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

Hi,

On Tue, 25 Aug 2026 at 17:02, Lorenzo Stoakes (ARM) [off-list ref] 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.

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