Hi Itaru, On Mon, Apr 13, 2026 at 08:19:25AM +0900, Itaru Kitayama wrote: > 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?
Guest stage-2 is disabled by not setting HCR_EL2.VM in prepare_hyp(), and stage-1 is disabled by not writing to SCTLR_EL12 in init_vcpu(), effectively using the default value set by L0. However since SCTLR_EL1 has many architecturally UNKNOWN bits (including SCTLR_EL1.M), it should be better to write a value before running L2 I suppose... Thanks, Wei-Lin Chang > > Itaru. > > > > > Signed-off-by: Wei-Lin Chang <[email protected]> > > --- > > 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 > >
