Re: [PATCH v4 12/12] KVM: selftests: Trigger L2->L1 exits stress save+restore and #PF test

On Mon, Jul 27, 2026 at 5:09 PM <[email protected]> wrote:
>
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] The test unconditionally enables `KVM_CAP_EXCEPTION_PAYLOAD` in `run_test()`, causing the test to crash on older kernels before reaching the capability check in `main()`.
> --
>
> --- Patch [12]: [PATCH v4 12/12] KVM: selftests: Trigger L2->L1 exits stress save+restore and #PF test ---
> commit 30592840747b18628e46af30e613a95b722da3cc
> Author: Yosry Ahmed <[email protected]>
>
> KVM: selftests: Trigger L2->L1 exits stress save+restore and #PF test
>
> This commit extends the testing coverage in L2 by forcing a nested VM-Exit
> from L2 to L1 right after restore on every other iteration. To force the
> nested VM-Exit, it injects a #UD into the saved vCPU state and intercepts
> #UD from L1.
>
> > diff --git a/tools/testing/selftests/kvm/x86/save_restore_pf_stress_test.c b/tools/testing/selftests/kvm/x86/save_restore_pf_stress_test.c
> > index 0e5ddeb5af444..ba1d723001e94 100644
> > --- a/tools/testing/selftests/kvm/x86/save_restore_pf_stress_test.c
> > +++ b/tools/testing/selftests/kvm/x86/save_restore_pf_stress_test.c
> [ ... ]
> > @@ -156,6 +178,7 @@ static void run_test(bool nested)
> >
> >       vm = vm_create_with_one_vcpu(&vcpu, nested ? l1_guest_code : guest_access_memory);
> >       vm_install_exception_handler(vm, PF_VECTOR, guest_pf_handler);
> > +     vm_enable_cap(vm, KVM_CAP_EXCEPTION_PAYLOAD, -2ul);
> >
> >       if (nested) {
> >               if (kvm_cpu_has(X86_FEATURE_SVM))
> [ ... ]
> > @@ -247,7 +278,9 @@ int main(int argc, char *argv[])
> >       pr_info("Running save+restore stress test...\n");
> >       run_test(/*nested=*/false);
> >
> > -     if (!kvm_cpu_has(X86_FEATURE_SVM) && !kvm_cpu_has(X86_FEATURE_VMX)) {
> > +     if (!kvm_has_cap(KVM_CAP_EXCEPTION_PAYLOAD) ||
> > +         !kvm_has_cap(KVM_CAP_NESTED_STATE) ||
> > +         (!kvm_cpu_has(X86_FEATURE_SVM) && !kvm_cpu_has(X86_FEATURE_VMX))) {
>
> [Severity: Medium]
> Will this test crash on older kernels that lack KVM_CAP_EXCEPTION_PAYLOAD?
>
> Because run_test(false) is called before this capability check in main(),
> run_test() will unconditionally call vm_enable_cap() for
> KVM_CAP_EXCEPTION_PAYLOAD.
>
> Could this prevent the test from gracefully skipping on environments without
> this capability?

Oh I missed this. Yeah we need to make enabling the CAP conditional on
nested=true.