x86: use possible_cpus=NUM to extend the possible cpus allowed

Impact: add new boot parameter

Use possible_cpus=NUM kernel parameter to extend the number of possible
cpus.

The ability to HOTPLUG ON cpus that are "possible" but not "present" is
dealt with in a later patch.

Signed-off-by: Mike Travis <travis@sgi.com>

3 files changed, 42 insertions, 20 deletions

diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt
index 94bbc27ddd4f..9d620c153b04 100644
--- a/Documentation/cpu-hotplug.txt
+++ b/Documentation/cpu-hotplug.txt
@@ -50,16 +50,17 @@ additional_cpus=n (*)	Use this to limit hotpluggable cpus. This option sets
                         cpu_possible_map = cpu_present_map + additional_cpus
 
 (*) Option valid only for following architectures
-- x86_64, ia64
+- ia64
 
-ia64 and x86_64 use the number of disabled local apics in ACPI tables MADT
-to determine the number of potentially hot-pluggable cpus. The implementation
-should only rely on this to count the # of cpus, but *MUST* not rely on the
-apicid values in those tables for disabled apics. In the event BIOS doesn't
-mark such hot-pluggable cpus as disabled entries, one could use this
-parameter "additional_cpus=x" to represent those cpus in the cpu_possible_map.
+ia64 uses the number of disabled local apics in ACPI tables MADT to
+determine the number of potentially hot-pluggable cpus. The implementation
+should only rely on this to count the # of cpus, but *MUST* not rely
+on the apicid values in those tables for disabled apics. In the event
+BIOS doesn't mark such hot-pluggable cpus as disabled entries, one could
+use this parameter "additional_cpus=x" to represent those cpus in the
+cpu_possible_map.
 
-possible_cpus=n         [s390 only] use this to set hotpluggable cpus.
+possible_cpus=n         [s390,x86_64] use this to set hotpluggable cpus.
                         This option sets possible_cpus bits in
                         cpu_possible_map. Thus keeping the numbers of bits set
                         constant even if the machine gets rebooted.
diff --git a/arch/x86/kernel/apic.c b/arch/x86/kernel/apic.c
index 93cf2d13f335..f7a32a3beb2f 100644
--- a/arch/x86/kernel/apic.c
+++ b/arch/x86/kernel/apic.c
@@ -1819,28 +1819,32 @@ void disconnect_bsp_APIC(int virt_wire_setup)
 void __cpuinit generic_processor_info(int apicid, int version)
 {
         int cpu;
-        cpumask_t tmp_map;
 
         /*
          * Validate version
          */
         if (version == 0x0) {
                 pr_warning("BIOS bug, APIC version is 0 for CPU#%d! "
-                        "fixing up to 0x10. (tell your hw vendor)\n",
-                        version);
+                           "fixing up to 0x10. (tell your hw vendor)\n",
+                                version);
                 version = 0x10;
         }
         apic_version[apicid] = version;
 
-        if (num_processors >= NR_CPUS) {
-                pr_warning("WARNING: NR_CPUS limit of %i reached."
-                        "  Processor ignored.\n", NR_CPUS);
+        if (num_processors >= nr_cpu_ids) {
+                int max = nr_cpu_ids;
+                int thiscpu = max + disabled_cpus;
+
+                pr_warning(
+                        "ACPI: NR_CPUS/possible_cpus limit of %i reached."
+                        "  Processor %d/0x%x ignored.\n", max, thiscpu, apicid);
+
+                disabled_cpus++;
                 return;
         }
 
         num_processors++;
-        cpus_complement(tmp_map, cpu_present_map);
-        cpu = first_cpu(tmp_map);
+        cpu = cpumask_next_zero(-1, cpu_present_mask);
 
         physid_set(apicid, phys_cpu_present_map);
         if (apicid == boot_cpu_physical_apicid) {
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index be9466788043..1a9941b11150 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1252,6 +1252,15 @@ void __init native_smp_cpus_done(unsigned int max_cpus)
         check_nmi_watchdog();
 }
 
+static int __initdata setup_possible_cpus = -1;
+static int __init _setup_possible_cpus(char *str)
+{
+        get_option(&str, &setup_possible_cpus);
+        return 0;
+}
+early_param("possible_cpus", _setup_possible_cpus);
+
+
 /*
  * cpu_possible_map should be static, it cannot change as cpu's
  * are onlined, or offlined. The reason is per-cpu data-structures
@@ -1264,7 +1273,7 @@ void __init native_smp_cpus_done(unsigned int max_cpus)
  *
  * Three ways to find out the number of additional hotplug CPUs:
  * - If the BIOS specified disabled CPUs in ACPI/mptables use that.
- * - The user can overwrite it with additional_cpus=NUM
+ * - The user can overwrite it with possible_cpus=NUM
  * - Otherwise don't reserve additional CPUs.
  * We do this because additional CPUs waste a lot of memory.
  * -AK
@@ -1277,9 +1286,17 @@ __init void prefill_possible_map(void)
         if (!num_processors)
                 num_processors = 1;
 
-        possible = num_processors + disabled_cpus;
-        if (possible > NR_CPUS)
-                possible = NR_CPUS;
+        if (setup_possible_cpus == -1)
+                possible = num_processors + disabled_cpus;
+        else
+                possible = setup_possible_cpus;
+
+        if (possible > CONFIG_NR_CPUS) {
+                printk(KERN_WARNING
+                        "%d Processors exceeds NR_CPUS limit of %d\n",
+                        possible, CONFIG_NR_CPUS);
+                possible = CONFIG_NR_CPUS;
+        }
 
         printk(KERN_INFO "SMP: Allowing %d CPUs, %d hotplug CPUs\n",
                 possible, max_t(int, possible - num_processors, 0));