Re: [PATCH v2 03/28] KVM: selftests: Test address translation for Hyper-V direct L2 hypercalls

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] selftests/kvm: assertion failure in hyperv_evmcs test due to redundant vm_enable_ept()
--

commit 3101456ba54ccd614ac31b337348b4588da927e6
Author: Paolo Bonzini <pbonzini@redhat.com>

KVM: selftests: Test address translation for Hyper-V direct L2 hypercalls
    
Test that the TLB flush hypercalls, when executed by L2, translate their
input addresses through the guest's EPT or NPT.

> diff --git a/tools/testing/selftests/kvm/x86/hyperv_evmcs.c b/tools/testing/selftests/kvm/x86/hyperv_evmcs.c
> index 63ea1533e4ead..fa80bc78aef70 100644
> --- a/tools/testing/selftests/kvm/x86/hyperv_evmcs.c
> +++ b/tools/testing/selftests/kvm/x86/hyperv_evmcs.c

[ ... ]

> @@ -212,6 +216,7 @@ static struct kvm_vcpu *save_restore_vm(struct kvm_vm *vm,
>  
>  	/* Restore state in a new VM.  */
>  	vcpu = vm_recreate_with_one_vcpu(vm);
> +	vm_enable_ept(vm);

[Severity: Medium]
Does this redundant vm_enable_ept() call cause an assertion failure?

The hyperv_evmcs test periodically simulates live migration by calling
save_restore_vm(). This function calls vm_recreate_with_one_vcpu(), which
recreates the vCPU but preserves the existing kvm_vm object and its
initialized stage2_mmu configuration.

Calling vm_enable_ept(vm) here delegates to tdp_mmu_init(). Since
tdp_mmu_init() expects to run only once per VM, it checks:

    TEST_ASSERT(!vm->stage2_mmu.pgtable_levels, "TDP MMU already initialized");

Because pgtable_levels was already set to 4 during the initial
vm_enable_ept(vm) call in main(), this assertion fails, crashing the test
unconditionally on the very first live migration cycle.

>  	vcpu_set_hv_cpuid(vcpu);
>  	vcpu_enable_evmcs(vcpu);
>  	vcpu_load_state(vcpu, state);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260918081543.139871-1-pbonzini@redhat.com?part=3