Merge tag 's390-6.8-2' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux

[linux-2.6-microblaze.git] / include / linux / mm_types.h

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_MM_TYPES_H
#define _LINUX_MM_TYPES_H

#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/maple_tree.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 <linux/percpu_counter.h>

#include <asm/mmu.h>

#ifndef AT_VECTOR_SIZE_ARCH
#define AT_VECTOR_SIZE_ARCH 0
#endif
#define AT_VECTOR_SIZE (2*(AT_VECTOR_SIZE_ARCH + AT_VECTOR_SIZE_BASE + 1))

#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.
 */
#ifdef CONFIG_HAVE_ALIGNED_STRUCT_PAGE
#define _struct_page_alignment  __aligned(2 * sizeof(unsigned long))
#else
#define _struct_page_alignment  __aligned(sizeof(unsigned long))
#endif

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;
                                };

                                /* Or, free page */
                                struct list_head buddy_list;
                                struct list_head pcp_list;
                        };
                        /* See page-flags.h for PAGE_MAPPING_FLAGS */
                        struct address_space *mapping;
                        union {
                                pgoff_t index;          /* Our offset within mapping. */
                                unsigned long share;    /* share count for fsdax */
                        };
                        /**
                         * @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;
                        atomic_long_t pp_ref_count;
                };
                struct {        /* Tail pages of compound page */
                        unsigned long compound_head;    /* Bit zero is set */
                };
                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.
                         * ZONE_DEVICE MEMORY_DEVICE_FS_DAX pages also
                         * 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;

#ifdef CONFIG_MEMCG
        unsigned long memcg_data;
#endif

        /*
         * 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 */

#ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
        int _last_cpupid;
#endif

#ifdef CONFIG_KMSAN
        /*
         * KMSAN metadata for this page:
         *  - shadow page: every bit indicates whether the corresponding
         *    bit of the original page is initialized (0) or not (1);
         *  - origin page: every 4 bytes contain an id of the stack trace
         *    where the uninitialized value was created.
         */
        struct page *kmsan_shadow;
        struct page *kmsan_origin;
#endif
} _struct_page_alignment;

/*
 * struct encoded_page - a nonexistent type marking this pointer
 *
 * An 'encoded_page' pointer is a pointer to a regular 'struct page', but
 * with the low bits of the pointer indicating extra context-dependent
 * information. Not super-common, but happens in mmu_gather and mlock
 * handling, and this acts as a type system check on that use.
 *
 * We only really have two guaranteed bits in general, although you could
 * play with 'struct page' alignment (see CONFIG_HAVE_ALIGNED_STRUCT_PAGE)
 * for more.
 *
 * Use the supplied helper functions to endcode/decode the pointer and bits.
 */
struct encoded_page;
#define ENCODE_PAGE_BITS 3ul
static __always_inline struct encoded_page *encode_page(struct page *page, unsigned long flags)
{
        BUILD_BUG_ON(flags > ENCODE_PAGE_BITS);
        return (struct encoded_page *)(flags | (unsigned long)page);
}

static inline unsigned long encoded_page_flags(struct encoded_page *page)
{
        return ENCODE_PAGE_BITS & (unsigned long)page;
}

static inline struct page *encoded_page_ptr(struct encoded_page *page)
{
        return (struct page *)(~ENCODE_PAGE_BITS & (unsigned long)page);
}

/*
 * 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;

