Re: [Qemu-devel] CPU TLB flush with multithread TCG.

["Alex Bennée" <alex.bennee@linaro.org>]

Frederic Konrad <fred.konrad@greensocs.com> writes:

> Hi everybody,
>
> In multithread tlb_flush is broken as CPUA can flush an other CPUB and 
> CPUB can be
> executing code, and fixing this can be quite hard:
>    * We need to exit the CPU which is flushed.
>    * Makes sure the CPU is stopped.
>    * Then we can flush tlb.
> The big issues are:
>    * Two threads can be doing a flush at the same time.
>    * Something can restart the CPU during the flush.
>
> A better idea I think is that instead of flushing tlb we can put a flag 
> in CPUState such
> as flush_request and ask the cpu to exit.
> Then later once the CPU is exited we can flush tlbs if flush_request is set.
> It will ensure that the CPU won't execute code as it's associated thread 
> will be
> flushing.
>
> Can this work?

Does this imply deferring the work? Surely if we don't flush when
instructed things could break down very quickly?



>
> Thanks,
> Fred

-- 
Alex Bennée