kernel/memremap.c - pub/scm/linux/kernel/git/afaerber/linux-actions - Git at Google

 /* SPDX-License-Identifier: GPL-2.0 */
 /* Copyright(c) 2015 Intel Corporation. All rights reserved. */
 #include <linux/radix-tree.h>
 #include <linux/device.h>
 #include <linux/types.h>
 #include <linux/pfn_t.h>
 #include <linux/io.h>
 #include <linux/kasan.h>
 #include <linux/mm.h>
 #include <linux/memory_hotplug.h>
 #include <linux/swap.h>
 #include <linux/swapops.h>
 #include <linux/wait_bit.h>

 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)

 static unsigned long order_at(struct resource *res, unsigned long pgoff)
 {
 	unsigned long phys_pgoff = PHYS_PFN(res->start) + pgoff;
 	unsigned long nr_pages, mask;

 	nr_pages = PHYS_PFN(resource_size(res));
 	if (nr_pages == pgoff)
 		return ULONG_MAX;

 	/*
 	 * What is the largest aligned power-of-2 range available from
 	 * this resource pgoff to the end of the resource range,
 	 * considering the alignment of the current pgoff?
 	 */
 	mask = phys_pgoff | rounddown_pow_of_two(nr_pages - pgoff);
 	if (!mask)
 		return ULONG_MAX;

 	return find_first_bit(&mask, BITS_PER_LONG);
 }

 #define foreach_order_pgoff(res, order, pgoff) \
 	for (pgoff = 0, order = order_at((res), pgoff); order < ULONG_MAX; \
 			pgoff += 1UL << order, order = order_at((res), pgoff))

 #if IS_ENABLED(CONFIG_DEVICE_PRIVATE)
 vm_fault_t device_private_entry_fault(struct vm_area_struct *vma,
 		       unsigned long addr,
 		       swp_entry_t entry,
 		       unsigned int flags,
 		       pmd_t *pmdp)
 {
 	struct page *page = device_private_entry_to_page(entry);

 	/*
 	 * The page_fault() callback must migrate page back to system memory
 	 * so that CPU can access it. This might fail for various reasons
 	 * (device issue, device was unsafely unplugged, ...). When such
 	 * error conditions happen, the callback must return VM_FAULT_SIGBUS.
 	 *
 	 * Note that because memory cgroup charges are accounted to the device
 	 * memory, this should never fail because of memory restrictions (but
 	 * allocation of regular system page might still fail because we are
 	 * out of memory).
 	 *
 	 * There is a more in-depth description of what that callback can and
 	 * cannot do, in include/linux/memremap.h
 	 */
 	return page->pgmap->page_fault(vma, addr, page, flags, pmdp);
 }
 EXPORT_SYMBOL(device_private_entry_fault);
 #endif /* CONFIG_DEVICE_PRIVATE */

 static void pgmap_radix_release(struct resource *res, unsigned long end_pgoff)
 {
 	unsigned long pgoff, order;

 	mutex_lock(&pgmap_lock);
 	foreach_order_pgoff(res, order, pgoff) {
 		if (pgoff >= end_pgoff)
 			break;
 		radix_tree_delete(&pgmap_radix, PHYS_PFN(res->start) + pgoff);
 	}
 	mutex_unlock(&pgmap_lock);

 	synchronize_rcu();
 }

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

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

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

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

 static unsigned long pfn_next(unsigned long pfn)
 {
 	if (pfn % 1024 == 0)
 		cond_resched();
 	return pfn + 1;
 }

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

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

 	for_each_device_pfn(pfn, pgmap)
 		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(res->start + resource_size(res), SECTION_SIZE)
 		- align_start;

 	mem_hotplug_begin();
 	arch_remove_memory(align_start, align_size, pgmap->altmap_valid ?
 			&pgmap->altmap : NULL);
 	kasan_remove_zero_shadow(__va(align_start), align_size);
 	mem_hotplug_done();

 	untrack_pfn(NULL, PHYS_PFN(align_start), align_size);
 	pgmap_radix_release(res, -1);
 	dev_WARN_ONCE(dev, pgmap->altmap.alloc,
 		      "%s: failed to free all reserved pages\n", __func__);
 }

