x86: Side-step lguest problem by only building cmpxchg8b_emu for pre-Pentium

Commit 79e1dd05d1a22 "x86: Provide an alternative() based
cmpxchg64()" broke lguest, even on systems which have cmpxchg8b
support.  The emulation code gets used until alternatives get
run, but it contains native instructions, not their paravirt
alternatives.

The simplest fix is to turn this code off except for 386 and 486
builds.

Reported-by: Johannes Stezenbach <js@sig21.net>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Cc: lguest@ozlabs.org
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <200910261426.05769.rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
index f2824fb8c79cad23ad747977e1e32ab4d6b555a1..2649840d888ffeac6fe8ec6b77f73a599ed73ee1 100644 (file)
--- a/arch/x86/Kconfig.cpu
+++ b/arch/x86/Kconfig.cpu
@@ -400,7 +400,7 @@ config X86_TSC
 
 config X86_CMPXCHG64
        def_bool y
-       depends on X86_PAE || X86_64 || MCORE2 || MPENTIUM4 || MPENTIUMM || MPENTIUMIII || MPENTIUMII || M686 || MATOM
+       depends on !M386 && !M486
 
 # this should be set for all -march=.. options where the compiler
 # generates cmov.