On Oct 23, 2013, at 5:15 AM, Scott Wood wrote:
> On Wed, 2013-10-23 at 00:07 -0500, Kumar Gala wrote:
>> On Oct 18, 2013, at 2:38 AM, Wolfgang Denk wrote:
>>> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
>>> 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)
>>> return 0;
>>> }
>>>
>>> + /* Emulating the lwsync insn as a sync insn */
>>> + if (instword == PPC_INST_LWSYNC) {
>>> + PPC_WARN_EMULATED(lwsync, regs);
>>> + asm volatile("sync" : : : "memory");
>>
>> Do we really need the inline asm? Doesn't the fact of just taking an
>> exception and returning from it equate to a sync.
>
> No, it doesn't equate to a sync. See the discussion here:
> http://patchwork.ozlabs.org/patch/256747/
>
Thanks.
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
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