kernel/memremap.c - linux - Git at Google

 /*
  * Copyright(c) 2015 Intel Corporation. All rights reserved.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of version 2 of the GNU General Public License as
  * published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it will be useful, but
  * WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * General Public License for more details.
  */
 #include <linux/radix-tree.h>
 #include <linux/memremap.h>
 #include <linux/device.h>
 #include <linux/types.h>
 #include <linux/pfn_t.h>
 #include <linux/io.h>
 #include <linux/mm.h>
 #include <linux/memory_hotplug.h>

 #ifndef ioremap_cache
 /* temporary while we convert existing ioremap_cache users to memremap */
 __weak void __iomem *ioremap_cache(resource_size_t offset, unsigned long size)
 {
 	return ioremap(offset, size);
 }
 #endif

 #ifndef arch_memremap_wb
 static void *arch_memremap_wb(resource_size_t offset, unsigned long size)
 {
 	return (__force void *)ioremap_cache(offset, size);
 }
 #endif

 static void *try_ram_remap(resource_size_t offset, size_t size)
 {
 	unsigned long pfn = PHYS_PFN(offset);

 	/* In the simple case just return the existing linear address */
 	if (pfn_valid(pfn) && !PageHighMem(pfn_to_page(pfn)))
 		return __va(offset);
 	return NULL; /* fallback to arch_memremap_wb */
 }

 /**
  * memremap() - remap an iomem_resource as cacheable memory
  * @offset: iomem resource start address
  * @size: size of remap
  * @flags: any of MEMREMAP_WB, MEMREMAP_WT and MEMREMAP_WC
  *
  * memremap() is "ioremap" for cases where it is known that the resource
  * being mapped does not have i/o side effects and the __iomem
  * annotation is not applicable. In the case of multiple flags, the different
  * mapping types will be attempted in the order listed below until one of
  * them succeeds.
  *
  * MEMREMAP_WB - matches the default mapping for System RAM on
  * the architecture.  This is usually a read-allocate write-back cache.
  * Morever, if MEMREMAP_WB is specified and the requested remap region is RAM
  * memremap() will bypass establishing a new mapping and instead return
  * a pointer into the direct map.
  *
  * MEMREMAP_WT - establish a mapping whereby writes either bypass the
  * cache or are written through to memory and never exist in a
  * cache-dirty state with respect to program visibility.  Attempts to
  * map System RAM with this mapping type will fail.
  *
  * MEMREMAP_WC - establish a writecombine mapping, whereby writes may
  * be coalesced together (e.g. in the CPU's write buffers), but is otherwise
  * uncached. Attempts to map System RAM with this mapping type will fail.
  */
 void *memremap(resource_size_t offset, size_t size, unsigned long flags)
 {
 	int is_ram = region_intersects(offset, size,
 				       IORESOURCE_SYSTEM_RAM, IORES_DESC_NONE);
 	void *addr = NULL;

 	if (!flags)
 		return NULL;

 	if (is_ram == REGION_MIXED) {
 		WARN_ONCE(1, "memremap attempted on mixed range %pa size: %#lx\n",
 				&offset, (unsigned long) size);
 		return NULL;
 	}

 	/* Try all mapping types requested until one returns non-NULL */
 	if (flags & MEMREMAP_WB) {
 		/*
 		 * MEMREMAP_WB is special in that it can be satisifed
 		 * from the direct map.  Some archs depend on the
 		 * capability of memremap() to autodetect cases where
 		 * the requested range is potentially in System RAM.
 		 */
 		if (is_ram == REGION_INTERSECTS)
 			addr = try_ram_remap(offset, size);
 		if (!addr)
 			addr = arch_memremap_wb(offset, size);
 	}

 	/*
 	 * If we don't have a mapping yet and other request flags are
 	 * present then we will be attempting to establish a new virtual
 	 * address mapping.  Enforce that this mapping is not aliasing
 	 * System RAM.
 	 */
 	if (!addr && is_ram == REGION_INTERSECTS && flags != MEMREMAP_WB) {
 		WARN_ONCE(1, "memremap attempted on ram %pa size: %#lx\n",
 				&offset, (unsigned long) size);
 		return NULL;
 	}

 	if (!addr && (flags & MEMREMAP_WT))
 		addr = ioremap_wt(offset, size);

 	if (!addr && (flags & MEMREMAP_WC))
 		addr = ioremap_wc(offset, size);

