x86_cpu_to_apicid[] gets set to BAD_APICID when bringup of a secondary
CPU fails, yet srat_detect_node() wants to use this as array index.

An alternative would be to backport -unstable c/s 21436:b127760a4725.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -1098,10 +1098,13 @@ void __init __start_xen(unsigned long mb
             __cpu_up(i);
         }
 
-        /* Set up cpu_to_node[]. */
-        srat_detect_node(i);
-        /* Set up node_to_cpumask based on cpu_to_node[]. */
-        numa_add_cpu(i);        
+        if ( cpu_online(i) )
+        {
+            /* Set up cpu_to_node[]. */
+            srat_detect_node(i);
+            /* Set up node_to_cpumask based on cpu_to_node[]. */
+            numa_add_cpu(i);
+        }
     }
 
     printk("Brought up %ld CPUs\n", (long)num_online_cpus());