KVM: selftests: Add a VMX test for LA57 nested state

Add a selftest that verifies KVM's ability to save and restore
nested state when the L1 guest is using 5-level paging and the L2
guest is using 4-level paging. Specifically, canonicality tests of
the VMCS12 host-state fields should accept 57-bit virtual addresses.

Signed-off-by: Jim Mattson <jmattson@google.com>
Link: https://patch.msgid.link/20251028225827.2269128-5-jmattson@google.com
[sean: rename to vmx_nested_la57_state_test to prep nested_<test> namespace]
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: jsmattsonjr

tools/testing/selftests/kvm/Makefile.kvm

@@ -119,6 +119,7 @@ TEST_GEN_PROGS_x86 += x86/vmx_dirty_log_test
 TEST_GEN_PROGS_x86 += x86/vmx_exception_with_invalid_guest_state
 TEST_GEN_PROGS_x86 += x86/vmx_msrs_test
 TEST_GEN_PROGS_x86 += x86/vmx_invalid_nested_guest_state
+TEST_GEN_PROGS_x86 += x86/vmx_nested_la57_state_test
 TEST_GEN_PROGS_x86 += x86/vmx_set_nested_state_test
 TEST_GEN_PROGS_x86 += x86/apic_bus_clock_test
 TEST_GEN_PROGS_x86 += x86/xapic_ipi_test

tools/testing/selftests/kvm/x86/vmx_nested_la57_state_test.c

@@ -0,0 +1,132 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2025, Google LLC.
+ *
+ * Test KVM's ability to save and restore nested state when the L1 guest
+ * is using 5-level paging and the L2 guest is using 4-level paging.
+ *
+ * This test would have failed prior to commit 9245fd6b8531 ("KVM: x86:
+ * model canonical checks more precisely").
+ */
+#include "test_util.h"
+#include "kvm_util.h"
+#include "processor.h"
+#include "vmx.h"
+
+#define LA57_GS_BASE 0xff2bc0311fb00000ull
+
+static void l2_guest_code(void)
+{
+	/*
+	 * Sync with L0 to trigger save/restore.  After
+	 * resuming, execute VMCALL to exit back to L1.
+	 */
+	GUEST_SYNC(1);
+	vmcall();
+}
+
+static void l1_guest_code(struct vmx_pages *vmx_pages)
+{
+#define L2_GUEST_STACK_SIZE 64
+	unsigned long l2_guest_stack[L2_GUEST_STACK_SIZE];
+	u64 guest_cr4;
+	vm_paddr_t pml5_pa, pml4_pa;
+	u64 *pml5;
+	u64 exit_reason;
+
+	/* Set GS_BASE to a value that is only canonical with LA57. */
+	wrmsr(MSR_GS_BASE, LA57_GS_BASE);
+	GUEST_ASSERT(rdmsr(MSR_GS_BASE) == LA57_GS_BASE);
+
+	GUEST_ASSERT(vmx_pages->vmcs_gpa);
+	GUEST_ASSERT(prepare_for_vmx_operation(vmx_pages));
+	GUEST_ASSERT(load_vmcs(vmx_pages));
+
+	prepare_vmcs(vmx_pages, l2_guest_code,
+		     &l2_guest_stack[L2_GUEST_STACK_SIZE]);
+
+	/*
+	 * Set up L2 with a 4-level page table by pointing its CR3 to
+	 * L1's first PML4 table and clearing CR4.LA57. This creates
+	 * the CR4.LA57 mismatch that exercises the bug.
+	 */
+	pml5_pa = get_cr3() & PHYSICAL_PAGE_MASK;
+	pml5 = (u64 *)pml5_pa;
+	pml4_pa = pml5[0] & PHYSICAL_PAGE_MASK;
+	vmwrite(GUEST_CR3, pml4_pa);
+
+	guest_cr4 = vmreadz(GUEST_CR4);
+	guest_cr4 &= ~X86_CR4_LA57;
+	vmwrite(GUEST_CR4, guest_cr4);
+
+	GUEST_ASSERT(!vmlaunch());
+
+	exit_reason = vmreadz(VM_EXIT_REASON);
+	GUEST_ASSERT(exit_reason == EXIT_REASON_VMCALL);
+}
+
+void guest_code(struct vmx_pages *vmx_pages)
+{
+	l1_guest_code(vmx_pages);
+	GUEST_DONE();
+}
+
+int main(int argc, char *argv[])
+{
+	vm_vaddr_t vmx_pages_gva = 0;
+	struct kvm_vm *vm;
+	struct kvm_vcpu *vcpu;
+	struct kvm_x86_state *state;
+	struct ucall uc;
+	int stage;
+
+	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_VMX));
+	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_LA57));
+	TEST_REQUIRE(kvm_has_cap(KVM_CAP_NESTED_STATE));
+
+	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
+
+	/*
+	 * L1 needs to read its own PML5 table to set up L2. Identity map
+	 * the PML5 table to facilitate this.
+	 */
+	virt_map(vm, vm->pgd, vm->pgd, 1);
+
+	vcpu_alloc_vmx(vm, &vmx_pages_gva);
+	vcpu_args_set(vcpu, 1, vmx_pages_gva);
+
+	for (stage = 1;; stage++) {
+		vcpu_run(vcpu);
+		TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);
+
+		switch (get_ucall(vcpu, &uc)) {
+		case UCALL_ABORT:
+			REPORT_GUEST_ASSERT(uc);
+			/* NOT REACHED */
+		case UCALL_SYNC:
+			break;
+		case UCALL_DONE:
+			goto done;
+		default:
+			TEST_FAIL("Unknown ucall %lu", uc.cmd);
+		}
+
+		TEST_ASSERT(uc.args[1] == stage,
+			    "Expected stage %d, got stage %lu", stage, (ulong)uc.args[1]);
+		if (stage == 1) {
+			pr_info("L2 is active; performing save/restore.\n");
+			state = vcpu_save_state(vcpu);
+
+			kvm_vm_release(vm);
+
+			/* Restore state in a new VM. */
+			vcpu = vm_recreate_with_one_vcpu(vm);
+			vcpu_load_state(vcpu, state);
+			kvm_x86_state_cleanup(state);
+		}
+	}
+
+done:
+	kvm_vm_free(vm);
+	return 0;
+}