Re: [Qemu-devel] [PATCH v2 3/3] target-ppc: tlbie should have global effect

[Nikunj A Dadhania]

Benjamin Herrenschmidt <address@hidden> writes:

> On Fri, 2016-09-09 at 18:44 +0530, Nikunj A Dadhania wrote:
>> +static inline void tlb_clear_flag(CPUState *cs)
>> +{
>> +    PowerPCCPU *cpu = POWERPC_CPU(cs);
>> +    CPUPPCState *env = &cpu->env;
>> +
>> +    env->tlb_need_flush = 0;
>> +}
>
> What is the point of making this a separate function ?

When I wrote, i thought this would be used from various places. But dont
think its a requirement. Will inline it.

> Also I'm not 100% certain about the correctness of clearing
> TLB_NEED_GLOBAL_FLUSH on the "other" guy.
>
> We could have the situation where:
>
>       cpu 1:                                  cpu 2:
>       sets both                               ..
>       isync (clears local flush)              ..
>       <insert new translation>
>       ..                                      set both
>       ..                                      ..
>       ..                                      ..
>       ptesync (clears global flush)           .. (both gets cleared)
>
> Now here, you can see that cpu2 never does a global flush and so the
> new translation inserted by cpu 1 is not cleared while architecturally
> it should be.

Right, will only clear the local flag.

> That being said, I doubt the above scenario can happen in practice,
> but I think it's safer if you only clear the local bit on the "other"
> CPUs.

Regards,
Nikunj