 /**
  * devm_memremap_pages - remap and provide memmap backing for the given resource
  * @dev: hosting device for @res
  * @pgmap: pointer to a struct dev_pgmap
  *
  * Notes:
  * 1/ At a minimum the res, ref and type members of @pgmap must be initialized
  *    by the caller before passing it to this function
  *
  * 2/ The altmap field may optionally be initialized, in which case altmap_valid
  *    must be set to true
  *
  * 3/ pgmap.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().
  *
  * 4/ 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 dev_pagemap *pgmap)
 {
 	resource_size_t align_start, align_size, align_end;
 	struct vmem_altmap *altmap = pgmap->altmap_valid ?
 			&pgmap->altmap : NULL;
 	struct resource *res = &pgmap->res;
 	unsigned long pfn, pgoff, order;
 	pgprot_t pgprot = PAGE_KERNEL;
 	int error, nid, is_ram;
 	struct dev_pagemap *conflict_pgmap;

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

 	conflict_pgmap = get_dev_pagemap(PHYS_PFN(align_start), NULL);
 	if (conflict_pgmap) {
 		dev_WARN(dev, "Conflicting mapping in same section\n");
 		put_dev_pagemap(conflict_pgmap);
 		return ERR_PTR(-ENOMEM);
 	}

 	conflict_pgmap = get_dev_pagemap(PHYS_PFN(align_end), NULL);
 	if (conflict_pgmap) {
 		dev_WARN(dev, "Conflicting mapping in same section\n");
 		put_dev_pagemap(conflict_pgmap);
 		return ERR_PTR(-ENOMEM);
 	}

 	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 (!pgmap->ref)
 		return ERR_PTR(-EINVAL);

 	pgmap->dev = dev;

 	mutex_lock(&pgmap_lock);
 	error = 0;

 	foreach_order_pgoff(res, order, pgoff) {
 		error = __radix_tree_insert(&pgmap_radix,
 				PHYS_PFN(res->start) + pgoff, order, pgmap);
 		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 = kasan_add_zero_shadow(__va(align_start), align_size);
 	if (error) {
 		mem_hotplug_done();
 		goto err_kasan;
 	}

 	error = arch_add_memory(nid, align_start, align_size, altmap, false);
 	if (!error)
 		move_pfn_range_to_zone(&NODE_DATA(nid)->node_zones[ZONE_DEVICE],
 					align_start >> PAGE_SHIFT,
 					align_size >> PAGE_SHIFT, altmap);
 	mem_hotplug_done();
 	if (error)
 		goto err_add_memory;

 	for_each_device_pfn(pfn, pgmap) {
 		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(pgmap->ref);
 	}

 	devm_add_action(dev, devm_memremap_pages_release, pgmap);

 	return __va(res->start);

  err_add_memory:
 	kasan_remove_zero_shadow(__va(align_start), align_size);
  err_kasan:
 	untrack_pfn(NULL, PHYS_PFN(align_start), align_size);
  err_pfn_remap:
  err_radix:
 	pgmap_radix_release(res, pgoff);
 	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;
 }

 /**
  * get_dev_pagemap() - take a new live reference on the dev_pagemap for @pfn
  * @pfn: page frame number to lookup page_map
  * @pgmap: optional known pgmap that already has a reference
  *
  * If @pgmap is non-NULL and covers @pfn it will be returned as-is.  If @pgmap
  * is non-NULL but does not cover @pfn the reference to it will be released.
  */
 struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
 		struct dev_pagemap *pgmap)
 {
 	resource_size_t phys = PFN_PHYS(pfn);

