Re: [PATCH v6 06/18] xen/pvcalls: handle commands from the frontend

[Stefano Stabellini]

On Tue, 4 Jul 2017, Juergen Gross wrote:
> On 03/07/17 23:08, Stefano Stabellini wrote:
> > When the other end notifies us that there are commands to be read
> > (pvcalls_back_event), wake up the backend thread to parse the command.
> > 
> > The command ring works like most other Xen rings, so use the usual
> > ring macros to read and write to it. The functions implementing the
> > commands are empty stubs for now.
> > 
> > Signed-off-by: Stefano Stabellini <stefano@xxxxxxxxxxx>
> > CC: boris.ostrovsky@xxxxxxxxxx
> > CC: jgross@xxxxxxxx
> > ---
> >  drivers/xen/pvcalls-back.c | 144 ++++++++++++++++++++++++++++++++++++++++-----
> >  1 file changed, 129 insertions(+), 15 deletions(-)
> > 
> > diff --git a/drivers/xen/pvcalls-back.c b/drivers/xen/pvcalls-back.c
> > index e4c2e46..9e00971 100644
> > --- a/drivers/xen/pvcalls-back.c
> > +++ b/drivers/xen/pvcalls-back.c
> > @@ -47,16 +47,135 @@ struct pvcalls_fedata {
> >  	struct list_head socket_mappings;
> >  	struct radix_tree_root socketpass_mappings;
> >  	struct semaphore socket_lock;
> > -	struct workqueue_struct *wq;
> > -	struct work_struct register_work;

I realize that this changes should actually be folded in the previous
patch (wq and register_work shouldn't be added in the first place). I'll
fix the patches.


