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>

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index a2065d3b3b396f4503f4e4f42acc2af2bd4b307b..0e4329ed91ef61da5a86e5d604d1ad96109efbfb 100644 (file)
--- 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);
 
        /*