Hi Lorenzo, On Tue, Aug 25, 2026 at 05:00:42PM +0100, Lorenzo Stoakes (ARM) wrote: > From: Jack Thomson <[email protected]> > > Add an arm64 nested-virt selftest for KVM_PRE_FAULT_MEMORY. The guest > enters vEL1 and exits to userspace with a nested/shadow stage-2 MMU as > the vCPU's last-run context. > > Before prefaulting, userspace enables HCR_EL2.VM and points VTTBR_EL2 at > an empty nested stage-2 root. A prefault implementation that incorrectly > treats the userspace GPA as an L2 IPA will fail the ioctl; the correct > path targets the canonical stage-2 and succeeds. > > Restore the original nested state before resuming the guest, then touch > the prefaulted range to check that vEL1 still runs correctly. > > Signed-off-by: Jack Thomson <[email protected]> > [ljs: partial progress, >4 KiB pgsize, commit msg, comment fixups] > Signed-off-by: Lorenzo Stoakes (ARM) <[email protected]> > --- > tools/testing/selftests/kvm/Makefile.kvm | 1 + > .../selftests/kvm/arm64/nv_pre_fault_memory_test.c | 206 > +++++++++++++++++++++ > 2 files changed, 207 insertions(+)
I wonder whether this selftest can use functions Wei-Lin proposed some time ago [1]: [email protected] or would you prefer this test as propose, since it is clear as to what needs to be done to enter L2. Thanks, Itaru. > > diff --git a/tools/testing/selftests/kvm/Makefile.kvm > b/tools/testing/selftests/kvm/Makefile.kvm > index 66a9a4e62888..1e0edd0f99f7 100644 > --- a/tools/testing/selftests/kvm/Makefile.kvm > +++ b/tools/testing/selftests/kvm/Makefile.kvm > @@ -173,6 +173,7 @@ TEST_GEN_PROGS_arm64 += arm64/debug-exceptions > TEST_GEN_PROGS_arm64 += arm64/hello_el2 > TEST_GEN_PROGS_arm64 += arm64/host_sve > TEST_GEN_PROGS_arm64 += arm64/hypercalls > +TEST_GEN_PROGS_arm64 += arm64/nv_pre_fault_memory_test > TEST_GEN_PROGS_arm64 += arm64/external_aborts > TEST_GEN_PROGS_arm64 += arm64/mmio_sign_ext > TEST_GEN_PROGS_arm64 += arm64/page_fault_test > diff --git a/tools/testing/selftests/kvm/arm64/nv_pre_fault_memory_test.c > b/tools/testing/selftests/kvm/arm64/nv_pre_fault_memory_test.c > new file mode 100644 > index 000000000000..b3833aea2a34 > --- /dev/null > +++ b/tools/testing/selftests/kvm/arm64/nv_pre_fault_memory_test.c > @@ -0,0 +1,206 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +/* > + * nv_pre_fault_memory_test - Test KVM_PRE_FAULT_MEMORY on a vCPU whose > + * last-run context is nested. > + * > + * The guest starts at vEL2, mirrors its EL2 translation regime into the > + * real EL1 registers, drops HCR_EL2.TGE and ERETs to vEL1, then exits to > + * userspace from vEL1 so that the vCPU's last-run context selects a > + * shadow stage-2 MMU. Userspace then enables an empty nested stage-2 > + * before prefaulting. Prefaulting must target the canonical stage-2, > + * regardless of the vCPU's nested state. > + */ > +#include "kvm_util.h" > +#include "processor.h" > +#include "test_util.h" > +#include "ucall.h" > + > +#include <asm/sysreg.h> > +#include <linux/sizes.h> > + > +#define TEST_MEM_SLOT 10 > +#define NESTED_S2_ROOT_SLOT 11 > +#define TEST_MEM_SIZE SZ_2M > +#define TEST_MEM_GPA SZ_1G > +#define NESTED_S2_ROOT_GPA (TEST_MEM_GPA + TEST_MEM_SIZE) > + > +struct nested_s2_state { > + u64 