 	return addr;
 }
 EXPORT_SYMBOL(memremap);

 void memunmap(void *addr)
 {
 	if (is_vmalloc_addr(addr))
 		iounmap((void __iomem *) addr);
 }
 EXPORT_SYMBOL(memunmap);

 static void devm_memremap_release(struct device *dev, void *res)
 {
 	memunmap(*(void **)res);
 }

 static int devm_memremap_match(struct device *dev, void *res, void *match_data)
 {
 	return *(void **)res == match_data;
 }

 void *devm_memremap(struct device *dev, resource_size_t offset,
 		size_t size, unsigned long flags)
 {
 	void **ptr, *addr;

 	ptr = devres_alloc_node(devm_memremap_release, sizeof(*ptr), GFP_KERNEL,
 			dev_to_node(dev));
 	if (!ptr)
 		return ERR_PTR(-ENOMEM);

 	addr = memremap(offset, size, flags);
 	if (addr) {
 		*ptr = addr;
 		devres_add(dev, ptr);
 	} else {
 		devres_free(ptr);
 		return ERR_PTR(-ENXIO);
 	}

 	return addr;
 }
 EXPORT_SYMBOL(devm_memremap);

 void devm_memunmap(struct device *dev, void *addr)
 {
 	WARN_ON(devres_release(dev, devm_memremap_release,
 				devm_memremap_match, addr));
 }
 EXPORT_SYMBOL(devm_memunmap);

 #ifdef CONFIG_ZONE_DEVICE
 static DEFINE_MUTEX(pgmap_lock);
 static RADIX_TREE(pgmap_radix, GFP_KERNEL);
 #define SECTION_MASK ~((1UL << PA_SECTION_SHIFT) - 1)
 #define SECTION_SIZE (1UL << PA_SECTION_SHIFT)

 struct page_map {
 	struct resource res;
 	struct percpu_ref *ref;
 	struct dev_pagemap pgmap;
 	struct vmem_altmap altmap;
 };

 static void pgmap_radix_release(struct resource *res)
 {
 	resource_size_t key, align_start, align_size, align_end;

 	align_start = res->start & ~(SECTION_SIZE - 1);
 	align_size = ALIGN(resource_size(res), SECTION_SIZE);
 	align_end = align_start + align_size - 1;

 	mutex_lock(&pgmap_lock);
 	for (key = res->start; key <= res->end; key += SECTION_SIZE)
 		radix_tree_delete(&pgmap_radix, key >> PA_SECTION_SHIFT);
 	mutex_unlock(&pgmap_lock);
 }

 static unsigned long pfn_first(struct page_map *page_map)
 {
 	struct dev_pagemap *pgmap = &page_map->pgmap;
 	const struct resource *res = &page_map->res;
 	struct vmem_altmap *altmap = pgmap->altmap;
 	unsigned long pfn;

 	pfn = res->start >> PAGE_SHIFT;
 	if (altmap)
 		pfn += vmem_altmap_offset(altmap);
 	return pfn;
 }

 static unsigned long pfn_end(struct page_map *page_map)
 {
 	const struct resource *res = &page_map->res;

 	return (res->start + resource_size(res)) >> PAGE_SHIFT;
 }

 #define for_each_device_pfn(pfn, map) \
 	for (pfn = pfn_first(map); pfn < pfn_end(map); pfn++)

 static void devm_memremap_pages_release(struct device *dev, void *data)
 {
 	struct page_map *page_map = data;
 	struct resource *res = &page_map->res;
 	resource_size_t align_start, align_size;
 	struct dev_pagemap *pgmap = &page_map->pgmap;
 	unsigned long pfn;

 	for_each_device_pfn(pfn, page_map)
 		put_page(pfn_to_page(pfn));

 	if (percpu_ref_tryget_live(pgmap->ref)) {
 		dev_WARN(dev, "%s: page mapping is still live!\n", __func__);
 		percpu_ref_put(pgmap->ref);
 	}

 	/* pages are dead and unused, undo the arch mapping */
 	align_start = res->start & ~(SECTION_SIZE - 1);
 	align_size = ALIGN(resource_size(res), SECTION_SIZE);

 	mem_hotplug_begin();
 	arch_remove_memory(align_start, align_size);
 	mem_hotplug_done();

 	untrack_pfn(NULL, PHYS_PFN(align_start), align_size);
 	pgmap_radix_release(res);
 	dev_WARN_ONCE(dev, pgmap->altmap && pgmap->altmap->alloc,
 			"%s: failed to free all reserved pages\n", __func__);
 }

