Wolfgang Mauerer wrote:
> Jan Kiszka wrote:
>> Wolfgang Mauerer wrote:
>>> Jan Kiszka wrote:
>>>> If we enter __ipipe_handle_exception over a non-root domain and leave it
>>>> due to migration in the event handler over root, we must not restore the
>>>> root domain state so far saved on entry. This caused subtle pipeline
>>>> state corruptions. Instead, only save and restore them if we were
>>>> entering over root.
>>>>
>>>> However, the x86-32 regs.flags fixup is required nevertheless to take
>>>> care of mismatches between the root domain state and the hardware flags
>>>> on entry. That may happen if we fault in the iret path. But also in this
>>>> case we must not restore an invalid root domain state. So if we entered
>>>> over non-root, pick up the input for __fixup_if from the root domain
>>>> after running the ipipe handler.
>>>>
>>>> Signed-off-by: Jan Kiszka <jan.kis...@siemens.com>
>>>> ---
>>>>
>>>> Next try. But this time I think I finally understood what scenario
>>>> __fixup_if is actually fixing. Please correct me if I'm still missing
>>>> one.
>>> looks good - it works for my test cases and solves the problems with
>>> the hw/pipeline state mismatch during early bootup. But do you happen
>>> to have any scenario at hand with ipipe_domain_root_p && !root_entry?
>>> Couldn't trigger this one yet so only the raw_irqs_disabled_flags
>>> fixup is excercised, though I guess it can't do any harm to really
>>> ensure that the explanation fits reality this time...
>> You mean non-root entry -> migration -> __fixup_if? In that case we pick
>> up the flags for fixup _after_ the migration (raw_irqs_disabled()). Or
>> what do you mean?
> 
> (...)
>>>> -  if (unlikely(!ipipe_root_domain_p)) {
>>>> +  if (likely(ipipe_root_domain_p)) {
>>>> +          /*
>>>> +           * 32-bit: In case we faulted in the iret path, regs.flags do
>>>> +           * not match the root domain state as the low-level return
>>>> +           * code will evaluate it. Fix this up, either by the root
>>>> +           * state sampled on entry or, if we migrated to root, with the
>>>> +           * current state.
>>>> +           */
>>>> +          __fixup_if(root_entry ? raw_irqs_disabled_flags(flags) :
>>>> +                                  raw_irqs_disabled(), regs);
> 
> I'm referring to the case that evaluates to
> __fixup_if(raw_irqs_disabled(), regs); That is, something that
> triggers
> 
>               if (!root_entry)
>                       do_something();
> 
> Could be that we're talking about to the same case, although I'm not
> sure ;-)

Right, that's the case I described above. What problem do you precisely
see or what concerns to you have about the suggested behavior?

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

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