topology: Create logical package id Joseph Salisbury <joseph.salisbury@canonical.com> - 2016-05-06 23:00 +0200
    Re: [v4.6-rc1 Regression] x86/topology: Create logical package id Ingo Molnar <mingo@kernel.org> - 2016-05-07 07:20 +0200
    [tip:x86/urgent] x86/topology: Handle CPUID bogosity gracefully tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2016-05-07 10:20 +0200

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