KVM: selftests: Add a VM backpointer to 'struct vcpu'

Add a backpointer to 'struct vcpu' so that tests can get at the owning
VM when passing around a vCPU object.  Long term, this will be little
more than a nice-to-have feature, but in the short term it is a critical
step toward purging the VM+vcpu_id ioctl mess without introducing even
more churn.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/include/kvm_util_base.h

@@ -47,6 +47,7 @@ struct vcpu {
 	struct list_head list;
 	uint32_t id;
 	int fd;
+	struct kvm_vm *vm;
 	struct kvm_run *state;
 	struct kvm_dirty_gfn *dirty_gfns;
 	uint32_t fetch_index;

tools/testing/selftests/kvm/lib/kvm_util.c

@@ -1099,6 +1099,7 @@ void vm_vcpu_add(struct kvm_vm *vm, uint32_t vcpuid)
 	vcpu = calloc(1, sizeof(*vcpu));
 	TEST_ASSERT(vcpu != NULL, "Insufficient Memory");
 
+	vcpu->vm = vm;
 	vcpu->id = vcpuid;
 	vcpu->fd = __vm_ioctl(vm, KVM_CREATE_VCPU, (void *)(unsigned long)vcpuid);
 	TEST_ASSERT(vcpu->fd >= 0, KVM_IOCTL_ERROR(KVM_CREATE_VCPU, vcpu->fd));