/* SPDX-License-Identifier: GPL-2.0 */

#include <linux/mm_types_task.h>

#include <linux/auxvec.h>
#include <linux/kref.h>
#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/rbtree.h>
#include <linux/rwsem.h>
#include <linux/completion.h>
#include <linux/cpumask.h>
#include <linux/uprobes.h>
#include <linux/rcupdate.h>
#include <linux/page-flags-layout.h>
#include <linux/workqueue.h>
#include <linux/seqlock.h>

#include <asm/mmu.h>


#define INIT_PASID	0

struct address_space;
struct mem_cgroup;

 * Each physical page in the system has a struct page associated with
 * it to keep track of whatever it is we are using the page for at the
 * moment. Note that we have no way to track which tasks are using
 * a page, though if it is a pagecache page, rmap structures can tell us
 * who is mapping it.
 * If you allocate the page using alloc_pages(), you can use some of the
 * space in struct page for your own purposes.  The five words in the main
 * union are available, except for bit 0 of the first word which must be
 * kept clear.  Many users use this word to store a pointer to an object
 * which is guaranteed to be aligned.  If you use the same storage as
 * page->mapping, you must restore it to NULL before freeing the page.
 * If your page will not be mapped to userspace, you can also use the four
 * bytes in the mapcount union, but you must call page_mapcount_reset()
 * before freeing it.
 * If you want to use the refcount field, it must be used in such a way
 * that other CPUs temporarily incrementing and then decrementing the
 * refcount does not cause problems.  On receiving the page from
 * alloc_pages(), the refcount will be positive.
 * If you allocate pages of order > 0, you can use some of the fields
 * in each subpage, but you may need to restore some of their values
 * afterwards.
 * SLUB uses cmpxchg_double() to atomically update its freelist and counters.
 * That requires that freelist & counters in struct slab be adjacent and
 * double-word aligned. Because struct slab currently just reinterprets the
 * bits of struct page, we align all struct pages to double-word boundaries,
 * and ensure that 'freelist' is aligned within struct slab.
#define _struct_page_alignment	__aligned(2 * sizeof(unsigned long))
#define _struct_page_alignment

struct page {
	unsigned long flags;		/* Atomic flags, some possibly
					 * updated asynchronously */
	 * Five words (20/40 bytes) are available in this union.
	 * WARNING: bit 0 of the first word is used for PageTail(). That
	 * means the other users of this union MUST NOT use the bit to
	 * avoid collision and false-positive PageTail().
	union {
		struct {	/* Page cache and anonymous pages */
			 * @lru: Pageout list, eg. active_list protected by
			 * lruvec->lru_lock.  Sometimes used as a generic list
			 * by the page owner.
			union {
				struct list_head lru;
				/* Or, for the Unevictable "LRU list" slot */
				struct {
					/* Always even, to negate PageTail */
					void *__filler;
					/* Count page's or folio's mlocks */
					unsigned int mlock_count;
			/* See page-flags.h for PAGE_MAPPING_FLAGS */
			struct address_space *mapping;
			pgoff_t index;		/* Our offset within mapping. */
			 * @private: Mapping-private opaque data.
			 * Usually used for buffer_heads if PagePrivate.
			 * Used for swp_entry_t if PageSwapCache.
			 * Indicates order in the buddy system if PageBuddy.
			unsigned long private;
		struct {	/* page_pool used by netstack */
			 * @pp_magic: magic value to avoid recycling non
			 * page_pool allocated pages.
			unsigned long pp_magic;
			struct page_pool *pp;
			unsigned long _pp_mapping_pad;
			unsigned long dma_addr;
			union {
				 * dma_addr_upper: might require a 64-bit
				 * value on 32-bit architectures.
				unsigned long dma_addr_upper;
				 * For frag page support, not supported in
				 * 32-bit architectures with 64-bit DMA.
				atomic_long_t pp_frag_count;
		struct {	/* Tail pages of compound page */
			unsigned long compound_head;	/* Bit zero is set */

