Merge tag 'for-linus-5.12b-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip

Pull more xen updates from Juergen Gross:

- A small series for Xen event channels adding some sysfs nodes for per
pv-device settings and statistics, and two fixes of theoretical
problems.

- two minor fixes (one for an unlikely error path, one for a comment).

* tag 'for-linus-5.12b-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip:
xen-front-pgdir-shbuf: don't record wrong grant handle upon error
xen: Replace lkml.org links with lore
xen/evtchn: use READ/WRITE_ONCE() for accessing ring indices
xen/evtchn: use smp barriers for user event ring
xen/events: add per-xenbus device event statistics and settings

Documentation/ABI/testing/sysfs-devices-xenbus

···
+What:		/sys/devices/*/xenbus/event_channels
+Date:		February 2021
+Contact:	Xen Developers mailing list <[e-mail]>
+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 <[e-mail]>
+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 <[e-mail]>
+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 <[e-mail]>
+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 <[e-mail]>
+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

···
 
 	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;
 }
···
 		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;
 	}
···
 
 	if (VALID_EVTCHN(evtchn)) {
 		unsigned int cpu = cpu_from_irq(irq);
+		struct xenbus_device *dev;
 
 		xen_evtchn_close(evtchn);
 
···
 			break;
 		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;
···
 {
 	int irq;
 	struct irq_info *info;
+	struct xenbus_device *dev;
 
 	irq = get_evtchn_to_irq(port);
 	if (irq == -1)
···
 	}
 
 	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();

drivers/xen/evtchn.c

···
 {
 	struct user_evtchn *evtchn = data;
 	struct per_user_data *u = evtchn->user;
+	unsigned int prod, cons;
 
 	WARN(!evtchn->enabled,
 	     "Interrupt for port %u, but apparently not enabled; per-user %p\n",
···
 
 	spin_lock(&u->ring_prod_lock);
 
-	if ((u->ring_prod - u->ring_cons) < u->ring_size) {
-		*evtchn_ring_entry(u, u->ring_prod) = evtchn->port;
-		wmb(); /* Ensure ring contents visible */
-		if (u->ring_cons == u->ring_prod++) {
+	prod = READ_ONCE(u->ring_prod);
+	cons = READ_ONCE(u->ring_cons);
+
+	if ((prod - cons) < u->ring_size) {
+		*evtchn_ring_entry(u, prod) = evtchn->port;
+		smp_wmb(); /* Ensure ring contents visible */
+		WRITE_ONCE(u->ring_prod, prod + 1);
+		if (cons == prod) {
 			wake_up_interruptible(&u->evtchn_wait);
 			kill_fasync(&u->evtchn_async_queue,
 				    SIGIO, POLL_IN);
···
 		if (u->ring_overflow)
 			goto unlock_out;
 
-		c = u->ring_cons;
-		p = u->ring_prod;
+		c = READ_ONCE(u->ring_cons);
+		p = READ_ONCE(u->ring_prod);
 		if (c != p)
 			break;
 
···
 			return -EAGAIN;
 
 		rc = wait_event_interruptible(u->evtchn_wait,
-					      u->ring_cons != u->ring_prod);
+			READ_ONCE(u->ring_cons) != READ_ONCE(u->ring_prod));
 		if (rc)
 			return rc;
 	}
···
 	}
 
 	rc = -EFAULT;
-	rmb(); /* Ensure that we see the port before we copy it. */
+	smp_rmb(); /* Ensure that we see the port before we copy it. */
 	if (copy_to_user(buf, evtchn_ring_entry(u, c), bytes1) ||
 	    ((bytes2 != 0) &&
 	     copy_to_user(&buf[bytes1], &u->ring[0], bytes2)))
 		goto unlock_out;
 
-	u->ring_cons += (bytes1 + bytes2) / sizeof(evtchn_port_t);
+	WRITE_ONCE(u->ring_cons, c + (bytes1 + bytes2) / sizeof(evtchn_port_t));
 	rc = bytes1 + bytes2;
 
  unlock_out:
···
 		/* Initialise the ring to empty. Clear errors. */
 		mutex_lock(&u->ring_cons_mutex);
 		spin_lock_irq(&u->ring_prod_lock);
-		u->ring_cons = u->ring_prod = u->ring_overflow = 0;
+		WRITE_ONCE(u->ring_cons, 0);
+		WRITE_ONCE(u->ring_prod, 0);
+		u->ring_overflow = 0;
 		spin_unlock_irq(&u->ring_prod_lock);
 		mutex_unlock(&u->ring_cons_mutex);
 		rc = 0;
···
 	struct per_user_data *u = file->private_data;
 
 	poll_wait(file, &u->evtchn_wait, wait);
-	if (u->ring_cons != u->ring_prod)
+	if (READ_ONCE(u->ring_cons) != READ_ONCE(u->ring_prod))
 		mask |= EPOLLIN | EPOLLRDNORM;
 	if (u->ring_overflow)
 		mask = EPOLLERR;

drivers/xen/xen-acpi-processor.c

···
  * Copyright 2012 by Oracle Inc
  * Author: Konrad Rzeszutek Wilk <[e-mail]>
  *
- * This code borrows ideas from https://lkml.org/lkml/2011/11/30/249
+ * This code borrows ideas from
+ * https://lore.kernel.org/lkml/[e-mail]
  * so many thanks go to Kevin Tian <[e-mail]>
  * and Yu Ke <[e-mail]>.
  */

drivers/xen/xen-front-pgdir-shbuf.c

···
 
 	/* Save handles even if error, so we can unmap. */
 	for (cur_page = 0; cur_page < buf->num_pages; cur_page++) {
-		buf->backend_map_handles[cur_page] = map_ops[cur_page].handle;
-		if (unlikely(map_ops[cur_page].status != GNTST_okay))
+		if (likely(map_ops[cur_page].status == GNTST_okay)) {
+			buf->backend_map_handles[cur_page] =
+				map_ops[cur_page].handle;
+		} else {
+			buf->backend_map_handles[cur_page] =
+				INVALID_GRANT_HANDLE;
+			if (!ret)
+				ret = -ENXIO;
 			dev_err(&buf->xb_dev->dev,
 				"Failed to map page %d: %d\n",
 				cur_page, map_ops[cur_page].status);
+		}
 	}
 
 	if (ret) {

drivers/xen/xenbus/xenbus_probe.c

···
 }
 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);
···
 		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);
···
 	struct xenbus_driver *drv = to_xenbus_driver(_dev->driver);
 
 	DPRINTK("%s", dev->nodename);
+
+	sysfs_remove_group(&dev->dev.kobj, &xenbus_group);
 
 	free_otherend_watch(dev);
 

include/xen/xenbus.h

···
 	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)