[PATCH] x86_64: Dont record local apic ids when they are disabled in MADT

Some broken BIOS's had processors disabled, but
same apic id as a valid processor. This causes
acpi_processor_start() to think this disabled
cpu is ok, and croak. So we dont record bad
apicid's anymore.

http://bugzilla.kernel.org/show_bug.cgi?id=5930

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/acpi/boot.c

@@ -248,10 +248,17 @@ acpi_parse_lapic(acpi_table_entry_header * header, const unsigned long end)
 
 	acpi_table_print_madt_entry(header);
 
-	/* Register even disabled CPUs for cpu hotplug */
-
-	x86_acpiid_to_apicid[processor->acpi_id] = processor->id;
+	/* Record local apic id only when enabled */
+	if (processor->flags.enabled)
+		x86_acpiid_to_apicid[processor->acpi_id] = processor->id;
 
+	/*
+	 * We need to register disabled CPU as well to permit
+	 * counting disabled CPUs. This allows us to size
+	 * cpus_possible_map more accurately, to permit
+	 * to not preallocating memory for all NR_CPUS
+	 * when we use CPU hotplug.
+	 */
 	mp_register_lapic(processor->id,	/* APIC ID */
 			  processor->flags.enabled);	/* Enabled? */