 	/*
 	 * In the cached case we're already holding a live reference.
 	 */
 	if (pgmap) {
 		if (phys >= pgmap->res.start && phys <= pgmap->res.end)
 			return pgmap;
 		put_dev_pagemap(pgmap);
 	}

 	/* fall back to slow path lookup */
 	rcu_read_lock();
 	pgmap = radix_tree_lookup(&pgmap_radix, PHYS_PFN(phys));
 	if (pgmap && !percpu_ref_tryget_live(pgmap->ref))
 		pgmap = NULL;
 	rcu_read_unlock();

 	return pgmap;
 }
 EXPORT_SYMBOL_GPL(get_dev_pagemap);

 #ifdef CONFIG_DEV_PAGEMAP_OPS
 DEFINE_STATIC_KEY_FALSE(devmap_managed_key);
 EXPORT_SYMBOL(devmap_managed_key);
 static atomic_t devmap_enable;

 /*
  * Toggle the static key for ->page_free() callbacks when dev_pagemap
  * pages go idle.
  */
 void dev_pagemap_get_ops(void)
 {
 	if (atomic_inc_return(&devmap_enable) == 1)
 		static_branch_enable(&devmap_managed_key);
 }
 EXPORT_SYMBOL_GPL(dev_pagemap_get_ops);

 void dev_pagemap_put_ops(void)
 {
 	if (atomic_dec_and_test(&devmap_enable))
 		static_branch_disable(&devmap_managed_key);
 }
 EXPORT_SYMBOL_GPL(dev_pagemap_put_ops);

 void __put_devmap_managed_page(struct page *page)
 {
 	int count = page_ref_dec_return(page);

 	/*
 	 * If refcount is 1 then page is freed and refcount is stable as nobody
 	 * holds a reference on the page.
 	 */
 	if (count == 1) {
 		/* Clear Active bit in case of parallel mark_page_accessed */
 		__ClearPageActive(page);
 		__ClearPageWaiters(page);

 		mem_cgroup_uncharge(page);

 		page->pgmap->page_free(page, page->pgmap->data);
 	} else if (!count)
 		__put_page(page);
 }
 EXPORT_SYMBOL(__put_devmap_managed_page);
 #endif /* CONFIG_DEV_PAGEMAP_OPS */
	/* SPDX-License-Identifier: GPL-2.0 */
	/* Copyright(c) 2015 Intel Corporation. All rights reserved. */
	#include <linux/radix-tree.h>
	#include <linux/device.h>
	#include <linux/types.h>
	#include <linux/pfn_t.h>
	#include <linux/io.h>
	#include <linux/kasan.h>
	#include <linux/mm.h>
	#include <linux/memory_hotplug.h>
	#include <linux/swap.h>
	#include <linux/swapops.h>
	#include <linux/wait_bit.h>

	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)

	static unsigned long order_at(struct resource *res, unsigned long pgoff)
	{
	unsigned long phys_pgoff = PHYS_PFN(res->start) + pgoff;
	unsigned long nr_pages, mask;

	nr_pages = PHYS_PFN(resource_size(res));
	if (nr_pages == pgoff)
	return ULONG_MAX;

	/*
	* What is the largest aligned power-of-2 range available from
	* this resource pgoff to the end of the resource range,
	* considering the alignment of the current pgoff?
	*/
	mask = phys_pgoff \| rounddown_pow_of_two(nr_pages - pgoff);
	if (!mask)
	return ULONG_MAX;

	return find_first_bit(&mask, BITS_PER_LONG);
	}

	#define foreach_order_pgoff(res, order, pgoff) \
	for (pgoff = 0, order = order_at((res), pgoff); order < ULONG_MAX; \
	pgoff += 1UL << order, order = order_at((res), pgoff))

	#if IS_ENABLED(CONFIG_DEVICE_PRIVATE)
	vm_fault_t device_private_entry_fault(struct vm_area_struct *vma,
	unsigned long addr,
	swp_entry_t entry,
	unsigned int flags,
	pmd_t *pmdp)
	{
	struct page *page = device_private_entry_to_page(entry);

