memory.c

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/*
 *  linux/mm/memory.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 */

/*
 * demand-loading started 01.12.91 - seems it is high on the list of
 * things wanted, and it should be easy to implement. - Linus
 */

/*
 * Ok, demand-loading was easy, shared pages a little bit tricker. Shared
 * pages started 02.12.91, seems to work. - Linus.
 *
 * Tested sharing by executing about 30 /bin/sh: under the old kernel it
 * would have taken more than the 6M I have free, but it worked well as
 * far as I could see.
 *
 * Also corrected some "invalidate()"s - I wasn't doing enough of them.
 */

/*
 * Real VM (paging to/from disk) started 18.12.91. Much more work and
 * thought has to go into this. Oh, well..
 * 19.12.91  -  works, somewhat. Sometimes I get faults, don't know why.
 *      Found it. Everything seems to work now.
 * 20.12.91  -  Ok, making the swap-device changeable like the root.
 */

/*
 * 05.04.94  -  Multi-page memory management added for v1.1.
 *      Idea by Alex Bligh ([email protected])
 *
 * 16.07.99  -  Support of BIGMEM added by Gerhard Wichert, Siemens AG
 *      ([email protected])
 *
 * Aug/Sep 2004 Changed to four level page tables (Andi Kleen)
 */

#include <linux/kernel_stat.h>
#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/mman.h>
#include <linux/swap.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/ksm.h>
#include <linux/rmap.h>
#include <linux/export.h>
#include <linux/delayacct.h>
#include <linux/init.h>
#include <linux/writeback.h>
#include <linux/memcontrol.h>
#include <linux/mmu_notifier.h>
#include <linux/kallsyms.h>
#include <linux/swapops.h>
#include <linux/elf.h>
#include <linux/gfp.h>

#include <asm/io.h>
#include <asm/pgalloc.h>
#include <asm/uaccess.h>
#include <asm/tlb.h>
#include <asm/tlbflush.h>
#include <asm/pgtable.h>

#include "internal.h"

#ifndef CONFIG_NEED_MULTIPLE_NODES
/* use the per-pgdat data instead for discontigmem - mbligh */
unsigned long max_mapnr;
struct page *mem_map;

EXPORT_SYMBOL(max_mapnr);
EXPORT_SYMBOL(mem_map);
#endif

unsigned long num_physpages;
/*
 * A number of key systems in x86 including ioremap() rely on the assumption
 * that high_memory defines the upper bound on direct map memory, then end
 * of ZONE_NORMAL.  Under CONFIG_DISCONTIG this means that max_low_pfn and
 * highstart_pfn must be the same; there must be no gap between ZONE_NORMAL
 * and ZONE_HIGHMEM.
 */
void * high_memory;

EXPORT_SYMBOL(num_physpages);
EXPORT_SYMBOL(high_memory);

/*
 * Randomize the address space (stacks, mmaps, brk, etc.).
 *
 * ( When CONFIG_COMPAT_BRK=y we exclude brk from randomization,
 *   as ancient (libc5 based) binaries can segfault. )
 */
int randomize_va_space __read_mostly =
#ifdef CONFIG_COMPAT_BRK
                    1;
#else
                    2;
#endif

static int __init disable_randmaps(char *s)
{
    randomize_va_space = 0;
    return 1;
}
__setup("norandmaps", disable_randmaps);

unsigned long zero_pfn __read_mostly;
unsigned long highest_memmap_pfn __read_mostly;

/*
 * CONFIG_MMU architectures set up ZERO_PAGE in their paging_init()
 */
static int __init init_zero_pfn(void)
{
    zero_pfn = page_to_pfn(ZERO_PAGE(0));
    return 0;
}
core_initcall(init_zero_pfn);


#if defined(SPLIT_RSS_COUNTING)

void sync_mm_rss(struct mm_struct *mm)
{
    int i;

    for (i = 0; i < NR_MM_COUNTERS; i++) {
        if (current->rss_stat.count[i]) {
            add_mm_counter(mm, i, current->rss_stat.count[i]);
            current->rss_stat.count[i] = 0;
        }
    }
    current->rss_stat.events = 0;
}

static void add_mm_counter_fast(struct mm_struct *mm, int member, int val)
{
    struct task_struct *task = current;

    if (likely(task->mm == mm))
        task->rss_stat.count[member] += val;
    else
        add_mm_counter(mm, member, val);
}
#define inc_mm_counter_fast(mm, member) add_mm_counter_fast(mm, member, 1)
#define dec_mm_counter_fast(mm, member) add_mm_counter_fast(mm, member, -1)

/* sync counter once per 64 page faults */
#define TASK_RSS_EVENTS_THRESH  (64)
static void check_sync_rss_stat(struct task_struct *task)
{
    if (unlikely(task != current))
        return;
    if (unlikely(task->rss_stat.events++ > TASK_RSS_EVENTS_THRESH))
        sync_mm_rss(task->mm);
}
#else /* SPLIT_RSS_COUNTING */

#define inc_mm_counter_fast(mm, member) inc_mm_counter(mm, member)
#define dec_mm_counter_fast(mm, member) dec_mm_counter(mm, member)

static void check_sync_rss_stat(struct task_struct *task)
{
}

#endif /* SPLIT_RSS_COUNTING */

#ifdef HAVE_GENERIC_MMU_GATHER

static int tlb_next_batch(struct mmu_gather *tlb)
{
    struct mmu_gather_batch *batch;

    batch = tlb->active;
    if (batch->next) {
        tlb->active = batch->next;
        return 1;
    }

    batch = (void *)__get_free_pages(GFP_NOWAIT | __GFP_NOWARN, 0);
    if (!batch)
        return 0;

    batch->next = NULL;
    batch->nr   = 0;
    batch->max  = MAX_GATHER_BATCH;

    tlb->active->next = batch;
    tlb->active = batch;

    return 1;
}

/* tlb_gather_mmu
 *  Called to initialize an (on-stack) mmu_gather structure for page-table
 *  tear-down from @mm. The @fullmm argument is used when @mm is without
 *  users and we're going to destroy the full address space (exit/execve).
 */
void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, bool fullmm)
{
    tlb->mm = mm;

    tlb->fullmm     = fullmm;
    tlb->start  = -1UL;
    tlb->end    = 0;
    tlb->need_flush = 0;
    tlb->fast_mode  = (num_possible_cpus() == 1);
    tlb->local.next = NULL;
    tlb->local.nr   = 0;
    tlb->local.max  = ARRAY_SIZE(tlb->__pages);
    tlb->active     = &tlb->local;

#ifdef CONFIG_HAVE_RCU_TABLE_FREE
    tlb->batch = NULL;
#endif
}

void tlb_flush_mmu(struct mmu_gather *tlb)
{
    struct mmu_gather_batch *batch;

    if (!tlb->need_flush)
        return;
    tlb->need_flush = 0;
    tlb_flush(tlb);
#ifdef CONFIG_HAVE_RCU_TABLE_FREE
    tlb_table_flush(tlb);
#endif

    if (tlb_fast_mode(tlb))
        return;

    for (batch = &tlb->local; batch; batch = batch->next) {
        free_pages_and_swap_cache(batch->pages, batch->nr);
        batch->nr = 0;
    }
    tlb->active = &tlb->local;
}

/* tlb_finish_mmu
 *  Called at the end of the shootdown operation to free up any resources
 *  that were required.
 */
void tlb_finish_mmu(struct mmu_gather *tlb, unsigned long start, unsigned long end)
{
    struct mmu_gather_batch *batch, *next;

    tlb->start = start;
    tlb->end   = end;
    tlb_flush_mmu(tlb);

    /* keep the page table cache within bounds */
    check_pgt_cache();

    for (batch = tlb->local.next; batch; batch = next) {
        next = batch->next;
        free_pages((unsigned long)batch, 0);
    }
    tlb->local.next = NULL;
}

/* __tlb_remove_page
 *  Must perform the equivalent to __free_pte(pte_get_and_clear(ptep)), while
 *  handling the additional races in SMP caused by other CPUs caching valid
 *  mappings in their TLBs. Returns the number of free page slots left.
 *  When out of page slots we must call tlb_flush_mmu().
 */
int __tlb_remove_page(struct mmu_gather *tlb, struct page *page)
{
    struct mmu_gather_batch *batch;

    VM_BUG_ON(!tlb->need_flush);

    if (tlb_fast_mode(tlb)) {
        free_page_and_swap_cache(page);
        return 1; /* avoid calling tlb_flush_mmu() */
    }

    batch = tlb->active;
    batch->pages[batch->nr++] = page;
    if (batch->nr == batch->max) {
        if (!tlb_next_batch(tlb))
            return 0;
        batch = tlb->active;
    }
    VM_BUG_ON(batch->nr > batch->max);

    return batch->max - batch->nr;
}

#endif /* HAVE_GENERIC_MMU_GATHER */

#ifdef CONFIG_HAVE_RCU_TABLE_FREE

/*
 * See the comment near struct mmu_table_batch.
 */

static void tlb_remove_table_smp_sync(void *arg)
{
    /* Simply deliver the interrupt */
}

static void tlb_remove_table_one(void *table)
{
    /*
     * This isn't an RCU grace period and hence the page-tables cannot be
     * assumed to be actually RCU-freed.
     *
     * It is however sufficient for software page-table walkers that rely on
     * IRQ disabling. See the comment near struct mmu_table_batch.
     */
    smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
    __tlb_remove_table(table);
}

static void tlb_remove_table_rcu(struct rcu_head *head)
{
    struct mmu_table_batch *batch;
    int i;

    batch = container_of(head, struct mmu_table_batch, rcu);

    for (i = 0; i < batch->nr; i++)
        __tlb_remove_table(batch->tables[i]);

    free_page((unsigned long)batch);
}

void tlb_table_flush(struct mmu_gather *tlb)
{
    struct mmu_table_batch **batch = &tlb->batch;

    if (*batch) {
        call_rcu_sched(&(*batch)->rcu, tlb_remove_table_rcu);
        *batch = NULL;
    }
}

void tlb_remove_table(struct mmu_gather *tlb, void *table)
{
    struct mmu_table_batch **batch = &tlb->batch;

    tlb->need_flush = 1;

    /*
     * When there's less then two users of this mm there cannot be a
     * concurrent page-table walk.
     */
    if (atomic_read(&tlb->mm->mm_users) < 2) {
        __tlb_remove_table(table);
        return;
    }

    if (*batch == NULL) {
        *batch = (struct mmu_table_batch *)__get_free_page(GFP_NOWAIT | __GFP_NOWARN);
        if (*batch == NULL) {
            tlb_remove_table_one(table);
            return;
        }
        (*batch)->nr = 0;
    }
    (*batch)->tables[(*batch)->nr++] = table;
    if ((*batch)->nr == MAX_TABLE_BATCH)
        tlb_table_flush(tlb);
}

#endif /* CONFIG_HAVE_RCU_TABLE_FREE */

/*
 * If a p?d_bad entry is found while walking page tables, report
 * the error, before resetting entry to p?d_none.  Usually (but
 * very seldom) called out from the p?d_none_or_clear_bad macros.
 */

void pgd_clear_bad(pgd_t *pgd)
{
    pgd_ERROR(*pgd);
    pgd_clear(pgd);
}

void pud_clear_bad(pud_t *pud)
{
    pud_ERROR(*pud);
    pud_clear(pud);
}

void pmd_clear_bad(pmd_t *pmd)
{
    pmd_ERROR(*pmd);
    pmd_clear(pmd);
}

/*
 * Note: this doesn't free the actual pages themselves. That
 * has been handled earlier when unmapping all the memory regions.
 */
static void free_pte_range(struct mmu_gather *tlb, pmd_t *pmd,
               unsigned long addr)
{
    pgtable_t token = pmd_pgtable(*pmd);
    pmd_clear(pmd);
    pte_free_tlb(tlb, token, addr);
    tlb->mm->nr_ptes--;
}

static inline void free_pmd_range(struct mmu_gather *tlb, pud_t *pud,
                unsigned long addr, unsigned long end,
                unsigned long floor, unsigned long ceiling)
{
    pmd_t *pmd;
    unsigned long next;
    unsigned long start;

    start = addr;
    pmd = pmd_offset(pud, addr);
    do {
        next = pmd_addr_end(addr, end);
        if (pmd_none_or_clear_bad(pmd))
            continue;
        free_pte_range(tlb, pmd, addr);
    } while (pmd++, addr = next, addr != end);

    start &= PUD_MASK;
    if (start < floor)
        return;
    if (ceiling) {
        ceiling &= PUD_MASK;
        if (!ceiling)
            return;
    }
    if (end - 1 > ceiling - 1)
        return;

    pmd = pmd_offset(pud, start);
    pud_clear(pud);
    pmd_free_tlb(tlb, pmd, start);
}

static inline void free_pud_range(struct mmu_gather *tlb, pgd_t *pgd,
                unsigned long addr, unsigned long end,
                unsigned long floor, unsigned long ceiling)
{
    pud_t *pud;
    unsigned long next;
    unsigned long start;

    start = addr;
    pud = pud_offset(pgd, addr);
    do {
        next = pud_addr_end(addr, end);
        if (pud_none_or_clear_bad(pud))
            continue;
        free_pmd_range(tlb, pud, addr, next, floor, ceiling);
    } while (pud++, addr = next, addr != end);

    start &= PGDIR_MASK;
    if (start < floor)
        return;
    if (ceiling) {
        ceiling &= PGDIR_MASK;
        if (!ceiling)
            return;
    }
    if (end - 1 > ceiling - 1)
        return;

    pud = pud_offset(pgd, start);
    pgd_clear(pgd);
    pud_free_tlb(tlb, pud, start);
}

