xen/events: add per-xenbus device event statistics and settings

Add syfs nodes for each xenbus device showing event statistics (number
of events and spurious events, number of associated event channels)
and for setting a spurious event threshold in case a frontend is
sending too many events without being rogue on purpose.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20210219154030.10892-7-jgross@suse.com
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

Documentation/ABI/testing/sysfs-devices-xenbus

@@ -0,0 +1,41 @@
+What:		/sys/devices/*/xenbus/event_channels
+Date:		February 2021
+Contact:	Xen Developers mailing list <xen-devel@lists.xenproject.org>
+Description:
+		Number of Xen event channels associated with a kernel based
+		paravirtualized device frontend or backend.
+
+What:		/sys/devices/*/xenbus/events
+Date:		February 2021
+Contact:	Xen Developers mailing list <xen-devel@lists.xenproject.org>
+Description:
+		Total number of Xen events received for a Xen pv device
+		frontend or backend.
+
+What:		/sys/devices/*/xenbus/jiffies_eoi_delayed
+Date:		February 2021
+Contact:	Xen Developers mailing list <xen-devel@lists.xenproject.org>
+Description:
+		Summed up time in jiffies the EOI of an interrupt for a Xen
+		pv device has been delayed in order to avoid stalls due to
+		event storms. This value rising is a first sign for a rogue
+		other end of the pv device.
+
+What:		/sys/devices/*/xenbus/spurious_events
+Date:		February 2021
+Contact:	Xen Developers mailing list <xen-devel@lists.xenproject.org>
+Description:
+		Number of events received for a Xen pv device which did not
+		require any action. Too many spurious events in a row will
+		trigger delayed EOI processing.
+
+What:		/sys/devices/*/xenbus/spurious_threshold
+Date:		February 2021
+Contact:	Xen Developers mailing list <xen-devel@lists.xenproject.org>
+Description:
+		Controls the tolerated number of subsequent spurious events
+		before delayed EOI processing is triggered for a Xen pv
+		device. Default is 1. This can be modified in case the other
+		end of the pv device is issuing spurious events on a regular
+		basis and is known not to be malicious on purpose. Raising
+		the value for such cases can improve pv device performance.

drivers/xen/events/events_base.c

@@ -323,6 +323,8 @@ static int xen_irq_info_evtchn_setup(unsigned irq,
 
 	ret = xen_irq_info_common_setup(info, irq, IRQT_EVTCHN, evtchn, 0);
 	info->u.interdomain = dev;
+	if (dev)
+		atomic_inc(&dev->event_channels);
 
 	return ret;
 }
@@ -568,18 +570,28 @@ static void xen_irq_lateeoi_locked(struct irq_info *info, bool spurious)
 		return;
 
 	if (spurious) {
+		struct xenbus_device *dev = info->u.interdomain;
+		unsigned int threshold = 1;
+
+		if (dev && dev->spurious_threshold)
+			threshold = dev->spurious_threshold;
+
 		if ((1 << info->spurious_cnt) < (HZ << 2)) {
 			if (info->spurious_cnt != 0xFF)
 				info->spurious_cnt++;
 		}
-		if (info->spurious_cnt > 1) {
+		if (info->spurious_cnt > threshold) {
-			delay = 1 << (info->spurious_cnt - 2);
+			delay = 1 << (info->spurious_cnt - 1 - threshold);
 			if (delay > HZ)
 				delay = HZ;
 			if (!info->eoi_time)
 				info->eoi_cpu = smp_processor_id();
 			info->eoi_time = get_jiffies_64() + delay;
+			if (dev)
+				atomic_add(delay, &dev->jiffies_eoi_delayed);
 		}
+		if (dev)
+			atomic_inc(&dev->spurious_events);
 	} else {
 		info->spurious_cnt = 0;
 	}
@@ -908,6 +920,7 @@ static void __unbind_from_irq(unsigned int irq)
 
 	if (VALID_EVTCHN(evtchn)) {
 		unsigned int cpu = cpu_from_irq(irq);
+		struct xenbus_device *dev;
 
 		xen_evtchn_close(evtchn);
 
