Comment 19 for bug 1573231

On Fri, 6 May 2016, Joseph Salisbury wrote:
> A kernel bug report was opened against Ubuntu [0]. After a kernel
> bisect, it was found that reverting the following commit resolved this bug:
>
> commit 1f12e32f4cd5243ae46d8b933181be0d022c6793
> Author: Thomas Gleixner <email address hidden>
> Date: Mon Feb 22 22:19:15 2016 +0000
>
> x86/topology: Create logical package id
>
> To build successfully with this commit reverted, I also had to revert
> commits: e7ee3e8,2d4de83,87f01cc and 33c3cc7.
>
> The regression was introduced as of v4.6-rc1.
>
> 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;
+ }
+
  __max_logical_packages = DIV_ROUND_UP(total_cpus, ncpus);

  /*