 /* assumes rcu_read_lock() held at entry */
 struct dev_pagemap *find_dev_pagemap(resource_size_t phys)
 {
 	struct page_map *page_map;

 	WARN_ON_ONCE(!rcu_read_lock_held());

 	page_map = radix_tree_lookup(&pgmap_radix, phys >> PA_SECTION_SHIFT);
 	return page_map ? &page_map->pgmap : NULL;
 }

 /**
  * devm_memremap_pages - remap and provide memmap backing for the given resource
  * @dev: hosting device for @res
  * @res: "host memory" address range
  * @ref: a live per-cpu reference count
  * @altmap: optional descriptor for allocating the memmap from @res
  *
  * Notes:
  * 1/ @ref must be 'live' on entry and 'dead' before devm_memunmap_pages() time
  *    (or devm release event). The expected order of events is that @ref has
  *    been through percpu_ref_kill() before devm_memremap_pages_release(). The
  *    wait for the completion of all references being dropped and
  *    percpu_ref_exit() must occur after devm_memremap_pages_release().
  *
  * 2/ @res is expected to be a host memory range that could feasibly be
  *    treated as a "System RAM" range, i.e. not a device mmio range, but
  *    this is not enforced.
  */
 void *devm_memremap_pages(struct device *dev, struct resource *res,
 		struct percpu_ref *ref, struct vmem_altmap *altmap)
 {
 	resource_size_t key, align_start, align_size, align_end;
 	pgprot_t pgprot = PAGE_KERNEL;
 	struct dev_pagemap *pgmap;
 	struct page_map *page_map;
 	int error, nid, is_ram;
 	unsigned long pfn;

 	align_start = res->start & ~(SECTION_SIZE - 1);
 	align_size = ALIGN(res->start + resource_size(res), SECTION_SIZE)
 		- align_start;
 	is_ram = region_intersects(align_start, align_size,
 		IORESOURCE_SYSTEM_RAM, IORES_DESC_NONE);

 	if (is_ram == REGION_MIXED) {
 		WARN_ONCE(1, "%s attempted on mixed region %pr\n",
 				__func__, res);
 		return ERR_PTR(-ENXIO);
 	}

 	if (is_ram == REGION_INTERSECTS)
 		return __va(res->start);

 	if (!ref)
 		return ERR_PTR(-EINVAL);

 	page_map = devres_alloc_node(devm_memremap_pages_release,
 			sizeof(*page_map), GFP_KERNEL, dev_to_node(dev));
 	if (!page_map)
 		return ERR_PTR(-ENOMEM);
 	pgmap = &page_map->pgmap;

 	memcpy(&page_map->res, res, sizeof(*res));

 	pgmap->dev = dev;
 	if (altmap) {
 		memcpy(&page_map->altmap, altmap, sizeof(*altmap));
 		pgmap->altmap = &page_map->altmap;
 	}
 	pgmap->ref = ref;
 	pgmap->res = &page_map->res;

 	mutex_lock(&pgmap_lock);
 	error = 0;
 	align_end = align_start + align_size - 1;
 	for (key = align_start; key <= align_end; key += SECTION_SIZE) {
 		struct dev_pagemap *dup;

 		rcu_read_lock();
 		dup = find_dev_pagemap(key);
 		rcu_read_unlock();
 		if (dup) {
 			dev_err(dev, "%s: %pr collides with mapping for %s\n",
 					__func__, res, dev_name(dup->dev));
 			error = -EBUSY;
 			break;
 		}
 		error = radix_tree_insert(&pgmap_radix, key >> PA_SECTION_SHIFT,
 				page_map);
 		if (error) {
 			dev_err(dev, "%s: failed: %d\n", __func__, error);
 			break;
 		}
 	}
 	mutex_unlock(&pgmap_lock);
 	if (error)
 		goto err_radix;

 	nid = dev_to_node(dev);
 	if (nid < 0)
 		nid = numa_mem_id();

 	error = track_pfn_remap(NULL, &pgprot, PHYS_PFN(align_start), 0,
 			align_size);
 	if (error)
 		goto err_pfn_remap;

 	mem_hotplug_begin();
 	error = arch_add_memory(nid, align_start, align_size, true);
 	mem_hotplug_done();
 	if (error)
 		goto err_add_memory;

 	for_each_device_pfn(pfn, page_map) {
 		struct page *page = pfn_to_page(pfn);

