From 56402d63eefe22179f7311a51ff2094731420406 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 6 May 2016 20:48:16 +0200
Subject: [PATCH] x86/topology: Handle CPUID bogosity gracefully
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.
Reported-and-tested-by: Joseph Salisbury <joseph.salisbury@canonical.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1605062046270.3540@nanos
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
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 a2065d3b3b396..0e4329ed91ef6 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);
/*
--
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