KVM: selftests: Convert s390x/diag318_test_handler away from VCPU_ID

Convert diag318_test_handler to use vm_create_with_vcpus() and pass around a
'struct kvm_vcpu' object instead of passing around vCPU IDs.  Note, this is
a "functional" change in the sense that the test now creates a vCPU with
vcpu_id==0 instead of vcpu_id==6.  The non-zero VCPU_ID was 100% arbitrary
and added little to no validation coverage.  If testing non-zero vCPU IDs
is desirable for generic tests, that can be done in the future by tweaking
the VM creation helpers.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/lib/s390x/diag318_test_handler.c

@@ -8,8 +8,6 @@
 #include "test_util.h"
 #include "kvm_util.h"
 
-#define VCPU_ID	6
-
 #define ICPT_INSTRUCTION	0x04
 #define IPA0_DIAG		0x8300
 
@@ -27,14 +25,15 @@ static void guest_code(void)
  */
 static uint64_t diag318_handler(void)
 {
+	struct kvm_vcpu *vcpu;
 	struct kvm_vm *vm;
 	struct kvm_run *run;
 	uint64_t reg;
 	uint64_t diag318_info;
 
-	vm = vm_create_default(VCPU_ID, 0, guest_code);
-	vcpu_run(vm, VCPU_ID);
-	run = vcpu_state(vm, VCPU_ID);
+	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
+	vcpu_run(vm, vcpu->id);
+	run = vcpu->run;
 
 	TEST_ASSERT(run->exit_reason == KVM_EXIT_S390_SIEIC,
 		    "DIAGNOSE 0x0318 instruction was not intercepted");