/**
 * 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()).
 * @swap: 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.
 * @virtual: Virtual address in the kernel direct map.
 * @_last_cpupid: IDs of last CPU and last process that accessed the folio.
 * @_entire_mapcount: Do not use directly, call folio_entire_mapcount().
 * @_nr_pages_mapped: Do not use directly, call folio_mapcount().
 * @_pincount: Do not use directly, call folio_maybe_dma_pinned().
 * @_folio_nr_pages: Do not use directly, call folio_nr_pages().
 * @_hugetlb_subpool: Do not use directly, use accessor in hugetlb.h.
 * @_hugetlb_cgroup: Do not use directly, use accessor in hugetlb_cgroup.h.
 * @_hugetlb_cgroup_rsvd: Do not use directly, use accessor in hugetlb_cgroup.h.
 * @_hugetlb_hwpoison: Do not use directly, call raw_hwp_list_head().
 * @_deferred_list: Folios to be split under memory pressure.
 *
 * 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;
                        union {
                                void *private;
                                swp_entry_t swap;
                        };
                        atomic_t _mapcount;
                        atomic_t _refcount;
#ifdef CONFIG_MEMCG
                        unsigned long memcg_data;
#endif
#if defined(WANT_PAGE_VIRTUAL)
                        void *virtual;
#endif
#ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
                        int _last_cpupid;
#endif
        /* private: the union with struct page is transitional */
                };
                struct page page;
        };
        union {
                struct {
                        unsigned long _flags_1;
                        unsigned long _head_1;
                        unsigned long _folio_avail;
        /* public: */
                        atomic_t _entire_mapcount;
                        atomic_t _nr_pages_mapped;
                        atomic_t _pincount;
#ifdef CONFIG_64BIT
                        unsigned int _folio_nr_pages;
#endif
        /* private: the union with struct page is transitional */
                };
                struct page __page_1;
        };
        union {
                struct {
                        unsigned long _flags_2;
                        unsigned long _head_2;
        /* public: */
                        void *_hugetlb_subpool;
                        void *_hugetlb_cgroup;
                        void *_hugetlb_cgroup_rsvd;
                        void *_hugetlb_hwpoison;
        /* private: the union with struct page is transitional */
                };
                struct {
                        unsigned long _flags_2a;
                        unsigned long _head_2a;
        /* public: */
                        struct list_head _deferred_list;
        /* private: the union with struct page is transitional */
                };
                struct page __page_2;
        };
};

#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);
#ifdef CONFIG_MEMCG
FOLIO_MATCH(memcg_data, memcg_data);
#endif
#if defined(WANT_PAGE_VIRTUAL)
FOLIO_MATCH(virtual, virtual);
#endif
#ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
FOLIO_MATCH(_last_cpupid, _last_cpupid);
#endif
#undef FOLIO_MATCH
#define FOLIO_MATCH(pg, fl)                                             \
        static_assert(offsetof(struct folio, fl) ==                     \
                        offsetof(struct page, pg) + sizeof(struct page))
FOLIO_MATCH(flags, _flags_1);
FOLIO_MATCH(compound_head, _head_1);
#undef FOLIO_MATCH
#define FOLIO_MATCH(pg, fl)                                             \
        static_assert(offsetof(struct folio, fl) ==                     \
                        offsetof(struct page, pg) + 2 * sizeof(struct page))
FOLIO_MATCH(flags, _flags_2);
FOLIO_MATCH(compound_head, _head_2);
FOLIO_MATCH(flags, _flags_2a);
FOLIO_MATCH(compound_head, _head_2a);
#undef FOLIO_MATCH

/**
 * struct ptdesc -    Memory descriptor for page tables.
 * @__page_flags:     Same as page flags. Unused for page tables.
 * @pt_rcu_head:      For freeing page table pages.
 * @pt_list:          List of used page tables. Used for s390 and x86.
 * @_pt_pad_1:        Padding that aliases with page's compound head.
 * @pmd_huge_pte:     Protected by ptdesc->ptl, used for THPs.
 * @__page_mapping:   Aliases with page->mapping. Unused for page tables.
 * @pt_mm:            Used for x86 pgds.
 * @pt_frag_refcount: For fragmented page table tracking. Powerpc only.
 * @_pt_pad_2:        Padding to ensure proper alignment.
 * @ptl:              Lock for the page table.
 * @__page_type:      Same as page->page_type. Unused for page tables.
 * @__page_refcount:  Same as page refcount.
 * @pt_memcg_data:    Memcg data. Tracked for page tables here.
 *
 * This struct overlays struct page for now. Do not modify without a good
 * understanding of the issues.
 */
struct ptdesc {
        unsigned long __page_flags;

        union {
                struct rcu_head pt_rcu_head;
                struct list_head pt_list;
                struct {
                        unsigned long _pt_pad_1;
                        pgtable_t pmd_huge_pte;
                };
        };
        unsigned long __page_mapping;

        union {
                struct mm_struct *pt_mm;
                atomic_t pt_frag_refcount;
        };

        union {
                unsigned long _pt_pad_2;
#if ALLOC_SPLIT_PTLOCKS
                spinlock_t *ptl;
#else
                spinlock_t ptl;
#endif
        };
        unsigned int __page_type;
        atomic_t __page_refcount;
#ifdef CONFIG_MEMCG
        unsigned long pt_memcg_data;
#endif
};