			/* First tail page only */
			unsigned char compound_dtor;
			unsigned char compound_order;
			atomic_t compound_mapcount;
			atomic_t compound_pincount;
#ifdef CONFIG_64BIT
			unsigned int compound_nr; /* 1 << compound_order */
		struct {	/* Second tail page of compound page */
			unsigned long _compound_pad_1;	/* compound_head */
			unsigned long _compound_pad_2;
			/* For both global and memcg */
			struct list_head deferred_list;
		struct {	/* Page table pages */
			unsigned long _pt_pad_1;	/* compound_head */
			pgtable_t pmd_huge_pte; /* protected by page->ptl */
			unsigned long _pt_pad_2;	/* mapping */
			union {
				struct mm_struct *pt_mm; /* x86 pgds only */
				atomic_t pt_frag_refcount; /* powerpc */
			spinlock_t *ptl;
			spinlock_t ptl;
		struct {	/* ZONE_DEVICE pages */
			/** @pgmap: Points to the hosting device page map. */
			struct dev_pagemap *pgmap;
			void *zone_device_data;
			 * ZONE_DEVICE private pages are counted as being
			 * mapped so the next 3 words hold the mapping, index,
			 * and private fields from the source anonymous or
			 * page cache page while the page is migrated to device
			 * private memory.
			 * use the mapping, index, and private fields when
			 * pmem backed DAX files are mapped.

		/** @rcu_head: You can use this to free a page by RCU. */
		struct rcu_head rcu_head;

	union {		/* This union is 4 bytes in size. */
		 * If the page can be mapped to userspace, encodes the number
		 * of times this page is referenced by a page table.
		atomic_t _mapcount;

		 * If the page is neither PageSlab nor mappable to userspace,
		 * the value stored here may help determine what this page
		 * is used for.  See page-flags.h for a list of page types
		 * which are currently stored here.
		unsigned int page_type;

	/* Usage count. *DO NOT USE DIRECTLY*. See page_ref.h */
	atomic_t _refcount;

	unsigned long memcg_data;

	 * On machines where all RAM is mapped into kernel address space,
	 * we can simply calculate the virtual address. On machines with
	 * highmem some memory is mapped into kernel virtual memory
	 * dynamically, so we need a place to store that address.
	 * Note that this field could be 16 bits on x86 ... ;)
	 * Architectures with slow multiplication can define
	 * WANT_PAGE_VIRTUAL in asm/page.h
#if defined(WANT_PAGE_VIRTUAL)
	void *virtual;			/* Kernel virtual address (NULL if
					   not kmapped, ie. highmem) */
#endif /* WANT_PAGE_VIRTUAL */

	int _last_cpupid;
} _struct_page_alignment;

 * struct folio - Represents a contiguous set of bytes.
 * @flags: Identical to the page flags.
 * @lru: Least Recently Used list; tracks how recently this folio was used.
 * @mlock_count: Number of times this folio has been pinned by mlock().
 * @mapping: The file this page belongs to, or refers to the anon_vma for
 *    anonymous memory.
 * @index: Offset within the file, in units of pages.  For anonymous memory,
 *    this is the index from the beginning of the mmap.
 * @private: Filesystem per-folio data (see folio_attach_private()).
 *    Used for swp_entry_t if folio_test_swapcache().
 * @_mapcount: Do not access this member directly.  Use folio_mapcount() to
 *    find out how many times this folio is mapped by userspace.
 * @_refcount: Do not access this member directly.  Use folio_ref_count()
 *    to find how many references there are to this folio.
 * @memcg_data: Memory Control Group data.
 * A folio is a physically, virtually and logically contiguous set
 * of bytes.  It is a power-of-two in size, and it is aligned to that
 * same power-of-two.  It is at least as large as %PAGE_SIZE.  If it is
 * in the page cache, it is at a file offset which is a multiple of that
 * power-of-two.  It may be mapped into userspace at an address which is
 * at an arbitrary page offset, but its kernel virtual address is aligned
 * to its size.
struct folio {
	/* private: don't document the anon union */
	union {
		struct {
	/* public: */
			unsigned long flags;
			union {
				struct list_head lru;
	/* private: avoid cluttering the output */
				struct {
					void *__filler;
	/* public: */
					unsigned int mlock_count;
	/* private: */
	/* public: */
			struct address_space *mapping;
			pgoff_t index;
			void *private;
			atomic_t _mapcount;
			atomic_t _refcount;
			unsigned long memcg_data;
	/* private: the union with struct page is transitional */
		struct page page;