/*
 * This function frees user-level page tables of a process.
 *
 * Must be called with pagetable lock held.
 */
void free_pgd_range(struct mmu_gather *tlb,
            unsigned long addr, unsigned long end,
            unsigned long floor, unsigned long ceiling)
{
    pgd_t *pgd;
    unsigned long next;

    /*
     * The next few lines have given us lots of grief...
     *
     * Why are we testing PMD* at this top level?  Because often
     * there will be no work to do at all, and we'd prefer not to
     * go all the way down to the bottom just to discover that.
     *
     * Why all these "- 1"s?  Because 0 represents both the bottom
     * of the address space and the top of it (using -1 for the
     * top wouldn't help much: the masks would do the wrong thing).
     * The rule is that addr 0 and floor 0 refer to the bottom of
     * the address space, but end 0 and ceiling 0 refer to the top
     * Comparisons need to use "end - 1" and "ceiling - 1" (though
     * that end 0 case should be mythical).
     *
     * Wherever addr is brought up or ceiling brought down, we must
     * be careful to reject "the opposite 0" before it confuses the
     * subsequent tests.  But what about where end is brought down
     * by PMD_SIZE below? no, end can't go down to 0 there.
     *
     * Whereas we round start (addr) and ceiling down, by different
     * masks at different levels, in order to test whether a table
     * now has no other vmas using it, so can be freed, we don't
     * bother to round floor or end up - the tests don't need that.
     */

    addr &= PMD_MASK;
    if (addr < floor) {
        addr += PMD_SIZE;
        if (!addr)
            return;
    }
    if (ceiling) {
        ceiling &= PMD_MASK;
        if (!ceiling)
            return;
    }
    if (end - 1 > ceiling - 1)
        end -= PMD_SIZE;
    if (addr > end - 1)
        return;

    pgd = pgd_offset(tlb->mm, addr);
    do {
        next = pgd_addr_end(addr, end);
        if (pgd_none_or_clear_bad(pgd))
            continue;
        free_pud_range(tlb, pgd, addr, next, floor, ceiling);
    } while (pgd++, addr = next, addr != end);
}

void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *vma,
        unsigned long floor, unsigned long ceiling)
{
    while (vma) {
        struct vm_area_struct *next = vma->vm_next;
        unsigned long addr = vma->vm_start;

        /*
         * Hide vma from rmap and truncate_pagecache before freeing
         * pgtables
         */
        unlink_anon_vmas(vma);
        unlink_file_vma(vma);

        if (is_vm_hugetlb_page(vma)) {
            hugetlb_free_pgd_range(tlb, addr, vma->vm_end,
                floor, next? next->vm_start: ceiling);
        } else {
            /*
             * Optimization: gather nearby vmas into one call down
             */
            while (next && next->vm_start <= vma->vm_end + PMD_SIZE
                   && !is_vm_hugetlb_page(next)) {
                vma = next;
                next = vma->vm_next;
                unlink_anon_vmas(vma);
                unlink_file_vma(vma);
            }
            free_pgd_range(tlb, addr, vma->vm_end,
                floor, next? next->vm_start: ceiling);
        }
        vma = next;
    }
}

int __pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma,
        pmd_t *pmd, unsigned long address)
{
    pgtable_t new = pte_alloc_one(mm, address);
    int wait_split_huge_page;
    if (!new)
        return -ENOMEM;

    /*
     * Ensure all pte setup (eg. pte page lock and page clearing) are
     * visible before the pte is made visible to other CPUs by being
     * put into page tables.
     *
     * The other side of the story is the pointer chasing in the page
     * table walking code (when walking the page table without locking;
     * ie. most of the time). Fortunately, these data accesses consist
     * of a chain of data-dependent loads, meaning most CPUs (alpha
     * being the notable exception) will already guarantee loads are
     * seen in-order. See the alpha page table accessors for the
     * smp_read_barrier_depends() barriers in page table walking code.
     */
    smp_wmb(); /* Could be smp_wmb__xxx(before|after)_spin_lock */

    spin_lock(&mm->page_table_lock);
    wait_split_huge_page = 0;
    if (likely(pmd_none(*pmd))) {   /* Has another populated it ? */
        mm->nr_ptes++;
        pmd_populate(mm, pmd, new);
        new = NULL;
    } else if (unlikely(pmd_trans_splitting(*pmd)))
        wait_split_huge_page = 1;
    spin_unlock(&mm->page_table_lock);
    if (new)
        pte_free(mm, new);
    if (wait_split_huge_page)
        wait_split_huge_page(vma->anon_vma, pmd);
    return 0;
}

int __pte_alloc_kernel(pmd_t *pmd, unsigned long address)
{
    pte_t *new = pte_alloc_one_kernel(&init_mm, address);
    if (!new)
        return -ENOMEM;

    smp_wmb(); /* See comment in __pte_alloc */

    spin_lock(&init_mm.page_table_lock);
    if (likely(pmd_none(*pmd))) {   /* Has another populated it ? */
        pmd_populate_kernel(&init_mm, pmd, new);
        new = NULL;
    } else
        VM_BUG_ON(pmd_trans_splitting(*pmd));
    spin_unlock(&init_mm.page_table_lock);
    if (new)
        pte_free_kernel(&init_mm, new);
    return 0;
}

static inline void init_rss_vec(int *rss)
{
    memset(rss, 0, sizeof(int) * NR_MM_COUNTERS);
}

static inline void add_mm_rss_vec(struct mm_struct *mm, int *rss)
{
    int i;

    if (current->mm == mm)
        sync_mm_rss(mm);
    for (i = 0; i < NR_MM_COUNTERS; i++)
        if (rss[i])
            add_mm_counter(mm, i, rss[i]);
}

/*
 * This function is called to print an error when a bad pte
 * is found. For example, we might have a PFN-mapped pte in
 * a region that doesn't allow it.
 *
 * The calling function must still handle the error.
 */
static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
              pte_t pte, struct page *page)
{
    pgd_t *pgd = pgd_offset(vma->vm_mm, addr);
    pud_t *pud = pud_offset(pgd, addr);
    pmd_t *pmd = pmd_offset(pud, addr);
    struct address_space *mapping;
    pgoff_t index;
    static unsigned long resume;
    static unsigned long nr_shown;
    static unsigned long nr_unshown;

    /*
     * Allow a burst of 60 reports, then keep quiet for that minute;
     * or allow a steady drip of one report per second.
     */
    if (nr_shown == 60) {
        if (time_before(jiffies, resume)) {
            nr_unshown++;
            return;
        }
        if (nr_unshown) {
            printk(KERN_ALERT
                "BUG: Bad page map: %lu messages suppressed\n",
                nr_unshown);
            nr_unshown = 0;
        }
        nr_shown = 0;
    }
    if (nr_shown++ == 0)
        resume = jiffies + 60 * HZ;

    mapping = vma->vm_file ? vma->vm_file->f_mapping : NULL;
    index = linear_page_index(vma, addr);

    printk(KERN_ALERT
        "BUG: Bad page map in process %s  pte:%08llx pmd:%08llx\n",
        current->comm,
        (long long)pte_val(pte), (long long)pmd_val(*pmd));
    if (page)
        dump_page(page);
    printk(KERN_ALERT
        "addr:%p vm_flags:%08lx anon_vma:%p mapping:%p index:%lx\n",
        (void *)addr, vma->vm_flags, vma->anon_vma, mapping, index);
    /*
     * Choose text because data symbols depend on CONFIG_KALLSYMS_ALL=y
     */
    if (vma->vm_ops)
        print_symbol(KERN_ALERT "vma->vm_ops->fault: %s\n",
                (unsigned long)vma->vm_ops->fault);
    if (vma->vm_file && vma->vm_file->f_op)
        print_symbol(KERN_ALERT "vma->vm_file->f_op->mmap: %s\n",
                (unsigned long)vma->vm_file->f_op->mmap);
    dump_stack();
    add_taint(TAINT_BAD_PAGE);
}

static inline bool is_cow_mapping(vm_flags_t flags)
{
    return (flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
}

#ifndef is_zero_pfn
static inline int is_zero_pfn(unsigned long pfn)
{
    return pfn == zero_pfn;
}
#endif

#ifndef my_zero_pfn
static inline unsigned long my_zero_pfn(unsigned long addr)
{
    return zero_pfn;
}
#endif

/*
 * vm_normal_page -- This function gets the "struct page" associated with a pte.
 *
 * "Special" mappings do not wish to be associated with a "struct page" (either
 * it doesn't exist, or it exists but they don't want to touch it). In this
 * case, NULL is returned here. "Normal" mappings do have a struct page.
 *
 * There are 2 broad cases. Firstly, an architecture may define a pte_special()
 * pte bit, in which case this function is trivial. Secondly, an architecture
 * may not have a spare pte bit, which requires a more complicated scheme,
 * described below.
 *
 * A raw VM_PFNMAP mapping (ie. one that is not COWed) is always considered a
 * special mapping (even if there are underlying and valid "struct pages").
 * COWed pages of a VM_PFNMAP are always normal.
 *
 * The way we recognize COWed pages within VM_PFNMAP mappings is through the
 * rules set up by "remap_pfn_range()": the vma will have the VM_PFNMAP bit
 * set, and the vm_pgoff will point to the first PFN mapped: thus every special
 * mapping will always honor the rule
 *
 *  pfn_of_page == vma->vm_pgoff + ((addr - vma->vm_start) >> PAGE_SHIFT)
 *
 * And for normal mappings this is false.
 *
 * This restricts such mappings to be a linear translation from virtual address
 * to pfn. To get around this restriction, we allow arbitrary mappings so long
 * as the vma is not a COW mapping; in that case, we know that all ptes are
 * special (because none can have been COWed).
 *
 *
 * In order to support COW of arbitrary special mappings, we have VM_MIXEDMAP.
 *
 * VM_MIXEDMAP mappings can likewise contain memory with or without "struct
 * page" backing, however the difference is that _all_ pages with a struct
 * page (that is, those where pfn_valid is true) are refcounted and considered
 * normal pages by the VM. The disadvantage is that pages are refcounted
 * (which can be slower and simply not an option for some PFNMAP users). The
 * advantage is that we don't have to follow the strict linearity rule of
 * PFNMAP mappings in order to support COWable mappings.
 *
 */
#ifdef __HAVE_ARCH_PTE_SPECIAL
# define HAVE_PTE_SPECIAL 1
#else
# define HAVE_PTE_SPECIAL 0
#endif
struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
                pte_t pte)
{
    unsigned long pfn = pte_pfn(pte);

    if (HAVE_PTE_SPECIAL) {
        if (likely(!pte_special(pte)))
            goto check_pfn;
        if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
            return NULL;
        if (!is_zero_pfn(pfn))
            print_bad_pte(vma, addr, pte, NULL);
        return NULL;
    }

    /* !HAVE_PTE_SPECIAL case follows: */

    if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
        if (vma->vm_flags & VM_MIXEDMAP) {
            if (!pfn_valid(pfn))
                return NULL;
            goto out;
        } else {
            unsigned long off;
            off = (addr - vma->vm_start) >> PAGE_SHIFT;
            if (pfn == vma->vm_pgoff + off)
                return NULL;
            if (!is_cow_mapping(vma->vm_flags))
                return NULL;
        }
    }

    if (is_zero_pfn(pfn))
        return NULL;
check_pfn:
    if (unlikely(pfn > highest_memmap_pfn)) {
        print_bad_pte(vma, addr, pte, NULL);
        return NULL;
    }

    /*
     * NOTE! We still have PageReserved() pages in the page tables.
     * eg. VDSO mappings can cause them to exist.
     */
out:
    return pfn_to_page(pfn);
}

/*
 * copy one vm_area from one task to the other. Assumes the page tables
 * already present in the new task to be cleared in the whole range
 * covered by this vma.
 */

static inline unsigned long
copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
        pte_t *dst_pte, pte_t *src_pte, struct vm_area_struct *vma,
        unsigned long addr, int *rss)
{
    unsigned long vm_flags = vma->vm_flags;
    pte_t pte = *src_pte;
    struct page *page;

    /* pte contains position in swap or file, so copy. */
    if (unlikely(!pte_present(pte))) {
        if (!pte_file(pte)) {
            swp_entry_t entry = pte_to_swp_entry(pte);

            if (swap_duplicate(entry) < 0)
                return entry.val;

            /* make sure dst_mm is on swapoff's mmlist. */
            if (unlikely(list_empty(&dst_mm->mmlist))) {
                spin_lock(&mmlist_lock);
                if (list_empty(&dst_mm->mmlist))
                    list_add(&dst_mm->mmlist,
                         &src_mm->mmlist);
                spin_unlock(&mmlist_lock);
            }
            if (likely(!non_swap_entry(entry)))
                rss[MM_SWAPENTS]++;
            else if (is_migration_entry(entry)) {
                page = migration_entry_to_page(entry);

                if (PageAnon(page))
                    rss[MM_ANONPAGES]++;
                else
                    rss[MM_FILEPAGES]++;

                if (is_write_migration_entry(entry) &&
                    is_cow_mapping(vm_flags)) {
                    /*
                     * COW mappings require pages in both
                     * parent and child to be set to read.
                     */
                    make_migration_entry_read(&entry);
                    pte = swp_entry_to_pte(entry);
                    set_pte_at(src_mm, addr, src_pte, pte);
                }
            }
        }
        goto out_set_pte;
    }

