KVM: selftests: Assert that STI blocking isn't set after event injection

Add an L1 (guest) assert to the nested exceptions test to verify that KVM
doesn't put VMRUN in an STI shadow (AMD CPUs bleed the shadow into the
guest's int_state if a #VMEXIT occurs before VMRUN fully completes).

Add a similar assert to the VMX side as well, because why not.

Reviewed-by: Jim Mattson <jmattson@google.com>
Link: https://lore.kernel.org/r/20250224165442.2338294-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

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

@@ -85,6 +85,7 @@ static void svm_run_l2(struct svm_test_data *svm, void *l2_code, int vector,
 
 	GUEST_ASSERT_EQ(ctrl->exit_code, (SVM_EXIT_EXCP_BASE + vector));
 	GUEST_ASSERT_EQ(ctrl->exit_info_1, error_code);
+	GUEST_ASSERT(!ctrl->int_state);
 }
 
 static void l1_svm_code(struct svm_test_data *svm)
@@ -122,6 +123,7 @@ static void vmx_run_l2(void *l2_code, int vector, uint32_t error_code)
 	GUEST_ASSERT_EQ(vmreadz(VM_EXIT_REASON), EXIT_REASON_EXCEPTION_NMI);
 	GUEST_ASSERT_EQ((vmreadz(VM_EXIT_INTR_INFO) & 0xff), vector);
 	GUEST_ASSERT_EQ(vmreadz(VM_EXIT_INTR_ERROR_CODE), error_code);
+	GUEST_ASSERT(!vmreadz(GUEST_INTERRUPTIBILITY_INFO));
 }
 
 static void l1_vmx_code(struct vmx_pages *vmx)