hcr_el2; > + u64 vttbr_el2; > +}; > + > +static void guest_el1_code(void) > +{ > + u64 offset; > + > + GUEST_ASSERT_EQ(get_current_el(), 1); > + > + /* Exit to userspace with the vEL1 (nested) context live. */ > + GUEST_SYNC(1); > + > + /* > + * Touch the prefaulted range. vstage-2 is disabled, so the shadow > + * stage-2 is a 1:1 view of the canonical IPA space. > + */ > + for (offset = 0; offset < TEST_MEM_SIZE; offset += SZ_4K) > + READ_ONCE(*(u64 *)(TEST_MEM_GPA + offset)); > + > + GUEST_DONE(); > +} > + > +static void guest_code(void) > +{ > + u64 sp; > + > + GUEST_ASSERT_EQ(get_current_el(), 2); > + > + /* > + * Mirror the EL2 translation regime into the real EL1 registers so > + * that vEL1 runs on the test's stage-1 page tables. With E2H=1, the > + * _EL1 accessors read the EL2 registers, and the _EL12 accessors > + * write the real EL1 registers. > + */ > + write_sysreg_s(read_sysreg(sctlr_el1), SYS_SCTLR_EL12); > + write_sysreg_s(read_sysreg(tcr_el1), SYS_TCR_EL12); > + write_sysreg_s(read_sysreg(ttbr0_el1), SYS_TTBR0_EL12); > + write_sysreg_s(read_sysreg(mair_el1), SYS_MAIR_EL12); > + write_sysreg_s(read_sysreg(cpacr_el1), SYS_CPACR_EL12); > + > + /* Run vEL1 on the same stack. */ > + asm volatile("mov %0, sp" : "=r"(sp)); > + write_sysreg(sp, sp_el1); > + > + /* > + * Drop TGE so that vEL1 is a nested context rather than host EL0. > + * KVM backs it with a shadow stage-2 MMU even though vstage-2 is > + * disabled (HCR_EL2.VM=0). > + */ > + write_sysreg(read_sysreg(hcr_el2) & ~HCR_EL2_TGE, hcr_el2); > + isb(); > + > + write_sysreg(PSR_MODE_EL1h | PSR_F_BIT | PSR_I_BIT | PSR_A_BIT | > + PSR_D_BIT, spsr_el2); > + write_sysreg((u64)guest_el1_code, elr_el2); > + asm volatile("eret"); > + > + GUEST_ASSERT(false); > +} > + > +static void pre_fault(struct kvm_vcpu *vcpu, u64 gpa, u64 size) > +{ > + struct kvm_pre_fault_memory range = { > + .gpa = gpa, > + .size = size, > + }; > + int ret; > + > + do { > + ret = __vcpu_ioctl(vcpu, KVM_PRE_FAULT_MEMORY, &range); > + } while ((!ret && range.size) || > + (ret < 0 && (errno == EINTR || errno == EAGAIN))); > + > + TEST_ASSERT(!ret, "KVM_PRE_FAULT_MEMORY failed, ret: %d errno: %d", > + ret, errno); > + TEST_ASSERT_EQ(range.size, 0); > +} > + > +static struct nested_s2_state enable_empty_nested_s2(struct kvm_vcpu *vcpu) > +{ > + struct nested_s2_state state = { > + .hcr_el2 = vcpu_get_reg(vcpu, KVM_ARM64_SYS_REG(SYS_HCR_EL2)), > + .vttbr_el2 = vcpu_get_reg(vcpu, > + KVM_ARM64_SYS_REG(SYS_VTTBR_EL2)), > + }; > + > + TEST_ASSERT(!(state.hcr_el2 & HCR_EL2_TGE), > + "vCPU should be in nested/vEL1 context"); > + > + vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_VTTBR_EL2), > + NESTED_S2_ROOT_GPA); > + vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_HCR_EL2), > + state.hcr_el2 | HCR_EL2_VM); > + > + return state; > +} > + > +static void restore_nested_s2(struct kvm_vcpu *vcpu, > + struct nested_s2_state *state) > +{ > + vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_HCR_EL2), state->hcr_el2); > + vcpu_set_reg(vcpu, KVM_ARM64_SYS_REG(SYS_VTTBR_EL2), > + state->vttbr_el2); > +} > + > +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)); > + 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 >