    /*
     * If it's a COW mapping, write protect it both
     * in the parent and the child
     */
    if (is_cow_mapping(vm_flags)) {
        ptep_set_wrprotect(src_mm, addr, src_pte);
        pte = pte_wrprotect(pte);
    }

    /*
     * If it's a shared mapping, mark it clean in
     * the child
     */
    if (vm_flags & VM_SHARED)
        pte = pte_mkclean(pte);
    pte = pte_mkold(pte);

    page = vm_normal_page(vma, addr, pte);
    if (page) {
        get_page(page);
        page_dup_rmap(page);
        if (PageAnon(page))
            rss[MM_ANONPAGES]++;
        else
            rss[MM_FILEPAGES]++;
    }

out_set_pte:
    set_pte_at(dst_mm, addr, dst_pte, pte);
    return 0;
}

int copy_pte_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
           pmd_t *dst_pmd, pmd_t *src_pmd, struct vm_area_struct *vma,
           unsigned long addr, unsigned long end)
{
    pte_t *orig_src_pte, *orig_dst_pte;
    pte_t *src_pte, *dst_pte;
    spinlock_t *src_ptl, *dst_ptl;
    int progress = 0;
    int rss[NR_MM_COUNTERS];
    swp_entry_t entry = (swp_entry_t){0};

again:
    init_rss_vec(rss);

    dst_pte = pte_alloc_map_lock(dst_mm, dst_pmd, addr, &dst_ptl);
    if (!dst_pte)
        return -ENOMEM;
    src_pte = pte_offset_map(src_pmd, addr);
    src_ptl = pte_lockptr(src_mm, src_pmd);
    spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
    orig_src_pte = src_pte;
    orig_dst_pte = dst_pte;
    arch_enter_lazy_mmu_mode();

    do {
        /*
         * We are holding two locks at this point - either of them
         * could generate latencies in another task on another CPU.
         */
        if (progress >= 32) {
            progress = 0;
            if (need_resched() ||
                spin_needbreak(src_ptl) || spin_needbreak(dst_ptl))
                break;
        }
        if (pte_none(*src_pte)) {
            progress++;
            continue;
        }
        entry.val = copy_one_pte(dst_mm, src_mm, dst_pte, src_pte,
                            vma, addr, rss);
        if (entry.val)
            break;
        progress += 8;
    } while (dst_pte++, src_pte++, addr += PAGE_SIZE, addr != end);

    arch_leave_lazy_mmu_mode();
    spin_unlock(src_ptl);
    pte_unmap(orig_src_pte);
    add_mm_rss_vec(dst_mm, rss);
    pte_unmap_unlock(orig_dst_pte, dst_ptl);
    cond_resched();

    if (entry.val) {
        if (add_swap_count_continuation(entry, GFP_KERNEL) < 0)
            return -ENOMEM;
        progress = 0;
    }
    if (addr != end)
        goto again;
    return 0;
}

static inline int copy_pmd_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
        pud_t *dst_pud, pud_t *src_pud, struct vm_area_struct *vma,
        unsigned long addr, unsigned long end)
{
    pmd_t *src_pmd, *dst_pmd;
    unsigned long next;

    dst_pmd = pmd_alloc(dst_mm, dst_pud, addr);
    if (!dst_pmd)
        return -ENOMEM;
    src_pmd = pmd_offset(src_pud, addr);
    do {
        next = pmd_addr_end(addr, end);
        if (pmd_trans_huge(*src_pmd)) {
            int err;
            VM_BUG_ON(next-addr != HPAGE_PMD_SIZE);
            err = copy_huge_pmd(dst_mm, src_mm,
                        dst_pmd, src_pmd, addr, vma);
            if (err == -ENOMEM)
                return -ENOMEM;
            if (!err)
                continue;
            /* fall through */
        }
        if (pmd_none_or_clear_bad(src_pmd))
            continue;
        if (copy_pte_range(dst_mm, src_mm, dst_pmd, src_pmd,
                        vma, addr, next))
            return -ENOMEM;
    } while (dst_pmd++, src_pmd++, addr = next, addr != end);
    return 0;
}

static inline int copy_pud_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
        pgd_t *dst_pgd, pgd_t *src_pgd, struct vm_area_struct *vma,
        unsigned long addr, unsigned long end)
{
    pud_t *src_pud, *dst_pud;
    unsigned long next;

    dst_pud = pud_alloc(dst_mm, dst_pgd, addr);
    if (!dst_pud)
        return -ENOMEM;
    src_pud = pud_offset(src_pgd, addr);
    do {
        next = pud_addr_end(addr, end);
        if (pud_none_or_clear_bad(src_pud))
            continue;
        if (copy_pmd_range(dst_mm, src_mm, dst_pud, src_pud,
                        vma, addr, next))
            return -ENOMEM;
    } while (dst_pud++, src_pud++, addr = next, addr != end);
    return 0;
}

int copy_page_range(struct mm_struct *dst_mm, struct mm_struct *src_mm,
        struct vm_area_struct *vma)
{
    pgd_t *src_pgd, *dst_pgd;
    unsigned long next;
    unsigned long addr = vma->vm_start;
    unsigned long end = vma->vm_end;
    unsigned long mmun_start;   /* For mmu_notifiers */
    unsigned long mmun_end;     /* For mmu_notifiers */
    bool is_cow;
    int ret;

    /*
     * Don't copy ptes where a page fault will fill them correctly.
     * Fork becomes much lighter when there are big shared or private
     * readonly mappings. The tradeoff is that copy_page_range is more
     * efficient than faulting.
     */
    if (!(vma->vm_flags & (VM_HUGETLB | VM_NONLINEAR |
                   VM_PFNMAP | VM_MIXEDMAP))) {
        if (!vma->anon_vma)
            return 0;
    }

    if (is_vm_hugetlb_page(vma))
        return copy_hugetlb_page_range(dst_mm, src_mm, vma);

    if (unlikely(vma->vm_flags & VM_PFNMAP)) {
        /*
         * We do not free on error cases below as remove_vma
         * gets called on error from higher level routine
         */
        ret = track_pfn_copy(vma);
        if (ret)
            return ret;
    }

    /*
     * We need to invalidate the secondary MMU mappings only when
     * there could be a permission downgrade on the ptes of the
     * parent mm. And a permission downgrade will only happen if
     * is_cow_mapping() returns true.
     */
    is_cow = is_cow_mapping(vma->vm_flags);
    mmun_start = addr;
    mmun_end   = end;
    if (is_cow)
        mmu_notifier_invalidate_range_start(src_mm, mmun_start,
                            mmun_end);

    ret = 0;
    dst_pgd = pgd_offset(dst_mm, addr);
    src_pgd = pgd_offset(src_mm, addr);
    do {
        next = pgd_addr_end(addr, end);
        if (pgd_none_or_clear_bad(src_pgd))
            continue;
        if (unlikely(copy_pud_range(dst_mm, src_mm, dst_pgd, src_pgd,
                        vma, addr, next))) {
            ret = -ENOMEM;
            break;
        }
    } while (dst_pgd++, src_pgd++, addr = next, addr != end);

    if (is_cow)
        mmu_notifier_invalidate_range_end(src_mm, mmun_start, mmun_end);
    return ret;
}

static unsigned long zap_pte_range(struct mmu_gather *tlb,
                struct vm_area_struct *vma, pmd_t *pmd,
                unsigned long addr, unsigned long end,
                struct zap_details *details)
{
    struct mm_struct *mm = tlb->mm;
    int force_flush = 0;
    int rss[NR_MM_COUNTERS];
    spinlock_t *ptl;
    pte_t *start_pte;
    pte_t *pte;

again:
    init_rss_vec(rss);
    start_pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
    pte = start_pte;
    arch_enter_lazy_mmu_mode();
    do {
        pte_t ptent = *pte;
        if (pte_none(ptent)) {
            continue;
        }

        if (pte_present(ptent)) {
            struct page *page;

            page = vm_normal_page(vma, addr, ptent);
            if (unlikely(details) && page) {
                /*
                 * unmap_shared_mapping_pages() wants to
                 * invalidate cache without truncating:
                 * unmap shared but keep private pages.
                 */
                if (details->check_mapping &&
                    details->check_mapping != page->mapping)
                    continue;
                /*
                 * Each page->index must be checked when
                 * invalidating or truncating nonlinear.
                 */
                if (details->nonlinear_vma &&
                    (page->index < details->first_index ||
                     page->index > details->last_index))
                    continue;
            }
            ptent = ptep_get_and_clear_full(mm, addr, pte,
                            tlb->fullmm);
            tlb_remove_tlb_entry(tlb, pte, addr);
            if (unlikely(!page))
                continue;
            if (unlikely(details) && details->nonlinear_vma
                && linear_page_index(details->nonlinear_vma,
                        addr) != page->index)
                set_pte_at(mm, addr, pte,
                       pgoff_to_pte(page->index));
            if (PageAnon(page))
                rss[MM_ANONPAGES]--;
            else {
                if (pte_dirty(ptent))
                    set_page_dirty(page);
                if (pte_young(ptent) &&
                    likely(!VM_SequentialReadHint(vma)))
                    mark_page_accessed(page);
                rss[MM_FILEPAGES]--;
            }
            page_remove_rmap(page);
            if (unlikely(page_mapcount(page) < 0))
                print_bad_pte(vma, addr, ptent, page);
            force_flush = !__tlb_remove_page(tlb, page);
            if (force_flush)
                break;
            continue;
        }
        /*
         * If details->check_mapping, we leave swap entries;
         * if details->nonlinear_vma, we leave file entries.
         */
        if (unlikely(details))
            continue;
        if (pte_file(ptent)) {
            if (unlikely(!(vma->vm_flags & VM_NONLINEAR)))
                print_bad_pte(vma, addr, ptent, NULL);
        } else {
            swp_entry_t entry = pte_to_swp_entry(ptent);

            if (!non_swap_entry(entry))
                rss[MM_SWAPENTS]--;
            else if (is_migration_entry(entry)) {
                struct page *page;

                page = migration_entry_to_page(entry);

                if (PageAnon(page))
                    rss[MM_ANONPAGES]--;
                else
                    rss[MM_FILEPAGES]--;
            }
            if (unlikely(!free_swap_and_cache(entry)))
                print_bad_pte(vma, addr, ptent, NULL);
        }
        pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
    } while (pte++, addr += PAGE_SIZE, addr != end);

    add_mm_rss_vec(mm, rss);
    arch_leave_lazy_mmu_mode();
    pte_unmap_unlock(start_pte, ptl);

    /*
     * mmu_gather ran out of room to batch pages, we break out of
     * the PTE lock to avoid doing the potential expensive TLB invalidate
     * and page-free while holding it.
     */
    if (force_flush) {
        force_flush = 0;

#ifdef HAVE_GENERIC_MMU_GATHER
        tlb->start = addr;
        tlb->end = end;
#endif
        tlb_flush_mmu(tlb);
        if (addr != end)
            goto again;
    }

    return addr;
}

static inline unsigned long zap_pmd_range(struct mmu_gather *tlb,
                struct vm_area_struct *vma, pud_t *pud,
                unsigned long addr, unsigned long end,
                struct zap_details *details)
{
    pmd_t *pmd;
    unsigned long next;

    pmd = pmd_offset(pud, addr);
    do {
        next = pmd_addr_end(addr, end);
        if (pmd_trans_huge(*pmd)) {
            if (next - addr != HPAGE_PMD_SIZE) {
#ifdef CONFIG_DEBUG_VM
                if (!rwsem_is_locked(&tlb->mm->mmap_sem)) {
                    pr_err("%s: mmap_sem is unlocked! addr=0x%lx end=0x%lx vma->vm_start=0x%lx vma->vm_end=0x%lx\n",
                        __func__, addr, end,
                        vma->vm_start,
                        vma->vm_end);
                    BUG();
                }
#endif
                split_huge_page_pmd(vma->vm_mm, pmd);
            } else if (zap_huge_pmd(tlb, vma, pmd, addr))
                goto next;
            /* fall through */
        }
        /*
         * Here there can be other concurrent MADV_DONTNEED or
         * trans huge page faults running, and if the pmd is
         * none or trans huge it can change under us. This is
         * because MADV_DONTNEED holds the mmap_sem in read
         * mode.
         */
        if (pmd_none_or_trans_huge_or_clear_bad(pmd))
            goto next;
        next = zap_pte_range(tlb, vma, pmd, addr, next, details);
next:
        cond_resched();
    } while (pmd++, addr = next, addr != end);

    return addr;
}

static inline unsigned long zap_pud_range(struct mmu_gather *tlb,
                struct vm_area_struct *vma, pgd_t *pgd,
                unsigned long addr, unsigned long end,
                struct zap_details *details)
{
    pud_t *pud;
    unsigned long next;

    pud = pud_offset(pgd, addr);
    do {
        next = pud_addr_end(addr, end);
        if (pud_none_or_clear_bad(pud))
            continue;
        next = zap_pmd_range(tlb, vma, pud, addr, next, details);
    } while (pud++, addr = next, addr != end);

    return addr;
}

static void unmap_page_range(struct mmu_gather *tlb,
                 struct vm_area_struct *vma,
                 unsigned long addr, unsigned long end,
                 struct zap_details *details)
{
    pgd_t *pgd;
    unsigned long next;

    if (details && !details->check_mapping && !details->nonlinear_vma)
        details = NULL;

