ACK: [SRU][Xenial][Yakkety][PATCH 1/1] UBUNTU: SAUCE: (no-up) x86/topology: Handle CPUID bogosity gracefully

[Colin Ian King]

On 09/05/16 17:17, Joseph Salisbury wrote:
> From: Thomas Gleixner <tglx at linutronix.de>
> 
> BugLink: http://bugs.launchpad.net/bugs/1573231
> 
> Joseph reported that a XEN guest dies with a division by 0 in the package
> topology setup code. This happens if cpu_info.x86_max_cores is zero.
> 
> Handle that case and emit a warning. This does not fix the underlying XEN bug,
> but makes the code more robust.
> 
> Cc: Peter Zijlstra <peterz at infradead.org>
> Cc: Boris Ostrovsky <boris.ostrovsky at oracle.com>
> Cc: David Vrabel <david.vrabel at citrix.com>
> Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1605062046270.3540@nanos
> Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
> Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>
> ---
>  arch/x86/kernel/smpboot.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index a61a97a..96f49a2 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -332,6 +332,11 @@ static void __init smp_init_package_map(void)
>  	 * 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);
>  
>  	/*
> 
Seems like a sane fix/workaround to the issue.

Acked-by: Colin Ian King <colin.king at canonical.com>