#define TABLE_MATCH(pg, pt)                                             \
        static_assert(offsetof(struct page, pg) == offsetof(struct ptdesc, pt))
TABLE_MATCH(flags, __page_flags);
TABLE_MATCH(compound_head, pt_list);
TABLE_MATCH(compound_head, _pt_pad_1);
TABLE_MATCH(mapping, __page_mapping);
TABLE_MATCH(rcu_head, pt_rcu_head);
TABLE_MATCH(page_type, __page_type);
TABLE_MATCH(_refcount, __page_refcount);
#ifdef CONFIG_MEMCG
TABLE_MATCH(memcg_data, pt_memcg_data);
#endif
#undef TABLE_MATCH
static_assert(sizeof(struct ptdesc) <= sizeof(struct page));

#define ptdesc_page(pt)                 (_Generic((pt),                 \
        const struct ptdesc *:          (const struct page *)(pt),      \
        struct ptdesc *:                (struct page *)(pt)))

#define ptdesc_folio(pt)                (_Generic((pt),                 \
        const struct ptdesc *:          (const struct folio *)(pt),     \
        struct ptdesc *:                (struct folio *)(pt)))

#define page_ptdesc(p)                  (_Generic((p),                  \
        const struct page *:            (const struct ptdesc *)(p),     \
        struct page *:                  (struct ptdesc *)(p)))

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

#define PAGE_FRAG_CACHE_MAX_SIZE        __ALIGN_MASK(32768, ~PAGE_MASK)
#define PAGE_FRAG_CACHE_MAX_ORDER       get_order(PAGE_FRAG_CACHE_MAX_SIZE)

/*
 * 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;
#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
        __u16 offset;
        __u16 size;
#else
        __u32 offset;
#endif
        /* 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 */
};

#ifdef CONFIG_USERFAULTFD
#define NULL_VM_UFFD_CTX ((struct vm_userfaultfd_ctx) { NULL, })
struct vm_userfaultfd_ctx {
        struct userfaultfd_ctx *ctx;
};
#else /* CONFIG_USERFAULTFD */
#define NULL_VM_UFFD_CTX ((struct vm_userfaultfd_ctx) {})
struct vm_userfaultfd_ctx {};
#endif /* CONFIG_USERFAULTFD */

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

#ifdef CONFIG_ANON_VMA_NAME
/*
 * mmap_lock should be read-locked when calling anon_vma_name(). Caller should
 * either keep holding the lock while using the returned pointer or it should
 * raise anon_vma_name refcount before releasing the lock.
 */
struct anon_vma_name *anon_vma_name(struct vm_area_struct *vma);
struct anon_vma_name *anon_vma_name_alloc(const char *name);
void anon_vma_name_free(struct kref *kref);
#else /* CONFIG_ANON_VMA_NAME */
static inline struct anon_vma_name *anon_vma_name(struct vm_area_struct *vma)
{
        return NULL;
}

static inline struct anon_vma_name *anon_vma_name_alloc(const char *name)
{
        return NULL;
}
#endif

struct vma_lock {
        struct rw_semaphore lock;
};

struct vma_numab_state {
        /*
         * Initialised as time in 'jiffies' after which VMA
         * should be scanned.  Delays first scan of new VMA by at
         * least sysctl_numa_balancing_scan_delay:
         */
        unsigned long next_scan;

        /*
         * Time in jiffies when pids_active[] is reset to
         * detect phase change behaviour:
         */
        unsigned long pids_active_reset;

        /*
         * Approximate tracking of PIDs that trapped a NUMA hinting
         * fault. May produce false positives due to hash collisions.
         *
         *   [0] Previous PID tracking
         *   [1] Current PID tracking
         *
         * Window moves after next_pid_reset has expired approximately
         * every VMA_PID_RESET_PERIOD jiffies:
         */
        unsigned long pids_active[2];

