x86/cpu: Allow higher NR_CPUS values

The current range for SMP configs is 2 - 512 CPUs, or a full
4096 in the case of MAXSMP.  There are machines that have 1024
CPUs in them today and configuring a kernel for that means you
are forced to set MAXSMP.  This adds additional unnecessary
overhead.  While that overhead might be considered tiny for
large machines, it isn't necessarily so if you are building a
kernel that runs across a wide variety of machines.

To cover the range of more common machines today, we allow
NR_CPUS to be up to 4096 when CPUMASK_OFFSTACK is enabled.

Signed-off-by: Josh Boyer <[email protected]>
Cc: [email protected]
Cc: Russ Anderson <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Andrew Morton <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

arch/x86/Kconfig

@@ -825,14 +825,16 @@ config MAXSMP
 config NR_CPUS
 	int "Maximum number of CPUs" if SMP && !MAXSMP
 	range 2 8 if SMP && X86_32 && !X86_BIGSMP
-	range 2 512 if SMP && !MAXSMP
+	range 2 512 if SMP && !MAXSMP && !CPUMASK_OFFSTACK
+	range 2 4096 if SMP && !MAXSMP && CPUMASK_OFFSTACK && X86_64
 	default "1" if !SMP
 	default "4096" if MAXSMP
 	default "32" if SMP && (X86_NUMAQ || X86_SUMMIT || X86_BIGSMP || X86_ES7000)
 	default "8" if SMP
 	---help---
 	  This allows you to specify the maximum number of CPUs which this
-	  kernel will support.  The maximum supported value is 512 and the
+	  kernel will support.  If CPUMASK_OFFSTACK is enabled, the maximum
+	  supported value is 4096, otherwise the maximum value is 512.  The
 	  minimum value which makes sense is 2.
 
 	  This is purely to save memory - each supported CPU adds