static_assert(sizeof(struct page) == sizeof(struct folio));
#define FOLIO_MATCH(pg, fl)						\
	static_assert(offsetof(struct page, pg) == offsetof(struct folio, fl))
FOLIO_MATCH(flags, flags);
FOLIO_MATCH(lru, lru);
FOLIO_MATCH(mapping, mapping);
FOLIO_MATCH(compound_head, lru);
FOLIO_MATCH(index, index);
FOLIO_MATCH(private, private);
FOLIO_MATCH(_mapcount, _mapcount);
FOLIO_MATCH(_refcount, _refcount);
FOLIO_MATCH(memcg_data, memcg_data);

static inline atomic_t *folio_mapcount_ptr(struct folio *folio)
	struct page *tail = &folio->page + 1;
	return &tail->compound_mapcount;

static inline atomic_t *compound_mapcount_ptr(struct page *page)
	return &page[1].compound_mapcount;

static inline atomic_t *compound_pincount_ptr(struct page *page)
	return &page[1].compound_pincount;

 * Used for sizing the vmemmap region on some architectures
#define STRUCT_PAGE_MAX_SHIFT	(order_base_2(sizeof(struct page)))


 * page_private can be used on tail pages.  However, PagePrivate is only
 * checked by the VM on the head page.  So page_private on the tail pages
 * should be used for data that's ancillary to the head page (eg attaching
 * buffer heads to tail pages after attaching buffer heads to the head page)
#define page_private(page)		((page)->private)

static inline void set_page_private(struct page *page, unsigned long private)
	page->private = private;

static inline void *folio_get_private(struct folio *folio)
	return folio->private;

struct page_frag_cache {
	void * va;
	__u16 offset;
	__u16 size;
	__u32 offset;
	/* we maintain a pagecount bias, so that we dont dirty cache line
	 * containing page->_refcount every time we allocate a fragment.
	unsigned int		pagecnt_bias;
	bool pfmemalloc;

typedef unsigned long vm_flags_t;

 * A region containing a mapping of a non-memory backed file under NOMMU
 * conditions.  These are held in a global tree and are pinned by the VMAs that
 * map parts of them.
struct vm_region {
	struct rb_node	vm_rb;		/* link in global region tree */
	vm_flags_t	vm_flags;	/* VMA vm_flags */
	unsigned long	vm_start;	/* start address of region */
	unsigned long	vm_end;		/* region initialised to here */
	unsigned long	vm_top;		/* region allocated to here */
	unsigned long	vm_pgoff;	/* the offset in vm_file corresponding to vm_start */
	struct file	*vm_file;	/* the backing file or NULL */

	int		vm_usage;	/* region usage count (access under nommu_region_sem) */
	bool		vm_icache_flushed : 1; /* true if the icache has been flushed for
						* this region */

#define NULL_VM_UFFD_CTX ((struct vm_userfaultfd_ctx) { NULL, })
struct vm_userfaultfd_ctx {
	struct userfaultfd_ctx *ctx;
#define NULL_VM_UFFD_CTX ((struct vm_userfaultfd_ctx) {})
struct vm_userfaultfd_ctx {};

struct anon_vma_name {
	struct kref kref;
	/* The name needs to be at the end because it is dynamically sized. */
	char name[];

 * This struct describes a virtual memory area. There is one of these
 * per VM-area/task. A VM area is any part of the process virtual memory
 * space that has a special rule for the page-fault handlers (ie a shared
 * library, the executable area etc).
struct vm_area_struct {
	/* The first cache line has the info for VMA tree walking. */

	unsigned long vm_start;		/* Our start address within vm_mm. */
	unsigned long vm_end;		/* The first byte after our end address
					   within vm_mm. */

	/* linked list of VM areas per task, sorted by address */
	struct vm_area_struct *vm_next, *vm_prev;

	struct rb_node vm_rb;

