[PATCH v3 6/8] xen/events: add per-xenbus device event statistics and settings
From: Juergen Gross
Date: Fri Feb 19 2021 - 10:44:27 EST
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@xxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
V2:
- add documentation (Boris Ostrovsky)
---
.../ABI/testing/sysfs-devices-xenbus | 41 ++++++++++++
drivers/xen/events/events_base.c | 27 +++++++-
drivers/xen/xenbus/xenbus_probe.c | 66 +++++++++++++++++++
include/xen/xenbus.h | 7 ++
4 files changed, 139 insertions(+), 2 deletions(-)
create mode 100644 Documentation/ABI/testing/sysfs-devices-xenbus
diff --git a/Documentation/ABI/testing/sysfs-devices-xenbus b/Documentation/ABI/testing/sysfs-devices-xenbus
new file mode 100644
index 000000000000..fd796cb4f315
--- /dev/null
+++ b/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@xxxxxxxxxxxxxxxxxxxx>
+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@xxxxxxxxxxxxxxxxxxxx>
+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@xxxxxxxxxxxxxxxxxxxx>
+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@xxxxxxxxxxxxxxxxxxxx>
+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@xxxxxxxxxxxxxxxxxxxx>
+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.
diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index b60df189ecbc..a3636fb03417 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -332,6 +332,8 @@ 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;
}
@@ -606,18 +608,28 @@ 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;
}
@@ -954,6 +966,7 @@ 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);
@@ -964,6 +977,11 @@ 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;
}
@@ -1627,6 +1645,7 @@ 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)
@@ -1658,6 +1677,10 @@ void handle_irq_for_port(evtchn_port_t port, struct evtchn_loop_ctrl *ctrl)
if (xchg_acquire(&info->is_active, 1))
return;
+ 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);
diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index 8a75092bb148..97f0d234482d 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/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) {
diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h
index bf3cfc7c35d0..0b1386073d49 100644
--- a/include/xen/xenbus.h
+++ b/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)
--
2.26.2