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, 297 insertions, 0 deletions

diff --git a/lib/closure.c b/lib/closure.c
new file mode 100644
index 000000000..2bfe7d2a0
--- /dev/null
+++ b/lib/closure.c
@@ -0,0 +1,297 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Asynchronous refcounty things
+ *
+ * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
+ * Copyright 2012 Google, Inc.
+ */
+
+#include <linux/closure.h>
+#include <linux/debugfs.h>
+#include <linux/export.h>
+#include <linux/rcupdate.h>
+#include <linux/seq_file.h>
+#include <linux/sched/debug.h>
+
+static inline void closure_put_after_sub_checks(int flags)
+{
+	int r = flags & CLOSURE_REMAINING_MASK;
+
+	if (WARN(flags & CLOSURE_GUARD_MASK,
+		 "closure has guard bits set: %x (%u)",
+		 flags & CLOSURE_GUARD_MASK, (unsigned) __fls(r)))
+		r &= ~CLOSURE_GUARD_MASK;
+
+	WARN(!r && (flags & ~CLOSURE_DESTRUCTOR),
+	     "closure ref hit 0 with incorrect flags set: %x (%u)",
+	     flags & ~CLOSURE_DESTRUCTOR, (unsigned) __fls(flags));
+}
+
+static inline void closure_put_after_sub(struct closure *cl, int flags)
+{
+	closure_put_after_sub_checks(flags);
+
+	if (!(flags & CLOSURE_REMAINING_MASK)) {
+		smp_acquire__after_ctrl_dep();
+
+		cl->closure_get_happened = false;
+
+		if (cl->fn && !(flags & CLOSURE_DESTRUCTOR)) {
+			atomic_set(&cl->remaining,
+				   CLOSURE_REMAINING_INITIALIZER);
+			closure_queue(cl);
+		} else {
+			struct closure *parent = cl->parent;
+			closure_fn *destructor = cl->fn;
+
+			closure_debug_destroy(cl);
+
+			if (destructor)
+				destructor(&cl->work);
+
+			if (parent)
+				closure_put(parent);
+		}
+	}
+}
+
+/* For clearing flags with the same atomic op as a put */
+void closure_sub(struct closure *cl, int v)
+{
+	closure_put_after_sub(cl, atomic_sub_return_release(v, &cl->remaining));
+}
+EXPORT_SYMBOL(closure_sub);
+
+/*
+ * closure_put - decrement a closure's refcount
+ */
+void closure_put(struct closure *cl)
+{
+	closure_put_after_sub(cl, atomic_dec_return_release(&cl->remaining));
+}
+EXPORT_SYMBOL(closure_put);
+
+/*
+ * closure_wake_up - wake up all closures on a wait list, without memory barrier
+ */
+void __closure_wake_up(struct closure_waitlist *wait_list)
+{
+	struct llist_node *list;
+	struct closure *cl, *t;
+	struct llist_node *reverse = NULL;
+
+	list = llist_del_all(&wait_list->list);
+
+	/* We first reverse the list to preserve FIFO ordering and fairness */
+	reverse = llist_reverse_order(list);
+
+	/* Then do the wakeups */
+	llist_for_each_entry_safe(cl, t, reverse, list) {
+		closure_set_waiting(cl, 0);
+		closure_sub(cl, CLOSURE_WAITING + 1);
+	}
+}
+EXPORT_SYMBOL(__closure_wake_up);
+
+/**
+ * closure_wait - add a closure to a waitlist
+ * @waitlist: will own a ref on @cl, which will be released when
+ * closure_wake_up() is called on @waitlist.
+ * @cl: closure pointer.
+ *
+ */
+bool closure_wait(struct closure_waitlist *waitlist, struct closure *cl)
+{
+	if (atomic_read(&cl->remaining) & CLOSURE_WAITING)
+		return false;
+
+	cl->closure_get_happened = true;
+	closure_set_waiting(cl, _RET_IP_);
+	atomic_add(CLOSURE_WAITING + 1, &cl->remaining);
+	llist_add(&cl->list, &waitlist->list);
+
+	return true;
+}
+EXPORT_SYMBOL(closure_wait);
+
+struct closure_syncer {
+	struct task_struct	*task;
+	int			done;
+};
+
+static CLOSURE_CALLBACK(closure_sync_fn)
+{
+	struct closure *cl = container_of(ws, struct closure, work);
+	struct closure_syncer *s = cl->s;
+	struct task_struct *p;
+
+	rcu_read_lock();
+	p = READ_ONCE(s->task);
+	s->done = 1;
+	wake_up_process(p);
+	rcu_read_unlock();
+}
+
+void __sched __closure_sync(struct closure *cl)
+{
+	struct closure_syncer s = { .task = current };
+
+	cl->s = &s;
+	continue_at(cl, closure_sync_fn, NULL);
+
+	while (1) {
+		set_current_state(TASK_UNINTERRUPTIBLE);
+		if (s.done)
+			break;
+		schedule();
+	}
+
+	__set_current_state(TASK_RUNNING);
+}
+EXPORT_SYMBOL(__closure_sync);
+
+/*
+ * closure_return_sync - finish running a closure, synchronously (i.e. waiting
+ * for outstanding get()s to finish) and returning once closure refcount is 0.
