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, 279 insertions, 0 deletions

diff --git a/drivers/acpi/acpica/utcache.c b/drivers/acpi/acpica/utcache.c
new file mode 100644
index 000000000..6ec2a6e88
--- /dev/null
+++ b/drivers/acpi/acpica/utcache.c
@@ -0,0 +1,279 @@
+// SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0
+/******************************************************************************
+ *
+ * Module Name: utcache - local cache allocation routines
+ *
+ * Copyright (C) 2000 - 2026, Intel Corp.
+ *
+ *****************************************************************************/
+
+#include <acpi/acpi.h>
+#include "accommon.h"
+
+#define _COMPONENT          ACPI_UTILITIES
+ACPI_MODULE_NAME("utcache")
+
+#ifdef ACPI_USE_LOCAL_CACHE
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_os_create_cache
+ *
+ * PARAMETERS:  cache_name      - Ascii name for the cache
+ *              object_size     - Size of each cached object
+ *              max_depth       - Maximum depth of the cache (in objects)
+ *              return_cache    - Where the new cache object is returned
+ *
+ * RETURN:      Status
+ *
+ * DESCRIPTION: Create a cache object
+ *
+ ******************************************************************************/
+acpi_status
+acpi_os_create_cache(char *cache_name,
+		     u16 object_size,
+		     u16 max_depth, struct acpi_memory_list **return_cache)
+{
+	struct acpi_memory_list *cache;
+
+	ACPI_FUNCTION_ENTRY();
+
+	if (!cache_name || !return_cache || !object_size) {
+		return (AE_BAD_PARAMETER);
+	}
+
+	/* Create the cache object */
+
+	cache = acpi_os_allocate(sizeof(struct acpi_memory_list));
+	if (!cache) {
+		return (AE_NO_MEMORY);
+	}
+
+	/* Populate the cache object and return it */
+
+	memset(cache, 0, sizeof(struct acpi_memory_list));
+	cache->list_name = cache_name;
+	cache->object_size = object_size;
+	cache->max_depth = max_depth;
+
+	*return_cache = cache;
+	return (AE_OK);
+}
+
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_os_purge_cache
+ *
+ * PARAMETERS:  cache           - Handle to cache object
+ *
+ * RETURN:      Status
+ *
+ * DESCRIPTION: Free all objects within the requested cache.
+ *
+ ******************************************************************************/
+
+acpi_status acpi_os_purge_cache(struct acpi_memory_list *cache)
+{
+	void *next;
+	acpi_status status;
+
+	ACPI_FUNCTION_ENTRY();
+
+	if (!cache) {
+		return (AE_BAD_PARAMETER);
+	}
+
+	status = acpi_ut_acquire_mutex(ACPI_MTX_CACHES);
+	if (ACPI_FAILURE(status)) {
+		return (status);
+	}
+
+	/* Walk the list of objects in this cache */
+
+	while (cache->list_head) {
+
+		/* Delete and unlink one cached state object */
+
+		next = ACPI_GET_DESCRIPTOR_PTR(cache->list_head);
+		ACPI_FREE(cache->list_head);
+
+		cache->list_head = next;
+		cache->current_depth--;
+	}
+
+	(void)acpi_ut_release_mutex(ACPI_MTX_CACHES);
+	return (AE_OK);
+}
+
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_os_delete_cache
+ *
+ * PARAMETERS:  cache           - Handle to cache object
+ *
+ * RETURN:      Status
+ *
+ * DESCRIPTION: Free all objects within the requested cache and delete the
+ *              cache object.
+ *
+ ******************************************************************************/
+
+acpi_status acpi_os_delete_cache(struct acpi_memory_list *cache)
+{
+	acpi_status status;
+
+	ACPI_FUNCTION_ENTRY();
+
+	/* Purge all objects in the cache */
+
+	status = acpi_os_purge_cache(cache);
+	if (ACPI_FAILURE(status)) {
+		return (status);
+	}
+
+	/* Now we can delete the cache object */
+
+	acpi_os_free(cache);
+	return (AE_OK);
+}
+
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_os_release_object
+ *
+ * PARAMETERS:  cache       - Handle to cache object
+ *              object      - The object to be released
+ *
+ * RETURN:      None
+ *
+ * DESCRIPTION: Release an object to the specified cache. If cache is full,
+ *              the object is deleted.