> >  };
> >  
> > -static void pvcalls_back_work(struct work_struct *work)
> > +static int pvcalls_back_socket(struct xenbus_device *dev,
> > +		struct xen_pvcalls_request *req)
> >  {
> > +	return 0;
> > +}
> > +
> > +static int pvcalls_back_connect(struct xenbus_device *dev,
> > +				struct xen_pvcalls_request *req)
> > +{
> > +	return 0;
> > +}
> > +
> > +static int pvcalls_back_release(struct xenbus_device *dev,
> > +				struct xen_pvcalls_request *req)
> > +{
> > +	return 0;
> > +}
> > +
> > +static int pvcalls_back_bind(struct xenbus_device *dev,
> > +			     struct xen_pvcalls_request *req)
> > +{
> > +	return 0;
> > +}
> > +
> > +static int pvcalls_back_listen(struct xenbus_device *dev,
> > +			       struct xen_pvcalls_request *req)
> > +{
> > +	return 0;
> > +}
> > +
> > +static int pvcalls_back_accept(struct xenbus_device *dev,
> > +			       struct xen_pvcalls_request *req)
> > +{
> > +	return 0;
> > +}
> > +
> > +static int pvcalls_back_poll(struct xenbus_device *dev,
> > +			     struct xen_pvcalls_request *req)
> > +{
> > +	return 0;
> > +}
> > +
> > +static int pvcalls_back_handle_cmd(struct xenbus_device *dev,
> > +				   struct xen_pvcalls_request *req)
> > +{
> > +	int ret = 0;
> > +
> > +	switch (req->cmd) {
> > +	case PVCALLS_SOCKET:
> > +		ret = pvcalls_back_socket(dev, req);
> > +		break;
> > +	case PVCALLS_CONNECT:
> > +		ret = pvcalls_back_connect(dev, req);
> > +		break;
> > +	case PVCALLS_RELEASE:
> > +		ret = pvcalls_back_release(dev, req);
> > +		break;
> > +	case PVCALLS_BIND:
> > +		ret = pvcalls_back_bind(dev, req);
> > +		break;
> > +	case PVCALLS_LISTEN:
> > +		ret = pvcalls_back_listen(dev, req);
> > +		break;
> > +	case PVCALLS_ACCEPT:
> > +		ret = pvcalls_back_accept(dev, req);
> > +		break;
> > +	case PVCALLS_POLL:
> > +		ret = pvcalls_back_poll(dev, req);
> > +		break;
> > +	default:
> > +	{
> > +		struct pvcalls_fedata *fedata;
> > +		struct xen_pvcalls_response *rsp;
> > +
> > +		fedata = dev_get_drvdata(&dev->dev);
> > +		rsp = RING_GET_RESPONSE(
> > +				&fedata->ring, fedata->ring.rsp_prod_pvt++);
> > +		rsp->req_id = req->req_id;
> > +		rsp->cmd = req->cmd;
> > +		rsp->ret = -ENOTSUPP;
> > +		break;
> > +	}
> > +	}
> > +	return ret;
> > +}
> > +
> > +static void pvcalls_back_work(struct pvcalls_fedata *fedata)
> > +{
> > +	int notify, notify_all = 0, more = 1;
> > +	struct xen_pvcalls_request req;
> > +	struct xenbus_device *dev = fedata->dev;
> > +
> > +	while (more) {
> > +		while (RING_HAS_UNCONSUMED_REQUESTS(&fedata->ring)) {
> > +			RING_COPY_REQUEST(&fedata->ring,
> > +					  fedata->ring.req_cons++,
> > +					  &req);
> > +
> > +			if (!pvcalls_back_handle_cmd(dev, &req)) {
> > +				RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(
> > +					&fedata->ring, notify);
> > +				notify_all += notify;
> > +			}
> > +		}
> > +
> > +		if (notify_all) {
> > +			notify_remote_via_irq(fedata->irq);
> > +			notify_all = 0;
> > +		}
> > +
> > +		RING_FINAL_CHECK_FOR_REQUESTS(&fedata->ring, more);
> > +	}
> >  }
> >  
> >  static irqreturn_t pvcalls_back_event(int irq, void *dev_id)
> >  {
> > +	struct xenbus_device *dev = dev_id;
> > +	struct pvcalls_fedata *fedata = NULL;
> > +
> > +	if (dev == NULL)
> > +		return IRQ_HANDLED;
> > +
> > +	fedata = dev_get_drvdata(&dev->dev);
> > +	if (fedata == NULL)
> > +		return IRQ_HANDLED;
> > +
> > +	pvcalls_back_work(fedata);
> >  	return IRQ_HANDLED;
> >  }
> >  
> > @@ -87,18 +206,15 @@ static int backend_connect(struct xenbus_device *dev)
> >  		goto error;
> >  	}
> >  
> > -	err = bind_interdomain_evtchn_to_irqhandler(dev->otherend_id, evtchn,
> > -						    pvcalls_back_event, 0,
> > -						    "pvcalls-backend", dev);
> > +	err = bind_interdomain_evtchn_to_irq(dev->otherend_id, evtchn);
> >  	if (err < 0)
> >  		goto error;
> >  	fedata->irq = err;
> > -
> > -	fedata->wq = alloc_workqueue("pvcalls_back_wq", WQ_UNBOUND, 1);
> > -	if (!fedata->wq) {
> > -		err = -ENOMEM;
> > +	
> > +	err = request_threaded_irq(fedata->irq, NULL, pvcalls_back_event,
> > +				   IRQF_ONESHOT, "pvcalls-back", dev);
> > +	if (err < 0)
> >  		goto error;
> > -	}
> >  
> >  	err = xenbus_map_ring_valloc(dev, &ring_ref, 1, (void**)&fedata->sring);
> >  	if (err < 0)
> > @@ -107,7 +223,6 @@ static int backend_connect(struct xenbus_device *dev)
> >  	BACK_RING_INIT(&fedata->ring, fedata->sring, XEN_PAGE_SIZE * 1);
> >  	fedata->dev = dev;
> >  
> > -	INIT_WORK(&fedata->register_work, pvcalls_back_work);
> >  	INIT_LIST_HEAD(&fedata->socket_mappings);
> >  	INIT_RADIX_TREE(&fedata->socketpass_mappings, GFP_KERNEL);
> >  	sema_init(&fedata->socket_lock, 1);
> > @@ -116,15 +231,14 @@ static int backend_connect(struct xenbus_device *dev)
> >  	down(&pvcalls_back_global.frontends_lock);
> >  	list_add_tail(&fedata->list, &pvcalls_back_global.frontends);
> >  	up(&pvcalls_back_global.frontends_lock);
> > -	queue_work(fedata->wq, &fedata->register_work);
> > +
> > +	pvcalls_back_work(fedata);
> 
> Is this call really necessary? I believe this is racy in case an event
> is coming in at the same time.

No, it is not. I'll remove it.


> >  
> >  	return 0;
> >  
> >   error:
> >  	if (fedata->sring != NULL)
> >  		xenbus_unmap_ring_vfree(dev, fedata->sring);
> > -	if (fedata->wq)
> > -		destroy_workqueue(fedata->wq);
> >  	unbind_from_irqhandler(fedata->irq, dev);
> 
> Is it secure to unbind the irq handler _after_ unmapping the ring?

Good point, I'll change the order.