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>

1 files changed, 21 insertions, 4 deletions

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));