	/*
	* The page_fault() callback must migrate page back to system memory
	* so that CPU can access it. This might fail for various reasons
	* (device issue, device was unsafely unplugged, ...). When such
	* error conditions happen, the callback must return VM_FAULT_SIGBUS.
	*
	* Note that because memory cgroup charges are accounted to the device
	* memory, this should never fail because of memory restrictions (but
	* allocation of regular system page might still fail because we are
	* out of memory).
	*
	* There is a more in-depth description of what that callback can and
	* cannot do, in include/linux/memremap.h
	*/
	return page->pgmap->page_fault(vma, addr, page, flags, pmdp);
	}
	EXPORT_SYMBOL(device_private_entry_fault);
	#endif /* CONFIG_DEVICE_PRIVATE */

	static void pgmap_radix_release(struct resource *res, unsigned long end_pgoff)
	{
	unsigned long pgoff, order;

	mutex_lock(&pgmap_lock);
	foreach_order_pgoff(res, order, pgoff) {
	if (pgoff >= end_pgoff)
	break;
	radix_tree_delete(&pgmap_radix, PHYS_PFN(res->start) + pgoff);
	}
	mutex_unlock(&pgmap_lock);

	synchronize_rcu();
	}

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

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

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

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

	static unsigned long pfn_next(unsigned long pfn)
	{
	if (pfn % 1024 == 0)
	cond_resched();
	return pfn + 1;
	}

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

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

	for_each_device_pfn(pfn, pgmap)
	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(res->start + resource_size(res), SECTION_SIZE)
	- align_start;

	mem_hotplug_begin();
	arch_remove_memory(align_start, align_size, pgmap->altmap_valid ?
	&pgmap->altmap : NULL);
	kasan_remove_zero_shadow(__va(align_start), align_size);
	mem_hotplug_done();

	untrack_pfn(NULL, PHYS_PFN(align_start), align_size);
	pgmap_radix_release(res, -1);
	dev_WARN_ONCE(dev, pgmap->altmap.alloc,
	"%s: failed to free all reserved pages\n", __func__);
	}

	/**
	* devm_memremap_pages - remap and provide memmap backing for the given resource
	* @dev: hosting device for @res
	* @pgmap: pointer to a struct dev_pgmap
	*
	* Notes:
	* 1/ At a minimum the res, ref and type members of @pgmap must be initialized
	* by the caller before passing it to this function
	*
	* 2/ The altmap field may optionally be initialized, in which case altmap_valid
	* must be set to true
	*
	* 3/ pgmap.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().
	*
	* 4/ 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 dev_pagemap *pgmap)
	{
	resource_size_t align_start, align_size, align_end;
	struct vmem_altmap *altmap = pgmap->altmap_valid ?
	&pgmap->altmap : NULL;
	struct resource *res = &pgmap->res;
	unsigned long pfn, pgoff, order;
	pgprot_t pgprot = PAGE_KERNEL;
	int error, nid, is_ram;
	struct dev_pagemap *conflict_pgmap;

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

	conflict_pgmap = get_dev_pagemap(PHYS_PFN(align_start), NULL);
	if (conflict_pgmap) {
	dev_WARN(dev, "Conflicting mapping in same section\n");
	put_dev_pagemap(conflict_pgmap);
	return ERR_PTR(-ENOMEM);
	}

	conflict_pgmap = get_dev_pagemap(PHYS_PFN(align_end), NULL);
	if (conflict_pgmap) {
	dev_WARN(dev, "Conflicting mapping in same section\n");
	put_dev_pagemap(conflict_pgmap);
	return ERR_PTR(-ENOMEM);
	}

