1 files changed, 823 insertions, 0 deletions

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
new file mode 100644
index 000000000..49eb14271
--- /dev/null
+++ b/drivers/base/memory.c
@@ -0,0 +1,823 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Memory subsystem support
+ *
+ * Written by Matt Tolentino <matthew.e.tolentino@intel.com>
+ *            Dave Hansen <haveblue@us.ibm.com>
+ *
+ * This file provides the necessary infrastructure to represent
+ * a SPARSEMEM-memory-model system's physical memory in /sysfs.
+ * All arch-independent code that assumes MEMORY_HOTPLUG requires
+ * SPARSEMEM should be contained here, or in mm/memory_hotplug.c.
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/topology.h>
+#include <linux/capability.h>
+#include <linux/device.h>
+#include <linux/memory.h>
+#include <linux/memory_hotplug.h>
+#include <linux/mm.h>
+#include <linux/stat.h>
+#include <linux/slab.h>
+#include <linux/xarray.h>
+
+#include <linux/atomic.h>
+#include <linux/uaccess.h>
+
+#define MEMORY_CLASS_NAME	"memory"
+
+static const char *const online_type_to_str[] = {
+	[MMOP_OFFLINE] = "offline",
+	[MMOP_ONLINE] = "online",
+	[MMOP_ONLINE_KERNEL] = "online_kernel",
+	[MMOP_ONLINE_MOVABLE] = "online_movable",
+};
+
+int memhp_online_type_from_str(const char *str)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(online_type_to_str); i++) {
+		if (sysfs_streq(str, online_type_to_str[i]))
+			return i;
+	}
+	return -EINVAL;
+}
+
+#define to_memory_block(dev) container_of(dev, struct memory_block, dev)
+
+static int sections_per_block;
+
+static inline unsigned long memory_block_id(unsigned long section_nr)
+{
+	return section_nr / sections_per_block;
+}
+
+static inline unsigned long pfn_to_block_id(unsigned long pfn)
+{
+	return memory_block_id(pfn_to_section_nr(pfn));
+}
+
+static inline unsigned long phys_to_block_id(unsigned long phys)
+{
+	return pfn_to_block_id(PFN_DOWN(phys));
+}
+
+static int memory_subsys_online(struct device *dev);
+static int memory_subsys_offline(struct device *dev);
+
+static struct bus_type memory_subsys = {
+	.name = MEMORY_CLASS_NAME,
+	.dev_name = MEMORY_CLASS_NAME,
+	.online = memory_subsys_online,
+	.offline = memory_subsys_offline,
+};
+
+/*
+ * Memory blocks are cached in a local radix tree to avoid
+ * a costly linear search for the corresponding device on
+ * the subsystem bus.
+ */
+static DEFINE_XARRAY(memory_blocks);
+
+static BLOCKING_NOTIFIER_HEAD(memory_chain);
+
+int register_memory_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&memory_chain, nb);
+}
+EXPORT_SYMBOL(register_memory_notifier);
+
+void unregister_memory_notifier(struct notifier_block *nb)
+{
+	blocking_notifier_chain_unregister(&memory_chain, nb);
+}
+EXPORT_SYMBOL(unregister_memory_notifier);
+
+static void memory_block_release(struct device *dev)
+{
+	struct memory_block *mem = to_memory_block(dev);
+
+	kfree(mem);
+}
+
+unsigned long __weak memory_block_size_bytes(void)
+{
+	return MIN_MEMORY_BLOCK_SIZE;
+}
+EXPORT_SYMBOL_GPL(memory_block_size_bytes);
+
+/*
+ * Show the first physical section index (number) of this memory block.
+ */
+static ssize_t phys_index_show(struct device *dev,
+			       struct device_attribute *attr, char *buf)
+{
+	struct memory_block *mem = to_memory_block(dev);
+	unsigned long phys_index;
+
+	phys_index = mem->start_section_nr / sections_per_block;
+
+	return sysfs_emit(buf, "%08lx\n", phys_index);
+}
+
+/*
+ * Legacy interface that we cannot remove. Always indicate "removable"
+ * with CONFIG_MEMORY_HOTREMOVE - bad heuristic.
+ */
+static ssize_t removable_show(struct device *dev, struct device_attribute *attr,
+			      char *buf)
+{
+	return sysfs_emit(buf, "%d\n", (int)IS_ENABLED(CONFIG_MEMORY_HOTREMOVE));
+}
+
+/*
+ * online, offline, going offline, etc.