	 * Largest free memory gap in bytes to the left of this VMA.
	 * Either between this VMA and vma->vm_prev, or between one of the
	 * VMAs below us in the VMA rbtree and its ->vm_prev. This helps
	 * get_unmapped_area find a free area of the right size.
	unsigned long rb_subtree_gap;

	/* Second cache line starts here. */

	struct mm_struct *vm_mm;	/* The address space we belong to. */

	 * Access permissions of this VMA.
	 * See vmf_insert_mixed_prot() for discussion.
	pgprot_t vm_page_prot;
	unsigned long vm_flags;		/* Flags, see mm.h. */

	 * For areas with an address space and backing store,
	 * linkage into the address_space->i_mmap interval tree.
	 * For private anonymous mappings, a pointer to a null terminated string
	 * containing the name given to the vma, or NULL if unnamed.

	union {
		struct {
			struct rb_node rb;
			unsigned long rb_subtree_last;
		} shared;
		 * Serialized by mmap_sem. Never use directly because it is
		 * valid only when vm_file is NULL. Use anon_vma_name instead.
		struct anon_vma_name *anon_name;

	 * A file's MAP_PRIVATE vma can be in both i_mmap tree and anon_vma
	 * list, after a COW of one of the file pages.	A MAP_SHARED vma
	 * can only be in the i_mmap tree.  An anonymous MAP_PRIVATE, stack
	 * or brk vma (with NULL file) can only be in an anon_vma list.
	struct list_head anon_vma_chain; /* Serialized by mmap_lock &
					  * page_table_lock */
	struct anon_vma *anon_vma;	/* Serialized by page_table_lock */

	/* Function pointers to deal with this struct. */
	const struct vm_operations_struct *vm_ops;

	/* Information about our backing store: */
	unsigned long vm_pgoff;		/* Offset (within vm_file) in PAGE_SIZE
					   units */
	struct file * vm_file;		/* File we map to (can be NULL). */
	void * vm_private_data;		/* was vm_pte (shared mem) */

	atomic_long_t swap_readahead_info;
#ifndef CONFIG_MMU
	struct vm_region *vm_region;	/* NOMMU mapping region */
	struct mempolicy *vm_policy;	/* NUMA policy for the VMA */
	struct vm_userfaultfd_ctx vm_userfaultfd_ctx;
} __randomize_layout;

struct kioctx_table;
struct mm_struct {
	struct {
		struct vm_area_struct *mmap;		/* list of VMAs */
		struct rb_root mm_rb;
		u64 vmacache_seqnum;                   /* per-thread vmacache */
		unsigned long (*get_unmapped_area) (struct file *filp,
				unsigned long addr, unsigned long len,
				unsigned long pgoff, unsigned long flags);
		unsigned long mmap_base;	/* base of mmap area */
		unsigned long mmap_legacy_base;	/* base of mmap area in bottom-up allocations */
		/* Base addresses for compatible mmap() */
		unsigned long mmap_compat_base;
		unsigned long mmap_compat_legacy_base;
		unsigned long task_size;	/* size of task vm space */
		unsigned long highest_vm_end;	/* highest vma end address */
		pgd_t * pgd;

		 * @membarrier_state: Flags controlling membarrier behavior.
		 * This field is close to @pgd to hopefully fit in the same
		 * cache-line, which needs to be touched by switch_mm().
		atomic_t membarrier_state;

		 * @mm_users: The number of users including userspace.
		 * Use mmget()/mmget_not_zero()/mmput() to modify. When this
		 * drops to 0 (i.e. when the task exits and there are no other
		 * temporary reference holders), we also release a reference on
		 * @mm_count (which may then free the &struct mm_struct if
		 * @mm_count also drops to 0).
		atomic_t mm_users;

