Commit ae1b22f6 authored Oct 26, 2009 by Rusty Russell Committed by Ingo Molnar Oct 26, 2009

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



Commit 79e1dd05 "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>

parent 14a3f40a

arch/x86/Kconfig.cpu

+1 −1

Original line number	Diff line number	Diff line
		@@ -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.