+ */
+static ssize_t state_show(struct device *dev, struct device_attribute *attr,
+			  char *buf)
+{
+	struct memory_block *mem = to_memory_block(dev);
+	const char *output;
+
+	/*
+	 * We can probably put these states in a nice little array
+	 * so that they're not open-coded
+	 */
+	switch (mem->state) {
+	case MEM_ONLINE:
+		output = "online";
+		break;
+	case MEM_OFFLINE:
+		output = "offline";
+		break;
+	case MEM_GOING_OFFLINE:
+		output = "going-offline";
+		break;
+	default:
+		WARN_ON(1);
+		return sysfs_emit(buf, "ERROR-UNKNOWN-%ld\n", mem->state);
+	}
+
+	return sysfs_emit(buf, "%s\n", output);
+}
+
+int memory_notify(unsigned long val, void *v)
+{
+	return blocking_notifier_call_chain(&memory_chain, val, v);
+}
+
+/*
+ * MEMORY_HOTPLUG depends on SPARSEMEM in mm/Kconfig, so it is
+ * OK to have direct references to sparsemem variables in here.
+ */
+static int
+memory_block_action(unsigned long start_section_nr, unsigned long action,
+		    int online_type, int nid)
+{
+	unsigned long start_pfn;
+	unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
+	int ret;
+
+	start_pfn = section_nr_to_pfn(start_section_nr);
+
+	switch (action) {
+	case MEM_ONLINE:
+		ret = online_pages(start_pfn, nr_pages, online_type, nid);
+		break;
+	case MEM_OFFLINE:
+		ret = offline_pages(start_pfn, nr_pages);
+		break;
+	default:
+		WARN(1, KERN_WARNING "%s(%ld, %ld) unknown action: "
+		     "%ld\n", __func__, start_section_nr, action, action);
+		ret = -EINVAL;
+	}
+
+	return ret;
+}
+
+static int memory_block_change_state(struct memory_block *mem,
+		unsigned long to_state, unsigned long from_state_req)
+{
+	int ret = 0;
+
+	if (mem->state != from_state_req)
+		return -EINVAL;
+
+	if (to_state == MEM_OFFLINE)
+		mem->state = MEM_GOING_OFFLINE;
+
+	ret = memory_block_action(mem->start_section_nr, to_state,
+				  mem->online_type, mem->nid);
+
+	mem->state = ret ? from_state_req : to_state;
+
+	return ret;
+}
+
+/* The device lock serializes operations on memory_subsys_[online|offline] */
+static int memory_subsys_online(struct device *dev)
+{
+	struct memory_block *mem = to_memory_block(dev);
+	int ret;
+
+	if (mem->state == MEM_ONLINE)
+		return 0;
+
+	/*
+	 * When called via device_online() without configuring the online_type,
+	 * we want to default to MMOP_ONLINE.
+	 */
+	if (mem->online_type == MMOP_OFFLINE)
+		mem->online_type = MMOP_ONLINE;
+
+	ret = memory_block_change_state(mem, MEM_ONLINE, MEM_OFFLINE);
+	mem->online_type = MMOP_OFFLINE;
+
+	return ret;
+}
+
+static int memory_subsys_offline(struct device *dev)
+{
+	struct memory_block *mem = to_memory_block(dev);
+
+	if (mem->state == MEM_OFFLINE)
+		return 0;
+
+	return memory_block_change_state(mem, MEM_OFFLINE, MEM_ONLINE);
+}
+
+static ssize_t state_store(struct device *dev, struct device_attribute *attr,
+			   const char *buf, size_t count)
+{
+	const int online_type = memhp_online_type_from_str(buf);
+	struct memory_block *mem = to_memory_block(dev);
+	int ret;
+
+	if (online_type < 0)
+		return -EINVAL;
+
+	ret = lock_device_hotplug_sysfs();
+	if (ret)
+		return ret;
+
+	switch (online_type) {
+	case MMOP_ONLINE_KERNEL:
+	case MMOP_ONLINE_MOVABLE:
+	case MMOP_ONLINE:
+		/* mem->online_type is protected by device_hotplug_lock */
+		mem->online_type = online_type;
+		ret = device_online(&mem->dev);
+		break;
+	case MMOP_OFFLINE:
+		ret = device_offline(&mem->dev);
+		break;
+	default:
+		ret = -EINVAL; /* should never happen */
+	}
+
+	unlock_device_hotplug();
+
+	if (ret < 0)
+		return ret;
+	if (ret)
+		return -EINVAL;
+
+	return count;
+}
+
+/*
+ * Legacy interface that we cannot remove: s390x exposes the storage increment
+ * covered by a memory block, allowing for identifying which memory blocks
+ * comprise a storage increment. Since a memory block spans complete
+ * storage increments nowadays, this interface is basically unused. Other
+ * archs never exposed != 0.