    BUG_ON(addr >= end);
    mem_cgroup_uncharge_start();
    tlb_start_vma(tlb, vma);
    pgd = pgd_offset(vma->vm_mm, addr);
    do {
        next = pgd_addr_end(addr, end);
        if (pgd_none_or_clear_bad(pgd))
            continue;
        next = zap_pud_range(tlb, vma, pgd, addr, next, details);
    } while (pgd++, addr = next, addr != end);
    tlb_end_vma(tlb, vma);
    mem_cgroup_uncharge_end();
}


static void unmap_single_vma(struct mmu_gather *tlb,
        struct vm_area_struct *vma, unsigned long start_addr,
        unsigned long end_addr,
        struct zap_details *details)
{
    unsigned long start = max(vma->vm_start, start_addr);
    unsigned long end;

    if (start >= vma->vm_end)
        return;
    end = min(vma->vm_end, end_addr);
    if (end <= vma->vm_start)
        return;

    if (vma->vm_file)
        uprobe_munmap(vma, start, end);

    if (unlikely(vma->vm_flags & VM_PFNMAP))
        untrack_pfn(vma, 0, 0);

    if (start != end) {
        if (unlikely(is_vm_hugetlb_page(vma))) {
            /*
             * It is undesirable to test vma->vm_file as it
             * should be non-null for valid hugetlb area.
             * However, vm_file will be NULL in the error
             * cleanup path of do_mmap_pgoff. When
             * hugetlbfs ->mmap method fails,
             * do_mmap_pgoff() nullifies vma->vm_file
             * before calling this function to clean up.
             * Since no pte has actually been setup, it is
             * safe to do nothing in this case.
             */
            if (vma->vm_file) {
                mutex_lock(&vma->vm_file->f_mapping->i_mmap_mutex);
                __unmap_hugepage_range_final(tlb, vma, start, end, NULL);
                mutex_unlock(&vma->vm_file->f_mapping->i_mmap_mutex);
            }
        } else
            unmap_page_range(tlb, vma, start, end, details);
    }
}

void unmap_vmas(struct mmu_gather *tlb,
        struct vm_area_struct *vma, unsigned long start_addr,
        unsigned long end_addr)
{
    struct mm_struct *mm = vma->vm_mm;

    mmu_notifier_invalidate_range_start(mm, start_addr, end_addr);
    for ( ; vma && vma->vm_start < end_addr; vma = vma->vm_next)
        unmap_single_vma(tlb, vma, start_addr, end_addr, NULL);
    mmu_notifier_invalidate_range_end(mm, start_addr, end_addr);
}

void zap_page_range(struct vm_area_struct *vma, unsigned long start,
        unsigned long size, struct zap_details *details)
{
    struct mm_struct *mm = vma->vm_mm;
    struct mmu_gather tlb;
    unsigned long end = start + size;

    lru_add_drain();
    tlb_gather_mmu(&tlb, mm, 0);
    update_hiwater_rss(mm);
    mmu_notifier_invalidate_range_start(mm, start, end);
    for ( ; vma && vma->vm_start < end; vma = vma->vm_next)
        unmap_single_vma(&tlb, vma, start, end, details);
    mmu_notifier_invalidate_range_end(mm, start, end);
    tlb_finish_mmu(&tlb, start, end);
}

static void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
        unsigned long size, struct zap_details *details)
{
    struct mm_struct *mm = vma->vm_mm;
    struct mmu_gather tlb;
    unsigned long end = address + size;

    lru_add_drain();
    tlb_gather_mmu(&tlb, mm, 0);
    update_hiwater_rss(mm);
    mmu_notifier_invalidate_range_start(mm, address, end);
    unmap_single_vma(&tlb, vma, address, end, details);
    mmu_notifier_invalidate_range_end(mm, address, end);
    tlb_finish_mmu(&tlb, address, end);
}

int zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
        unsigned long size)
{
    if (address < vma->vm_start || address + size > vma->vm_end ||
                !(vma->vm_flags & VM_PFNMAP))
        return -1;
    zap_page_range_single(vma, address, size, NULL);
    return 0;
}
EXPORT_SYMBOL_GPL(zap_vma_ptes);

struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
            unsigned int flags)
{
    pgd_t *pgd;
    pud_t *pud;
    pmd_t *pmd;
    pte_t *ptep, pte;
    spinlock_t *ptl;
    struct page *page;
    struct mm_struct *mm = vma->vm_mm;

    page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
    if (!IS_ERR(page)) {
        BUG_ON(flags & FOLL_GET);
        goto out;
    }

    page = NULL;
    pgd = pgd_offset(mm, address);
    if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
        goto no_page_table;

    pud = pud_offset(pgd, address);
    if (pud_none(*pud))
        goto no_page_table;
    if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
        BUG_ON(flags & FOLL_GET);
        page = follow_huge_pud(mm, address, pud, flags & FOLL_WRITE);
        goto out;
    }
    if (unlikely(pud_bad(*pud)))
        goto no_page_table;

    pmd = pmd_offset(pud, address);
    if (pmd_none(*pmd))
        goto no_page_table;
    if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) {
        BUG_ON(flags & FOLL_GET);
        page = follow_huge_pmd(mm, address, pmd, flags & FOLL_WRITE);
        goto out;
    }
    if (pmd_trans_huge(*pmd)) {
        if (flags & FOLL_SPLIT) {
            split_huge_page_pmd(mm, pmd);
            goto split_fallthrough;
        }
        spin_lock(&mm->page_table_lock);
        if (likely(pmd_trans_huge(*pmd))) {
            if (unlikely(pmd_trans_splitting(*pmd))) {
                spin_unlock(&mm->page_table_lock);
                wait_split_huge_page(vma->anon_vma, pmd);
            } else {
                page = follow_trans_huge_pmd(vma, address,
                                 pmd, flags);
                spin_unlock(&mm->page_table_lock);
                goto out;
            }
        } else
            spin_unlock(&mm->page_table_lock);
        /* fall through */
    }
split_fallthrough:
    if (unlikely(pmd_bad(*pmd)))
        goto no_page_table;

    ptep = pte_offset_map_lock(mm, pmd, address, &ptl);

    pte = *ptep;
    if (!pte_present(pte))
        goto no_page;
    if ((flags & FOLL_WRITE) && !pte_write(pte))
        goto unlock;

    page = vm_normal_page(vma, address, pte);
    if (unlikely(!page)) {
        if ((flags & FOLL_DUMP) ||
            !is_zero_pfn(pte_pfn(pte)))
            goto bad_page;
        page = pte_page(pte);
    }

    if (flags & FOLL_GET)
        get_page_foll(page);
    if (flags & FOLL_TOUCH) {
        if ((flags & FOLL_WRITE) &&
            !pte_dirty(pte) && !PageDirty(page))
            set_page_dirty(page);
        /*
         * pte_mkyoung() would be more correct here, but atomic care
         * is needed to avoid losing the dirty bit: it is easier to use
         * mark_page_accessed().
         */
        mark_page_accessed(page);
    }
    if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
        /*
         * The preliminary mapping check is mainly to avoid the
         * pointless overhead of lock_page on the ZERO_PAGE
         * which might bounce very badly if there is contention.
         *
         * If the page is already locked, we don't need to
         * handle it now - vmscan will handle it later if and
         * when it attempts to reclaim the page.
         */
        if (page->mapping && trylock_page(page)) {
            lru_add_drain();  /* push cached pages to LRU */
            /*
             * Because we lock page here, and migration is
             * blocked by the pte's page reference, and we
             * know the page is still mapped, we don't even
             * need to check for file-cache page truncation.
             */
            mlock_vma_page(page);
            unlock_page(page);
        }
    }
unlock:
    pte_unmap_unlock(ptep, ptl);
out:
    return page;

bad_page:
    pte_unmap_unlock(ptep, ptl);
    return ERR_PTR(-EFAULT);

no_page:
    pte_unmap_unlock(ptep, ptl);
    if (!pte_none(pte))
        return page;

no_page_table:
    /*
     * When core dumping an enormous anonymous area that nobody
     * has touched so far, we don't want to allocate unnecessary pages or
     * page tables.  Return error instead of NULL to skip handle_mm_fault,
     * then get_dump_page() will return NULL to leave a hole in the dump.
     * But we can only make this optimization where a hole would surely
     * be zero-filled if handle_mm_fault() actually did handle it.
     */
    if ((flags & FOLL_DUMP) &&
        (!vma->vm_ops || !vma->vm_ops->fault))
        return ERR_PTR(-EFAULT);
    return page;
}

static inline int stack_guard_page(struct vm_area_struct *vma, unsigned long addr)
{
    return stack_guard_page_start(vma, addr) ||
           stack_guard_page_end(vma, addr+PAGE_SIZE);
}

int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
             unsigned long start, int nr_pages, unsigned int gup_flags,
             struct page **pages, struct vm_area_struct **vmas,
             int *nonblocking)
{
    int i;
    unsigned long vm_flags;

    if (nr_pages <= 0)
        return 0;

    VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));

    /* 
     * Require read or write permissions.
     * If FOLL_FORCE is set, we only require the "MAY" flags.
     */
    vm_flags  = (gup_flags & FOLL_WRITE) ?
            (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
    vm_flags &= (gup_flags & FOLL_FORCE) ?
            (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
    i = 0;

    do {
        struct vm_area_struct *vma;

        vma = find_extend_vma(mm, start);
        if (!vma && in_gate_area(mm, start)) {
            unsigned long pg = start & PAGE_MASK;
            pgd_t *pgd;
            pud_t *pud;
            pmd_t *pmd;
            pte_t *pte;

            /* user gate pages are read-only */
            if (gup_flags & FOLL_WRITE)
                return i ? : -EFAULT;
            if (pg > TASK_SIZE)
                pgd = pgd_offset_k(pg);
            else
                pgd = pgd_offset_gate(mm, pg);
            BUG_ON(pgd_none(*pgd));
            pud = pud_offset(pgd, pg);
            BUG_ON(pud_none(*pud));
            pmd = pmd_offset(pud, pg);
            if (pmd_none(*pmd))
                return i ? : -EFAULT;
            VM_BUG_ON(pmd_trans_huge(*pmd));
            pte = pte_offset_map(pmd, pg);
            if (pte_none(*pte)) {
                pte_unmap(pte);
                return i ? : -EFAULT;
            }
            vma = get_gate_vma(mm);
            if (pages) {
                struct page *page;

                page = vm_normal_page(vma, start, *pte);
                if (!page) {
                    if (!(gup_flags & FOLL_DUMP) &&
                         is_zero_pfn(pte_pfn(*pte)))
                        page = pte_page(*pte);
                    else {
                        pte_unmap(pte);
                        return i ? : -EFAULT;
                    }
                }
                pages[i] = page;
                get_page(page);
            }
            pte_unmap(pte);
            goto next_page;
        }

        if (!vma ||
            (vma->vm_flags & (VM_IO | VM_PFNMAP)) ||
            !(vm_flags & vma->vm_flags))
            return i ? : -EFAULT;

        if (is_vm_hugetlb_page(vma)) {
            i = follow_hugetlb_page(mm, vma, pages, vmas,
                    &start, &nr_pages, i, gup_flags);
            continue;
        }

        do {
            struct page *page;
            unsigned int foll_flags = gup_flags;

            /*
             * If we have a pending SIGKILL, don't keep faulting
             * pages and potentially allocating memory.
             */
            if (unlikely(fatal_signal_pending(current)))
                return i ? i : -ERESTARTSYS;

            cond_resched();
            while (!(page = follow_page(vma, start, foll_flags))) {
                int ret;
                unsigned int fault_flags = 0;

                /* For mlock, just skip the stack guard page. */
                if (foll_flags & FOLL_MLOCK) {
                    if (stack_guard_page(vma, start))
                        goto next_page;
                }
                if (foll_flags & FOLL_WRITE)
                    fault_flags |= FAULT_FLAG_WRITE;
                if (nonblocking)
                    fault_flags |= FAULT_FLAG_ALLOW_RETRY;
                if (foll_flags & FOLL_NOWAIT)
                    fault_flags |= (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT);

                ret = handle_mm_fault(mm, vma, start,
                            fault_flags);

                if (ret & VM_FAULT_ERROR) {
                    if (ret & VM_FAULT_OOM)
                        return i ? i : -ENOMEM;
                    if (ret & (VM_FAULT_HWPOISON |
                           VM_FAULT_HWPOISON_LARGE)) {
                        if (i)
                            return i;
                        else if (gup_flags & FOLL_HWPOISON)
                            return -EHWPOISON;
                        else
                            return -EFAULT;
                    }
                    if (ret & VM_FAULT_SIGBUS)
                        return i ? i : -EFAULT;
                    BUG();
                }

                if (tsk) {
                    if (ret & VM_FAULT_MAJOR)
                        tsk->maj_flt++;
                    else
                        tsk->min_flt++;
                }

                if (ret & VM_FAULT_RETRY) {
                    if (nonblocking)
                        *nonblocking = 0;
                    return i;
                }

                /*
                 * The VM_FAULT_WRITE bit tells us that
                 * do_wp_page has broken COW when necessary,
                 * even if maybe_mkwrite decided not to set
                 * pte_write. We can thus safely do subsequent
                 * page lookups as if they were reads. But only
                 * do so when looping for pte_write is futile:
                 * in some cases userspace may also be wanting
                 * to write to the gotten user page, which a
                 * read fault here might prevent (a readonly
                 * page might get reCOWed by userspace write).
                 */
                if ((ret & VM_FAULT_WRITE) &&
                    !(vma->vm_flags & VM_WRITE))
                    foll_flags &= ~FOLL_WRITE;

                cond_resched();
            }
            if (IS_ERR(page))
                return i ? i : PTR_ERR(page);
            if (pages) {
                pages[i] = page;

                flush_anon_page(vma, page, start);
                flush_dcache_page(page);
            }
next_page:
            if (vmas)
                vmas[i] = vma;
            i++;
            start += PAGE_SIZE;
            nr_pages--;
        } while (nr_pages && start < vma->vm_end);
    } while (nr_pages);
    return i;
}
EXPORT_SYMBOL(__get_user_pages);

