Re: [Xen-devel] [PATCH] x86/nmi: Make external NMI injection reliably crash the host

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 26.08.14 at 17:26, <ross.lagerwall@xxxxxxxxxx> wrote:
> On 08/26/2014 01:59 PM, Jan Beulich wrote:
>>>>> On 26.08.14 at 12:10, <ross.lagerwall@xxxxxxxxxx> wrote:
>>> @@ -3323,7 +3323,7 @@ void do_nmi(const struct cpu_user_regs *regs)
>>>               pci_serr_error(regs);
>>>           if ( reason & 0x40 )
>>>               io_check_error(regs);
>>> -        if ( !(reason & 0xc0) && !nmi_watchdog )
>>> +        if ( !(reason & 0xc0) )
>>>               unknown_nmi_error(regs, reason);
>>
>> As much as I like the original idea, I'm afraid this won't fly: I do
>> know of systems where bad motherboard design leads to neither
>> of these two bits ever getting set. I.e. at the very minimum we'd
>> need a command line option to restore old behavior. Personally I
>> think it should in fact remain default behavior, and new behavior
>> should only be enabled via command line option.
> 
> Well the old behavior was different depending on whether the watchdog 
> was enabled or not. Since the watchdog was disabled by default, that's 
> no different from the behavior here.
> 
> So are you thinking something like an ignore_unknown_nmi boolean 
> parameter that defaults to true?

More like a "watchdog=force" one, but right, since the watchdog
isn't being enabled by default, maybe making it an opt-out instead
of opt-in would indeed be acceptable.

Jan


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