KVM: selftests: Add a test for L2 clearing EFER.SVME without intercept

Add a test that verifies KVM's newly introduced behavior of synthesizing
a triple fault in L1 if L2 clears EFER.SVME without an L1 interception
(which is architecturally undefined).

Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Link: https://patch.msgid.link/20260209195142.2554532-3-yosry.ahmed@linux.dev
Signed-off-by: Sean Christopherson <seanjc@google.com>

2 files changed, 56 insertions, 0 deletions

diff --git a/tools/testing/selftests/kvm/Makefile.kvm b/tools/testing/selftests/kvm/Makefile.kvm
index f12e7c17d379..ba87cd31872b 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_clear_efer_svme
 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
diff --git a/tools/testing/selftests/kvm/x86/svm_nested_clear_efer_svme.c b/tools/testing/selftests/kvm/x86/svm_nested_clear_efer_svme.c
new file mode 100644
index 000000000000..a521a9eed061
--- /dev/null
+++ b/tools/testing/selftests/kvm/x86/svm_nested_clear_efer_svme.c
@@ -0,0 +1,55 @@
+// 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
+
+static void l2_guest_code(void)
+{
+	unsigned long efer = rdmsr(MSR_EFER);
+
+	/* generic_svm_setup() initializes EFER_SVME set for L2 */
+	GUEST_ASSERT(efer & EFER_SVME);
+	wrmsr(MSR_EFER, efer & ~EFER_SVME);
+
+	/* Unreachable, L1 should be shutdown */
+	GUEST_ASSERT(0);
+}
+
+static void l1_guest_code(struct svm_test_data *svm)
+{
+	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, svm->vmcb_gpa);
+
+	/* Unreachable, L1 should be shutdown */
+	GUEST_ASSERT(0);
+}
+
+int main(int argc, char *argv[])
+{
+	struct kvm_vcpu *vcpu;
+	struct kvm_vm *vm;
+	vm_vaddr_t nested_gva = 0;
+
+	TEST_REQUIRE(kvm_cpu_has(X86_FEATURE_SVM));
+
+	vm = vm_create_with_one_vcpu(&vcpu, l1_guest_code);
+
+	vcpu_alloc_svm(vm, &nested_gva);
+	vcpu_args_set(vcpu, 1, nested_gva);
+
+	vcpu_run(vcpu);
+	TEST_ASSERT_KVM_EXIT_REASON(vcpu, KVM_EXIT_SHUTDOWN);
+
+	kvm_vm_free(vm);
+	return 0;
+}