Re: VMX: Host NMI triggering on NMI vmexit

[Jan Kiszka <jan.kiszka@web.de>]

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Avi Kivity wrote:
> Jan Kiszka wrote:
>> Sheng,
>>
>> out of curiosity: vmx_vcpu_run invokes 'int $2' to trigger a host NMI if
>> the VM exited due to an external NMI event. According to Intel specs I
>> have, software-triggered NMIs do not block hardware NMIs. So are we
>> facing the risk to receive another NMI while running the first handler?
>> Or will the VM be left with the hardware blocking logic armed? Or does
>> Linux not care about NMI handler re-entrance?
>>   
> 
> All good questions.  Usually this doesn't happen since NMI sources are
> far apart (oprofile, watchdog).

Only true until you have multiple unsynchronized NMI sources, e.g.
inter-CPU NMIs of kgdb + a watchdog. I just stumbled over several bugs
in kvm's and my own NMI code that were triggered by such a scenario
(sigh...).

> 
> Maybe the answer is to generate the local nmi via an IPI-to-self command
> to the local apic.
> 

That sounds like a good idea, will look into this right after fixing the
other NMI issues.

Jan


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