+ *
+ * Unlike closure_sync() this doesn't reinit the ref to 1; subsequent
+ * closure_get_not_zero() calls waill fail.
+ */
+void __sched closure_return_sync(struct closure *cl)
+{
+	struct closure_syncer s = { .task = current };
+
+	cl->s = &s;
+	set_closure_fn(cl, closure_sync_fn, NULL);
+
+	unsigned flags = atomic_sub_return_release(1 + CLOSURE_RUNNING - CLOSURE_DESTRUCTOR,
+						   &cl->remaining);
+
+	closure_put_after_sub_checks(flags);
+
+	if (unlikely(flags & CLOSURE_REMAINING_MASK)) {
+		while (1) {
+			set_current_state(TASK_UNINTERRUPTIBLE);
+			if (s.done)
+				break;
+			schedule();
+		}
+
+		__set_current_state(TASK_RUNNING);
+	}
+
+	if (cl->parent)
+		closure_put(cl->parent);
+}
+EXPORT_SYMBOL(closure_return_sync);
+
+int __sched __closure_sync_timeout(struct closure *cl, unsigned long timeout)
+{
+	struct closure_syncer s = { .task = current };
+	int ret = 0;
+
+	cl->s = &s;
+	continue_at(cl, closure_sync_fn, NULL);
+
+	while (1) {
+		set_current_state(TASK_UNINTERRUPTIBLE);
+		if (s.done)
+			break;
+		if (!timeout) {
+			/*
+			 * Carefully undo the continue_at() - but only if it
+			 * hasn't completed, i.e. the final closure_put() hasn't
+			 * happened yet:
+			 */
+			unsigned old, new, v = atomic_read(&cl->remaining);
+			do {
+				old = v;
+				if (!old || (old & CLOSURE_RUNNING))
+					goto success;
+
+				new = old + CLOSURE_REMAINING_INITIALIZER;
+			} while ((v = atomic_cmpxchg(&cl->remaining, old, new)) != old);
+			ret = -ETIME;
+		}
+
+		timeout = schedule_timeout(timeout);
+	}
+success:
+	__set_current_state(TASK_RUNNING);
+	return ret;
+}
+EXPORT_SYMBOL(__closure_sync_timeout);
+
+#ifdef CONFIG_DEBUG_CLOSURES
+
+static LIST_HEAD(closure_list);
+static DEFINE_SPINLOCK(closure_list_lock);
+
+void closure_debug_create(struct closure *cl)
+{
+	unsigned long flags;
+
+	BUG_ON(cl->magic == CLOSURE_MAGIC_ALIVE);
+	cl->magic = CLOSURE_MAGIC_ALIVE;
+
+	spin_lock_irqsave(&closure_list_lock, flags);
+	list_add(&cl->all, &closure_list);
+	spin_unlock_irqrestore(&closure_list_lock, flags);
+}
+EXPORT_SYMBOL(closure_debug_create);
+
+void closure_debug_destroy(struct closure *cl)
+{
+	unsigned long flags;
+
+	if (cl->magic == CLOSURE_MAGIC_STACK)
+		return;
+
+	BUG_ON(cl->magic != CLOSURE_MAGIC_ALIVE);
+	cl->magic = CLOSURE_MAGIC_DEAD;
+
+	spin_lock_irqsave(&closure_list_lock, flags);
+	list_del(&cl->all);
+	spin_unlock_irqrestore(&closure_list_lock, flags);
+}
+EXPORT_SYMBOL(closure_debug_destroy);
+
+static int debug_show(struct seq_file *f, void *data)
+{
+	struct closure *cl;
+
+	spin_lock_irq(&closure_list_lock);
+
+	list_for_each_entry(cl, &closure_list, all) {
+		int r = atomic_read(&cl->remaining);
+
+		seq_printf(f, "%p: %pS -> %pS p %p r %i ",
+			   cl, (void *) cl->ip, cl->fn, cl->parent,
+			   r & CLOSURE_REMAINING_MASK);
+
+		seq_printf(f, "%s%s\n",
+			   test_bit(WORK_STRUCT_PENDING_BIT,
+				    work_data_bits(&cl->work)) ? "Q" : "",
+			   r & CLOSURE_RUNNING	? "R" : "");
+
+		if (r & CLOSURE_WAITING)
+			seq_printf(f, " W %pS\n",
+				   (void *) cl->waiting_on);
+
+		seq_putc(f, '\n');
+	}
+
+	spin_unlock_irq(&closure_list_lock);
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(debug);
+
+static int __init closure_debug_init(void)
+{
+	debugfs_create_file("closures", 0400, NULL, NULL, &debug_fops);
+	return 0;
+}
+late_initcall(closure_debug_init)
+
+#endif