+ */
+static ssize_t phys_device_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct memory_block *mem = to_memory_block(dev);
+	unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr);
+
+	return sysfs_emit(buf, "%d\n",
+			  arch_get_memory_phys_device(start_pfn));
+}
+
+#ifdef CONFIG_MEMORY_HOTREMOVE
+static int print_allowed_zone(char *buf, int len, int nid,
+			      unsigned long start_pfn, unsigned long nr_pages,
+			      int online_type, struct zone *default_zone)
+{
+	struct zone *zone;
+
+	zone = zone_for_pfn_range(online_type, nid, start_pfn, nr_pages);
+	if (zone == default_zone)
+		return 0;
+
+	return sysfs_emit_at(buf, len, " %s", zone->name);
+}
+
+static ssize_t valid_zones_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct memory_block *mem = to_memory_block(dev);
+	unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr);
+	unsigned long nr_pages = PAGES_PER_SECTION * sections_per_block;
+	struct zone *default_zone;
+	int len = 0;
+	int nid;
+
+	/*
+	 * Check the existing zone. Make sure that we do that only on the
+	 * online nodes otherwise the page_zone is not reliable
+	 */
+	if (mem->state == MEM_ONLINE) {
+		/*
+		 * The block contains more than one zone can not be offlined.
+		 * This can happen e.g. for ZONE_DMA and ZONE_DMA32
+		 */
+		default_zone = test_pages_in_a_zone(start_pfn,
+						    start_pfn + nr_pages);
+		if (!default_zone)
+			return sysfs_emit(buf, "%s\n", "none");
+		len += sysfs_emit_at(buf, len, "%s", default_zone->name);
+		goto out;
+	}
+
+	nid = mem->nid;
+	default_zone = zone_for_pfn_range(MMOP_ONLINE, nid, start_pfn,
+					  nr_pages);
+
+	len += sysfs_emit_at(buf, len, "%s", default_zone->name);
+	len += print_allowed_zone(buf, len, nid, start_pfn, nr_pages,
+				  MMOP_ONLINE_KERNEL, default_zone);
+	len += print_allowed_zone(buf, len, nid, start_pfn, nr_pages,
+				  MMOP_ONLINE_MOVABLE, default_zone);
+out:
+	len += sysfs_emit_at(buf, len, "\n");
+	return len;
+}
+static DEVICE_ATTR_RO(valid_zones);
+#endif
+
+static DEVICE_ATTR_RO(phys_index);
+static DEVICE_ATTR_RW(state);
+static DEVICE_ATTR_RO(phys_device);
+static DEVICE_ATTR_RO(removable);
+
+/*
+ * Show the memory block size (shared by all memory blocks).
+ */
+static ssize_t block_size_bytes_show(struct device *dev,
+				     struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%lx\n", memory_block_size_bytes());
+}
+
+static DEVICE_ATTR_RO(block_size_bytes);
+
+/*
+ * Memory auto online policy.
+ */
+
+static ssize_t auto_online_blocks_show(struct device *dev,
+				       struct device_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%s\n",
+			  online_type_to_str[memhp_default_online_type]);
+}
+
+static ssize_t auto_online_blocks_store(struct device *dev,
+					struct device_attribute *attr,
+					const char *buf, size_t count)
+{
+	const int online_type = memhp_online_type_from_str(buf);
+
+	if (online_type < 0)
+		return -EINVAL;
+
+	memhp_default_online_type = online_type;
+	return count;
+}
+
+static DEVICE_ATTR_RW(auto_online_blocks);
+
+/*
+ * Some architectures will have custom drivers to do this, and
+ * will not need to do it from userspace.  The fake hot-add code
+ * as well as ppc64 will do all of their discovery in userspace
+ * and will require this interface.
