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Date:	Mon, 26 Oct 2009 11:38:46 GMT
From:	tip-bot for Rusty Russell <>
Subject: [tip:x86/urgent] x86: Side-step lguest problem by only building cmpxchg8b_emu for pre-Pentium

Commit-ID:  ae1b22f6e46c03cede7cea234d0bf2253b4261cf
Author:     Rusty Russell <>
AuthorDate: Mon, 26 Oct 2009 14:26:04 +1030
Committer:  Ingo Molnar <>
CommitDate: Mon, 26 Oct 2009 12:33:02 +0100

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

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

Reported-by: Johannes Stezenbach <>
Signed-off-by: Rusty Russell <>
Acked-by: H. Peter Anvin <>
Cc: Arjan van de Ven <>
Cc: Jeremy Fitzhardinge <>
Cc: Linus Torvalds <>
LKML-Reference: <>
Signed-off-by: Ingo Molnar <>
 arch/x86/Kconfig.cpu |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
index f2824fb..2649840 100644
--- 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.
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