        /* MM scan sequence ID when scan first started after VMA creation */
        int start_scan_seq;

        /*
         * MM scan sequence ID when the VMA was last completely scanned.
         * A VMA is not eligible for scanning if prev_scan_seq == numa_scan_seq
         */
        int prev_scan_seq;
};

/*
 * 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. */

        union {
                struct {
                        /* VMA covers [vm_start; vm_end) addresses within mm */
                        unsigned long vm_start;
                        unsigned long vm_end;
                };
#ifdef CONFIG_PER_VMA_LOCK
                struct rcu_head vm_rcu; /* Used for deferred freeing. */
#endif
        };

        struct mm_struct *vm_mm;        /* The address space we belong to. */
        pgprot_t vm_page_prot;          /* Access permissions of this VMA. */

        /*
         * Flags, see mm.h.
         * To modify use vm_flags_{init|reset|set|clear|mod} functions.
         */
        union {
                const vm_flags_t vm_flags;
                vm_flags_t __private __vm_flags;
        };

#ifdef CONFIG_PER_VMA_LOCK
        /*
         * Can only be written (using WRITE_ONCE()) while holding both:
         *  - mmap_lock (in write mode)
         *  - vm_lock->lock (in write mode)
         * Can be read reliably while holding one of:
         *  - mmap_lock (in read or write mode)
         *  - vm_lock->lock (in read or write mode)
         * Can be read unreliably (using READ_ONCE()) for pessimistic bailout
         * while holding nothing (except RCU to keep the VMA struct allocated).
         *
         * This sequence counter is explicitly allowed to overflow; sequence
         * counter reuse can only lead to occasional unnecessary use of the
         * slowpath.
         */
        int vm_lock_seq;
        struct vma_lock *vm_lock;

        /* Flag to indicate areas detached from the mm->mm_mt tree */
        bool detached;
#endif

        /*
         * For areas with an address space and backing store,
         * linkage into the address_space->i_mmap interval tree.
         *
         */
        struct {
                struct rb_node rb;
                unsigned long rb_subtree_last;
        } shared;

        /*
         * 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) */

#ifdef CONFIG_ANON_VMA_NAME
        /*
         * For private and shared anonymous mappings, a pointer to a null
         * terminated string containing the name given to the vma, or NULL if
         * unnamed. Serialized by mmap_lock. Use anon_vma_name to access.
         */
        struct anon_vma_name *anon_name;
#endif
#ifdef CONFIG_SWAP
        atomic_long_t swap_readahead_info;
#endif
#ifndef CONFIG_MMU
        struct vm_region *vm_region;    /* NOMMU mapping region */
#endif
#ifdef CONFIG_NUMA
        struct mempolicy *vm_policy;    /* NUMA policy for the VMA */
#endif
#ifdef CONFIG_NUMA_BALANCING
        struct vma_numab_state *numab_state;    /* NUMA Balancing state */
#endif
        struct vm_userfaultfd_ctx vm_userfaultfd_ctx;
} __randomize_layout;

#ifdef CONFIG_NUMA
#define vma_policy(vma) ((vma)->vm_policy)
#else
#define vma_policy(vma) NULL
#endif

#ifdef CONFIG_SCHED_MM_CID
struct mm_cid {
        u64 time;
        int cid;
};
#endif

struct kioctx_table;
struct mm_struct {
        struct {
                /*
                 * Fields which are often written to are placed in a separate
                 * cache line.
                 */
                struct {
                        /**
                         * @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;
                } ____cacheline_aligned_in_smp;

                struct maple_tree mm_mt;
#ifdef CONFIG_MMU
                unsigned long (*get_unmapped_area) (struct file *filp,
                                unsigned long addr, unsigned long len,
                                unsigned long pgoff, unsigned long flags);
#endif
                unsigned long mmap_base;        /* base of mmap area */
                unsigned long mmap_legacy_base; /* base of mmap area in bottom-up allocations */
#ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
                /* Base addresses for compatible mmap() */
                unsigned long mmap_compat_base;
                unsigned long mmap_compat_legacy_base;
#endif
                unsigned long task_size;        /* size of task vm space */
                pgd_t * pgd;

#ifdef CONFIG_MEMBARRIER
                /**
                 * @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;
#endif

