Add a simple NV selftest that uses the NV library functions to eret from
vEL2 to EL1, then call an hvc to jump back to vEL2.

Signed-off-by: Wei-Lin Chang <weilin.chang@arm.com>
---
 tools/testing/selftests/kvm/Makefile.kvm      |  1 +
 .../selftests/kvm/arm64/hello_nested.c        | 65 +++++++++++++++++++
 2 files changed, 66 insertions(+)
 create mode 100644 tools/testing/selftests/kvm/arm64/hello_nested.c

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index 5e681e8e0cd7..d7499609cd0c 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -167,6 +167,7 @@ TEST_GEN_PROGS_arm64 += arm64/arch_timer_edge_cases
 TEST_GEN_PROGS_arm64 += arm64/at
 TEST_GEN_PROGS_arm64 += arm64/debug-exceptions
 TEST_GEN_PROGS_arm64 += arm64/hello_el2
+TEST_GEN_PROGS_arm64 += arm64/hello_nested
 TEST_GEN_PROGS_arm64 += arm64/host_sve
 TEST_GEN_PROGS_arm64 += arm64/hypercalls
 TEST_GEN_PROGS_arm64 += arm64/external_aborts
diff --git a/tools/testing/selftests/kvm/arm64/hello_nested.c b/tools/testing/selftests/kvm/arm64/hello_nested.c
new file mode 100644
index 000000000000..16c600539810
--- /dev/null
+++ b/tools/testing/selftests/kvm/arm64/hello_nested.c
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * hello_nested - Go from vEL2 to EL1 then back
+ */
+#include "kvm_util.h"
+#include "nested.h"
+#include "processor.h"
+#include "test_util.h"
+#include "ucall.h"
+
+static void l2_guest_code(void)
+{
+	/* nothing */
+}
+
+static void guest_code(void)
+{
+	GUEST_ASSERT_EQ(get_current_el(), 2);
+	GUEST_PRINTF("vEL2 entry\n");
+	run_l2();
+	GUEST_DONE();
+}
+
+int main(void)
+{
+	struct kvm_vcpu_init init;
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	struct ucall uc;
+
+	TEST_REQUIRE(kvm_check_cap(KVM_CAP_ARM_EL2));
+	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);
+
+	prepare_l2_stack(vm, vcpu);
+	prepare_hyp_state(vm, vcpu);
+	prepare_eret_destination(vm, vcpu, l2_guest_code);
+	prepare_nested_sync_handler(vm, vcpu);
+
+	while (true) {
+		vcpu_run(vcpu);
+
+		switch (get_ucall(vcpu, &uc)) {
+		case UCALL_PRINTF:
+			pr_info("%s", uc.buffer);
+			break;
+		case UCALL_DONE:
+			pr_info("DONE!\n");
+			goto end;
+		case UCALL_ABORT:
+			REPORT_GUEST_ASSERT(uc);
+			fallthrough;
+		default:
+			TEST_FAIL("Unhandled ucall: %ld\n", uc.cmd);
+		}
+	}
+
+end:
+	kvm_vm_free(vm);
+	return 0;
+}
-- 
2.43.0