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

[Mark Burton]

> On 11 Feb 2015, at 04:33, Alex Bennée <address@hidden> wrote:
> 
> 
> Frederic Konrad <address@hidden> 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?
> 

thats exactly the question. 
Cheers
Mark.

> 
> 
>> 
>> Thanks,
>> Fred
> 
> -- 
> Alex Bennée


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        mark.burton