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, 155 insertions, 0 deletions

diff --git a/include/net/netdev_lock.h b/include/net/netdev_lock.h
new file mode 100644
index 000000000..9fb3e9385
--- /dev/null
+++ b/include/net/netdev_lock.h
@@ -0,0 +1,155 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _NET_NETDEV_LOCK_H
+#define _NET_NETDEV_LOCK_H
+
+#include <linux/lockdep.h>
+#include <linux/netdevice.h>
+#include <linux/rtnetlink.h>
+
+static inline bool netdev_trylock(struct net_device *dev)
+{
+	return mutex_trylock(&dev->lock);
+}
+
+static inline void netdev_assert_locked(const struct net_device *dev)
+{
+	lockdep_assert_held(&dev->lock);
+}
+
+static inline void
+netdev_assert_locked_or_invisible(const struct net_device *dev)
+{
+	if (dev->reg_state == NETREG_REGISTERED ||
+	    dev->reg_state == NETREG_UNREGISTERING)
+		netdev_assert_locked(dev);
+}
+
+static inline bool netdev_need_ops_lock(const struct net_device *dev)
+{
+	bool ret = dev->request_ops_lock || !!dev->queue_mgmt_ops;
+
+#if IS_ENABLED(CONFIG_NET_SHAPER)
+	ret |= !!dev->netdev_ops->net_shaper_ops;
+#endif
+
+	return ret;
+}
+
+static inline void netdev_lock_ops(struct net_device *dev)
+{
+	if (netdev_need_ops_lock(dev))
+		netdev_lock(dev);
+}
+
+static inline void netdev_unlock_ops(struct net_device *dev)
+{
+	if (netdev_need_ops_lock(dev))
+		netdev_unlock(dev);
+}
+
+static inline void netdev_lock_ops_to_full(struct net_device *dev)
+{
+	if (netdev_need_ops_lock(dev))
+		netdev_assert_locked(dev);
+	else
+		netdev_lock(dev);
+}
+
+static inline void netdev_unlock_full_to_ops(struct net_device *dev)
+{
+	if (netdev_need_ops_lock(dev))
+		netdev_assert_locked(dev);
+	else
+		netdev_unlock(dev);
+}
+
+static inline void netdev_assert_locked_ops_compat(const struct net_device *dev)
+{
+	if (netdev_need_ops_lock(dev))
+		lockdep_assert_held(&dev->lock);
+	else
+		ASSERT_RTNL();
+}
+
+static inline void
+netdev_assert_locked_ops_compat_or_invisible(const struct net_device *dev)
+{
+	if (dev->reg_state == NETREG_REGISTERED ||
+	    dev->reg_state == NETREG_UNREGISTERING)
+		netdev_assert_locked_ops_compat(dev);
+}
+
+static inline void netdev_assert_locked_ops(const struct net_device *dev)
+{
+	if (netdev_need_ops_lock(dev))
+		netdev_assert_locked(dev);
+}
+
+static inline void netdev_lock_ops_compat(struct net_device *dev)
+{
+	if (netdev_need_ops_lock(dev))
+		netdev_lock(dev);
+	else
+		rtnl_lock();
+}
+
+static inline void netdev_unlock_ops_compat(struct net_device *dev)
+{
+	if (netdev_need_ops_lock(dev))
+		netdev_unlock(dev);
+	else
+		rtnl_unlock();
+}
+
+/* Matching "ops protected" category from netdevice.h */
+static inline int netdev_is_locked_ops_compat(const struct net_device *dev)
+{
+	if (netdev_need_ops_lock(dev))
+		return lockdep_is_held(&dev->lock);
+	return lockdep_rtnl_is_held();
+}
+
+static inline int netdev_lock_cmp_fn(const struct lockdep_map *a,
+				     const struct lockdep_map *b)
+{
+	if (a == b)
+		return 0;
+
+	/* Allow locking multiple devices only under rtnl_lock,
+	 * the exact order doesn't matter.
+	 * Note that upper devices don't lock their ops, so nesting
+	 * mostly happens in batched device removal for now.
+	 */
+	return lockdep_rtnl_is_held() ? -1 : 1;
+}
+
+#define netdev_lockdep_set_classes(dev)				\
+{								\
+	static struct lock_class_key qdisc_tx_busylock_key;	\
+	static struct lock_class_key qdisc_xmit_lock_key;	\
+	static struct lock_class_key dev_addr_list_lock_key;	\
+	static struct lock_class_key dev_instance_lock_key;	\
+	unsigned int i;						\
+								\
+	(dev)->qdisc_tx_busylock = &qdisc_tx_busylock_key;	\
+	lockdep_set_class(&(dev)->addr_list_lock,		\
+			  &dev_addr_list_lock_key);		\
+	lockdep_set_class(&(dev)->lock,				\
+			  &dev_instance_lock_key);		\
+	lock_set_cmp_fn(&dev->lock, netdev_lock_cmp_fn, NULL);	\
+	for (i = 0; i < (dev)->num_tx_queues; i++)		\
+		lockdep_set_class(&(dev)->_tx[i]._xmit_lock,	\
+				  &qdisc_xmit_lock_key);	\
+}
+
+#define netdev_lock_dereference(p, dev)				\
+	rcu_dereference_protected(p, lockdep_is_held(&(dev)->lock))
+
+#define netdev_ops_lock_dereference(p, dev)				\
+	rcu_dereference_protected(p, netdev_is_locked_ops_compat(dev))
+
+int netdev_debug_event(struct notifier_block *nb, unsigned long event,
+		       void *ptr);
+
+#endif