Re: [PATCH v3 10/10] KVM: selftests: Trigger L2->L1 exits stress save+restore and #PF test

[Sean Christopherson <seanjc@google.com>]

On Mon, Jul 27, 2026, Yosry Ahmed wrote:
> > > As I mentioned above, I prefer taking a dependency on
> > > KVM_CAP_EXCEPTION_PAYLOAD rather than varying coverage. At least for
> > > the nested case, I think I can move the TEST_REQUIRE() into the
> > > 'nested' case, but then it's probably better to leave it as an arg to
> > > allow for meaningfully running the test in L0.
> >
> > The problem is that TEST_REQUIRE() skips the whole test, regardless of when it's
> > called.  I.e. if you go that route, passes for the non-nested case will show up
> > as skips.  TEST_REQUIRE() really is intended to be used when something is a hard
> > requirement.
> >
> > > Actually, what if we just skip the nested case completely if
> > > KVM_CAP_EXCEPTION_PAYLOAD isn't available?
> >
> > Can you use KVM_NMI instead of KVM_SET_VCPU_EVENTS to effect the nested #VMEXIT?
> > That ioctl is so ancient that I'm a-ok skipping any CAP check for it.
> 
> Hmm actually I just realized I missed a CAP check for
> KVM_CAP_NESTED_STATE here. I don't think it's worth looking into
> dropping KVM_CAP_EXCEPTION_PAYLOAD, because we will need a CAP check
> anyway, and both of these were introduced very close in time (4.19 and
> 4.20, both 8 years ago).
> 
> So I think the simplest thing to do here is just run the nested test
> cases if both CAPs are available and skip it otherwise. Practically, I
> doubt there will be a lot of people running upstream selftests on
> <4.20 kernels for this to actually matter.

Yeah, works for me.