KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 221 insertions, 0 deletions

diff --git a/drivers/input/input-poller.c b/drivers/input/input-poller.c
new file mode 100644
index 000000000..54dc07fca
--- /dev/null
+++ b/drivers/input/input-poller.c
@@ -0,0 +1,221 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Support for polling mode for input devices.
+ */
+
+#include <linux/device.h>
+#include <linux/export.h>
+#include <linux/input.h>
+#include <linux/jiffies.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/workqueue.h>
+#include "input-poller.h"
+
+struct input_dev_poller {
+	void (*poll)(struct input_dev *dev);
+
+	unsigned int poll_interval; /* msec */
+	unsigned int poll_interval_max; /* msec */
+	unsigned int poll_interval_min; /* msec */
+
+	struct input_dev *input;
+	struct delayed_work work;
+};
+
+static void input_dev_poller_queue_work(struct input_dev_poller *poller)
+{
+	unsigned long delay;
+
+	delay = msecs_to_jiffies(poller->poll_interval);
+	if (delay >= HZ)
+		delay = round_jiffies_relative(delay);
+
+	queue_delayed_work(system_freezable_wq, &poller->work, delay);
+}
+
+static void input_dev_poller_work(struct work_struct *work)
+{
+	struct input_dev_poller *poller =
+		container_of(work, struct input_dev_poller, work.work);
+
+	poller->poll(poller->input);
+	input_dev_poller_queue_work(poller);
+}
+
+void input_dev_poller_finalize(struct input_dev_poller *poller)
+{
+	if (!poller->poll_interval)
+		poller->poll_interval = 500;
+	if (!poller->poll_interval_max)
+		poller->poll_interval_max = poller->poll_interval;
+}
+
+void input_dev_poller_start(struct input_dev_poller *poller)
+{
+	/* Only start polling if polling is enabled */
+	if (poller->poll_interval > 0) {
+		poller->poll(poller->input);
+		input_dev_poller_queue_work(poller);
+	}
+}
+
+void input_dev_poller_stop(struct input_dev_poller *poller)
+{
+	cancel_delayed_work_sync(&poller->work);
+}
+
+int input_setup_polling(struct input_dev *dev,
+			void (*poll_fn)(struct input_dev *dev))
+{
+	struct input_dev_poller *poller;
+
+	poller = kzalloc_obj(*poller);
+	if (!poller) {
+		/*
+		 * We want to show message even though kzalloc() may have
+		 * printed backtrace as knowing what instance of input
+		 * device we were dealing with is helpful.
+		 */
+		dev_err(dev->dev.parent ?: &dev->dev,
+			"%s: unable to allocate poller structure\n", __func__);
+		return -ENOMEM;
+	}
+
+	INIT_DELAYED_WORK(&poller->work, input_dev_poller_work);
+	poller->input = dev;
+	poller->poll = poll_fn;
+
+	dev->poller = poller;
+	return 0;
+}
+EXPORT_SYMBOL(input_setup_polling);
+
+static bool input_dev_ensure_poller(struct input_dev *dev)
+{
+	if (!dev->poller) {
+		dev_err(dev->dev.parent ?: &dev->dev,
+			"poller structure has not been set up\n");
+		return false;
+	}
+
+	return true;
+}
+
+void input_set_poll_interval(struct input_dev *dev, unsigned int interval)
+{
+	if (input_dev_ensure_poller(dev))
+		dev->poller->poll_interval = interval;
+}
+EXPORT_SYMBOL(input_set_poll_interval);
+
+void input_set_min_poll_interval(struct input_dev *dev, unsigned int interval)
+{
+	if (input_dev_ensure_poller(dev))
+		dev->poller->poll_interval_min = interval;
+}
+EXPORT_SYMBOL(input_set_min_poll_interval);
+
+void input_set_max_poll_interval(struct input_dev *dev, unsigned int interval)
+{
+	if (input_dev_ensure_poller(dev))
+		dev->poller->poll_interval_max = interval;
+}
+EXPORT_SYMBOL(input_set_max_poll_interval);
+
+int input_get_poll_interval(struct input_dev *dev)
+{
+	if (!dev->poller)
+		return -EINVAL;
+
+	return dev->poller->poll_interval;
+}
+EXPORT_SYMBOL(input_get_poll_interval);
+
+/* SYSFS interface */
+
+static ssize_t input_dev_get_poll_interval(struct device *dev,
+					   struct device_attribute *attr,
+					   char *buf)
+{
+	struct input_dev *input = to_input_dev(dev);
+
+	return sprintf(buf, "%d\n", input->poller->poll_interval);
+}
+
+static ssize_t input_dev_set_poll_interval(struct device *dev,
+					   struct device_attribute *attr,
+					   const char *buf, size_t count)
+{
+	struct input_dev *input = to_input_dev(dev);
+	struct input_dev_poller *poller = input->poller;
+	unsigned int interval;
+	int err;
+
+	err = kstrtouint(buf, 0, &interval);
+	if (err)
+		return err;
+
+	if (interval < poller->poll_interval_min)
+		return -EINVAL;
+
+	if (interval > poller->poll_interval_max)
+		return -EINVAL;
+
+	guard(mutex)(&input->mutex);
+
+	poller->poll_interval = interval;
+
+	if (input_device_enabled(input)) {
+		cancel_delayed_work_sync(&poller->work);
+		if (poller->poll_interval > 0)
+			input_dev_poller_queue_work(poller);
+	}
+
+	return count;
+}
+
+static DEVICE_ATTR(poll, 0644,
+		   input_dev_get_poll_interval, input_dev_set_poll_interval);
+
+static ssize_t input_dev_get_poll_max(struct device *dev,
+				      struct device_attribute *attr, char *buf)
+{
+	struct input_dev *input = to_input_dev(dev);
+
+	return sprintf(buf, "%d\n", input->poller->poll_interval_max);
+}
+
+static DEVICE_ATTR(max, 0444, input_dev_get_poll_max, NULL);
+
+static ssize_t input_dev_get_poll_min(struct device *dev,
+				     struct device_attribute *attr, char *buf)
+{
+	struct input_dev *input = to_input_dev(dev);
+
+	return sprintf(buf, "%d\n", input->poller->poll_interval_min);
+}
+
+static DEVICE_ATTR(min, 0444, input_dev_get_poll_min, NULL);
+
+static umode_t input_poller_attrs_visible(struct kobject *kobj,
+					  struct attribute *attr, int n)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct input_dev *input = to_input_dev(dev);
+
+	return input->poller ? attr->mode : 0;
+}
+
+static struct attribute *input_poller_attrs[] = {
+	&dev_attr_poll.attr,
+	&dev_attr_max.attr,
+	&dev_attr_min.attr,
+	NULL
+};
+
+struct attribute_group input_poller_attribute_group = {
+	.is_visible	= input_poller_attrs_visible,
+	.attrs		= input_poller_attrs,
+};