+ */
+#ifdef CONFIG_ARCH_MEMORY_PROBE
+static ssize_t probe_store(struct device *dev, struct device_attribute *attr,
+			   const char *buf, size_t count)
+{
+	u64 phys_addr;
+	int nid, ret;
+	unsigned long pages_per_block = PAGES_PER_SECTION * sections_per_block;
+
+	ret = kstrtoull(buf, 0, &phys_addr);
+	if (ret)
+		return ret;
+
+	if (phys_addr & ((pages_per_block << PAGE_SHIFT) - 1))
+		return -EINVAL;
+
+	ret = lock_device_hotplug_sysfs();
+	if (ret)
+		return ret;
+
+	nid = memory_add_physaddr_to_nid(phys_addr);
+	ret = __add_memory(nid, phys_addr,
+			   MIN_MEMORY_BLOCK_SIZE * sections_per_block,
+			   MHP_NONE);
+
+	if (ret)
+		goto out;
+
+	ret = count;
+out:
+	unlock_device_hotplug();
+	return ret;
+}
+
+static DEVICE_ATTR_WO(probe);
+#endif
+
+#ifdef CONFIG_MEMORY_FAILURE
+/*
+ * Support for offlining pages of memory
+ */
+
+/* Soft offline a page */
+static ssize_t soft_offline_page_store(struct device *dev,
+				       struct device_attribute *attr,
+				       const char *buf, size_t count)
+{
+	int ret;
+	u64 pfn;
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+	if (kstrtoull(buf, 0, &pfn) < 0)
+		return -EINVAL;
+	pfn >>= PAGE_SHIFT;
+	ret = soft_offline_page(pfn, 0);
+	return ret == 0 ? count : ret;
+}
+
+/* Forcibly offline a page, including killing processes. */
+static ssize_t hard_offline_page_store(struct device *dev,
+				       struct device_attribute *attr,
+				       const char *buf, size_t count)
+{
+	int ret;
+	u64 pfn;
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+	if (kstrtoull(buf, 0, &pfn) < 0)
+		return -EINVAL;
+	pfn >>= PAGE_SHIFT;
+	ret = memory_failure(pfn, 0);
+	return ret ? ret : count;
+}
+
+static DEVICE_ATTR_WO(soft_offline_page);
+static DEVICE_ATTR_WO(hard_offline_page);
+#endif
+
+/* See phys_device_show(). */
+int __weak arch_get_memory_phys_device(unsigned long start_pfn)
+{
+	return 0;
+}
+
+/*
+ * A reference for the returned memory block device is acquired.
+ *
+ * Called under device_hotplug_lock.
+ */
+static struct memory_block *find_memory_block_by_id(unsigned long block_id)
+{
+	struct memory_block *mem;
+
+	mem = xa_load(&memory_blocks, block_id);
+	if (mem)
+		get_device(&mem->dev);
+	return mem;
+}
+
+/*
+ * Called under device_hotplug_lock.
+ */
+struct memory_block *find_memory_block(struct mem_section *section)
+{
+	unsigned long block_id = memory_block_id(__section_nr(section));
+
+	return find_memory_block_by_id(block_id);
+}
+
+static struct attribute *memory_memblk_attrs[] = {
+	&dev_attr_phys_index.attr,
+	&dev_attr_state.attr,
+	&dev_attr_phys_device.attr,
+	&dev_attr_removable.attr,
+#ifdef CONFIG_MEMORY_HOTREMOVE
+	&dev_attr_valid_zones.attr,
+#endif
+	NULL
+};
+
+static struct attribute_group memory_memblk_attr_group = {
+	.attrs = memory_memblk_attrs,
+};
+
+static const struct attribute_group *memory_memblk_attr_groups[] = {
+	&memory_memblk_attr_group,
+	NULL,
+};
+
+/*
+ * register_memory - Setup a sysfs device for a memory block
+ */
+static
+int register_memory(struct memory_block *memory)
+{
+	int ret;
+
+	memory->dev.bus = &memory_subsys;
+	memory->dev.id = memory->start_section_nr / sections_per_block;
+	memory->dev.release = memory_block_release;
+	memory->dev.groups = memory_memblk_attr_groups;
+	memory->dev.offline = memory->state == MEM_OFFLINE;
+
+	ret = device_register(&memory->dev);
+	if (ret) {
+		put_device(&memory->dev);
+		return ret;
+	}
+	ret = xa_err(xa_store(&memory_blocks, memory->dev.id, memory,
+			      GFP_KERNEL));
+	if (ret)
+		device_unregister(&memory->dev);
+
+	return ret;
+}
+
+static int init_memory_block(unsigned long block_id, unsigned long state)
+{
+	struct memory_block *mem;
+	int ret = 0;
+
+	mem = find_memory_block_by_id(block_id);
+	if (mem) {
+		put_device(&mem->dev);
+		return -EEXIST;
+	}