		 * @mm_count: The number of references to &struct mm_struct
		 * (@mm_users count as 1).
		 * Use mmgrab()/mmdrop() to modify. When this drops to 0, the
		 * &struct mm_struct is freed.
		atomic_t mm_count;

		atomic_long_t pgtables_bytes;	/* PTE page table pages */
		int map_count;			/* number of VMAs */

		spinlock_t page_table_lock; /* Protects page tables and some
					     * counters
		 * With some kernel config, the current mmap_lock's offset
		 * inside 'mm_struct' is at 0x120, which is very optimal, as
		 * its two hot fields 'count' and 'owner' sit in 2 different
		 * cachelines,  and when mmap_lock is highly contended, both
		 * of the 2 fields will be accessed frequently, current layout
		 * will help to reduce cache bouncing.
		 * So please be careful with adding new fields before
		 * mmap_lock, which can easily push the 2 fields into one
		 * cacheline.
		struct rw_semaphore mmap_lock;

		struct list_head mmlist; /* List of maybe swapped mm's.	These
					  * are globally strung together off
					  * init_mm.mmlist, and are protected
					  * by mmlist_lock

		unsigned long hiwater_rss; /* High-watermark of RSS usage */
		unsigned long hiwater_vm;  /* High-water virtual memory usage */

		unsigned long total_vm;	   /* Total pages mapped */
		unsigned long locked_vm;   /* Pages that have PG_mlocked set */
		atomic64_t    pinned_vm;   /* Refcount permanently increased */
		unsigned long data_vm;	   /* VM_WRITE & ~VM_SHARED & ~VM_STACK */
		unsigned long exec_vm;	   /* VM_EXEC & ~VM_WRITE & ~VM_STACK */
		unsigned long stack_vm;	   /* VM_STACK */
		unsigned long def_flags;

		 * @write_protect_seq: Locked when any thread is write
		 * protecting pages mapped by this mm to enforce a later COW,
		 * for instance during page table copying for fork().
		seqcount_t write_protect_seq;

		spinlock_t arg_lock; /* protect the below fields */

		unsigned long start_code, end_code, start_data, end_data;
		unsigned long start_brk, brk, start_stack;
		unsigned long arg_start, arg_end, env_start, env_end;

		unsigned long saved_auxv[AT_VECTOR_SIZE]; /* for /proc/PID/auxv */

		 * Special counters, in some configurations protected by the
		 * page_table_lock, in other configurations by being atomic.
		struct mm_rss_stat rss_stat;

		struct linux_binfmt *binfmt;

		/* Architecture-specific MM context */
		mm_context_t context;

		unsigned long flags; /* Must use atomic bitops to access */

		spinlock_t			ioctx_lock;
		struct kioctx_table __rcu	*ioctx_table;
		 * "owner" points to a task that is regarded as the canonical
		 * user/owner of this mm. All of the following must be true in
		 * order for it to be changed:
		 * current == mm->owner
		 * current->mm != mm
		 * new_owner->mm == mm
		 * new_owner->alloc_lock is held
		struct task_struct __rcu *owner;
		struct user_namespace *user_ns;

		/* store ref to file /proc/<pid>/exe symlink points to */
		struct file __rcu *exe_file;
		struct mmu_notifier_subscriptions *notifier_subscriptions;
		pgtable_t pmd_huge_pte; /* protected by page_table_lock */
		 * numa_next_scan is the next time that the PTEs will be marked
		 * pte_numa. NUMA hinting faults will gather statistics and
		 * migrate pages to new nodes if necessary.
		unsigned long numa_next_scan;

		/* Restart point for scanning and setting pte_numa */
		unsigned long numa_scan_offset;

		/* numa_scan_seq prevents two threads setting pte_numa */
		int numa_scan_seq;
		 * An operation with batched TLB flushing is going on. Anything
		 * that can move process memory needs to flush the TLB when
		 * moving a PROT_NONE or PROT_NUMA mapped page.
		atomic_t tlb_flush_pending;
		/* See flush_tlb_batched_pending() */
		atomic_t tlb_flush_batched;
		struct uprobes_state uprobes_state;
		struct rcu_head delayed_drop;
		atomic_long_t hugetlb_usage;
		struct work_struct async_put_work;

		u32 pasid;
		 * Represent how many pages of this process are involved in KSM
		 * merging.
		unsigned long ksm_merging_pages;
	} __randomize_layout;

