[PATCH v6 31/31] KVM: selftest: Add a selftest for VMRUN/#VMEXIT with unmappable vmcb12

[Yosry Ahmed]

Add a test that verifies that KVM correctly injects a #GP for nested
VMRUN and a shutdown for nested #VMEXIT, if the GPA of vmcb12 cannot be
mapped.

Signed-off-by: Yosry Ahmed <yosry@xxxxxxxxxx>
---
 tools/testing/selftests/kvm/Makefile.kvm      |  1 +
 .../kvm/x86/svm_nested_invalid_vmcb12_gpa.c   | 95 +++++++++++++++++++
 2 files changed, 96 insertions(+)
 create mode 100644 tools/testing/selftests/kvm/x86/svm_nested_invalid_vmcb12_gpa.c

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index 36b48e766e499..f12e7c17d379d 100644
--- a/tools/testing/selftests/kvm/Makefile.kvm
+++ b/tools/testing/selftests/kvm/Makefile.kvm
@@ -110,6 +110,7 @@ TEST_GEN_PROGS_x86 += x86/state_test
 TEST_GEN_PROGS_x86 += x86/vmx_preemption_timer_test
 TEST_GEN_PROGS_x86 += x86/svm_vmcall_test
 TEST_GEN_PROGS_x86 += x86/svm_int_ctl_test
+TEST_GEN_PROGS_x86 += x86/svm_nested_invalid_vmcb12_gpa
 TEST_GEN_PROGS_x86 += x86/svm_nested_shutdown_test
 TEST_GEN_PROGS_x86 += x86/svm_nested_soft_inject_test
 TEST_GEN_PROGS_x86 += x86/svm_lbr_nested_state
diff --git a/tools/testing/selftests/kvm/x86/svm_nested_invalid_vmcb12_gpa.c b/tools/testing/selftests/kvm/x86/svm_nested_invalid_vmcb12_gpa.c
new file mode 100644
index 0000000000000..5b0dec4240937
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86/svm_nested_invalid_vmcb12_gpa.c
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2026, Google LLC.
+ */
+#include "kvm_util.h"
+#include "vmx.h"
+#include "svm_util.h"
+#include "kselftest.h"
+
+
+#define L2_GUEST_STACK_SIZE 64
+
+#define SYNC_GP 101
+#define SYNC_L2_STARTED 102
+
+extern char invalid_vmrun;
+
+static void guest_gp_handler(struct ex_regs *regs)
+{
+	GUEST_SYNC(SYNC_GP);
+	regs->rip = (uintptr_t)&invalid_vmrun;
+}
+
+static void l2_guest_code(void)
+{
+	GUEST_SYNC(SYNC_L2_STARTED);
+	vmcall();
+}
+
+static void l1_guest_code(struct svm_test_data *svm, u64 invalid_vmcb12_gpa)
+{
+	unsigned long l2_guest_stack[L2_GUEST_STACK_SIZE];
+
+	generic_svm_setup(svm, l2_guest_code,
+			  &l2_guest_stack[L2_GUEST_STACK_SIZE]);
+
+	run_guest(svm->vmcb, invalid_vmcb12_gpa); /* #GP */
+
+	/* GP handler should jump here */
+	asm volatile ("invalid_vmrun:");
+	run_guest(svm->vmcb, svm->vmcb_gpa);
+	GUEST_ASSERT(svm->vmcb->control.exit_code == SVM_EXIT_VMMCALL);
+	GUEST_DONE();
+}
+
+int main(int argc, char *argv[])
+{
+	struct kvm_x86_state *state;
+	vm_vaddr_t nested_gva = 0;
+	struct kvm_vcpu *vcpu;
+	uint32_t maxphyaddr;
+	u64 max_legal_gpa;
+	struct kvm_vm *vm;
+	struct ucall uc;
+
+	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_SVM));
+
+	vm = vm_create_with_one_vcpu(&vcpu, l1_guest_code);
+	vm_install_exception_handler(vcpu->vm, GP_VECTOR, guest_gp_handler);
+
+	/*
+	 * Find the max legal GPA that is not backed by a memslot (i.e. cannot
+	 * be mapped by KVM).
+	 */
+	maxphyaddr = kvm_cpuid_property(vcpu->cpuid, X86_PROPERTY_MAX_PHY_ADDR);
+	max_legal_gpa = BIT_ULL(maxphyaddr) - PAGE_SIZE;
+	vcpu_alloc_svm(vm, &nested_gva);
+	vcpu_args_set(vcpu, 2, nested_gva, max_legal_gpa);
+
+	/* VMRUN with max_legal_gpa, KVM injects a #GP */
+	vcpu_run(vcpu);
+	TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);
+	TEST_ASSERT_EQ(get_ucall(vcpu, &uc), UCALL_SYNC);
+	TEST_ASSERT_EQ(uc.args[1], SYNC_GP);
+
+	/*
+	 * Enter L2 (with a legit vmcb12 GPA), then overwrite vmcb12 GPA with
+	 * max_legal_gpa. KVM will fail to map vmcb12 on nested VM-Exit and
+	 * cause a shutdown.
+	 */
+	vcpu_run(vcpu);
+	TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_IO);
+	TEST_ASSERT_EQ(get_ucall(vcpu, &uc), UCALL_SYNC);
+	TEST_ASSERT_EQ(uc.args[1], SYNC_L2_STARTED);
+
+	state = vcpu_save_state(vcpu);
+	state->nested.hdr.svm.vmcb_pa = max_legal_gpa;
+	vcpu_load_state(vcpu, state);
+	vcpu_run(vcpu);
+	TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_SHUTDOWN);
+
+	kvm_x86_state_cleanup(state);
+	kvm_vm_free(vm);
+	return 0;
+}
-- 
2.53.0.414.gf7e9f6c205-goog