 		/*
 		 * ZONE_DEVICE pages union ->lru with a ->pgmap back
 		 * pointer.  It is a bug if a ZONE_DEVICE page is ever
 		 * freed or placed on a driver-private list.  Seed the
 		 * storage with LIST_POISON* values.
 		 */
 		list_del(&page->lru);
 		page->pgmap = pgmap;
 		percpu_ref_get(ref);
 	}
 	devres_add(dev, page_map);
 	return __va(res->start);

  err_add_memory:
 	untrack_pfn(NULL, PHYS_PFN(align_start), align_size);
  err_pfn_remap:
  err_radix:
 	pgmap_radix_release(res);
 	devres_free(page_map);
 	return ERR_PTR(error);
 }
 EXPORT_SYMBOL(devm_memremap_pages);

 unsigned long vmem_altmap_offset(struct vmem_altmap *altmap)
 {
 	/* number of pfns from base where pfn_to_page() is valid */
 	return altmap->reserve + altmap->free;
 }

 void vmem_altmap_free(struct vmem_altmap *altmap, unsigned long nr_pfns)
 {
 	altmap->alloc -= nr_pfns;
 }

 struct vmem_altmap *to_vmem_altmap(unsigned long memmap_start)
 {
 	/*
 	 * 'memmap_start' is the virtual address for the first "struct
 	 * page" in this range of the vmemmap array.  In the case of
 	 * CONFIG_SPARSEMEM_VMEMMAP a page_to_pfn conversion is simple
 	 * pointer arithmetic, so we can perform this to_vmem_altmap()
 	 * conversion without concern for the initialization state of
 	 * the struct page fields.
 	 */
 	struct page *page = (struct page *) memmap_start;
 	struct dev_pagemap *pgmap;

 	/*
 	 * Unconditionally retrieve a dev_pagemap associated with the
 	 * given physical address, this is only for use in the
 	 * arch_{add|remove}_memory() for setting up and tearing down
 	 * the memmap.
 	 */
 	rcu_read_lock();
 	pgmap = find_dev_pagemap(__pfn_to_phys(page_to_pfn(page)));
 	rcu_read_unlock();

 	return pgmap ? pgmap->altmap : NULL;
 }
 #endif /* CONFIG_ZONE_DEVICE */
	/*
	* Copyright(c) 2015 Intel Corporation. All rights reserved.
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of version 2 of the GNU General Public License as
	* published by the Free Software Foundation.
	*
	* This program is distributed in the hope that it will be useful, but
	* WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* General Public License for more details.
	*/
	#include <linux/radix-tree.h>
	#include <linux/memremap.h>
	#include <linux/device.h>
	#include <linux/types.h>
	#include <linux/pfn_t.h>
	#include <linux/io.h>
	#include <linux/mm.h>
	#include <linux/memory_hotplug.h>

	#ifndef ioremap_cache
	/* temporary while we convert existing ioremap_cache users to memremap */
	__weak void __iomem *ioremap_cache(resource_size_t offset, unsigned long size)
	{
	return ioremap(offset, size);
	}
	#endif

	#ifndef arch_memremap_wb
	static void *arch_memremap_wb(resource_size_t offset, unsigned long size)
	{
	return (__force void *)ioremap_cache(offset, size);
	}
	#endif

	static void *try_ram_remap(resource_size_t offset, size_t size)
	{
	unsigned long pfn = PHYS_PFN(offset);

	/* In the simple case just return the existing linear address */
	if (pfn_valid(pfn) && !PageHighMem(pfn_to_page(pfn)))
	return __va(offset);
	return NULL; /* fallback to arch_memremap_wb */
	}

