Re: [RFC] x86, NMI, Treat unknown NMI as hardware error

[Huang Ying <ying.huang@intel.com>]

On 05/17/2011 04:53 PM, Ingo Molnar wrote:
> 
> * Huang Ying <ying.huang@intel.com> wrote:
> 
>> On 05/16/2011 07:29 PM, Ingo Molnar wrote:
>>>
>>> * Don Zickus <dzickus@redhat.com> wrote:
>>>
>>>> On Fri, May 13, 2011 at 05:20:33PM +0200, Ingo Molnar wrote:
>>>>>
>>>>> * huang ying <huang.ying.caritas@gmail.com> wrote:
>>>>>
>>>>>>> What should be done instead is to add an event for unknown NMIs, which can 
>>>>>>> then be processed by the RAS daemon to implement policy.
>>>>>>>
>>>>>>> By using 'active' event filters it could even be set on a system to panic 
>>>>>>> the box by default.
>>>>>>
>>>>>> If there is real fatal hardware error, maybe we have no luxury to go from NMI 
>>>>>> handler to user space RAS daemon to determine what to do. System may explode, 
>>>>>> bad data may go to disk before that.
>>>>>
>>>>> That is why i suggested:
>>>>>
>>>>>   > > By using 'active' event filters it could even be set on a system to panic 
>>>>>   > > the box by default.
>>>>>
>>>>> event filters are evaluated in the kernel, so the panic could be instantaneous, 
>>>>> without the event having to reach user-space.
>>>>
>>>> Interesting.  Question though, what do you mean by 'event filtering'.  Is 
>>>> that different then setting 'unknown_nmi_panic' panic on the commandline or 
>>>> procfs?
>>>>
>>>> Or are you suggesting something like registering another callback on the 
>>>> die_chain that looks for DIE_NMIUNKNOWN as the event, swallows them and 
>>>> implements the policy?  That way only on HEST related platforms would 
>>>> register them while others would keep the default of 'Dazed and confused' 
>>>> messages?
>>>
>>> The idea is that "event filters", which are an existing upstream feature and 
>>> which can be used in rather flexible ways:
>>>
>>>   http://lkml.org/lkml/2011/4/27/660
>>>
>>> Could be used to trigger non-standard policy action as well - such as to panic 
>>> the box.
>>>
>>> This would replace various very limited /debugfs and /sys event filtering hacks 
>>> (and hardcoded policies) such as arch/x86/kernel/cpu/mcheck/mce-severity.c, and 
>>> it would allow nonstandard behavior like 'panic the box on unknown NMIs' as 
>>> well.
>>>
>>> This could be set by the RAS daemon, and it could be propagated to the kernel 
>>> boot line as well, where event filter syntax would look like this:
>>>
>>>   events=nmi::unknown"if (reason == 0) panic();"
>>>
>>> (Where the 'reason' field of the NMI event is the current legacy 'reason' value 
>>> there.)
>>>
>>> The filter code would have to be modified to be able to recognize the panic() 
>>> bit, but that's desirable anyway and it is a one-time effort.
>>>
>>> This:
>>>
>>>   events=nmi::unknown:"if (reason == 0) ignore();"
>>>
>>> would be a possible outcome as well, on certain boxes - to skip certain events.
>>
>> We can determine whether NMI is unknown in kernel now.  If you want to push 
>> all unknown NMI logic into user space (although I don't think that is the 
>> best solution), is it not sufficient that just check system in user space 
>> (via PCI ID or DMI ID, etc) and set existing "unknown_nmi_panic" accordingly?
> 
> yeah - no need to push the 'reason' if it's not needed.
> 
> We want the kernel defaults to be sane - i.e. this is not to 'push' anything to 
> user-space in a forced way, this is to make *optional*, different policy action 
> possible to configure.

OK.  Then, what is the proper default behavior?  We think Linux kernel
should treat unknown NMI as hardware error reporting, at least on some
modern machines (via a white list).  Do you agree?

Best Regards,
Huang Ying