Re: [PATCH] KVM: VMX: Fix race between pending IRQ and NMI

[Jan Kiszka <jan.kiszka@siemens.com>]

Avi Kivity wrote:
> Jan Kiszka wrote:
>>>>> But I think I see a bigger issue - if we inject an regular interrupt
>>>>> while another is pending, then we will encounter this problem.  Looks
>>>>> like we have to enable the interrupt window after injecting an
>>>>> interrupt
>>>>> if there are still pending interrupts.
>>>>>             
>>>> Yeah, probably. I'm just wondering now if we can set
>>>> exit-on-interrupt-window while the vcpu state is interruptible (ie.
>>>> _before_ the injection). There is some entry check like this for NMIs,
>>>> but maybe no for interrupts. Need to check.
>>>>         
>>> Turns out it's not necessary, since the guest eoi will cause an exit and
>>> allow the code to request an interrupt window.
>>>     
>>
>> But you added explicit handling now nevertheless?
>>   
> 
> Yes, in case some eoi-less mode is introduced either by hardware or
> paravirt.  I regard the fact that it works as accidental (though applies
> to  x86 virtualization in general).
> 
>>> I've added an apic test program so we can track these issues
>>> (user/test/x86/apic.c).
>>>
>>>     
>>
>> That's good. BTW, your NMI race fix is still lacking support for the
>> -no-kvm-irqchip case. Will post an according patch later today.
>>   
> 
> Actually, I couldn't get the 5.2 guest to boot with -no-kvm-irqchip: it
> hangs and needs some help by running 'info registers'.

Oh, yes, someone borked something here. That must have happened just
recently I think. And it must be a userspace bug as some older kvm that
happened to hang around here (-74) works fine against latest kernel. No
time to investigate further right now, sorry.

Jan

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