	 * The mm_cpumask needs to be at the end of mm_struct, because it
	 * is dynamically sized based on nr_cpu_ids.
	unsigned long cpu_bitmap[];

extern struct mm_struct init_mm;

/* Pointer magic because the dynamic array size confuses some compilers. */
static inline void mm_init_cpumask(struct mm_struct *mm)
	unsigned long cpu_bitmap = (unsigned long)mm;

	cpu_bitmap += offsetof(struct mm_struct, cpu_bitmap);
	cpumask_clear((struct cpumask *)cpu_bitmap);

/* Future-safe accessor for struct mm_struct's cpu_vm_mask. */
static inline cpumask_t *mm_cpumask(struct mm_struct *mm)
	return (struct cpumask *)&mm->cpu_bitmap;

struct mmu_gather;
extern void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm);
extern void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm);
extern void tlb_finish_mmu(struct mmu_gather *tlb);

struct vm_fault;

 * typedef vm_fault_t - Return type for page fault handlers.
 * Page fault handlers return a bitmask of %VM_FAULT values.
typedef __bitwise unsigned int vm_fault_t;

 * enum vm_fault_reason - Page fault handlers return a bitmask of
 * these values to tell the core VM what happened when handling the
 * fault. Used to decide whether a process gets delivered SIGBUS or
 * just gets major/minor fault counters bumped up.
 * @VM_FAULT_OOM:		Out Of Memory
 * @VM_FAULT_SIGBUS:		Bad access
 * @VM_FAULT_MAJOR:		Page read from storage
 * @VM_FAULT_WRITE:		Special case for get_user_pages
 * @VM_FAULT_HWPOISON:		Hit poisoned small page
 * @VM_FAULT_HWPOISON_LARGE:	Hit poisoned large page. Index encoded
 *				in upper bits
 * @VM_FAULT_SIGSEGV:		segmentation fault
 * @VM_FAULT_NOPAGE:		->fault installed the pte, not return page
 * @VM_FAULT_LOCKED:		->fault locked the returned page
 * @VM_FAULT_RETRY:		->fault blocked, must retry
 * @VM_FAULT_FALLBACK:		huge page fault failed, fall back to small
 * @VM_FAULT_DONE_COW:		->fault has fully handled COW
 * @VM_FAULT_NEEDDSYNC:		->fault did not modify page tables and needs
 *				fsync() to complete (for synchronous page faults
 *				in DAX)
enum vm_fault_reason {
	VM_FAULT_OOM            = (__force vm_fault_t)0x000001,
	VM_FAULT_SIGBUS         = (__force vm_fault_t)0x000002,
	VM_FAULT_MAJOR          = (__force vm_fault_t)0x000004,
	VM_FAULT_WRITE          = (__force vm_fault_t)0x000008,
	VM_FAULT_HWPOISON       = (__force vm_fault_t)0x000010,
	VM_FAULT_HWPOISON_LARGE = (__force vm_fault_t)0x000020,
	VM_FAULT_SIGSEGV        = (__force vm_fault_t)0x000040,
	VM_FAULT_NOPAGE         = (__force vm_fault_t)0x000100,
	VM_FAULT_LOCKED         = (__force vm_fault_t)0x000200,
	VM_FAULT_RETRY          = (__force vm_fault_t)0x000400,
	VM_FAULT_FALLBACK       = (__force vm_fault_t)0x000800,
	VM_FAULT_DONE_COW       = (__force vm_fault_t)0x001000,
	VM_FAULT_NEEDDSYNC      = (__force vm_fault_t)0x002000,
	VM_FAULT_HINDEX_MASK    = (__force vm_fault_t)0x0f0000,

/* Encode hstate index for a hwpoisoned large page */
#define VM_FAULT_SET_HINDEX(x) ((__force vm_fault_t)((x) << 16))
#define VM_FAULT_GET_HINDEX(x) (((__force unsigned int)(x) >> 16) & 0xf)


