xen/event: Add reference counting to event channels

Event channels exposed to userspace by the evtchn module may be used by
other modules in an asynchronous manner, which requires that reference
counting be used to prevent the event channel from being closed before
the signals are delivered.

The reference count on new event channels defaults to -1 which indicates
the event channel is not referenced outside the kernel; evtchn_get fails
if called on such an event channel. The event channels made visible to
userspace by evtchn have a normal reference count.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 6e075cdd0c6bf56ff8daacf986d443de23c49998..a3bcd6175f4a6e288cd6ccd40bebbe7719b55862 100644 (file)
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -87,6 +87,7 @@ enum xen_irq_type {
  */
 struct irq_info {
        struct list_head list;
+       int refcnt;
        enum xen_irq_type type; /* type */
        unsigned irq;
        unsigned short evtchn;  /* event channel */
@@ -406,6 +407,7 @@ static void xen_irq_init(unsigned irq)
                panic("Unable to allocate metadata for IRQ%d\n", irq);
 
        info->type = IRQT_UNBOUND;
+       info->refcnt = -1;
 
        irq_set_handler_data(irq, info);
 
@@ -469,6 +471,8 @@ static void xen_free_irq(unsigned irq)
 
        irq_set_handler_data(irq, NULL);
 
+       WARN_ON(info->refcnt > 0);
+
        kfree(info);
 
        /* Legacy IRQ descriptors are managed by the arch. */
@@ -637,7 +641,7 @@ int xen_bind_pirq_gsi_to_irq(unsigned gsi,
        if (irq != -1) {
                printk(KERN_INFO "xen_map_pirq_gsi: returning irq %d for gsi %u\n",
                       irq, gsi);
-               goto out;       /* XXX need refcount? */
+               goto out;
        }
 
        irq = xen_allocate_irq_gsi(gsi);
@@ -939,9 +943,16 @@ static void unbind_from_irq(unsigned int irq)
 {
        struct evtchn_close close;
        int evtchn = evtchn_from_irq(irq);
+       struct irq_info *info = irq_get_handler_data(irq);
 
        mutex_lock(&irq_mapping_update_lock);
 
+       if (info->refcnt > 0) {
+               info->refcnt--;
+               if (info->refcnt != 0)
+                       goto done;
+       }
+
        if (VALID_EVTCHN(evtchn)) {
                close.port = evtchn;
                if (HYPERVISOR_event_channel_op(EVTCHNOP_close, &close) != 0)
@@ -970,6 +981,7 @@ static void unbind_from_irq(unsigned int irq)
 
        xen_free_irq(irq);
 
+ done:
        mutex_unlock(&irq_mapping_update_lock);
 }
 
@@ -1065,6 +1077,66 @@ void unbind_from_irqhandler(unsigned int irq, void *dev_id)
 }
 EXPORT_SYMBOL_GPL(unbind_from_irqhandler);
 
+int evtchn_make_refcounted(unsigned int evtchn)
+{
+       int irq = evtchn_to_irq[evtchn];
+       struct irq_info *info;
+
+       if (irq == -1)
+               return -ENOENT;
+
+       info = irq_get_handler_data(irq);
+
+       if (!info)
+               return -ENOENT;
+
+       WARN_ON(info->refcnt != -1);
+
+       info->refcnt = 1;
+
+       return 0;
+}
+EXPORT_SYMBOL_GPL(evtchn_make_refcounted);
+
+int evtchn_get(unsigned int evtchn)
+{
+       int irq;
+       struct irq_info *info;
+       int err = -ENOENT;
+
+       mutex_lock(&irq_mapping_update_lock);
+
+       irq = evtchn_to_irq[evtchn];
+       if (irq == -1)
+               goto done;
+
+       info = irq_get_handler_data(irq);
+
+       if (!info)
+               goto done;
+
+       err = -EINVAL;
+       if (info->refcnt <= 0)
+               goto done;
+
+       info->refcnt++;
+       err = 0;
+ done:
+       mutex_unlock(&irq_mapping_update_lock);
+
+       return err;
+}
+EXPORT_SYMBOL_GPL(evtchn_get);
+
+void evtchn_put(unsigned int evtchn)
+{
+       int irq = evtchn_to_irq[evtchn];
+       if (WARN_ON(irq == -1))
+               return;
+       unbind_from_irq(irq);
+}
+EXPORT_SYMBOL_GPL(evtchn_put);
+
 void xen_send_IPI_one(unsigned int cpu, enum ipi_vector vector)
 {
        int irq = per_cpu(ipi_to_irq, cpu)[vector];

diff --git a/drivers/xen/evtchn.c b/drivers/xen/evtchn.c
index dbc13e94b612b39759a01fb3605e956dbca807f6..b1f60a0c0bea3e00627293101fd3dd38bb1fd96e 100644 (file)
--- a/drivers/xen/evtchn.c
+++ b/drivers/xen/evtchn.c
@@ -268,7 +268,7 @@ static int evtchn_bind_to_user(struct per_user_data *u, int port)
        rc = bind_evtchn_to_irqhandler(port, evtchn_interrupt, IRQF_DISABLED,
                                       u->name, (void *)(unsigned long)port);
        if (rc >= 0)
-               rc = 0;
+               rc = evtchn_make_refcounted(port);
 
        return rc;
 }

diff --git a/include/xen/events.h b/include/xen/events.h
index d287997d3eab3ab9eeea0b802bf41eaa9238f97c..0f773708e02c034f624ca61a3e186bb8e9d68080 100644 (file)
--- a/include/xen/events.h
+++ b/include/xen/events.h
@@ -37,6 +37,13 @@ int bind_interdomain_evtchn_to_irqhandler(unsigned int remote_domain,
  */
 void unbind_from_irqhandler(unsigned int irq, void *dev_id);
 
+/*
+ * Allow extra references to event channels exposed to userspace by evtchn
+ */
+int evtchn_make_refcounted(unsigned int evtchn);
+int evtchn_get(unsigned int evtchn);
+void evtchn_put(unsigned int evtchn);
+
 void xen_send_IPI_one(unsigned int cpu, enum ipi_vector vector);
 int resend_irq_on_evtchn(unsigned int irq);
 void rebind_evtchn_irq(int evtchn, int irq);