[RFC/WIP] powerpc: Fix 32-bit handling of MSR_EE on exceptions

[Christophe Leroy]

Le 20/12/2018 à 23:35, Benjamin Herrenschmidt a écrit :
> 
>>>    /*
>>>     * MSR_KERNEL is > 0x10000 on 4xx/Book-E since it include MSR_CE.
>>> @@ -205,20 +208,46 @@ transfer_to_handler_cont:
>>>    	mflr	r9
>>>    	lwz	r11,0(r9)		/* virtual address of handler */
>>>    	lwz	r9,4(r9)		/* where to go when done */
>>> +#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PERF_EVENTS)
>>> +	mtspr	SPRN_NRI, r0
>>> +#endif
>>
>> That's not part of your patch, it's already in the tree.
> 
> Yup rebase glitch.
> 
>   .../...
> 
>> I tested it on the 8xx with the below changes in addition. No issue seen
>> so far.
> 
> Thanks !
> 
> I'll merge that in.

I'm currently working on a refactorisation and simplification of
exception and syscall entry on ppc32.

I plan to take your patch in my serie as it helps quite a bit. I hope 
you don't mind. I expect to come out with a series this week.

> 
> The main obscure area is that business with the irqsoff tracer and thus
> the need to create stack frames around calls to trace_hardirqs_* ... we
> do it in some places and not others, but I've not managed to make it
> crash either. I need to get to the bottom of that, and possibly provide
> proper macro helpers like ppc64 has to do it.

I can't see anything special around this in ppc32 code. As far as I 
understand, a stack frame is put in place when there is a need to
save and restore some volatile registers. At the places where nothing 
needs to be saved, nothing is done. I think that's the normal way for 
any function call, isn't it ?

Christophe