                /**
                 * @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;

#ifdef CONFIG_SCHED_MM_CID
                /**
                 * @pcpu_cid: Per-cpu current cid.
                 *
                 * Keep track of the currently allocated mm_cid for each cpu.
                 * The per-cpu mm_cid values are serialized by their respective
                 * runqueue locks.
                 */
                struct mm_cid __percpu *pcpu_cid;
                /*
                 * @mm_cid_next_scan: Next mm_cid scan (in jiffies).
                 *
                 * When the next mm_cid scan is due (in jiffies).
                 */
                unsigned long mm_cid_next_scan;
#endif
#ifdef CONFIG_MMU
                atomic_long_t pgtables_bytes;   /* size of all page tables */
#endif
                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
                                          */
#ifdef CONFIG_PER_VMA_LOCK
                /*
                 * This field has lock-like semantics, meaning it is sometimes
                 * accessed with ACQUIRE/RELEASE semantics.
                 * Roughly speaking, incrementing the sequence number is
                 * equivalent to releasing locks on VMAs; reading the sequence
                 * number can be part of taking a read lock on a VMA.
                 *
                 * Can be modified under write mmap_lock using RELEASE
                 * semantics.
                 * Can be read with no other protection when holding write
                 * mmap_lock.
                 * Can be read with ACQUIRE semantics if not holding write
                 * mmap_lock.
                 */
                int mm_lock_seq;
#endif


                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 */

                struct percpu_counter rss_stat[NR_MM_COUNTERS];

                struct linux_binfmt *binfmt;

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

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

#ifdef CONFIG_AIO
                spinlock_t                      ioctx_lock;
                struct kioctx_table __rcu       *ioctx_table;
#endif
#ifdef CONFIG_MEMCG
                /*
                 * "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;
#endif
                struct user_namespace *user_ns;

                /* store ref to file /proc/<pid>/exe symlink points to */
                struct file __rcu *exe_file;
#ifdef CONFIG_MMU_NOTIFIER
                struct mmu_notifier_subscriptions *notifier_subscriptions;
#endif
#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
                pgtable_t pmd_huge_pte; /* protected by page_table_lock */
#endif
#ifdef CONFIG_NUMA_BALANCING
                /*
                 * numa_next_scan is the next time that PTEs will be remapped
                 * PROT_NONE to trigger NUMA hinting faults; such faults gather
                 * statistics and migrate pages to new nodes if necessary.
                 */
                unsigned long numa_next_scan;

                /* Restart point for scanning and remapping PTEs. */
                unsigned long numa_scan_offset;

                /* numa_scan_seq prevents two threads remapping PTEs. */
                int numa_scan_seq;
#endif
                /*
                 * 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 mapped page.
                 */
                atomic_t tlb_flush_pending;
#ifdef CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
                /* See flush_tlb_batched_pending() */
                atomic_t tlb_flush_batched;
#endif
                struct uprobes_state uprobes_state;
#ifdef CONFIG_PREEMPT_RT
                struct rcu_head delayed_drop;
#endif
#ifdef CONFIG_HUGETLB_PAGE
                atomic_long_t hugetlb_usage;
#endif
                struct work_struct async_put_work;

#ifdef CONFIG_IOMMU_SVA
                u32 pasid;
#endif
#ifdef CONFIG_KSM
                /*
                 * Represent how many pages of this process are involved in KSM
                 * merging (not including ksm_zero_pages).
                 */
                unsigned long ksm_merging_pages;
                /*
                 * Represent how many pages are checked for ksm merging
                 * including merged and not merged.
                 */
                unsigned long ksm_rmap_items;
                /*
                 * Represent how many empty pages are merged with kernel zero
                 * pages when enabling KSM use_zero_pages.
                 */
                unsigned long ksm_zero_pages;
#endif /* CONFIG_KSM */
#ifdef CONFIG_LRU_GEN_WALKS_MMU
                struct {
                        /* this mm_struct is on lru_gen_mm_list */
                        struct list_head list;
                        /*
                         * Set when switching to this mm_struct, as a hint of
                         * whether it has been used since the last time per-node
                         * page table walkers cleared the corresponding bits.
                         */
                        unsigned long bitmap;
#ifdef CONFIG_MEMCG
                        /* points to the memcg of "owner" above */
                        struct mem_cgroup *memcg;
#endif
                } lru_gen;
#endif /* CONFIG_LRU_GEN_WALKS_MMU */
        } __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[];
};