/*
 * fixup_user_fault() - manually resolve a user page fault
 * @tsk:    the task_struct to use for page fault accounting, or
 *      NULL if faults are not to be recorded.
 * @mm:     mm_struct of target mm
 * @address:    user address
 * @fault_flags:flags to pass down to handle_mm_fault()
 *
 * This is meant to be called in the specific scenario where for locking reasons
 * we try to access user memory in atomic context (within a pagefault_disable()
 * section), this returns -EFAULT, and we want to resolve the user fault before
 * trying again.
 *
 * Typically this is meant to be used by the futex code.
 *
 * The main difference with get_user_pages() is that this function will
 * unconditionally call handle_mm_fault() which will in turn perform all the
 * necessary SW fixup of the dirty and young bits in the PTE, while
 * handle_mm_fault() only guarantees to update these in the struct page.
 *
 * This is important for some architectures where those bits also gate the
 * access permission to the page because they are maintained in software.  On
 * such architectures, gup() will not be enough to make a subsequent access
 * succeed.
 *
 * This should be called with the mm_sem held for read.
 */
int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
             unsigned long address, unsigned int fault_flags)
{
    struct vm_area_struct *vma;
    int ret;

    vma = find_extend_vma(mm, address);
    if (!vma || address < vma->vm_start)
        return -EFAULT;

    ret = handle_mm_fault(mm, vma, address, fault_flags);
    if (ret & VM_FAULT_ERROR) {
        if (ret & VM_FAULT_OOM)
            return -ENOMEM;
        if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
            return -EHWPOISON;
        if (ret & VM_FAULT_SIGBUS)
            return -EFAULT;
        BUG();
    }
    if (tsk) {
        if (ret & VM_FAULT_MAJOR)
            tsk->maj_flt++;
        else
            tsk->min_flt++;
    }
    return 0;
}

/*
 * get_user_pages() - pin user pages in memory
 * @tsk:    the task_struct to use for page fault accounting, or
 *      NULL if faults are not to be recorded.
 * @mm:     mm_struct of target mm
 * @start:  starting user address
 * @nr_pages:   number of pages from start to pin
 * @write:  whether pages will be written to by the caller
 * @force:  whether to force write access even if user mapping is
 *      readonly. This will result in the page being COWed even
 *      in MAP_SHARED mappings. You do not want this.
 * @pages:  array that receives pointers to the pages pinned.
 *      Should be at least nr_pages long. Or NULL, if caller
 *      only intends to ensure the pages are faulted in.
 * @vmas:   array of pointers to vmas corresponding to each page.
 *      Or NULL if the caller does not require them.
 *
 * Returns number of pages pinned. This may be fewer than the number
 * requested. If nr_pages is 0 or negative, returns 0. If no pages
 * were pinned, returns -errno. Each page returned must be released
 * with a put_page() call when it is finished with. vmas will only
 * remain valid while mmap_sem is held.
 *
 * Must be called with mmap_sem held for read or write.
 *
 * get_user_pages walks a process's page tables and takes a reference to
 * each struct page that each user address corresponds to at a given
 * instant. That is, it takes the page that would be accessed if a user
 * thread accesses the given user virtual address at that instant.
 *
 * This does not guarantee that the page exists in the user mappings when
 * get_user_pages returns, and there may even be a completely different
 * page there in some cases (eg. if mmapped pagecache has been invalidated
 * and subsequently re faulted). However it does guarantee that the page
 * won't be freed completely. And mostly callers simply care that the page
 * contains data that was valid *at some point in time*. Typically, an IO
 * or similar operation cannot guarantee anything stronger anyway because
 * locks can't be held over the syscall boundary.
 *
 * If write=0, the page must not be written to. If the page is written to,
 * set_page_dirty (or set_page_dirty_lock, as appropriate) must be called
 * after the page is finished with, and before put_page is called.
 *
 * get_user_pages is typically used for fewer-copy IO operations, to get a
 * handle on the memory by some means other than accesses via the user virtual
 * addresses. The pages may be submitted for DMA to devices or accessed via
 * their kernel linear mapping (via the kmap APIs). Care should be taken to
 * use the correct cache flushing APIs.
 *
 * See also get_user_pages_fast, for performance critical applications.
 */
int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
        unsigned long start, int nr_pages, int write, int force,
        struct page **pages, struct vm_area_struct **vmas)
{
    int flags = FOLL_TOUCH;

    if (pages)
        flags |= FOLL_GET;
    if (write)
        flags |= FOLL_WRITE;
    if (force)
        flags |= FOLL_FORCE;

    return __get_user_pages(tsk, mm, start, nr_pages, flags, pages, vmas,
                NULL);
}
EXPORT_SYMBOL(get_user_pages);

#ifdef CONFIG_ELF_CORE
struct page *get_dump_page(unsigned long addr)
{
    struct vm_area_struct *vma;
    struct page *page;

    if (__get_user_pages(current, current->mm, addr, 1,
                 FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma,
                 NULL) < 1)
        return NULL;
    flush_cache_page(vma, addr, page_to_pfn(page));
    return page;
}
#endif /* CONFIG_ELF_CORE */

pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
            spinlock_t **ptl)
{
    pgd_t * pgd = pgd_offset(mm, addr);
    pud_t * pud = pud_alloc(mm, pgd, addr);
    if (pud) {
        pmd_t * pmd = pmd_alloc(mm, pud, addr);
        if (pmd) {
            VM_BUG_ON(pmd_trans_huge(*pmd));
            return pte_alloc_map_lock(mm, pmd, addr, ptl);
        }
    }
    return NULL;
}

/*
 * This is the old fallback for page remapping.
 *
 * For historical reasons, it only allows reserved pages. Only
 * old drivers should use this, and they needed to mark their
 * pages reserved for the old functions anyway.
 */
static int insert_page(struct vm_area_struct *vma, unsigned long addr,
            struct page *page, pgprot_t prot)
{
    struct mm_struct *mm = vma->vm_mm;
    int retval;
    pte_t *pte;
    spinlock_t *ptl;

    retval = -EINVAL;
    if (PageAnon(page))
        goto out;
    retval = -ENOMEM;
    flush_dcache_page(page);
    pte = get_locked_pte(mm, addr, &ptl);
    if (!pte)
        goto out;
    retval = -EBUSY;
    if (!pte_none(*pte))
        goto out_unlock;

    /* Ok, finally just insert the thing.. */
    get_page(page);
    inc_mm_counter_fast(mm, MM_FILEPAGES);
    page_add_file_rmap(page);
    set_pte_at(mm, addr, pte, mk_pte(page, prot));

    retval = 0;
    pte_unmap_unlock(pte, ptl);
    return retval;
out_unlock:
    pte_unmap_unlock(pte, ptl);
out:
    return retval;
}

int vm_insert_page(struct vm_area_struct *vma, unsigned long addr,
            struct page *page)
{
    if (addr < vma->vm_start || addr >= vma->vm_end)
        return -EFAULT;
    if (!page_count(page))
        return -EINVAL;
    if (!(vma->vm_flags & VM_MIXEDMAP)) {
        BUG_ON(down_read_trylock(&vma->vm_mm->mmap_sem));
        BUG_ON(vma->vm_flags & VM_PFNMAP);
        vma->vm_flags |= VM_MIXEDMAP;
    }
    return insert_page(vma, addr, page, vma->vm_page_prot);
}
EXPORT_SYMBOL(vm_insert_page);

static int insert_pfn(struct vm_area_struct *vma, unsigned long addr,
            unsigned long pfn, pgprot_t prot)
{
    struct mm_struct *mm = vma->vm_mm;
    int retval;
    pte_t *pte, entry;
    spinlock_t *ptl;

    retval = -ENOMEM;
    pte = get_locked_pte(mm, addr, &ptl);
    if (!pte)
        goto out;
    retval = -EBUSY;
    if (!pte_none(*pte))
        goto out_unlock;

    /* Ok, finally just insert the thing.. */
    entry = pte_mkspecial(pfn_pte(pfn, prot));
    set_pte_at(mm, addr, pte, entry);
    update_mmu_cache(vma, addr, pte); /* XXX: why not for insert_page? */

    retval = 0;
out_unlock:
    pte_unmap_unlock(pte, ptl);
out:
    return retval;
}

int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
            unsigned long pfn)
{
    int ret;
    pgprot_t pgprot = vma->vm_page_prot;
    /*
     * Technically, architectures with pte_special can avoid all these
     * restrictions (same for remap_pfn_range).  However we would like
     * consistency in testing and feature parity among all, so we should
     * try to keep these invariants in place for everybody.
     */
    BUG_ON(!(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)));
    BUG_ON((vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) ==
                        (VM_PFNMAP|VM_MIXEDMAP));
    BUG_ON((vma->vm_flags & VM_PFNMAP) && is_cow_mapping(vma->vm_flags));
    BUG_ON((vma->vm_flags & VM_MIXEDMAP) && pfn_valid(pfn));

    if (addr < vma->vm_start || addr >= vma->vm_end)
        return -EFAULT;
    if (track_pfn_insert(vma, &pgprot, pfn))
        return -EINVAL;

    ret = insert_pfn(vma, addr, pfn, pgprot);

    return ret;
}
EXPORT_SYMBOL(vm_insert_pfn);

int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
            unsigned long pfn)
{
    BUG_ON(!(vma->vm_flags & VM_MIXEDMAP));

    if (addr < vma->vm_start || addr >= vma->vm_end)
        return -EFAULT;

    /*
     * If we don't have pte special, then we have to use the pfn_valid()
     * based VM_MIXEDMAP scheme (see vm_normal_page), and thus we *must*
     * refcount the page if pfn_valid is true (hence insert_page rather
     * than insert_pfn).  If a zero_pfn were inserted into a VM_MIXEDMAP
     * without pte special, it would there be refcounted as a normal page.
     */
    if (!HAVE_PTE_SPECIAL && pfn_valid(pfn)) {
        struct page *page;

        page = pfn_to_page(pfn);
        return insert_page(vma, addr, page, vma->vm_page_prot);
    }
    return insert_pfn(vma, addr, pfn, vma->vm_page_prot);
}
EXPORT_SYMBOL(vm_insert_mixed);

/*
 * maps a range of physical memory into the requested pages. the old
 * mappings are removed. any references to nonexistent pages results
 * in null mappings (currently treated as "copy-on-access")
 */
static int remap_pte_range(struct mm_struct *mm, pmd_t *pmd,
            unsigned long addr, unsigned long end,
            unsigned long pfn, pgprot_t prot)
{
    pte_t *pte;
    spinlock_t *ptl;

    pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
    if (!pte)
        return -ENOMEM;
    arch_enter_lazy_mmu_mode();
    do {
        BUG_ON(!pte_none(*pte));
        set_pte_at(mm, addr, pte, pte_mkspecial(pfn_pte(pfn, prot)));
        pfn++;
    } while (pte++, addr += PAGE_SIZE, addr != end);
    arch_leave_lazy_mmu_mode();
    pte_unmap_unlock(pte - 1, ptl);
    return 0;
}

static inline int remap_pmd_range(struct mm_struct *mm, pud_t *pud,
            unsigned long addr, unsigned long end,
            unsigned long pfn, pgprot_t prot)
{
    pmd_t *pmd;
    unsigned long next;

    pfn -= addr >> PAGE_SHIFT;
    pmd = pmd_alloc(mm, pud, addr);
    if (!pmd)
        return -ENOMEM;
    VM_BUG_ON(pmd_trans_huge(*pmd));
    do {
        next = pmd_addr_end(addr, end);
        if (remap_pte_range(mm, pmd, addr, next,
                pfn + (addr >> PAGE_SHIFT), prot))
            return -ENOMEM;
    } while (pmd++, addr = next, addr != end);
    return 0;
}

static inline int remap_pud_range(struct mm_struct *mm, pgd_t *pgd,
            unsigned long addr, unsigned long end,
            unsigned long pfn, pgprot_t prot)
{
    pud_t *pud;
    unsigned long next;

    pfn -= addr >> PAGE_SHIFT;
    pud = pud_alloc(mm, pgd, addr);
    if (!pud)
        return -ENOMEM;
    do {
        next = pud_addr_end(addr, end);
        if (remap_pmd_range(mm, pud, addr, next,
                pfn + (addr >> PAGE_SHIFT), prot))
            return -ENOMEM;
    } while (pud++, addr = next, addr != end);
    return 0;
}

int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
            unsigned long pfn, unsigned long size, pgprot_t prot)
{
    pgd_t *pgd;
    unsigned long next;
    unsigned long end = addr + PAGE_ALIGN(size);
    struct mm_struct *mm = vma->vm_mm;
    int err;