	{ VM_FAULT_OOM,                 "OOM" },	\
	{ VM_FAULT_SIGBUS,              "SIGBUS" },	\
	{ VM_FAULT_MAJOR,               "MAJOR" },	\
	{ VM_FAULT_WRITE,               "WRITE" },	\
	{ VM_FAULT_HWPOISON,            "HWPOISON" },	\
	{ VM_FAULT_SIGSEGV,             "SIGSEGV" },	\
	{ VM_FAULT_NOPAGE,              "NOPAGE" },	\
	{ VM_FAULT_LOCKED,              "LOCKED" },	\
	{ VM_FAULT_RETRY,               "RETRY" },	\
	{ VM_FAULT_FALLBACK,            "FALLBACK" },	\
	{ VM_FAULT_DONE_COW,            "DONE_COW" },	\

struct vm_special_mapping {
	const char *name;	/* The name, e.g. "[vdso]". */

	 * If .fault is not provided, this points to a
	 * NULL-terminated array of pages that back the special mapping.
	 * This must not be NULL unless .fault is provided.
	struct page **pages;

	 * If non-NULL, then this is called to resolve page faults
	 * on the special mapping.  If used, .pages is not checked.
	vm_fault_t (*fault)(const struct vm_special_mapping *sm,
				struct vm_area_struct *vma,
				struct vm_fault *vmf);

	int (*mremap)(const struct vm_special_mapping *sm,
		     struct vm_area_struct *new_vma);

enum tlb_flush_reason {

  * A swap entry has to fit into a "unsigned long", as the entry is hidden
  * in the "index" field of the swapper address space.
typedef struct {
	unsigned long val;
} swp_entry_t;

 * enum fault_flag - Fault flag definitions.
 * @FAULT_FLAG_WRITE: Fault was a write fault.
 * @FAULT_FLAG_MKWRITE: Fault was mkwrite of existing PTE.
 * @FAULT_FLAG_ALLOW_RETRY: Allow to retry the fault if blocked.
 * @FAULT_FLAG_RETRY_NOWAIT: Don't drop mmap_lock and wait when retrying.
 * @FAULT_FLAG_KILLABLE: The fault task is in SIGKILL killable region.
 * @FAULT_FLAG_TRIED: The fault has been tried once.
 * @FAULT_FLAG_USER: The fault originated in userspace.
 * @FAULT_FLAG_REMOTE: The fault is not for current task/mm.
 * @FAULT_FLAG_INSTRUCTION: The fault was during an instruction fetch.
 * @FAULT_FLAG_INTERRUPTIBLE: The fault can be interrupted by non-fatal signals.
 * @FAULT_FLAG_UNSHARE: The fault is an unsharing request to unshare (and mark
 *                      exclusive) a possibly shared anonymous page that is
 *                      mapped R/O.
 * @FAULT_FLAG_ORIG_PTE_VALID: whether the fault has vmf->orig_pte cached.
 *                        We should only access orig_pte if this flag set.
 * About @FAULT_FLAG_ALLOW_RETRY and @FAULT_FLAG_TRIED: we can specify
 * whether we would allow page faults to retry by specifying these two
 * fault flags correctly.  Currently there can be three legal combinations:
 * (a) ALLOW_RETRY and !TRIED:  this means the page fault allows retry, and
 *                              this is the first try
 * (b) ALLOW_RETRY and TRIED:   this means the page fault allows retry, and
 *                              we've already tried at least once
 * (c) !ALLOW_RETRY and !TRIED: this means the page fault does not allow retry
 * The unlisted combination (!ALLOW_RETRY && TRIED) is illegal and should never
 * be used.  Note that page faults can be allowed to retry for multiple times,
 * in which case we'll have an initial fault with flags (a) then later on
 * continuous faults with flags (b).  We should always try to detect pending
 * signals before a retry to make sure the continuous page faults can still be
 * interrupted if necessary.
 * The combination FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE is illegal.
 * FAULT_FLAG_UNSHARE is ignored and treated like an ordinary read fault when
 * no existing R/O-mapped anonymous page is encountered.
enum fault_flag {
	FAULT_FLAG_WRITE =		1 << 0,
	FAULT_FLAG_TRIED = 		1 << 5,
	FAULT_FLAG_USER =		1 << 6,

typedef unsigned int __bitwise zap_flags_t;

#endif /* _LINUX_MM_TYPES_H */