+ *
+ ******************************************************************************/
+
+acpi_status acpi_os_release_object(struct acpi_memory_list *cache, void *object)
+{
+	acpi_status status;
+
+	ACPI_FUNCTION_ENTRY();
+
+	if (!cache || !object) {
+		return (AE_BAD_PARAMETER);
+	}
+
+	/* If cache is full, just free this object */
+
+	if (cache->current_depth >= cache->max_depth) {
+		ACPI_FREE(object);
+		ACPI_MEM_TRACKING(cache->total_freed++);
+	}
+
+	/* Otherwise put this object back into the cache */
+
+	else {
+		status = acpi_ut_acquire_mutex(ACPI_MTX_CACHES);
+		if (ACPI_FAILURE(status)) {
+			return (status);
+		}
+
+		/* Mark the object as cached */
+
+		memset(object, 0xCA, cache->object_size);
+		ACPI_SET_DESCRIPTOR_TYPE(object, ACPI_DESC_TYPE_CACHED);
+
+		/* Put the object at the head of the cache list */
+
+		ACPI_SET_DESCRIPTOR_PTR(object, cache->list_head);
+		cache->list_head = object;
+		cache->current_depth++;
+
+		(void)acpi_ut_release_mutex(ACPI_MTX_CACHES);
+	}
+
+	return (AE_OK);
+}
+
+/*******************************************************************************
+ *
+ * FUNCTION:    acpi_os_acquire_object
+ *
+ * PARAMETERS:  cache           - Handle to cache object
+ *
+ * RETURN:      the acquired object. NULL on error
+ *
+ * DESCRIPTION: Get an object from the specified cache. If cache is empty,
+ *              the object is allocated.
+ *
+ ******************************************************************************/
+
+void *acpi_os_acquire_object(struct acpi_memory_list *cache)
+{
+	acpi_status status;
+	void *object;
+
+	ACPI_FUNCTION_TRACE(os_acquire_object);
+
+	if (!cache) {
+		return_PTR(NULL);
+	}
+
+	status = acpi_ut_acquire_mutex(ACPI_MTX_CACHES);
+	if (ACPI_FAILURE(status)) {
+		return_PTR(NULL);
+	}
+
+	ACPI_MEM_TRACKING(cache->requests++);
+
+	/* Check the cache first */
+
+	if (cache->list_head) {
+
+		/* There is an object available, use it */
+
+		object = cache->list_head;
+		cache->list_head = ACPI_GET_DESCRIPTOR_PTR(object);
+
+		cache->current_depth--;
+
+		ACPI_MEM_TRACKING(cache->hits++);
+		ACPI_DEBUG_PRINT_RAW((ACPI_DB_EXEC,
+				      "%s: Object %p from %s cache\n",
+				      ACPI_GET_FUNCTION_NAME, object,
+				      cache->list_name));
+
+		status = acpi_ut_release_mutex(ACPI_MTX_CACHES);
+		if (ACPI_FAILURE(status)) {
+			return_PTR(NULL);
+		}
+
+		/* Clear (zero) the previously used Object */
+
+		memset(object, 0, cache->object_size);
+	} else {
+		/* The cache is empty, create a new object */
+
+#ifdef ACPI_DBG_TRACK_ALLOCATIONS
+		ACPI_MEM_TRACKING(cache->total_allocated++);
+
+		if ((cache->total_allocated - cache->total_freed) >
+		    cache->max_occupied) {
+			cache->max_occupied =
+			    cache->total_allocated - cache->total_freed;
+		}
+#endif
+
+		/* Avoid deadlock with ACPI_ALLOCATE_ZEROED */
+
+		status = acpi_ut_release_mutex(ACPI_MTX_CACHES);
+		if (ACPI_FAILURE(status)) {
+			return_PTR(NULL);
+		}
+
+		object = ACPI_ALLOCATE_ZEROED(cache->object_size);
+		if (!object) {
+			return_PTR(NULL);
+		}
+	}
+
+	return_PTR(object);
+}
+#endif				/* ACPI_USE_LOCAL_CACHE */