On Oct 23, 2013, at 5:15 AM, Scott Wood wrote:

On Wed, 2013-10-23 at 00:07 -0500, Kumar Gala wrote:

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On Oct 18, 2013, at 2:38 AM, Wolfgang Denk wrote:

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diff --git a/arch/powerpc/kernel/traps.c =

b/arch/powerpc/kernel/traps.c

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index f783c93..f330374 100644

--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c

@@ -986,6 +986,13 @@ static int emulate_instruction(struct pt_regs =

*regs)

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		return 0;
	}
=20
+	/* Emulating the lwsync insn as a sync insn */
+	if (instword =3D=3D PPC_INST_LWSYNC) {
+		PPC_WARN_EMULATED(lwsync, regs);
+		asm volatile("sync" : : : "memory");

=20
Do we really need the inline asm?  Doesn't the fact of just taking an =

exception and returning from it equate to a sync.

=20
No, it doesn't equate to a sync.  See the discussion here:
http://patchwork.ozlabs.org/patch/256747/
=20

Thanks.=20

I'm not sure I'm a fan of doing this as it silently hides a significant =
performance impact.

Could we possible re-write the userspace instruction to be a 'sync' when =
we hit this?

- k