Commit 06f45fe9 authored by Juergen Gross's avatar Juergen Gross Committed by Boris Ostrovsky
Browse files

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: default avatarJuergen Gross <jgross@suse.com>
Reviewed-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20210219154030.10892-7-jgross@suse.com


Signed-off-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
parent 7c70f3a7

Documentation/ABI/testing/sysfs-devices-xenbus

0 → 100644
+41 −0
Original line number Diff line number Diff line 
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

+25 −2
Original line number Diff line number Diff line
@@ -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) {

			delay = 1 << (info->spurious_cnt - 2);

		if (info->spurious_cnt > threshold) {

			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

+66 −0
Original line number Diff line number Diff line
@@ -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

+7 −0
Original line number Diff line number Diff line
@@ -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)