@@ -918,6 +931,11 @@ static void __unbind_from_irq(unsigned int irq)
 		case IRQT_IPI:
 			per_cpu(ipi_to_irq, cpu)[ipi_from_irq(irq)] = -1;
 			break;
+		case IRQT_EVTCHN:
+			dev = info->u.interdomain;
+			if (dev)
+				atomic_dec(&dev->event_channels);
+			break;
 		default:
 			break;
 		}
@@ -1581,6 +1599,7 @@ void handle_irq_for_port(evtchn_port_t port, struct evtchn_loop_ctrl *ctrl)
 {
 	int irq;
 	struct irq_info *info;
+	struct xenbus_device *dev;
 
 	irq = get_evtchn_to_irq(port);
 	if (irq == -1)
@@ -1610,6 +1629,10 @@ void handle_irq_for_port(evtchn_port_t port, struct evtchn_loop_ctrl *ctrl)
 
 	info = info_for_irq(irq);
 
+	dev = (info->type == IRQT_EVTCHN) ? info->u.interdomain : NULL;
+	if (dev)
+		atomic_inc(&dev->events);
+
 	if (ctrl->defer_eoi) {
 		info->eoi_cpu = smp_processor_id();
 		info->irq_epoch = __this_cpu_read(irq_epoch);

drivers/xen/xenbus/xenbus_probe.c

@@ -206,6 +206,65 @@ void xenbus_otherend_changed(struct xenbus_watch *watch,
 }
 EXPORT_SYMBOL_GPL(xenbus_otherend_changed);
 
+#define XENBUS_SHOW_STAT(name)						\
+static ssize_t show_##name(struct device *_dev,				\
+			   struct device_attribute *attr,		\
+			   char *buf)					\
+{									\
+	struct xenbus_device *dev = to_xenbus_device(_dev);		\
+									\
+	return sprintf(buf, "%d\n", atomic_read(&dev->name));		\
+}									\
+static DEVICE_ATTR(name, 0444, show_##name, NULL)
+
+XENBUS_SHOW_STAT(event_channels);
+XENBUS_SHOW_STAT(events);
+XENBUS_SHOW_STAT(spurious_events);
+XENBUS_SHOW_STAT(jiffies_eoi_delayed);
+
+static ssize_t show_spurious_threshold(struct device *_dev,
+				       struct device_attribute *attr,
+				       char *buf)
+{
+	struct xenbus_device *dev = to_xenbus_device(_dev);
+
+	return sprintf(buf, "%d\n", dev->spurious_threshold);
+}
+
+static ssize_t set_spurious_threshold(struct device *_dev,
+				      struct device_attribute *attr,
+				      const char *buf, size_t count)
+{
+	struct xenbus_device *dev = to_xenbus_device(_dev);
+	unsigned int val;
+	ssize_t ret;
+
+	ret = kstrtouint(buf, 0, &val);
+	if (ret)
+		return ret;
+
+	dev->spurious_threshold = val;
+
+	return count;
+}
+
+static DEVICE_ATTR(spurious_threshold, 0644, show_spurious_threshold,
+		   set_spurious_threshold);
+
+static struct attribute *xenbus_attrs[] = {
+	&dev_attr_event_channels.attr,
+	&dev_attr_events.attr,
+	&dev_attr_spurious_events.attr,
+	&dev_attr_jiffies_eoi_delayed.attr,
+	&dev_attr_spurious_threshold.attr,
+	NULL
+};
+
+static const struct attribute_group xenbus_group = {
+	.name = "xenbus",
+	.attrs = xenbus_attrs,
+};
+
 int xenbus_dev_probe(struct device *_dev)
 {
 	struct xenbus_device *dev = to_xenbus_device(_dev);
@@ -253,6 +312,11 @@ int xenbus_dev_probe(struct device *_dev)
 		return err;
 	}
 
+	dev->spurious_threshold = 1;
+	if (sysfs_create_group(&dev->dev.kobj, &xenbus_group))
+		dev_warn(&dev->dev, "sysfs_create_group on %s failed.\n",
+			 dev->nodename);
+
 	return 0;
 fail_put:
 	module_put(drv->driver.owner);
@@ -269,6 +333,8 @@ int xenbus_dev_remove(struct device *_dev)
 
 	DPRINTK("%s", dev->nodename);
 
+	sysfs_remove_group(&dev->dev.kobj, &xenbus_group);
+
 	free_otherend_watch(dev);
 
 	if (drv->remove) {

include/xen/xenbus.h

@@ -88,6 +88,13 @@ struct xenbus_device {
 	struct completion down;
 	struct work_struct work;
 	struct semaphore reclaim_sem;
+
+	/* Event channel based statistics and settings. */
+	atomic_t event_channels;
+	atomic_t events;
+	atomic_t spurious_events;
+	atomic_t jiffies_eoi_delayed;
+	unsigned int spurious_threshold;
 };
 
 static inline struct xenbus_device *to_xenbus_device(struct device *dev)