Re: [PATCH 8/8] KVM: selftests: Add nested pre-fault test for arm64

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Thu, Sep 10, 2026 at 07:57:03PM +0100, Fuad Tabba wrote:
> Hi,
>
> On Tue, 25 Aug 2026 at 17:02, Lorenzo Stoakes (ARM) <ljs@kernel.org> wrote:
> ..
> > +int main(void)
> > +{
> > +       struct nested_s2_state s2;
> > +       struct kvm_vcpu_init init;
> > +       struct kvm_vcpu *vcpu;
> > +       struct kvm_vm *vm;
> > +       struct ucall uc;
> > +       u64 npages;
> > +
> > +       TEST_REQUIRE(kvm_check_cap(KVM_CAP_ARM_EL2));
>
> Would test_supports_el2() work better here? It honours the NV=0
> opt-out, and since HAS_EL2 is set unconditionally below, NV=0 doesn't
> disable this test as things stand.

That sounds sensible :) Will fix on respin.

>
> Cheers,
> /fuad
>
> > +       TEST_REQUIRE(kvm_check_cap(KVM_CAP_PRE_FAULT_MEMORY));
> > +
> > +       vm = vm_create(1);
> > +
> > +       kvm_get_default_vcpu_target(vm, &init);
> > +       init.features[0] |= BIT(KVM_ARM_VCPU_HAS_EL2);
> > +       vcpu = aarch64_vcpu_add(vm, 0, &init, guest_code);
> > +       kvm_arch_vm_finalize_vcpus(vm);
> > +
> > +       npages = TEST_MEM_SIZE / vm->page_size;
> > +       vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS, TEST_MEM_GPA,
> > +                                   TEST_MEM_SLOT, npages, 0);
> > +       virt_map(vm, TEST_MEM_GPA, TEST_MEM_GPA, npages);
> > +
> > +       vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS,
> > +                                   NESTED_S2_ROOT_GPA, NESTED_S2_ROOT_SLOT,
> > +                                   vm_adjust_num_guest_pages(vm->mode, 1), 0);
> > +
> > +       /* Run the guest until it has ERET'd from vEL2 to vEL1. */
> > +       vcpu_run(vcpu);
> > +       switch (get_ucall(vcpu, &uc)) {
> > +       case UCALL_SYNC:
> > +               TEST_ASSERT_EQ(uc.args[1], 1);
> > +               break;
> > +       case UCALL_ABORT:
> > +               REPORT_GUEST_ASSERT(uc);
> > +               break;
> > +       default:
> > +               TEST_FAIL("Unhandled ucall: %ld", uc.cmd);
> > +       }
> > +
> > +       /*
> > +        * The vCPU's last-run context is vEL1, backed by a shadow stage-2
> > +        * MMU. Enable nested stage-2 with an empty root so that the ioctl
> > +        * fails if it tries to interpret the userspace GPA as an L2 IPA.
> > +        *
> > +        * Prefault in two halves so that the second ioctl exercises a
> > +        * repeated shadow-MMU attach and canonical stage-2 swap.
> > +        *
> > +        * (Note that an implementation that wrongly populates shadow
> > +        * stage-2 page tables would not be caught as userland can't
> > +        * inspect these.)
> > +        */
> > +       s2 = enable_empty_nested_s2(vcpu);
> > +       pre_fault(vcpu, TEST_MEM_GPA, TEST_MEM_SIZE / 2);
> > +       pre_fault(vcpu, TEST_MEM_GPA + TEST_MEM_SIZE / 2, TEST_MEM_SIZE / 2);
> > +       restore_nested_s2(vcpu, &s2);
> > +
> > +       /* Resume at vEL1 and touch the prefaulted range. */
> > +       vcpu_run(vcpu);
> > +       switch (get_ucall(vcpu, &uc)) {
> > +       case UCALL_DONE:
> > +               break;
> > +       case UCALL_ABORT:
> > +               REPORT_GUEST_ASSERT(uc);
> > +               break;
> > +       default:
> > +               TEST_FAIL("Unhandled ucall: %ld", uc.cmd);
> > +       }
> > +
> > +       kvm_vm_free(vm);
> > +       return 0;
> > +}
> >
> > --
> > 2.55.0
> >

--
Cheers, Lorenzo