+	mem = kzalloc(sizeof(*mem), GFP_KERNEL);
+	if (!mem)
+		return -ENOMEM;
+
+	mem->start_section_nr = block_id * sections_per_block;
+	mem->state = state;
+	mem->nid = NUMA_NO_NODE;
+
+	ret = register_memory(mem);
+
+	return ret;
+}
+
+static int add_memory_block(unsigned long base_section_nr)
+{
+	int section_count = 0;
+	unsigned long nr;
+
+	for (nr = base_section_nr; nr < base_section_nr + sections_per_block;
+	     nr++)
+		if (present_section_nr(nr))
+			section_count++;
+
+	if (section_count == 0)
+		return 0;
+	return init_memory_block(memory_block_id(base_section_nr),
+				 MEM_ONLINE);
+}
+
+static void unregister_memory(struct memory_block *memory)
+{
+	if (WARN_ON_ONCE(memory->dev.bus != &memory_subsys))
+		return;
+
+	WARN_ON(xa_erase(&memory_blocks, memory->dev.id) == NULL);
+
+	/* drop the ref. we got via find_memory_block() */
+	put_device(&memory->dev);
+	device_unregister(&memory->dev);
+}
+
+/*
+ * Create memory block devices for the given memory area. Start and size
+ * have to be aligned to memory block granularity. Memory block devices
+ * will be initialized as offline.
+ *
+ * Called under device_hotplug_lock.
+ */
+int create_memory_block_devices(unsigned long start, unsigned long size)
+{
+	const unsigned long start_block_id = pfn_to_block_id(PFN_DOWN(start));
+	unsigned long end_block_id = pfn_to_block_id(PFN_DOWN(start + size));
+	struct memory_block *mem;
+	unsigned long block_id;
+	int ret = 0;
+
+	if (WARN_ON_ONCE(!IS_ALIGNED(start, memory_block_size_bytes()) ||
+			 !IS_ALIGNED(size, memory_block_size_bytes())))
+		return -EINVAL;
+
+	for (block_id = start_block_id; block_id != end_block_id; block_id++) {
+		ret = init_memory_block(block_id, MEM_OFFLINE);
+		if (ret)
+			break;
+	}
+	if (ret) {
+		end_block_id = block_id;
+		for (block_id = start_block_id; block_id != end_block_id;
+		     block_id++) {
+			mem = find_memory_block_by_id(block_id);
+			if (WARN_ON_ONCE(!mem))
+				continue;
+			unregister_memory(mem);
+		}
+	}
+	return ret;
+}
+
+/*
+ * Remove memory block devices for the given memory area. Start and size
+ * have to be aligned to memory block granularity. Memory block devices
+ * have to be offline.
+ *
+ * Called under device_hotplug_lock.
+ */
+void remove_memory_block_devices(unsigned long start, unsigned long size)
+{
+	const unsigned long start_block_id = pfn_to_block_id(PFN_DOWN(start));
+	const unsigned long end_block_id = pfn_to_block_id(PFN_DOWN(start + size));
+	struct memory_block *mem;
+	unsigned long block_id;
+
+	if (WARN_ON_ONCE(!IS_ALIGNED(start, memory_block_size_bytes()) ||
+			 !IS_ALIGNED(size, memory_block_size_bytes())))
+		return;
+
+	for (block_id = start_block_id; block_id != end_block_id; block_id++) {
+		mem = find_memory_block_by_id(block_id);
+		if (WARN_ON_ONCE(!mem))
+			continue;
+		unregister_memory_block_under_nodes(mem);
+		unregister_memory(mem);
+	}
+}
+
+/* return true if the memory block is offlined, otherwise, return false */
+bool is_memblock_offlined(struct memory_block *mem)
+{
+	return mem->state == MEM_OFFLINE;
+}
+
+static struct attribute *memory_root_attrs[] = {
+#ifdef CONFIG_ARCH_MEMORY_PROBE
+	&dev_attr_probe.attr,
+#endif
+
+#ifdef CONFIG_MEMORY_FAILURE
+	&dev_attr_soft_offline_page.attr,
+	&dev_attr_hard_offline_page.attr,
+#endif
+
+	&dev_attr_block_size_bytes.attr,
+	&dev_attr_auto_online_blocks.attr,
+	NULL
+};
+
+static struct attribute_group memory_root_attr_group = {
+	.attrs = memory_root_attrs,
+};
+
+static const struct attribute_group *memory_root_attr_groups[] = {
+	&memory_root_attr_group,
+	NULL,
+};
+
+/*
+ * Initialize the sysfs support for memory devices. At the time this function
+ * is called, we cannot have concurrent creation/deletion of memory block
+ * devices, the device_hotplug_lock is not needed.
