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, 203 insertions, 0 deletions

diff --git a/lib/objpool.c b/lib/objpool.c
new file mode 100644
index 000000000..d98fadf1d
--- /dev/null
+++ b/lib/objpool.c
@@ -0,0 +1,203 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/objpool.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/atomic.h>
+#include <linux/irqflags.h>
+#include <linux/cpumask.h>
+#include <linux/log2.h>
+
+/*
+ * objpool: ring-array based lockless MPMC/FIFO queues
+ *
+ * Copyright: wuqiang.matt@bytedance.com,mhiramat@kernel.org
+ */
+
+/* initialize percpu objpool_slot */
+static int
+objpool_init_percpu_slot(struct objpool_head *pool,
+			 struct objpool_slot *slot,
+			 int nodes, void *context,
+			 objpool_init_obj_cb objinit)
+{
+	void *obj = (void *)&slot->entries[pool->capacity];
+	int i;
+
+	/* initialize elements of percpu objpool_slot */
+	slot->mask = pool->capacity - 1;
+
+	for (i = 0; i < nodes; i++) {
+		if (objinit) {
+			int rc = objinit(obj, context);
+			if (rc)
+				return rc;
+		}
+		slot->entries[slot->tail & slot->mask] = obj;
+		obj = obj + pool->obj_size;
+		slot->tail++;
+		slot->last = slot->tail;
+		pool->nr_objs++;
+	}
+
+	return 0;
+}
+
+/* allocate and initialize percpu slots */
+static int
+objpool_init_percpu_slots(struct objpool_head *pool, int nr_objs,
+			  void *context, objpool_init_obj_cb objinit)
+{
+	int i, cpu_count = 0;
+
+	for (i = 0; i < nr_cpu_ids; i++) {
+
+		struct objpool_slot *slot;
+		int nodes, size, rc;
+
+		/* skip the cpu node which could never be present */
+		if (!cpu_possible(i))
+			continue;
+
+		/* compute how many objects to be allocated with this slot */
+		nodes = nr_objs / pool->nr_possible_cpus;
+		if (cpu_count < (nr_objs % pool->nr_possible_cpus))
+			nodes++;
+		cpu_count++;
+
+		size = struct_size(slot, entries, pool->capacity) +
+			pool->obj_size * nodes;
+
+		/*
+		 * here we allocate percpu-slot & objs together in a single
+		 * allocation to make it more compact, taking advantage of
+		 * warm caches and TLB hits. in default vmalloc is used to
+		 * reduce the pressure of kernel slab system. as we know,
+		 * mimimal size of vmalloc is one page since vmalloc would
+		 * always align the requested size to page size.
+		 * but if vmalloc fails or it is not available (e.g. GFP_ATOMIC)
+		 * allocate percpu slot with kmalloc.
+		 */
+		slot = NULL;
+
+		if ((pool->gfp & (GFP_ATOMIC | GFP_KERNEL)) != GFP_ATOMIC)
+			slot = __vmalloc_node(size, sizeof(void *), pool->gfp,
+				cpu_to_node(i), __builtin_return_address(0));
+
+		if (!slot) {
+			slot = kmalloc_node(size, pool->gfp, cpu_to_node(i));
+			if (!slot)
+				return -ENOMEM;
+		}
+		memset(slot, 0, size);
+		pool->cpu_slots[i] = slot;
+
+		/* initialize the objpool_slot of cpu node i */
+		rc = objpool_init_percpu_slot(pool, slot, nodes, context, objinit);
+		if (rc)
+			return rc;
+	}
+
+	return 0;
+}
+
+/* cleanup all percpu slots of the object pool */
+static void objpool_fini_percpu_slots(struct objpool_head *pool)
+{
+	int i;
+
+	if (!pool->cpu_slots)
+		return;
+
+	for (i = 0; i < nr_cpu_ids; i++)
+		kvfree(pool->cpu_slots[i]);
+	kfree(pool->cpu_slots);
+}
+
+/* initialize object pool and pre-allocate objects */
+int objpool_init(struct objpool_head *pool, int nr_objs, int object_size,
+		gfp_t gfp, void *context, objpool_init_obj_cb objinit,
+		objpool_fini_cb release)
+{
+	int rc, capacity, slot_size;
+
+	/* check input parameters */
+	if (nr_objs <= 0 || nr_objs > OBJPOOL_NR_OBJECT_MAX ||
+	    object_size <= 0 || object_size > OBJPOOL_OBJECT_SIZE_MAX)
+		return -EINVAL;
+
+	/* align up to unsigned long size */
+	object_size = ALIGN(object_size, sizeof(long));
+
+	/* calculate capacity of percpu objpool_slot */
+	capacity = roundup_pow_of_two(nr_objs);
+	if (!capacity)
+		return -EINVAL;
+
+	/* initialize objpool pool */
+	memset(pool, 0, sizeof(struct objpool_head));
+	pool->nr_possible_cpus = num_possible_cpus();
+	pool->obj_size = object_size;
+	pool->capacity = capacity;
+	pool->gfp = gfp & ~__GFP_ZERO;
+	pool->context = context;
+	pool->release = release;
+	slot_size = nr_cpu_ids * sizeof(struct objpool_slot *);
+	pool->cpu_slots = kzalloc(slot_size, pool->gfp);
+	if (!pool->cpu_slots)
+		return -ENOMEM;
+
+	/* initialize per-cpu slots */
+	rc = objpool_init_percpu_slots(pool, nr_objs, context, objinit);
+	if (rc)
+		objpool_fini_percpu_slots(pool);
+	else
+		refcount_set(&pool->ref, pool->nr_objs + 1);
+
+	return rc;
+}
+EXPORT_SYMBOL_GPL(objpool_init);
+
+/* release whole objpool forcely */
+void objpool_free(struct objpool_head *pool)
+{
+	if (!pool->cpu_slots)
+		return;
+
+	/* release percpu slots */
+	objpool_fini_percpu_slots(pool);
+
+	/* call user's cleanup callback if provided */
+	if (pool->release)
+		pool->release(pool, pool->context);
+}
+EXPORT_SYMBOL_GPL(objpool_free);
+
+/* drop the allocated object, rather reclaim it to objpool */
+int objpool_drop(void *obj, struct objpool_head *pool)
+{
+	if (!obj || !pool)
+		return -EINVAL;
+
+	if (refcount_dec_and_test(&pool->ref)) {
+		objpool_free(pool);
+		return 0;
+	}
+
+	return -EAGAIN;
+}
+EXPORT_SYMBOL_GPL(objpool_drop);
+
+/* drop unused objects and defref objpool for releasing */
+void objpool_fini(struct objpool_head *pool)
+{
+	int count = 1; /* extra ref for objpool itself */
+
+	/* drop all remained objects from objpool */
+	while (objpool_pop(pool))
+		count++;
+
+	if (refcount_sub_and_test(count, &pool->ref))
+		objpool_free(pool);
+}
+EXPORT_SYMBOL_GPL(objpool_fini);