Re: [PATCH 5/8] KVM: SVM: Re-inject INT3/INTO instead of retrying the instruction

Sean Christopherson
2022-04-04T21:49:48Z

On Mon, Apr 04, 2022, Maciej S. Szmigiero wrote:
> > > > index 47e7427d0395..a770a1c7ddd2 100644
> > > > --- a/arch/x86/kvm/svm/svm.h
> > > > +++ b/arch/x86/kvm/svm/svm.h
> > > > @@ -230,8 +230,8 @@ struct vcpu_svm {
> > > > bool nmi_singlestep;
> > > > u64 nmi_singlestep_guest_rflags;
> > > > - unsigned int3_injected;
> > > > - unsigned long int3_rip;
> > > > + unsigned soft_int_injected;
> > > > + unsigned long soft_int_linear_rip;
> > > > /* optional nested SVM features that are enabled for this guest */
> > > > bool nrips_enabled : 1;
> > >
> > >
> > > I mostly agree with this patch, but think that it doesn't address the
> > > original issue that Maciej wanted to address:
> > >
> > > Suppose that there is *no* instruction in L2 code which caused the software
> > > exception, but rather L1 set arbitrary next_rip, and set EVENTINJ to software
> > > exception with some vector, and that injection got interrupted.
> > >
> > > I don't think that this code will support this.
> >
> > Argh, you're right. Maciej's selftest injects without an instruction, but it doesn't
> > configure the scenario where that injection fails due to an exception+VM-Exit that
> > isn't intercepted by L1 and is handled by L0. The event_inj test gets the coverage
> > for the latter, but always has a backing instruction.
>
> Still reviewing the whole patch set, but want to clear this point quickly:
> The selftest does have an implicit intervening NPF (handled by L0) while
> injecting the first L1 -> L2 event.

I'll do some debug to figure out why the test passes for me. I'm guessing I either
got lucky, e.g. IDT was faulted in already, or I screwed up and the test doesn't
actually pass.