    /*
     * Physically remapped pages are special. Tell the
     * rest of the world about it:
     *   VM_IO tells people not to look at these pages
     *  (accesses can have side effects).
     *   VM_PFNMAP tells the core MM that the base pages are just
     *  raw PFN mappings, and do not have a "struct page" associated
     *  with them.
     *   VM_DONTEXPAND
     *      Disable vma merging and expanding with mremap().
     *   VM_DONTDUMP
     *      Omit vma from core dump, even when VM_IO turned off.
     *
     * There's a horrible special case to handle copy-on-write
     * behaviour that some programs depend on. We mark the "original"
     * un-COW'ed pages by matching them up with "vma->vm_pgoff".
     * See vm_normal_page() for details.
     */
    if (is_cow_mapping(vma->vm_flags)) {
        if (addr != vma->vm_start || end != vma->vm_end)
            return -EINVAL;
        vma->vm_pgoff = pfn;
    }

    err = track_pfn_remap(vma, &prot, pfn, addr, PAGE_ALIGN(size));
    if (err)
        return -EINVAL;

    vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;

    BUG_ON(addr >= end);
    pfn -= addr >> PAGE_SHIFT;
    pgd = pgd_offset(mm, addr);
    flush_cache_range(vma, addr, end);
    do {
        next = pgd_addr_end(addr, end);
        err = remap_pud_range(mm, pgd, addr, next,
                pfn + (addr >> PAGE_SHIFT), prot);
        if (err)
            break;
    } while (pgd++, addr = next, addr != end);

    if (err)
        untrack_pfn(vma, pfn, PAGE_ALIGN(size));

    return err;
}
EXPORT_SYMBOL(remap_pfn_range);

static int apply_to_pte_range(struct mm_struct *mm, pmd_t *pmd,
                     unsigned long addr, unsigned long end,
                     pte_fn_t fn, void *data)
{
    pte_t *pte;
    int err;
    pgtable_t token;
    spinlock_t *uninitialized_var(ptl);

    pte = (mm == &init_mm) ?
        pte_alloc_kernel(pmd, addr) :
        pte_alloc_map_lock(mm, pmd, addr, &ptl);
    if (!pte)
        return -ENOMEM;

    BUG_ON(pmd_huge(*pmd));

    arch_enter_lazy_mmu_mode();

    token = pmd_pgtable(*pmd);

    do {
        err = fn(pte++, token, addr, data);
        if (err)
            break;
    } while (addr += PAGE_SIZE, addr != end);

    arch_leave_lazy_mmu_mode();

    if (mm != &init_mm)
        pte_unmap_unlock(pte-1, ptl);
    return err;
}

static int apply_to_pmd_range(struct mm_struct *mm, pud_t *pud,
                     unsigned long addr, unsigned long end,
                     pte_fn_t fn, void *data)
{
    pmd_t *pmd;
    unsigned long next;
    int err;

    BUG_ON(pud_huge(*pud));

    pmd = pmd_alloc(mm, pud, addr);
    if (!pmd)
        return -ENOMEM;
    do {
        next = pmd_addr_end(addr, end);
        err = apply_to_pte_range(mm, pmd, addr, next, fn, data);
        if (err)
            break;
    } while (pmd++, addr = next, addr != end);
    return err;
}

static int apply_to_pud_range(struct mm_struct *mm, pgd_t *pgd,
                     unsigned long addr, unsigned long end,
                     pte_fn_t fn, void *data)
{
    pud_t *pud;
    unsigned long next;
    int err;

    pud = pud_alloc(mm, pgd, addr);
    if (!pud)
        return -ENOMEM;
    do {
        next = pud_addr_end(addr, end);
        err = apply_to_pmd_range(mm, pud, addr, next, fn, data);
        if (err)
            break;
    } while (pud++, addr = next, addr != end);
    return err;
}

/*
 * Scan a region of virtual memory, filling in page tables as necessary
 * and calling a provided function on each leaf page table.
 */
int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
            unsigned long size, pte_fn_t fn, void *data)
{
    pgd_t *pgd;
    unsigned long next;
    unsigned long end = addr + size;
    int err;

    BUG_ON(addr >= end);
    pgd = pgd_offset(mm, addr);
    do {
        next = pgd_addr_end(addr, end);
        err = apply_to_pud_range(mm, pgd, addr, next, fn, data);
        if (err)
            break;
    } while (pgd++, addr = next, addr != end);

    return err;
}
EXPORT_SYMBOL_GPL(apply_to_page_range);

/*
 * handle_pte_fault chooses page fault handler according to an entry
 * which was read non-atomically.  Before making any commitment, on
 * those architectures or configurations (e.g. i386 with PAE) which
 * might give a mix of unmatched parts, do_swap_page and do_nonlinear_fault
 * must check under lock before unmapping the pte and proceeding
 * (but do_wp_page is only called after already making such a check;
 * and do_anonymous_page can safely check later on).
 */
static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd,
                pte_t *page_table, pte_t orig_pte)
{
    int same = 1;
#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
    if (sizeof(pte_t) > sizeof(unsigned long)) {
        spinlock_t *ptl = pte_lockptr(mm, pmd);
        spin_lock(ptl);
        same = pte_same(*page_table, orig_pte);
        spin_unlock(ptl);
    }
#endif
    pte_unmap(page_table);
    return same;
}

static inline void cow_user_page(struct page *dst, struct page *src, unsigned long va, struct vm_area_struct *vma)
{
    /*
     * If the source page was a PFN mapping, we don't have
     * a "struct page" for it. We do a best-effort copy by
     * just copying from the original user address. If that
     * fails, we just zero-fill it. Live with it.
     */
    if (unlikely(!src)) {
        void *kaddr = kmap_atomic(dst);
        void __user *uaddr = (void __user *)(va & PAGE_MASK);

        /*
         * This really shouldn't fail, because the page is there
         * in the page tables. But it might just be unreadable,
         * in which case we just give up and fill the result with
         * zeroes.
         */
        if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE))
            clear_page(kaddr);
        kunmap_atomic(kaddr);
        flush_dcache_page(dst);
    } else
        copy_user_highpage(dst, src, va, vma);
}

/*
 * This routine handles present pages, when users try to write
 * to a shared page. It is done by copying the page to a new address
 * and decrementing the shared-page counter for the old page.
 *
 * Note that this routine assumes that the protection checks have been
 * done by the caller (the low-level page fault routine in most cases).
 * Thus we can safely just mark it writable once we've done any necessary
 * COW.
 *
 * We also mark the page dirty at this point even though the page will
 * change only once the write actually happens. This avoids a few races,
 * and potentially makes it more efficient.
 *
 * We enter with non-exclusive mmap_sem (to exclude vma changes,
 * but allow concurrent faults), with pte both mapped and locked.
 * We return with mmap_sem still held, but pte unmapped and unlocked.
 */
static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
        unsigned long address, pte_t *page_table, pmd_t *pmd,
        spinlock_t *ptl, pte_t orig_pte)
    __releases(ptl)
{
    struct page *old_page, *new_page = NULL;
    pte_t entry;
    int ret = 0;
    int page_mkwrite = 0;
    struct page *dirty_page = NULL;
    unsigned long mmun_start = 0;   /* For mmu_notifiers */
    unsigned long mmun_end = 0; /* For mmu_notifiers */

    old_page = vm_normal_page(vma, address, orig_pte);
    if (!old_page) {
        /*
         * VM_MIXEDMAP !pfn_valid() case
         *
         * We should not cow pages in a shared writeable mapping.
         * Just mark the pages writable as we can't do any dirty
         * accounting on raw pfn maps.
         */
        if ((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
                     (VM_WRITE|VM_SHARED))
            goto reuse;
        goto gotten;
    }

    /*
     * Take out anonymous pages first, anonymous shared vmas are
     * not dirty accountable.
     */
    if (PageAnon(old_page) && !PageKsm(old_page)) {
        if (!trylock_page(old_page)) {
            page_cache_get(old_page);
            pte_unmap_unlock(page_table, ptl);
            lock_page(old_page);
            page_table = pte_offset_map_lock(mm, pmd, address,
                             &ptl);
            if (!pte_same(*page_table, orig_pte)) {
                unlock_page(old_page);
                goto unlock;
            }
            page_cache_release(old_page);
        }
        if (reuse_swap_page(old_page)) {
            /*
             * The page is all ours.  Move it to our anon_vma so
             * the rmap code will not search our parent or siblings.
             * Protected against the rmap code by the page lock.
             */
            page_move_anon_rmap(old_page, vma, address);
            unlock_page(old_page);
            goto reuse;
        }
        unlock_page(old_page);
    } else if (unlikely((vma->vm_flags & (VM_WRITE|VM_SHARED)) ==
                    (VM_WRITE|VM_SHARED))) {
        /*
         * Only catch write-faults on shared writable pages,
         * read-only shared pages can get COWed by
         * get_user_pages(.write=1, .force=1).
         */
        if (vma->vm_ops && vma->vm_ops->page_mkwrite) {
            struct vm_fault vmf;
            int tmp;

            vmf.virtual_address = (void __user *)(address &
                                PAGE_MASK);
            vmf.pgoff = old_page->index;
            vmf.flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
            vmf.page = old_page;

            /*
             * Notify the address space that the page is about to
             * become writable so that it can prohibit this or wait
             * for the page to get into an appropriate state.
             *
             * We do this without the lock held, so that it can
             * sleep if it needs to.
             */
            page_cache_get(old_page);
            pte_unmap_unlock(page_table, ptl);

            tmp = vma->vm_ops->page_mkwrite(vma, &vmf);
            if (unlikely(tmp &
                    (VM_FAULT_ERROR | VM_FAULT_NOPAGE))) {
                ret = tmp;
                goto unwritable_page;
            }
            if (unlikely(!(tmp & VM_FAULT_LOCKED))) {
                lock_page(old_page);
                if (!old_page->mapping) {
                    ret = 0; /* retry the fault */
                    unlock_page(old_page);
                    goto unwritable_page;
                }
            } else
                VM_BUG_ON(!PageLocked(old_page));

            /*
             * Since we dropped the lock we need to revalidate
             * the PTE as someone else may have changed it.  If
             * they did, we just return, as we can count on the
             * MMU to tell us if they didn't also make it writable.
             */
            page_table = pte_offset_map_lock(mm, pmd, address,
                             &ptl);
            if (!pte_same(*page_table, orig_pte)) {
                unlock_page(old_page);
                goto unlock;
            }

            page_mkwrite = 1;
        }
        dirty_page = old_page;
        get_page(dirty_page);

reuse:
        flush_cache_page(vma, address, pte_pfn(orig_pte));
        entry = pte_mkyoung(orig_pte);
        entry = maybe_mkwrite(pte_mkdirty(entry), vma);
        if (ptep_set_access_flags(vma, address, page_table, entry,1))
            update_mmu_cache(vma, address, page_table);
        pte_unmap_unlock(page_table, ptl);
        ret |= VM_FAULT_WRITE;

        if (!dirty_page)
            return ret;

        /*
         * Yes, Virginia, this is actually required to prevent a race
         * with clear_page_dirty_for_io() from clearing the page dirty
         * bit after it clear all dirty ptes, but before a racing
         * do_wp_page installs a dirty pte.
         *
         * __do_fault is protected similarly.
         */
        if (!page_mkwrite) {
            wait_on_page_locked(dirty_page);
            set_page_dirty_balance(dirty_page, page_mkwrite);
            /* file_update_time outside page_lock */
            if (vma->vm_file)
                file_update_time(vma->vm_file);
        }
        put_page(dirty_page);
        if (page_mkwrite) {
            struct address_space *mapping = dirty_page->mapping;

            set_page_dirty(dirty_page);
            unlock_page(dirty_page);
            page_cache_release(dirty_page);
            if (mapping)    {
                /*
                 * Some device drivers do not set page.mapping
                 * but still dirty their pages
                 */
                balance_dirty_pages_ratelimited(mapping);
            }
        }

        return ret;
    }

    /*
     * Ok, we need to copy. Oh, well..
     */
    page_cache_get(old_page);
gotten:
    pte_unmap_unlock(page_table, ptl);

    if (unlikely(anon_vma_prepare(vma)))
        goto oom;

    if (is_zero_pfn(pte_pfn(orig_pte))) {
        new_page = alloc_zeroed_user_highpage_movable(vma, address);
        if (!new_page)
            goto oom;
    } else {
        new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
        if (!new_page)
            goto oom;
        cow_user_page(new_page, old_page, address, vma);
    }
    __SetPageUptodate(new_page);

    if (mem_cgroup_newpage_charge(new_page, mm, GFP_KERNEL))
        goto oom_free_new;

    mmun_start  = address & PAGE_MASK;
    mmun_end    = mmun_start + PAGE_SIZE;
    mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);

    /*
     * Re-check the pte - we dropped the lock
     */
    page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
    if (likely(pte_same(*page_table, orig_pte))) {
        if (old_page) {
            if (!PageAnon(old_page)) {
                dec_mm_counter_fast(mm, MM_FILEPAGES);
                inc_mm_counter_fast(mm, MM_ANONPAGES);
            }
        } else
            inc_mm_counter_fast(mm, MM_ANONPAGES);
        flush_cache_page(vma, address, pte_pfn(orig_pte));
        entry = mk_pte(new_page, vma->vm_page_prot);
        entry = maybe_mkwrite(pte_mkdirty(entry), vma);
        /*
         * Clear the pte entry and flush it first, before updating the
         * pte with the new entry. This will avoid a race condition
         * seen in the presence of one thread doing SMC and another
         * thread doing COW.
         */
        ptep_clear_flush(vma, address, page_table);
        page_add_new_anon_rmap(new_page, vma, address);
        /*
         * We call the notify macro here because, when using secondary
         * mmu page tables (such as kvm shadow page tables), we want the
         * new page to be mapped directly into the secondary page table.
         */
        set_pte_at_notify(mm, address, page_table, entry);
        update_mmu_cache(vma, address, page_table);
        if (old_page) {
            /*
             * Only after switching the pte to the new page may
             * we remove the mapcount here. Otherwise another
             * process may come and find the rmap count decremented
             * before the pte is switched to the new page, and
             * "reuse" the old page writing into it while our pte
             * here still points into it and can be read by other
             * threads.
             *
             * The critical issue is to order this
             * page_remove_rmap with the ptp_clear_flush above.
             * Those stores are ordered by (if nothing else,)
             * the barrier present in the atomic_add_negative
             * in page_remove_rmap.
             *
             * Then the TLB flush in ptep_clear_flush ensures that
             * no process can access the old page before the
             * decremented mapcount is visible. And the old page
             * cannot be reused until after the decremented
             * mapcount is visible. So transitively, TLBs to
             * old page will be flushed before it can be reused.
             */
            page_remove_rmap(old_page);
        }

