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

[sashiko-bot@kernel.org]

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 <yosry@kernel.org>

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?

>  		pr_info("Nested virtualization not supported, skipping nested test\n");
>  		return 0;
>  	}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260727235228.1007324-1-yosry@kernel.org?part=12