#define MM_MT_FLAGS     (MT_FLAGS_ALLOC_RANGE | MT_FLAGS_LOCK_EXTERN | \
                         MT_FLAGS_USE_RCU)
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;
}

#ifdef CONFIG_LRU_GEN

struct lru_gen_mm_list {
        /* mm_struct list for page table walkers */
        struct list_head fifo;
        /* protects the list above */
        spinlock_t lock;
};

#endif /* CONFIG_LRU_GEN */

#ifdef CONFIG_LRU_GEN_WALKS_MMU

void lru_gen_add_mm(struct mm_struct *mm);
void lru_gen_del_mm(struct mm_struct *mm);
void lru_gen_migrate_mm(struct mm_struct *mm);

static inline void lru_gen_init_mm(struct mm_struct *mm)
{
        INIT_LIST_HEAD(&mm->lru_gen.list);
        mm->lru_gen.bitmap = 0;
#ifdef CONFIG_MEMCG
        mm->lru_gen.memcg = NULL;
#endif
}

static inline void lru_gen_use_mm(struct mm_struct *mm)
{
        /*
         * When the bitmap is set, page reclaim knows this mm_struct has been
         * used since the last time it cleared the bitmap. So it might be worth
         * walking the page tables of this mm_struct to clear the accessed bit.
         */
        WRITE_ONCE(mm->lru_gen.bitmap, -1);
}

#else /* !CONFIG_LRU_GEN_WALKS_MMU */

static inline void lru_gen_add_mm(struct mm_struct *mm)
{
}

static inline void lru_gen_del_mm(struct mm_struct *mm)
{
}

static inline void lru_gen_migrate_mm(struct mm_struct *mm)
{
}

static inline void lru_gen_init_mm(struct mm_struct *mm)
{
}

static inline void lru_gen_use_mm(struct mm_struct *mm)
{
}

#endif /* CONFIG_LRU_GEN_WALKS_MMU */

struct vma_iterator {
        struct ma_state mas;
};

#define VMA_ITERATOR(name, __mm, __addr)                                \
        struct vma_iterator name = {                                    \
                .mas = {                                                \
                        .tree = &(__mm)->mm_mt,                         \
                        .index = __addr,                                \
                        .node = NULL,                                   \
                        .status = ma_start,                             \
                },                                                      \
        }

static inline void vma_iter_init(struct vma_iterator *vmi,
                struct mm_struct *mm, unsigned long addr)
{
        mas_init(&vmi->mas, &mm->mm_mt, addr);
}

#ifdef CONFIG_SCHED_MM_CID

enum mm_cid_state {
        MM_CID_UNSET = -1U,             /* Unset state has lazy_put flag set. */
        MM_CID_LAZY_PUT = (1U << 31),
};

static inline bool mm_cid_is_unset(int cid)
{
        return cid == MM_CID_UNSET;
}

static inline bool mm_cid_is_lazy_put(int cid)
{
        return !mm_cid_is_unset(cid) && (cid & MM_CID_LAZY_PUT);
}

static inline bool mm_cid_is_valid(int cid)
{
        return !(cid & MM_CID_LAZY_PUT);
}

static inline int mm_cid_set_lazy_put(int cid)
{
        return cid | MM_CID_LAZY_PUT;
}

static inline int mm_cid_clear_lazy_put(int cid)
{
        return cid & ~MM_CID_LAZY_PUT;
}

