On 11/05/2016 15:36, Sergey Fedorov wrote:
> On 11/05/16 15:58, Paolo Bonzini wrote:
>>
>> On 06/05/2016 20:22, Sergey Fedorov wrote:
>>> However, there's no sensible description of what is protected by tb_lock
>>> and mmap_lock. I think we need to have a clear documented description of
>>> the TCG locking scheme in order to be sure we do right things in MTTCG.
>> I think there was such a patch somewhere, but: tb_lock basically
>> protects tcg_ctx, while mmap_lock protects the user-mode emulation page
>> table (the equivalent for system emulation is the memory map which is
>> protected by the BQL). Furthermore, mmap_lock must be taken outside
>> tb_lock.
>
> What's a user-mode emulation page table? 'l1_map'?
Yes. It's used beyond TCG in user-mode emulation.
> It is used by system
> emulation to keep track of TBs per page and 'code_bitmap'. Shouldn't it
> be protected with 'mmap_lock' in system emulation?
tb_lock is used instead because it's taken everywhere system emulation
uses l1_map; so tb_lock is protecting l1_map too in system emulation.
As mentioned above, user-mode emulation uses l1_map in linux-user/mmap.c
via page_{get,set}_flags, which I guess is why the lock is separate.
None of us was involved in the original multi-threaded linux-user work,
we're reverse engineering it just like you. :)
Thanks,
Paolo
