x86/topology: Fix Intel HT disable

BugLink: http://bugs.launchpad.net/bugs/1570441

As per the comment in the code; due to BIOS it is sometimes impossible to know
if there actually are smp siblings until the machine is fully enumerated. So
we rather overestimate the number of possible packages.

Fixes: 1f12e32f ("x86/topology: Create logical package id")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: aherrmann@suse.com
Cc: jencce.kernel@gmail.com
Cc: bp@alien8.de
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Link: http://lkml.kernel.org/r/20160318150538.611014173@infradead.orgSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

(cherry picked from commit 63d1e995)
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Colin King <colin.king@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

arch/x86/kernel/smpboot.c

@@ -312,8 +312,21 @@ static void __init smp_init_package_map(void)
 	/*
 	 * Today neither Intel nor AMD support heterogenous systems. That
 	 * might change in the future....
+	 *
+	 * While ideally we'd want '* smp_num_siblings' in the below @ncpus
+	 * computation, this won't actually work since some Intel BIOSes
+	 * report inconsistent HT data when they disable HT.
+	 *
+	 * In particular, they reduce the APIC-IDs to only include the cores,
+	 * but leave the CPUID topology to say there are (2) siblings.
+	 * This means we don't know how many threads there will be until
+	 * after the APIC enumeration.
+	 *
+	 * By not including this we'll sometimes over-estimate the number of
+	 * logical packages by the amount of !present siblings, but this is
+	 * still better than MAX_LOCAL_APIC.
 	 */
-	ncpus = boot_cpu_data.x86_max_cores * smp_num_siblings;
+	ncpus = boot_cpu_data.x86_max_cores;
 	__max_logical_packages = DIV_ROUND_UP(nr_cpu_ids, ncpus);
 
 	/*