        /* Free the old page.. */
        new_page = old_page;
        ret |= VM_FAULT_WRITE;
    } else
        mem_cgroup_uncharge_page(new_page);

    if (new_page)
        page_cache_release(new_page);
unlock:
    pte_unmap_unlock(page_table, ptl);
    if (mmun_end > mmun_start)
        mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
    if (old_page) {
        /*
         * Don't let another task, with possibly unlocked vma,
         * keep the mlocked page.
         */
        if ((ret & VM_FAULT_WRITE) && (vma->vm_flags & VM_LOCKED)) {
            lock_page(old_page);    /* LRU manipulation */
            munlock_vma_page(old_page);
            unlock_page(old_page);
        }
        page_cache_release(old_page);
    }
    return ret;
oom_free_new:
    page_cache_release(new_page);
oom:
    if (old_page) {
        if (page_mkwrite) {
            unlock_page(old_page);
            page_cache_release(old_page);
        }
        page_cache_release(old_page);
    }
    return VM_FAULT_OOM;

unwritable_page:
    page_cache_release(old_page);
    return ret;
}

static void unmap_mapping_range_vma(struct vm_area_struct *vma,
        unsigned long start_addr, unsigned long end_addr,
        struct zap_details *details)
{
    zap_page_range_single(vma, start_addr, end_addr - start_addr, details);
}

static inline void unmap_mapping_range_tree(struct rb_root *root,
                        struct zap_details *details)
{
    struct vm_area_struct *vma;
    pgoff_t vba, vea, zba, zea;

    vma_interval_tree_foreach(vma, root,
            details->first_index, details->last_index) {

        vba = vma->vm_pgoff;
        vea = vba + ((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) - 1;
        /* Assume for now that PAGE_CACHE_SHIFT == PAGE_SHIFT */
        zba = details->first_index;
        if (zba < vba)
            zba = vba;
        zea = details->last_index;
        if (zea > vea)
            zea = vea;

        unmap_mapping_range_vma(vma,
            ((zba - vba) << PAGE_SHIFT) + vma->vm_start,
            ((zea - vba + 1) << PAGE_SHIFT) + vma->vm_start,
                details);
    }
}

static inline void unmap_mapping_range_list(struct list_head *head,
                        struct zap_details *details)
{
    struct vm_area_struct *vma;

    /*
     * In nonlinear VMAs there is no correspondence between virtual address
     * offset and file offset.  So we must perform an exhaustive search
     * across *all* the pages in each nonlinear VMA, not just the pages
     * whose virtual address lies outside the file truncation point.
     */
    list_for_each_entry(vma, head, shared.nonlinear) {
        details->nonlinear_vma = vma;
        unmap_mapping_range_vma(vma, vma->vm_start, vma->vm_end, details);
    }
}

void unmap_mapping_range(struct address_space *mapping,
        loff_t const holebegin, loff_t const holelen, int even_cows)
{
    struct zap_details details;
    pgoff_t hba = holebegin >> PAGE_SHIFT;
    pgoff_t hlen = (holelen + PAGE_SIZE - 1) >> PAGE_SHIFT;

    /* Check for overflow. */
    if (sizeof(holelen) > sizeof(hlen)) {
        long long holeend =
            (holebegin + holelen + PAGE_SIZE - 1) >> PAGE_SHIFT;
        if (holeend & ~(long long)ULONG_MAX)
            hlen = ULONG_MAX - hba + 1;
    }

    details.check_mapping = even_cows? NULL: mapping;
    details.nonlinear_vma = NULL;
    details.first_index = hba;
    details.last_index = hba + hlen - 1;
    if (details.last_index < details.first_index)
        details.last_index = ULONG_MAX;


    mutex_lock(&mapping->i_mmap_mutex);
    if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap)))
        unmap_mapping_range_tree(&mapping->i_mmap, &details);
    if (unlikely(!list_empty(&mapping->i_mmap_nonlinear)))
        unmap_mapping_range_list(&mapping->i_mmap_nonlinear, &details);
    mutex_unlock(&mapping->i_mmap_mutex);
}
EXPORT_SYMBOL(unmap_mapping_range);

/*
 * We enter with non-exclusive mmap_sem (to exclude vma changes,
 * but allow concurrent faults), and pte mapped but not yet locked.
 * We return with mmap_sem still held, but pte unmapped and unlocked.
 */
static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
        unsigned long address, pte_t *page_table, pmd_t *pmd,
        unsigned int flags, pte_t orig_pte)
{
    spinlock_t *ptl;
    struct page *page, *swapcache = NULL;
    swp_entry_t entry;
    pte_t pte;
    int locked;
    struct mem_cgroup *ptr;
    int exclusive = 0;
    int ret = 0;

    if (!pte_unmap_same(mm, pmd, page_table, orig_pte))
        goto out;

    entry = pte_to_swp_entry(orig_pte);
    if (unlikely(non_swap_entry(entry))) {
        if (is_migration_entry(entry)) {
            migration_entry_wait(mm, pmd, address);
        } else if (is_hwpoison_entry(entry)) {
            ret = VM_FAULT_HWPOISON;
        } else {
            print_bad_pte(vma, address, orig_pte, NULL);
            ret = VM_FAULT_SIGBUS;
        }
        goto out;
    }
    delayacct_set_flag(DELAYACCT_PF_SWAPIN);
    page = lookup_swap_cache(entry);
    if (!page) {
        page = swapin_readahead(entry,
                    GFP_HIGHUSER_MOVABLE, vma, address);
        if (!page) {
            /*
             * Back out if somebody else faulted in this pte
             * while we released the pte lock.
             */
            page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
            if (likely(pte_same(*page_table, orig_pte)))
                ret = VM_FAULT_OOM;
            delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
            goto unlock;
        }

        /* Had to read the page from swap area: Major fault */
        ret = VM_FAULT_MAJOR;
        count_vm_event(PGMAJFAULT);
        mem_cgroup_count_vm_event(mm, PGMAJFAULT);
    } else if (PageHWPoison(page)) {
        /*
         * hwpoisoned dirty swapcache pages are kept for killing
         * owner processes (which may be unknown at hwpoison time)
         */
        ret = VM_FAULT_HWPOISON;
        delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
        goto out_release;
    }

    locked = lock_page_or_retry(page, mm, flags);

    delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
    if (!locked) {
        ret |= VM_FAULT_RETRY;
        goto out_release;
    }

    /*
     * Make sure try_to_free_swap or reuse_swap_page or swapoff did not
     * release the swapcache from under us.  The page pin, and pte_same
     * test below, are not enough to exclude that.  Even if it is still
     * swapcache, we need to check that the page's swap has not changed.
     */
    if (unlikely(!PageSwapCache(page) || page_private(page) != entry.val))
        goto out_page;

    if (ksm_might_need_to_copy(page, vma, address)) {
        swapcache = page;
        page = ksm_does_need_to_copy(page, vma, address);

        if (unlikely(!page)) {
            ret = VM_FAULT_OOM;
            page = swapcache;
            swapcache = NULL;
            goto out_page;
        }
    }

    if (mem_cgroup_try_charge_swapin(mm, page, GFP_KERNEL, &ptr)) {
        ret = VM_FAULT_OOM;
        goto out_page;
    }

    /*
     * Back out if somebody else already faulted in this pte.
     */
    page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
    if (unlikely(!pte_same(*page_table, orig_pte)))
        goto out_nomap;

    if (unlikely(!PageUptodate(page))) {
        ret = VM_FAULT_SIGBUS;
        goto out_nomap;
    }

    /*
     * The page isn't present yet, go ahead with the fault.
     *
     * Be careful about the sequence of operations here.
     * To get its accounting right, reuse_swap_page() must be called
     * while the page is counted on swap but not yet in mapcount i.e.
     * before page_add_anon_rmap() and swap_free(); try_to_free_swap()
     * must be called after the swap_free(), or it will never succeed.
     * Because delete_from_swap_page() may be called by reuse_swap_page(),
     * mem_cgroup_commit_charge_swapin() may not be able to find swp_entry
     * in page->private. In this case, a record in swap_cgroup  is silently
     * discarded at swap_free().
     */

    inc_mm_counter_fast(mm, MM_ANONPAGES);
    dec_mm_counter_fast(mm, MM_SWAPENTS);
    pte = mk_pte(page, vma->vm_page_prot);
    if ((flags & FAULT_FLAG_WRITE) && reuse_swap_page(page)) {
        pte = maybe_mkwrite(pte_mkdirty(pte), vma);
        flags &= ~FAULT_FLAG_WRITE;
        ret |= VM_FAULT_WRITE;
        exclusive = 1;
    }
    flush_icache_page(vma, page);
    set_pte_at(mm, address, page_table, pte);
    do_page_add_anon_rmap(page, vma, address, exclusive);
    /* It's better to call commit-charge after rmap is established */
    mem_cgroup_commit_charge_swapin(page, ptr);

    swap_free(entry);
    if (vm_swap_full() || (vma->vm_flags & VM_LOCKED) || PageMlocked(page))
        try_to_free_swap(page);
    unlock_page(page);
    if (swapcache) {
        /*
         * Hold the lock to avoid the swap entry to be reused
         * until we take the PT lock for the pte_same() check
         * (to avoid false positives from pte_same). For
         * further safety release the lock after the swap_free
         * so that the swap count won't change under a
         * parallel locked swapcache.
         */
        unlock_page(swapcache);
        page_cache_release(swapcache);
    }

    if (flags & FAULT_FLAG_WRITE) {
        ret |= do_wp_page(mm, vma, address, page_table, pmd, ptl, pte);
        if (ret & VM_FAULT_ERROR)
            ret &= VM_FAULT_ERROR;
        goto out;
    }

    /* No need to invalidate - it was non-present before */
    update_mmu_cache(vma, address, page_table);
unlock:
    pte_unmap_unlock(page_table, ptl);
out:
    return ret;
out_nomap:
    mem_cgroup_cancel_charge_swapin(ptr);
    pte_unmap_unlock(page_table, ptl);
out_page:
    unlock_page(page);
out_release:
    page_cache_release(page);
    if (swapcache) {
        unlock_page(swapcache);
        page_cache_release(swapcache);
    }
    return ret;
}

/*
 * This is like a special single-page "expand_{down|up}wards()",
 * except we must first make sure that 'address{-|+}PAGE_SIZE'
 * doesn't hit another vma.
 */
static inline int check_stack_guard_page(struct vm_area_struct *vma, unsigned long address)
{
    address &= PAGE_MASK;
    if ((vma->vm_flags & VM_GROWSDOWN) && address == vma->vm_start) {
        struct vm_area_struct *prev = vma->vm_prev;

        /*
         * Is there a mapping abutting this one below?
         *
         * That's only ok if it's the same stack mapping
         * that has gotten split..
         */
        if (prev && prev->vm_end == address)
            return prev->vm_flags & VM_GROWSDOWN ? 0 : -ENOMEM;

        expand_downwards(vma, address - PAGE_SIZE);
    }
    if ((vma->vm_flags & VM_GROWSUP) && address + PAGE_SIZE == vma->vm_end) {
        struct vm_area_struct *next = vma->vm_next;

        /* As VM_GROWSDOWN but s/below/above/ */
        if (next && next->vm_start == address + PAGE_SIZE)
            return next->vm_flags & VM_GROWSUP ? 0 : -ENOMEM;

        expand_upwards(vma, address + PAGE_SIZE);
    }
    return 0;
}

/*
 * We enter with non-exclusive mmap_sem (to exclude vma changes,
 * but allow concurrent faults), and pte mapped but not yet locked.
 * We return with mmap_sem still held, but pte unmapped and unlocked.
 */
static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
        unsigned long address, pte_t *page_table, pmd_t *pmd,
        unsigned int flags)
{
    struct page *page;
    spinlock_t *ptl;
    pte_t entry;

    pte_unmap(page_table);

    /* Check if we need to add a guard page to the stack */
    if (check_stack_guard_page(vma, address) < 0)
        return VM_FAULT_SIGBUS;

    /* Use the zero-page for reads */
    if (!(flags & FAULT_FLAG_WRITE)) {
        entry = pte_mkspecial(pfn_pte(my_zero_pfn(address),
                        vma->vm_page_prot));
        page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
        if (!pte_none(*page_table))
            goto unlock;
        goto setpte;
    }

    /* Allocate our own private page. */
    if (unlikely(anon_vma_prepare(vma)))
        goto oom;
    page = alloc_zeroed_user_highpage_movable(vma, address);
    if (!page)
        goto oom;
    __SetPageUptodate(page);

    if (mem_cgroup_newpage_charge(page, mm, GFP_KERNEL))
        goto oom_free_page;

    entry = mk_pte(page, vma->vm_page_prot);
    if (vma->vm_flags & VM_WRITE)
        entry = pte_mkwrite(pte_mkdirty(entry));

    page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
    if (!pte_none(*page_table))
        goto release;

    inc_mm_counter_fast(mm, MM_ANONPAGES);
    page_add_new_anon_rmap(page, vma, address);
setpte:
    set_pte_at(mm, address, page_table, entry);

