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, 175 insertions, 0 deletions

diff --git a/sound/synth/util_mem.c b/sound/synth/util_mem.c
new file mode 100644
index 000000000..21893e561
--- /dev/null
+++ b/sound/synth/util_mem.c
@@ -0,0 +1,175 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (C) 2000 Takashi Iwai <tiwai@suse.de>
+ *
+ *  Generic memory management routines for soundcard memory allocation
+ */
+
+#include <linux/mutex.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <sound/core.h>
+#include <sound/util_mem.h>
+
+MODULE_AUTHOR("Takashi Iwai");
+MODULE_DESCRIPTION("Generic memory management routines for soundcard memory allocation");
+MODULE_LICENSE("GPL");
+
+#define get_memblk(p)	list_entry(p, struct snd_util_memblk, list)
+
+/*
+ * create a new memory manager
+ */
+struct snd_util_memhdr *
+snd_util_memhdr_new(int memsize)
+{
+	struct snd_util_memhdr *hdr;
+
+	hdr = kzalloc_obj(*hdr);
+	if (hdr == NULL)
+		return NULL;
+	hdr->size = memsize;
+	mutex_init(&hdr->block_mutex);
+	INIT_LIST_HEAD(&hdr->block);
+
+	return hdr;
+}
+
+/*
+ * free a memory manager
+ */
+void snd_util_memhdr_free(struct snd_util_memhdr *hdr)
+{
+	struct list_head *p;
+
+	if (!hdr)
+		return;
+	/* release all blocks */
+	while ((p = hdr->block.next) != &hdr->block) {
+		list_del(p);
+		kfree(get_memblk(p));
+	}
+	kfree(hdr);
+}
+
+/*
+ * allocate a memory block (without mutex)
+ */
+struct snd_util_memblk *
+__snd_util_mem_alloc(struct snd_util_memhdr *hdr, int size)
+{
+	struct snd_util_memblk *blk;
+	unsigned int units, prev_offset;
+	struct list_head *p;
+
+	if (snd_BUG_ON(!hdr || size <= 0))
+		return NULL;
+
+	/* word alignment */
+	units = size;
+	if (units & 1)
+		units++;
+	if (units > hdr->size)
+		return NULL;
+
+	/* look for empty block */
+	prev_offset = 0;
+	list_for_each(p, &hdr->block) {
+		blk = get_memblk(p);
+		if (blk->offset - prev_offset >= units)
+			goto __found;
+		prev_offset = blk->offset + blk->size;
+	}
+	if (hdr->size - prev_offset < units)
+		return NULL;
+
+__found:
+	return __snd_util_memblk_new(hdr, units, p->prev);
+}
+
+
+/*
+ * create a new memory block with the given size
+ * the block is linked next to prev
+ */
+struct snd_util_memblk *
+__snd_util_memblk_new(struct snd_util_memhdr *hdr, unsigned int units,
+		      struct list_head *prev)
+{
+	struct snd_util_memblk *blk;
+
+	blk = kmalloc(sizeof(struct snd_util_memblk) + hdr->block_extra_size,
+		      GFP_KERNEL);
+	if (blk == NULL)
+		return NULL;
+
+	if (prev == &hdr->block)
+		blk->offset = 0;
+	else {
+		struct snd_util_memblk *p = get_memblk(prev);
+		blk->offset = p->offset + p->size;
+	}
+	blk->size = units;
+	list_add(&blk->list, prev);
+	hdr->nblocks++;
+	hdr->used += units;
+	return blk;
+}
+
+
+/*
+ * allocate a memory block (with mutex)
+ */
+struct snd_util_memblk *
+snd_util_mem_alloc(struct snd_util_memhdr *hdr, int size)
+{
+	guard(mutex)(&hdr->block_mutex);
+	return __snd_util_mem_alloc(hdr, size);
+}
+
+
+/*
+ * remove the block from linked-list and free resource
+ * (without mutex)
+ */
+void
+__snd_util_mem_free(struct snd_util_memhdr *hdr, struct snd_util_memblk *blk)
+{
+	list_del(&blk->list);
+	hdr->nblocks--;
+	hdr->used -= blk->size;
+	kfree(blk);
+}
+
+/*
+ * free a memory block (with mutex)
+ */
+int snd_util_mem_free(struct snd_util_memhdr *hdr, struct snd_util_memblk *blk)
+{
+	if (snd_BUG_ON(!hdr || !blk))
+		return -EINVAL;
+
+	guard(mutex)(&hdr->block_mutex);
+	__snd_util_mem_free(hdr, blk);
+	return 0;
+}
+
+/*
+ * return available memory size
+ */
+int snd_util_mem_avail(struct snd_util_memhdr *hdr)
+{
+	guard(mutex)(&hdr->block_mutex);
+	return hdr->size - hdr->used;
+}
+
+
+EXPORT_SYMBOL(snd_util_memhdr_new);
+EXPORT_SYMBOL(snd_util_memhdr_free);
+EXPORT_SYMBOL(snd_util_mem_alloc);
+EXPORT_SYMBOL(snd_util_mem_free);
+EXPORT_SYMBOL(snd_util_mem_avail);
+EXPORT_SYMBOL(__snd_util_mem_alloc);
+EXPORT_SYMBOL(__snd_util_mem_free);
+EXPORT_SYMBOL(__snd_util_memblk_new);