[PATCH] [RFC] Emulate "lwsync" to run standard user land on e500 cores

[Kumar Gala]

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