5 files changed, 28 insertions, 7 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 736d45602886..51bceb0fb277 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1772,6 +1772,12 @@ and is between 256 and 4096 characters. It is defined in the file
                         purges which is reported from either PAL_VM_SUMMARY or
                         SAL PALO.
 
+        nr_cpus=        [SMP] Maximum number of processors that an SMP kernel
+                        could support.  nr_cpus=n : n >= 1 limits the kernel to
+                        supporting 'n' processors. Later in runtime you can not
+                        use hotplug cpu feature to put more cpu back to online.
+                        just like you compile the kernel NR_CPUS=n
+
         nr_uarts=       [SERIAL] maximum number of UARTs to be registered.
 
         numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
diff --git a/arch/ia64/kernel/acpi.c b/arch/ia64/kernel/acpi.c
index 40574ae11401..605a08b29721 100644
--- a/arch/ia64/kernel/acpi.c
+++ b/arch/ia64/kernel/acpi.c
@@ -881,8 +881,8 @@ __init void prefill_possible_map(void)
 
         possible = available_cpus + additional_cpus;
 
-        if (possible > NR_CPUS)
-                possible = NR_CPUS;
+        if (possible > nr_cpu_ids)
+                possible = nr_cpu_ids;
 
         printk(KERN_INFO "SMP: Allowing %d CPUs, %d hotplug CPUs\n",
                 possible, max((possible - available_cpus), 0));
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 678d0b8c26f3..eff2fe175422 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1213,11 +1213,12 @@ __init void prefill_possible_map(void)
 
         total_cpus = max_t(int, possible, num_processors + disabled_cpus);
 
-        if (possible > CONFIG_NR_CPUS) {
+        /* nr_cpu_ids could be reduced via nr_cpus= */
+        if (possible > nr_cpu_ids) {
                 printk(KERN_WARNING
                         "%d Processors exceeds NR_CPUS limit of %d\n",
-                        possible, CONFIG_NR_CPUS);
-                possible = CONFIG_NR_CPUS;
+                        possible, nr_cpu_ids);
+                possible = nr_cpu_ids;
         }
 
         printk(KERN_INFO "SMP: Allowing %d CPUs, %d hotplug CPUs\n",
diff --git a/drivers/acpi/numa.c b/drivers/acpi/numa.c
index 7ad48dfc12db..b8725461d887 100644
--- a/drivers/acpi/numa.c
+++ b/drivers/acpi/numa.c
@@ -279,9 +279,9 @@ int __init acpi_numa_init(void)
         /* SRAT: Static Resource Affinity Table */
         if (!acpi_table_parse(ACPI_SIG_SRAT, acpi_parse_srat)) {
                 acpi_table_parse_srat(ACPI_SRAT_TYPE_X2APIC_CPU_AFFINITY,
-                                      acpi_parse_x2apic_affinity, NR_CPUS);
+                                     acpi_parse_x2apic_affinity, nr_cpu_ids);
                 acpi_table_parse_srat(ACPI_SRAT_TYPE_CPU_AFFINITY,
-                                      acpi_parse_processor_affinity, NR_CPUS);
+                                     acpi_parse_processor_affinity, nr_cpu_ids);
                 ret = acpi_table_parse_srat(ACPI_SRAT_TYPE_MEMORY_AFFINITY,
                                             acpi_parse_memory_affinity,
                                             NR_NODE_MEMBLKS);
diff --git a/init/main.c b/init/main.c
index 845187822e5c..05b5283e98fa 100644
--- a/init/main.c
+++ b/init/main.c
@@ -149,6 +149,20 @@ static int __init nosmp(char *str)
 
 early_param("nosmp", nosmp);
 
+/* this is hard limit */
+static int __init nrcpus(char *str)
+{
+        int nr_cpus;
+
+        get_option(&str, &nr_cpus);
+        if (nr_cpus > 0 && nr_cpus < nr_cpu_ids)
+                nr_cpu_ids = nr_cpus;
+
+        return 0;
+}
+
+early_param("nr_cpus", nrcpus);
+
 static int __init maxcpus(char *str)
 {
         get_option(&str, &setup_max_cpus);