Re: [PATCH 3/3] KVM: nVMX: Clear IDT vectoring on nested VM-Exit for double/triple fault

[Xiaoyao Li]

On 4/7/2022 4:02 PM, Xiaoyao Li wrote:
> On 4/7/2022 8:23 AM, Sean Christopherson wrote:
> > Clear the IDT vectoring field in vmcs12 on next VM-Exit due to a double
> > or triple fault.  Per the SDM, a VM-Exit isn't considered to occur during
> > event delivery if the exit is due to an intercepted double fault or a
> > triple fault.  Opportunistically move the default clearing (no event
> > "pending") into the helper so that it's more obvious that KVM does indeed
> > handle this case.
> >
> > Note, the double fault case is worded rather wierdly in the SDM:
> >
> >    The original event results in a double-fault exception that causes the
> >    VM exit directly.
> >
> > Temporarily ignoring injected events, double faults can _only_ occur if
> > an exception occurs while attempting to deliver a different exception,
> > i.e. there's _always_ an original event.  And for injected double fault,
> > while there's no original event, injected events are never subject to
> > interception.
> >
> > Presumably the SDM is calling out that a the vectoring info will be valid
> > if a different exit occurs after a double fault, e.g. if a #PF occurs and
> > is intercepted while vectoring #DF, then the vectoring info will show the
> > double fault. 
>
> Wouldn't it be a tripe fault exit in this case?

It won't since #PF is intercepted by exception bitmap in your case.

> > In other words, the clause can simply be read as:
> >
> >    The VM exit is caused by a double-fault exception.