	/**
	* memremap() - remap an iomem_resource as cacheable memory
	* @offset: iomem resource start address
	* @size: size of remap
	* @flags: any of MEMREMAP_WB, MEMREMAP_WT and MEMREMAP_WC
	*
	* memremap() is "ioremap" for cases where it is known that the resource
	* being mapped does not have i/o side effects and the __iomem
	* annotation is not applicable. In the case of multiple flags, the different
	* mapping types will be attempted in the order listed below until one of
	* them succeeds.
	*
	* MEMREMAP_WB - matches the default mapping for System RAM on
	* the architecture. This is usually a read-allocate write-back cache.
	* Morever, if MEMREMAP_WB is specified and the requested remap region is RAM
	* memremap() will bypass establishing a new mapping and instead return
	* a pointer into the direct map.
	*
	* MEMREMAP_WT - establish a mapping whereby writes either bypass the
	* cache or are written through to memory and never exist in a
	* cache-dirty state with respect to program visibility. Attempts to
	* map System RAM with this mapping type will fail.
	*
	* MEMREMAP_WC - establish a writecombine mapping, whereby writes may
	* be coalesced together (e.g. in the CPU's write buffers), but is otherwise
	* uncached. Attempts to map System RAM with this mapping type will fail.
	*/
	void *memremap(resource_size_t offset, size_t size, unsigned long flags)
	{
	int is_ram = region_intersects(offset, size,
	IORESOURCE_SYSTEM_RAM, IORES_DESC_NONE);
	void *addr = NULL;

	if (!flags)
	return NULL;

	if (is_ram == REGION_MIXED) {
	WARN_ONCE(1, "memremap attempted on mixed range %pa size: %#lx\n",
	&offset, (unsigned long) size);
	return NULL;
	}

	/* Try all mapping types requested until one returns non-NULL */
	if (flags & MEMREMAP_WB) {
	/*
	* MEMREMAP_WB is special in that it can be satisifed
	* from the direct map. Some archs depend on the
	* capability of memremap() to autodetect cases where
	* the requested range is potentially in System RAM.
	*/
	if (is_ram == REGION_INTERSECTS)
	addr = try_ram_remap(offset, size);
	if (!addr)
	addr = arch_memremap_wb(offset, size);
	}

	/*
	* If we don't have a mapping yet and other request flags are
	* present then we will be attempting to establish a new virtual
	* address mapping. Enforce that this mapping is not aliasing
	* System RAM.
	*/
	if (!addr && is_ram == REGION_INTERSECTS && flags != MEMREMAP_WB) {
	WARN_ONCE(1, "memremap attempted on ram %pa size: %#lx\n",
	&offset, (unsigned long) size);
	return NULL;
	}

	if (!addr && (flags & MEMREMAP_WT))
	addr = ioremap_wt(offset, size);

	if (!addr && (flags & MEMREMAP_WC))
	addr = ioremap_wc(offset, size);

	return addr;
	}
	EXPORT_SYMBOL(memremap);

	void memunmap(void *addr)
	{
	if (is_vmalloc_addr(addr))
	iounmap((void __iomem *) addr);
	}
	EXPORT_SYMBOL(memunmap);

	static void devm_memremap_release(struct device dev, void res)
	{
	memunmap((void *)res);
	}

	static int devm_memremap_match(struct device dev, void res, void *match_data)
	{
	return (void *)res == match_data;
	}

	void devm_memremap(struct device dev, resource_size_t offset,
	size_t size, unsigned long flags)
	{
	void *ptr, addr;

	ptr = devres_alloc_node(devm_memremap_release, sizeof(*ptr), GFP_KERNEL,
	dev_to_node(dev));
	if (!ptr)
	return ERR_PTR(-ENOMEM);

	addr = memremap(offset, size, flags);
	if (addr) {
	*ptr = addr;
	devres_add(dev, ptr);
	} else {
	devres_free(ptr);
	return ERR_PTR(-ENXIO);
	}

	return addr;
	}
	EXPORT_SYMBOL(devm_memremap);

	void devm_memunmap(struct device dev, void addr)
	{
	WARN_ON(devres_release(dev, devm_memremap_release,
	devm_memremap_match, addr));
	}
	EXPORT_SYMBOL(devm_memunmap);

