Re: [PATCH v2 3/4] KVM: arm64: sefltests: Add basic NV selftest

[Itaru Kitayama]

On Sun, Apr 12, 2026 at 03:22:15PM +0100, Wei-Lin Chang wrote:
> This selftest simply starts an L1, which starts its own guest (L2). L2
> runs without stage-1 and 2 translations, it calls an HVC to jump back
> to L1.

How do you disable both the nested guest (L2)'s MMU and stage 2
translations?

Itaru.

> 
> Signed-off-by: Wei-Lin Chang <weilin.chang@xxxxxxx>
> ---
>  tools/testing/selftests/kvm/Makefile.kvm      |   1 +
>  .../selftests/kvm/arm64/hello_nested.c        | 103 ++++++++++++++++++
>  2 files changed, 104 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 3dc3e39f7025..e8c108e0c487 100644
> --- a/tools/testing/selftests/kvm/Makefile.kvm
> +++ b/tools/testing/selftests/kvm/Makefile.kvm
> @@ -168,6 +168,7 @@ 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..97387e4697b3
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/arm64/hello_nested.c
> @@ -0,0 +1,103 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * hello_nested - Go from vEL2 to EL1 then back
> + */
> +
> +#include "nested.h"
> +#include "processor.h"
> +#include "test_util.h"
> +#include "ucall.h"
> +
> +#define XLATE2GPA	(0xABCD)
> +#define L2STACKSZ	(0x100)
> +
> +/*
> + * TPIDR_EL2 is used to store vcpu id, so save and restore it.
> + */
> +static vm_paddr_t ucall_translate_to_gpa(void *gva)
> +{
> +	vm_paddr_t gpa;
> +	u64 vcpu_id = read_sysreg(tpidr_el2);
> +
> +	GUEST_SYNC2(XLATE2GPA, gva);
> +
> +	/* get the result from userspace */
> +	gpa = read_sysreg(tpidr_el2);
> +
> +	write_sysreg(vcpu_id, tpidr_el2);
> +
> +	return gpa;
> +}
> +
> +static void l2_guest_code(void)
> +{
> +	do_hvc();
> +}
> +
> +static void guest_code(void)
> +{
> +	struct vcpu vcpu;
> +	struct hyp_data hyp_data;
> +	int ret;
> +	vm_paddr_t l2_pc, l2_stack_top;
> +	/* force 16-byte alignment for the stack pointer */
> +	u8 l2_stack[L2STACKSZ] __attribute__((aligned(16)));
> +
> +	GUEST_ASSERT_EQ(get_current_el(), 2);
> +	GUEST_PRINTF("vEL2 entry\n");
> +
> +	l2_pc = ucall_translate_to_gpa(l2_guest_code);
> +	l2_stack_top = ucall_translate_to_gpa(&l2_stack[L2STACKSZ]);
> +
> +	init_vcpu(&vcpu, l2_pc, l2_stack_top);
> +	prepare_hyp();
> +
> +	ret = run_l2(&vcpu, &hyp_data);
> +	GUEST_ASSERT_EQ(ret, ARM_EXCEPTION_TRAP);
> +	GUEST_DONE();
> +}
> +
> +int main(void)
> +{
> +	struct kvm_vcpu_init init;
> +	struct kvm_vcpu *vcpu;
> +	struct kvm_vm *vm;
> +	struct ucall uc;
> +	vm_paddr_t gpa;
> +
> +	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);
> +
> +	while (true) {
> +		vcpu_run(vcpu);
> +
> +		switch (get_ucall(vcpu, &uc)) {
> +		case UCALL_SYNC:
> +			if (uc.args[0] == XLATE2GPA) {
> +				gpa = addr_gva2gpa(vm, (vm_vaddr_t)uc.args[1]);
> +				vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_TPIDR_EL2), gpa);
> +			}
> +			break;
> +		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
>