/* Accessor for struct mm_struct's cidmask. */
static inline cpumask_t *mm_cidmask(struct mm_struct *mm)
{
        unsigned long cid_bitmap = (unsigned long)mm;

        cid_bitmap += offsetof(struct mm_struct, cpu_bitmap);
        /* Skip cpu_bitmap */
        cid_bitmap += cpumask_size();
        return (struct cpumask *)cid_bitmap;
}

static inline void mm_init_cid(struct mm_struct *mm)
{
        int i;

        for_each_possible_cpu(i) {
                struct mm_cid *pcpu_cid = per_cpu_ptr(mm->pcpu_cid, i);

                pcpu_cid->cid = MM_CID_UNSET;
                pcpu_cid->time = 0;
        }
        cpumask_clear(mm_cidmask(mm));
}

static inline int mm_alloc_cid(struct mm_struct *mm)
{
        mm->pcpu_cid = alloc_percpu(struct mm_cid);
        if (!mm->pcpu_cid)
                return -ENOMEM;
        mm_init_cid(mm);
        return 0;
}

static inline void mm_destroy_cid(struct mm_struct *mm)
{
        free_percpu(mm->pcpu_cid);
        mm->pcpu_cid = NULL;
}

static inline unsigned int mm_cid_size(void)
{
        return cpumask_size();
}
#else /* CONFIG_SCHED_MM_CID */
static inline void mm_init_cid(struct mm_struct *mm) { }
static inline int mm_alloc_cid(struct mm_struct *mm) { return 0; }
static inline void mm_destroy_cid(struct mm_struct *mm) { }
static inline unsigned int mm_cid_size(void)
{
        return 0;
}
#endif /* CONFIG_SCHED_MM_CID */

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_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)
 * @VM_FAULT_COMPLETED:         ->fault completed, meanwhile mmap lock released
 * @VM_FAULT_HINDEX_MASK:       mask HINDEX value
 *
 */
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_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_COMPLETED      = (__force vm_fault_t)0x004000,
        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)

#define VM_FAULT_ERROR (VM_FAULT_OOM | VM_FAULT_SIGBUS |        \
                        VM_FAULT_SIGSEGV | VM_FAULT_HWPOISON |  \
                        VM_FAULT_HWPOISON_LARGE | VM_FAULT_FALLBACK)

#define VM_FAULT_RESULT_TRACE \
        { VM_FAULT_OOM,                 "OOM" },        \
        { VM_FAULT_SIGBUS,              "SIGBUS" },     \
        { VM_FAULT_MAJOR,               "MAJOR" },      \
        { VM_FAULT_HWPOISON,            "HWPOISON" },   \
        { VM_FAULT_HWPOISON_LARGE,      "HWPOISON_LARGE" },     \
        { 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" },   \
        { VM_FAULT_NEEDDSYNC,           "NEEDDSYNC" },  \
        { VM_FAULT_COMPLETED,           "COMPLETED" }

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 {
        TLB_FLUSH_ON_TASK_SWITCH,
        TLB_REMOTE_SHOOTDOWN,
        TLB_LOCAL_SHOOTDOWN,
        TLB_LOCAL_MM_SHOOTDOWN,
        TLB_REMOTE_SEND_IPI,
        NR_TLB_FLUSH_REASONS,
};

/**
 * 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 break COW in a
 *                      COW mapping, making sure that an exclusive anon page is
 *                      mapped after the fault.
 * @FAULT_FLAG_ORIG_PTE_VALID: whether the fault has vmf->orig_pte cached.
 *                        We should only access orig_pte if this flag set.
 * @FAULT_FLAG_VMA_LOCK: The fault is handled under VMA lock.
 *
 * 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
 * applied to mappings that are not COW mappings.
 */
enum fault_flag {
        FAULT_FLAG_WRITE =              1 << 0,
        FAULT_FLAG_MKWRITE =            1 << 1,
        FAULT_FLAG_ALLOW_RETRY =        1 << 2,
        FAULT_FLAG_RETRY_NOWAIT =       1 << 3,
        FAULT_FLAG_KILLABLE =           1 << 4,
        FAULT_FLAG_TRIED =              1 << 5,
        FAULT_FLAG_USER =               1 << 6,
        FAULT_FLAG_REMOTE =             1 << 7,
        FAULT_FLAG_INSTRUCTION =        1 << 8,
        FAULT_FLAG_INTERRUPTIBLE =      1 << 9,
        FAULT_FLAG_UNSHARE =            1 << 10,
        FAULT_FLAG_ORIG_PTE_VALID =     1 << 11,
        FAULT_FLAG_VMA_LOCK =           1 << 12,
};

typedef unsigned int __bitwise zap_flags_t;