	#ifdef CONFIG_ZONE_DEVICE
	static DEFINE_MUTEX(pgmap_lock);
	static RADIX_TREE(pgmap_radix, GFP_KERNEL);
	#define SECTION_MASK ~((1UL << PA_SECTION_SHIFT) - 1)
	#define SECTION_SIZE (1UL << PA_SECTION_SHIFT)

	struct page_map {
	struct resource res;
	struct percpu_ref *ref;
	struct dev_pagemap pgmap;
	struct vmem_altmap altmap;
	};

	static void pgmap_radix_release(struct resource *res)
	{
	resource_size_t key, align_start, align_size, align_end;

	align_start = res->start & ~(SECTION_SIZE - 1);
	align_size = ALIGN(resource_size(res), SECTION_SIZE);
	align_end = align_start + align_size - 1;

	mutex_lock(&pgmap_lock);
	for (key = res->start; key <= res->end; key += SECTION_SIZE)
	radix_tree_delete(&pgmap_radix, key >> PA_SECTION_SHIFT);
	mutex_unlock(&pgmap_lock);
	}

	static unsigned long pfn_first(struct page_map *page_map)
	{
	struct dev_pagemap *pgmap = &page_map->pgmap;
	const struct resource *res = &page_map->res;
	struct vmem_altmap *altmap = pgmap->altmap;
	unsigned long pfn;

	pfn = res->start >> PAGE_SHIFT;
	if (altmap)
	pfn += vmem_altmap_offset(altmap);
	return pfn;
	}

	static unsigned long pfn_end(struct page_map *page_map)
	{
	const struct resource *res = &page_map->res;

	return (res->start + resource_size(res)) >> PAGE_SHIFT;
	}

	#define for_each_device_pfn(pfn, map) \
	for (pfn = pfn_first(map); pfn < pfn_end(map); pfn++)

	static void devm_memremap_pages_release(struct device dev, void data)
	{
	struct page_map *page_map = data;
	struct resource *res = &page_map->res;
	resource_size_t align_start, align_size;
	struct dev_pagemap *pgmap = &page_map->pgmap;
	unsigned long pfn;

	for_each_device_pfn(pfn, page_map)
	put_page(pfn_to_page(pfn));

	if (percpu_ref_tryget_live(pgmap->ref)) {
	dev_WARN(dev, "%s: page mapping is still live!\n", __func__);
	percpu_ref_put(pgmap->ref);
	}

	/* pages are dead and unused, undo the arch mapping */
	align_start = res->start & ~(SECTION_SIZE - 1);
	align_size = ALIGN(resource_size(res), SECTION_SIZE);

	mem_hotplug_begin();
	arch_remove_memory(align_start, align_size);
	mem_hotplug_done();

	untrack_pfn(NULL, PHYS_PFN(align_start), align_size);
	pgmap_radix_release(res);
	dev_WARN_ONCE(dev, pgmap->altmap && pgmap->altmap->alloc,
	"%s: failed to free all reserved pages\n", __func__);
	}

	/* assumes rcu_read_lock() held at entry */
	struct dev_pagemap *find_dev_pagemap(resource_size_t phys)
	{
	struct page_map *page_map;

	WARN_ON_ONCE(!rcu_read_lock_held());

	page_map = radix_tree_lookup(&pgmap_radix, phys >> PA_SECTION_SHIFT);
	return page_map ? &page_map->pgmap : NULL;
	}

	/**
	* devm_memremap_pages - remap and provide memmap backing for the given resource
	* @dev: hosting device for @res
	* @res: "host memory" address range
	* @ref: a live per-cpu reference count
	* @altmap: optional descriptor for allocating the memmap from @res
	*
	* Notes:
	* 1/ @ref must be 'live' on entry and 'dead' before devm_memunmap_pages() time
	* (or devm release event). The expected order of events is that @ref has
	* been through percpu_ref_kill() before devm_memremap_pages_release(). The
	* wait for the completion of all references being dropped and
	* percpu_ref_exit() must occur after devm_memremap_pages_release().
	*
	* 2/ @res is expected to be a host memory range that could feasibly be
	* treated as a "System RAM" range, i.e. not a device mmio range, but
	* this is not enforced.
	*/
	void devm_memremap_pages(struct device dev, struct resource *res,
	struct percpu_ref ref, struct vmem_altmap altmap)
	{
	resource_size_t key, align_start, align_size, align_end;
	pgprot_t pgprot = PAGE_KERNEL;
	struct dev_pagemap *pgmap;
	struct page_map *page_map;
	int error, nid, is_ram;
	unsigned long pfn;

	align_start = res->start & ~(SECTION_SIZE - 1);
	align_size = ALIGN(res->start + resource_size(res), SECTION_SIZE)
	- align_start;
	is_ram = region_intersects(align_start, align_size,
	IORESOURCE_SYSTEM_RAM, IORES_DESC_NONE);

