Re: [RESEND PATCH 5/6] KVM: x86/VMX: add kvm_vmx_reinject_nmi_irq() for NMI/IRQ reinjection

Peter Zijlstra
2022-11-14T09:09:41Z

On Mon, Nov 14, 2022 at 04:39:40AM +0000, Li, Xin3 wrote:

> > But what about NMIs, afaict this is all horribly broken for NMIs.
> >
> > So the whole VMX thing latches the NMI (which stops NMI recursion), right?
> >
> > But then you drop out of noinstr code, which means any random exception can
> > happen (kprobes #BP, hw_breakpoint #DB, or even #PF due to random
> > nonsense like *SAN). This exception will do IRET and clear the NMI latch, all
> > before you get to run any of the NMI code.
>
> What you said here implies that we have this problem in the existing code.
> Because a fake iret stack is created to call the NMI handler in the IDT NMI
> descriptor, which lastly executes the IRET instruction.

I can't follow; of course the IDT handler terminates with IRET, it has
to no?

And yes, the current code appears to suffer the same defect.