/*
 * FOLL_PIN and FOLL_LONGTERM may be used in various combinations with each
 * other. Here is what they mean, and how to use them:
 *
 *
 * FIXME: For pages which are part of a filesystem, mappings are subject to the
 * lifetime enforced by the filesystem and we need guarantees that longterm
 * users like RDMA and V4L2 only establish mappings which coordinate usage with
 * the filesystem.  Ideas for this coordination include revoking the longterm
 * pin, delaying writeback, bounce buffer page writeback, etc.  As FS DAX was
 * added after the problem with filesystems was found FS DAX VMAs are
 * specifically failed.  Filesystem pages are still subject to bugs and use of
 * FOLL_LONGTERM should be avoided on those pages.
 *
 * In the CMA case: long term pins in a CMA region would unnecessarily fragment
 * that region.  And so, CMA attempts to migrate the page before pinning, when
 * FOLL_LONGTERM is specified.
 *
 * FOLL_PIN indicates that a special kind of tracking (not just page->_refcount,
 * but an additional pin counting system) will be invoked. This is intended for
 * anything that gets a page reference and then touches page data (for example,
 * Direct IO). This lets the filesystem know that some non-file-system entity is
 * potentially changing the pages' data. In contrast to FOLL_GET (whose pages
 * are released via put_page()), FOLL_PIN pages must be released, ultimately, by
 * a call to unpin_user_page().
 *
 * FOLL_PIN is similar to FOLL_GET: both of these pin pages. They use different
 * and separate refcounting mechanisms, however, and that means that each has
 * its own acquire and release mechanisms:
 *
 *     FOLL_GET: get_user_pages*() to acquire, and put_page() to release.
 *
 *     FOLL_PIN: pin_user_pages*() to acquire, and unpin_user_pages to release.
 *
 * FOLL_PIN and FOLL_GET are mutually exclusive for a given function call.
 * (The underlying pages may experience both FOLL_GET-based and FOLL_PIN-based
 * calls applied to them, and that's perfectly OK. This is a constraint on the
 * callers, not on the pages.)
 *
 * FOLL_PIN should be set internally by the pin_user_pages*() APIs, never
 * directly by the caller. That's in order to help avoid mismatches when
 * releasing pages: get_user_pages*() pages must be released via put_page(),
 * while pin_user_pages*() pages must be released via unpin_user_page().
 *
 * Please see Documentation/core-api/pin_user_pages.rst for more information.
 */

enum {
        /* check pte is writable */
        FOLL_WRITE = 1 << 0,
        /* do get_page on page */
        FOLL_GET = 1 << 1,
        /* give error on hole if it would be zero */
        FOLL_DUMP = 1 << 2,
        /* get_user_pages read/write w/o permission */
        FOLL_FORCE = 1 << 3,
        /*
         * if a disk transfer is needed, start the IO and return without waiting
         * upon it
         */
        FOLL_NOWAIT = 1 << 4,
        /* do not fault in pages */
        FOLL_NOFAULT = 1 << 5,
        /* check page is hwpoisoned */
        FOLL_HWPOISON = 1 << 6,
        /* don't do file mappings */
        FOLL_ANON = 1 << 7,
        /*
         * FOLL_LONGTERM indicates that the page will be held for an indefinite
         * time period _often_ under userspace control.  This is in contrast to
         * iov_iter_get_pages(), whose usages are transient.
         */
        FOLL_LONGTERM = 1 << 8,
        /* split huge pmd before returning */
        FOLL_SPLIT_PMD = 1 << 9,
        /* allow returning PCI P2PDMA pages */
        FOLL_PCI_P2PDMA = 1 << 10,
        /* allow interrupts from generic signals */
        FOLL_INTERRUPTIBLE = 1 << 11,
        /*
         * Always honor (trigger) NUMA hinting faults.
         *
         * FOLL_WRITE implicitly honors NUMA hinting faults because a
         * PROT_NONE-mapped page is not writable (exceptions with FOLL_FORCE
         * apply). get_user_pages_fast_only() always implicitly honors NUMA
         * hinting faults.
         */
        FOLL_HONOR_NUMA_FAULT = 1 << 12,

        /* See also internal only FOLL flags in mm/internal.h */
};

#endif /* _LINUX_MM_TYPES_H */