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

[Paolo Bonzini]

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.

Paolo