x86: more than 8 32-bit CPUs requires X86_BIGSMP

[Michael K. Johnson]

$ cat x86-more-than-8-cpus-requires-bigsmp.patch

Enforce NR_CPUS <= 8 limitation if X86_BIGSMP not set

Configuring more than 8 logical CPUs on 32-bit x86 requires
X86_BIGSMP to be set in order to boot successfully, if more than 8
logical CPUs are actually found at boot time.  The X86_BIGSMP help
text describes that it is required to be set if more than 8 CPUs
are configured, but this was previously not enforced.

This configuration error has affected multiple distributions:
    https://bugzilla.redhat.com/show_bug.cgi?id=480844
    https://issues.rpath.com/browse/RPL-3022

Signed-off-by: Michael K Johnson <johnsonm@xxxxxxxxx>

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index c9086e6..cdad0d9 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -664,6 +664,7 @@ 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
 	default "1" if !SMP
 	default "4096" if MAXSMP
--
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