Re: [PATCH] KVM/VMX: Invoke NMI non-IST entry instead of IST entry

[Thomas Gleixner]

On Tue, May 04 2021 at 23:56, Paolo Bonzini wrote:
> On 04/05/21 23:51, Sean Christopherson wrote:
>> On Tue, May 04, 2021, Paolo Bonzini wrote:
>>> On 04/05/21 23:23, Andy Lutomirski wrote:
>>>>> On May 4, 2021, at 2:21 PM, Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>>>>> FWIW, NMIs are masked if the VM-Exit was due to an NMI.
>>>
>>> Huh, indeed:  "An NMI causes subsequent NMIs to be blocked, but only after
>>> the VM exit completes".
>>>
>>>> Then this whole change is busted, since nothing will unmask NMIs. Revert it?
>>> Looks like the easiest way out indeed.
>> 
>> I've no objection to reverting to intn, but what does reverting versus handling
>> NMI on the kernel stack have to do with NMIs being blocked on VM-Exit due to NMI?
>> I'm struggling mightily to connect the dots.
>
> Nah, you're right: vmx_do_interrupt_nmi_irqoff will not call the handler 
> directly, rather it calls the IDT entrypoint which *will* do an IRET and 
> unmask NMIs.  I trusted Andy too much on this one. :)
>
> Thomas's posted patch ("[PATCH] KVM/VMX: Invoke NMI non-IST entry 
> instead of IST entry") looks good.

Well, looks good is one thing.

It would be more helpful if someone would actually review and/or test it.

Thanks,

        tglx