+ */
+void __init memory_dev_init(void)
+{
+	int ret;
+	unsigned long block_sz, nr;
+
+	/* Validate the configured memory block size */
+	block_sz = memory_block_size_bytes();
+	if (!is_power_of_2(block_sz) || block_sz < MIN_MEMORY_BLOCK_SIZE)
+		panic("Memory block size not suitable: 0x%lx\n", block_sz);
+	sections_per_block = block_sz / MIN_MEMORY_BLOCK_SIZE;
+
+	ret = subsys_system_register(&memory_subsys, memory_root_attr_groups);
+	if (ret)
+		panic("%s() failed to register subsystem: %d\n", __func__, ret);
+
+	/*
+	 * Create entries for memory sections that were found
+	 * during boot and have been initialized
+	 */
+	for (nr = 0; nr <= __highest_present_section_nr;
+	     nr += sections_per_block) {
+		ret = add_memory_block(nr);
+		if (ret)
+			panic("%s() failed to add memory block: %d\n", __func__,
+			      ret);
+	}
+}
+
+/**
+ * walk_memory_blocks - walk through all present memory blocks overlapped
+ *			by the range [start, start + size)
+ *
+ * @start: start address of the memory range
+ * @size: size of the memory range
+ * @arg: argument passed to func
+ * @func: callback for each memory section walked
+ *
+ * This function walks through all present memory blocks overlapped by the
+ * range [start, start + size), calling func on each memory block.
+ *
+ * In case func() returns an error, walking is aborted and the error is
+ * returned.
+ *
+ * Called under device_hotplug_lock.
+ */
+int walk_memory_blocks(unsigned long start, unsigned long size,
+		       void *arg, walk_memory_blocks_func_t func)
+{
+	const unsigned long start_block_id = phys_to_block_id(start);
+	const unsigned long end_block_id = phys_to_block_id(start + size - 1);
+	struct memory_block *mem;
+	unsigned long block_id;
+	int ret = 0;
+
+	if (!size)
+		return 0;
+
+	for (block_id = start_block_id; block_id <= end_block_id; block_id++) {
+		mem = find_memory_block_by_id(block_id);
+		if (!mem)
+			continue;
+
+		ret = func(mem, arg);
+		put_device(&mem->dev);
+		if (ret)
+			break;
+	}
+	return ret;
+}
+
+struct for_each_memory_block_cb_data {
+	walk_memory_blocks_func_t func;
+	void *arg;
+};
+
+static int for_each_memory_block_cb(struct device *dev, void *data)
+{
+	struct memory_block *mem = to_memory_block(dev);
+	struct for_each_memory_block_cb_data *cb_data = data;
+
+	return cb_data->func(mem, cb_data->arg);
+}
+
+/**
+ * for_each_memory_block - walk through all present memory blocks
+ *
+ * @arg: argument passed to func
+ * @func: callback for each memory block walked
+ *
+ * This function walks through all present memory blocks, calling func on
+ * each memory block.
+ *
+ * In case func() returns an error, walking is aborted and the error is
+ * returned.
+ */
+int for_each_memory_block(void *arg, walk_memory_blocks_func_t func)
+{
+	struct for_each_memory_block_cb_data cb_data = {
+		.func = func,
+		.arg = arg,
+	};
+
+	return bus_for_each_dev(&memory_subsys, NULL, &cb_data,
+				for_each_memory_block_cb);
+}