	if (is_ram == REGION_MIXED) {
	WARN_ONCE(1, "%s attempted on mixed region %pr\n",
	__func__, res);
	return ERR_PTR(-ENXIO);
	}

	if (is_ram == REGION_INTERSECTS)
	return __va(res->start);

	if (!ref)
	return ERR_PTR(-EINVAL);

	page_map = devres_alloc_node(devm_memremap_pages_release,
	sizeof(*page_map), GFP_KERNEL, dev_to_node(dev));
	if (!page_map)
	return ERR_PTR(-ENOMEM);
	pgmap = &page_map->pgmap;

	memcpy(&page_map->res, res, sizeof(*res));

	pgmap->dev = dev;
	if (altmap) {
	memcpy(&page_map->altmap, altmap, sizeof(*altmap));
	pgmap->altmap = &page_map->altmap;
	}
	pgmap->ref = ref;
	pgmap->res = &page_map->res;

	mutex_lock(&pgmap_lock);
	error = 0;
	align_end = align_start + align_size - 1;
	for (key = align_start; key <= align_end; key += SECTION_SIZE) {
	struct dev_pagemap *dup;

	rcu_read_lock();
	dup = find_dev_pagemap(key);
	rcu_read_unlock();
	if (dup) {
	dev_err(dev, "%s: %pr collides with mapping for %s\n",
	__func__, res, dev_name(dup->dev));
	error = -EBUSY;
	break;
	}
	error = radix_tree_insert(&pgmap_radix, key >> PA_SECTION_SHIFT,
	page_map);
	if (error) {
	dev_err(dev, "%s: failed: %d\n", __func__, error);
	break;
	}
	}
	mutex_unlock(&pgmap_lock);
	if (error)
	goto err_radix;

	nid = dev_to_node(dev);
	if (nid < 0)
	nid = numa_mem_id();

	error = track_pfn_remap(NULL, &pgprot, PHYS_PFN(align_start), 0,
	align_size);
	if (error)
	goto err_pfn_remap;

	mem_hotplug_begin();
	error = arch_add_memory(nid, align_start, align_size, true);
	mem_hotplug_done();
	if (error)
	goto err_add_memory;

	for_each_device_pfn(pfn, page_map) {
	struct page *page = pfn_to_page(pfn);

	/*
	* ZONE_DEVICE pages union ->lru with a ->pgmap back
	* pointer. It is a bug if a ZONE_DEVICE page is ever
	* freed or placed on a driver-private list. Seed the
	* storage with LIST_POISON* values.
	*/
	list_del(&page->lru);
	page->pgmap = pgmap;
	percpu_ref_get(ref);
	}
	devres_add(dev, page_map);
	return __va(res->start);

	err_add_memory:
	untrack_pfn(NULL, PHYS_PFN(align_start), align_size);
	err_pfn_remap:
	err_radix:
	pgmap_radix_release(res);
	devres_free(page_map);
	return ERR_PTR(error);
	}
	EXPORT_SYMBOL(devm_memremap_pages);

	unsigned long vmem_altmap_offset(struct vmem_altmap *altmap)
	{
	/* number of pfns from base where pfn_to_page() is valid */
	return altmap->reserve + altmap->free;
	}

	void vmem_altmap_free(struct vmem_altmap *altmap, unsigned long nr_pfns)
	{
	altmap->alloc -= nr_pfns;
	}

	struct vmem_altmap *to_vmem_altmap(unsigned long memmap_start)
	{
	/*
	* 'memmap_start' is the virtual address for the first "struct
	* page" in this range of the vmemmap array. In the case of
	* CONFIG_SPARSEMEM_VMEMMAP a page_to_pfn conversion is simple
	* pointer arithmetic, so we can perform this to_vmem_altmap()
	* conversion without concern for the initialization state of
	* the struct page fields.
	*/
	struct page page = (struct page ) memmap_start;
	struct dev_pagemap *pgmap;

	/*
	* Unconditionally retrieve a dev_pagemap associated with the
	* given physical address, this is only for use in the
	* arch_{add\|remove}_memory() for setting up and tearing down
	* the memmap.
	*/
	rcu_read_lock();
	pgmap = find_dev_pagemap(__pfn_to_phys(page_to_pfn(page)));
	rcu_read_unlock();

	return pgmap ? pgmap->altmap : NULL;
	}
	#endif /* CONFIG_ZONE_DEVICE */