x86: don't use P6_NOPs if compiling with CONFIG_X86_GENERIC

P6_NOPs are definitely not supported on some VIA CPUs, and possibly
(unverified) on AMD K7s.  It is also the only thing that prevents a
686 kernel from running on Transmeta TM3x00/5x00 (Crusoe) series.

The performance benefit over generic NOPs is very small, so when
building for generic consumption, avoid using them.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 10 insertions, 1 deletions

diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
index 86fd2a0e4597..6d50064db182 100644
--- a/arch/x86/Kconfig.cpu
+++ b/arch/x86/Kconfig.cpu
@@ -377,9 +377,18 @@ config X86_OOSTORE
         def_bool y
         depends on (MWINCHIP3D || MWINCHIP2 || MWINCHIPC6) && MTRR
 
+#
+# P6_NOPs are a relatively minor optimization that require a family >=
+# 6 processor, except that it is broken on certain VIA chips.
+# Furthermore, AMD chips prefer a totally different sequence of NOPs
+# (which work on all CPUs).  As a result, disallow these if we're
+# compiling X86_GENERIC but not X86_64 (these NOPs do work on all
+# x86-64 capable chips); the list of processors in the right-hand clause
+# are the cores that benefit from this optimization.
+#
 config X86_P6_NOP
         def_bool y
-        depends on (M686 || MPENTIUMII || MPENTIUMIII || MPENTIUMM || MCORE2 || PENTIUM4)
+        depends on (X86_64 || !X86_GENERIC) && (M686 || MPENTIUMII || MPENTIUMIII || MPENTIUMM || MCORE2 || PENTIUM4)
 
 config X86_TSC
         def_bool y