x86/Kconfig: Enforce limit of 512 CPUs with MAXSMP and no CPUMASK_OFFSTACK

The help text of NR_CPUS says that the maximum number of CPUs supported
without CPUMASK_OFFSTACK is 512. However, NR_CPUS_RANGE_END allows this
limit to be bypassed by MAXSMP even if CPUMASK_OFFSTACK is not set.

This scenario can currently only happen in the RT tree, since it has
"select CPUMASK_OFFSTACK if !PREEMPT_RT_FULL" in MAXSMP. However,
even if we ignore the RT tree, checking for MAXSMP in addition to
CPUMASK_OFFSTACK is redundant.

Signed-off-by: Scott Wood <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Mike Travis <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: x86-ml <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

Author: crwood-rh

arch/x86/Kconfig

@@ -1000,8 +1000,8 @@ config NR_CPUS_RANGE_END
 config NR_CPUS_RANGE_END
 	int
 	depends on X86_64
-	default 8192 if  SMP && ( MAXSMP ||  CPUMASK_OFFSTACK)
-	default  512 if  SMP && (!MAXSMP && !CPUMASK_OFFSTACK)
+	default 8192 if  SMP && CPUMASK_OFFSTACK
+	default  512 if  SMP && !CPUMASK_OFFSTACK
 	default    1 if !SMP
 
 config NR_CPUS_DEFAULT