	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 (!pgmap->ref)
	return ERR_PTR(-EINVAL);

	pgmap->dev = dev;

	mutex_lock(&pgmap_lock);
	error = 0;

	foreach_order_pgoff(res, order, pgoff) {
	error = __radix_tree_insert(&pgmap_radix,
	PHYS_PFN(res->start) + pgoff, order, pgmap);
	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 = kasan_add_zero_shadow(__va(align_start), align_size);
	if (error) {
	mem_hotplug_done();
	goto err_kasan;
	}

	error = arch_add_memory(nid, align_start, align_size, altmap, false);
	if (!error)
	move_pfn_range_to_zone(&NODE_DATA(nid)->node_zones[ZONE_DEVICE],
	align_start >> PAGE_SHIFT,
	align_size >> PAGE_SHIFT, altmap);
	mem_hotplug_done();
	if (error)
	goto err_add_memory;

	for_each_device_pfn(pfn, pgmap) {
	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(pgmap->ref);
	}

	devm_add_action(dev, devm_memremap_pages_release, pgmap);

	return __va(res->start);

	err_add_memory:
	kasan_remove_zero_shadow(__va(align_start), align_size);
	err_kasan:
	untrack_pfn(NULL, PHYS_PFN(align_start), align_size);
	err_pfn_remap:
	err_radix:
	pgmap_radix_release(res, pgoff);
	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;
	}

	/**
	* get_dev_pagemap() - take a new live reference on the dev_pagemap for @pfn
	* @pfn: page frame number to lookup page_map
	* @pgmap: optional known pgmap that already has a reference
	*
	* If @pgmap is non-NULL and covers @pfn it will be returned as-is. If @pgmap
	* is non-NULL but does not cover @pfn the reference to it will be released.
	*/
	struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
	struct dev_pagemap *pgmap)
	{
	resource_size_t phys = PFN_PHYS(pfn);

	/*
	* In the cached case we're already holding a live reference.
	*/
	if (pgmap) {
	if (phys >= pgmap->res.start && phys <= pgmap->res.end)
	return pgmap;
	put_dev_pagemap(pgmap);
	}

	/* fall back to slow path lookup */
	rcu_read_lock();
	pgmap = radix_tree_lookup(&pgmap_radix, PHYS_PFN(phys));
	if (pgmap && !percpu_ref_tryget_live(pgmap->ref))
	pgmap = NULL;
	rcu_read_unlock();

	return pgmap;
	}
	EXPORT_SYMBOL_GPL(get_dev_pagemap);

	#ifdef CONFIG_DEV_PAGEMAP_OPS
	DEFINE_STATIC_KEY_FALSE(devmap_managed_key);
	EXPORT_SYMBOL(devmap_managed_key);
	static atomic_t devmap_enable;

	/*
	* Toggle the static key for ->page_free() callbacks when dev_pagemap
	* pages go idle.
	*/
	void dev_pagemap_get_ops(void)
	{
	if (atomic_inc_return(&devmap_enable) == 1)
	static_branch_enable(&devmap_managed_key);
	}
	EXPORT_SYMBOL_GPL(dev_pagemap_get_ops);

	void dev_pagemap_put_ops(void)
	{
	if (atomic_dec_and_test(&devmap_enable))
	static_branch_disable(&devmap_managed_key);
	}
	EXPORT_SYMBOL_GPL(dev_pagemap_put_ops);

	void __put_devmap_managed_page(struct page *page)
	{
	int count = page_ref_dec_return(page);

	/*
	* If refcount is 1 then page is freed and refcount is stable as nobody
	* holds a reference on the page.
	*/
	if (count == 1) {
	/* Clear Active bit in case of parallel mark_page_accessed */
	__ClearPageActive(page);
	__ClearPageWaiters(page);

	mem_cgroup_uncharge(page);

	page->pgmap->page_free(page, page->pgmap->data);
	} else if (!count)
	__put_page(page);
	}
	EXPORT_SYMBOL(__put_devmap_managed_page);
	#endif /* CONFIG_DEV_PAGEMAP_OPS */