    /* No need to invalidate - it was non-present before */
    update_mmu_cache(vma, address, page_table);
unlock:
    pte_unmap_unlock(page_table, ptl);
    return 0;
release:
    mem_cgroup_uncharge_page(page);
    page_cache_release(page);
    goto unlock;
oom_free_page:
    page_cache_release(page);
oom:
    return VM_FAULT_OOM;
}

/*
 * __do_fault() tries to create a new page mapping. It aggressively
 * tries to share with existing pages, but makes a separate copy if
 * the FAULT_FLAG_WRITE is set in the flags parameter in order to avoid
 * the next page fault.
 *
 * As this is called only for pages that do not currently exist, we
 * do not need to flush old virtual caches or the TLB.
 *
 * We enter with non-exclusive mmap_sem (to exclude vma changes,
 * but allow concurrent faults), and pte neither mapped nor locked.
 * We return with mmap_sem still held, but pte unmapped and unlocked.
 */
static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
        unsigned long address, pmd_t *pmd,
        pgoff_t pgoff, unsigned int flags, pte_t orig_pte)
{
    pte_t *page_table;
    spinlock_t *ptl;
    struct page *page;
    struct page *cow_page;
    pte_t entry;
    int anon = 0;
    struct page *dirty_page = NULL;
    struct vm_fault vmf;
    int ret;
    int page_mkwrite = 0;

    /*
     * If we do COW later, allocate page befor taking lock_page()
     * on the file cache page. This will reduce lock holding time.
     */
    if ((flags & FAULT_FLAG_WRITE) && !(vma->vm_flags & VM_SHARED)) {

        if (unlikely(anon_vma_prepare(vma)))
            return VM_FAULT_OOM;

        cow_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
        if (!cow_page)
            return VM_FAULT_OOM;

        if (mem_cgroup_newpage_charge(cow_page, mm, GFP_KERNEL)) {
            page_cache_release(cow_page);
            return VM_FAULT_OOM;
        }
    } else
        cow_page = NULL;

    vmf.virtual_address = (void __user *)(address & PAGE_MASK);
    vmf.pgoff = pgoff;
    vmf.flags = flags;
    vmf.page = NULL;

    ret = vma->vm_ops->fault(vma, &vmf);
    if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE |
                VM_FAULT_RETRY)))
        goto uncharge_out;

    if (unlikely(PageHWPoison(vmf.page))) {
        if (ret & VM_FAULT_LOCKED)
            unlock_page(vmf.page);
        ret = VM_FAULT_HWPOISON;
        goto uncharge_out;
    }

    /*
     * For consistency in subsequent calls, make the faulted page always
     * locked.
     */
    if (unlikely(!(ret & VM_FAULT_LOCKED)))
        lock_page(vmf.page);
    else
        VM_BUG_ON(!PageLocked(vmf.page));

    /*
     * Should we do an early C-O-W break?
     */
    page = vmf.page;
    if (flags & FAULT_FLAG_WRITE) {
        if (!(vma->vm_flags & VM_SHARED)) {
            page = cow_page;
            anon = 1;
            copy_user_highpage(page, vmf.page, address, vma);
            __SetPageUptodate(page);
        } else {
            /*
             * If the page will be shareable, see if the backing
             * address space wants to know that the page is about
             * to become writable
             */
            if (vma->vm_ops->page_mkwrite) {
                int tmp;

                unlock_page(page);
                vmf.flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
                tmp = vma->vm_ops->page_mkwrite(vma, &vmf);
                if (unlikely(tmp &
                      (VM_FAULT_ERROR | VM_FAULT_NOPAGE))) {
                    ret = tmp;
                    goto unwritable_page;
                }
                if (unlikely(!(tmp & VM_FAULT_LOCKED))) {
                    lock_page(page);
                    if (!page->mapping) {
                        ret = 0; /* retry the fault */
                        unlock_page(page);
                        goto unwritable_page;
                    }
                } else
                    VM_BUG_ON(!PageLocked(page));
                page_mkwrite = 1;
            }
        }

    }

    page_table = pte_offset_map_lock(mm, pmd, address, &ptl);

    /*
     * This silly early PAGE_DIRTY setting removes a race
     * due to the bad i386 page protection. But it's valid
     * for other architectures too.
     *
     * Note that if FAULT_FLAG_WRITE is set, we either now have
     * an exclusive copy of the page, or this is a shared mapping,
     * so we can make it writable and dirty to avoid having to
     * handle that later.
     */
    /* Only go through if we didn't race with anybody else... */
    if (likely(pte_same(*page_table, orig_pte))) {
        flush_icache_page(vma, page);
        entry = mk_pte(page, vma->vm_page_prot);
        if (flags & FAULT_FLAG_WRITE)
            entry = maybe_mkwrite(pte_mkdirty(entry), vma);
        if (anon) {
            inc_mm_counter_fast(mm, MM_ANONPAGES);
            page_add_new_anon_rmap(page, vma, address);
        } else {
            inc_mm_counter_fast(mm, MM_FILEPAGES);
            page_add_file_rmap(page);
            if (flags & FAULT_FLAG_WRITE) {
                dirty_page = page;
                get_page(dirty_page);
            }
        }
        set_pte_at(mm, address, page_table, entry);

        /* no need to invalidate: a not-present page won't be cached */
        update_mmu_cache(vma, address, page_table);
    } else {
        if (cow_page)
            mem_cgroup_uncharge_page(cow_page);
        if (anon)
            page_cache_release(page);
        else
            anon = 1; /* no anon but release faulted_page */
    }

    pte_unmap_unlock(page_table, ptl);

    if (dirty_page) {
        struct address_space *mapping = page->mapping;
        int dirtied = 0;

        if (set_page_dirty(dirty_page))
            dirtied = 1;
        unlock_page(dirty_page);
        put_page(dirty_page);
        if ((dirtied || page_mkwrite) && mapping) {
            /*
             * Some device drivers do not set page.mapping but still
             * dirty their pages
             */
            balance_dirty_pages_ratelimited(mapping);
        }

        /* file_update_time outside page_lock */
        if (vma->vm_file && !page_mkwrite)
            file_update_time(vma->vm_file);
    } else {
        unlock_page(vmf.page);
        if (anon)
            page_cache_release(vmf.page);
    }

    return ret;

unwritable_page:
    page_cache_release(page);
    return ret;
uncharge_out:
    /* fs's fault handler get error */
    if (cow_page) {
        mem_cgroup_uncharge_page(cow_page);
        page_cache_release(cow_page);
    }
    return ret;
}

static int do_linear_fault(struct mm_struct *mm, struct vm_area_struct *vma,
        unsigned long address, pte_t *page_table, pmd_t *pmd,
        unsigned int flags, pte_t orig_pte)
{
    pgoff_t pgoff = (((address & PAGE_MASK)
            - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;

    pte_unmap(page_table);
    return __do_fault(mm, vma, address, pmd, pgoff, flags, orig_pte);
}

/*
 * Fault of a previously existing named mapping. Repopulate the pte
 * from the encoded file_pte if possible. This enables swappable
 * nonlinear vmas.
 *
 * We enter with non-exclusive mmap_sem (to exclude vma changes,
 * but allow concurrent faults), and pte mapped but not yet locked.
 * We return with mmap_sem still held, but pte unmapped and unlocked.
 */
static int do_nonlinear_fault(struct mm_struct *mm, struct vm_area_struct *vma,
        unsigned long address, pte_t *page_table, pmd_t *pmd,
        unsigned int flags, pte_t orig_pte)
{
    pgoff_t pgoff;

    flags |= FAULT_FLAG_NONLINEAR;

    if (!pte_unmap_same(mm, pmd, page_table, orig_pte))
        return 0;

    if (unlikely(!(vma->vm_flags & VM_NONLINEAR))) {
        /*
         * Page table corrupted: show pte and kill process.
         */
        print_bad_pte(vma, address, orig_pte, NULL);
        return VM_FAULT_SIGBUS;
    }

    pgoff = pte_to_pgoff(orig_pte);
    return __do_fault(mm, vma, address, pmd, pgoff, flags, orig_pte);
}

/*
 * These routines also need to handle stuff like marking pages dirty
 * and/or accessed for architectures that don't do it in hardware (most
 * RISC architectures).  The early dirtying is also good on the i386.
 *
 * There is also a hook called "update_mmu_cache()" that architectures
 * with external mmu caches can use to update those (ie the Sparc or
 * PowerPC hashed page tables that act as extended TLBs).
 *
 * We enter with non-exclusive mmap_sem (to exclude vma changes,
 * but allow concurrent faults), and pte mapped but not yet locked.
 * We return with mmap_sem still held, but pte unmapped and unlocked.
 */
int handle_pte_fault(struct mm_struct *mm,
             struct vm_area_struct *vma, unsigned long address,
             pte_t *pte, pmd_t *pmd, unsigned int flags)
{
    pte_t entry;
    spinlock_t *ptl;

    entry = *pte;
    if (!pte_present(entry)) {
        if (pte_none(entry)) {
            if (vma->vm_ops) {
                if (likely(vma->vm_ops->fault))
                    return do_linear_fault(mm, vma, address,
                        pte, pmd, flags, entry);
            }
            return do_anonymous_page(mm, vma, address,
                         pte, pmd, flags);
        }
        if (pte_file(entry))
            return do_nonlinear_fault(mm, vma, address,
                    pte, pmd, flags, entry);
        return do_swap_page(mm, vma, address,
                    pte, pmd, flags, entry);
    }

    ptl = pte_lockptr(mm, pmd);
    spin_lock(ptl);
    if (unlikely(!pte_same(*pte, entry)))
        goto unlock;
    if (flags & FAULT_FLAG_WRITE) {
        if (!pte_write(entry))
            return do_wp_page(mm, vma, address,
                    pte, pmd, ptl, entry);
        entry = pte_mkdirty(entry);
    }
    entry = pte_mkyoung(entry);
    if (ptep_set_access_flags(vma, address, pte, entry, flags & FAULT_FLAG_WRITE)) {
        update_mmu_cache(vma, address, pte);
    } else {
        /*
         * This is needed only for protection faults but the arch code
         * is not yet telling us if this is a protection fault or not.
         * This still avoids useless tlb flushes for .text page faults
         * with threads.
         */
        if (flags & FAULT_FLAG_WRITE)
            flush_tlb_fix_spurious_fault(vma, address);
    }
unlock:
    pte_unmap_unlock(pte, ptl);
    return 0;
}

/*
 * By the time we get here, we already hold the mm semaphore
 */
int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct *vma,
        unsigned long address, unsigned int flags)
{
    pgd_t *pgd;
    pud_t *pud;
    pmd_t *pmd;
    pte_t *pte;

    __set_current_state(TASK_RUNNING);

    count_vm_event(PGFAULT);
    mem_cgroup_count_vm_event(mm, PGFAULT);

    /* do counter updates before entering really critical section. */
    check_sync_rss_stat(current);

    if (unlikely(is_vm_hugetlb_page(vma)))
        return hugetlb_fault(mm, vma, address, flags);

retry:
    pgd = pgd_offset(mm, address);
    pud = pud_alloc(mm, pgd, address);
    if (!pud)
        return VM_FAULT_OOM;
    pmd = pmd_alloc(mm, pud, address);
    if (!pmd)
        return VM_FAULT_OOM;
    if (pmd_none(*pmd) && transparent_hugepage_enabled(vma)) {
        if (!vma->vm_ops)
            return do_huge_pmd_anonymous_page(mm, vma, address,
                              pmd, flags);
    } else {
        pmd_t orig_pmd = *pmd;
        int ret;

        barrier();
        if (pmd_trans_huge(orig_pmd)) {
            if (flags & FAULT_FLAG_WRITE &&
                !pmd_write(orig_pmd) &&
                !pmd_trans_splitting(orig_pmd)) {
                ret = do_huge_pmd_wp_page(mm, vma, address, pmd,
                              orig_pmd);
                /*
                 * If COW results in an oom, the huge pmd will
                 * have been split, so retry the fault on the
                 * pte for a smaller charge.
                 */
                if (unlikely(ret & VM_FAULT_OOM))
                    goto retry;
                return ret;
            }
            return 0;
        }
    }

    /*
     * Use __pte_alloc instead of pte_alloc_map, because we can't
     * run pte_offset_map on the pmd, if an huge pmd could
     * materialize from under us from a different thread.
     */
    if (unlikely(pmd_none(*pmd)) && __pte_alloc(mm, vma, pmd, address))
        return VM_FAULT_OOM;
    /* if an huge pmd materialized from under us just retry later */
    if (unlikely(pmd_trans_huge(*pmd)))
        return 0;
    /*
     * A regular pmd is established and it can't morph into a huge pmd
     * from under us anymore at this point because we hold the mmap_sem
     * read mode and khugepaged takes it in write mode. So now it's
     * safe to run pte_offset_map().
     */
    pte = pte_offset_map(pmd, address);

    return handle_pte_fault(mm, vma, address, pte, pmd, flags);
}

#ifndef __PAGETABLE_PUD_FOLDED
/*
 * Allocate page upper directory.
 * We've already handled the fast-path in-line.
 */
int __pud_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
{
    pud_t *new = pud_alloc_one(mm, address);
    if (!new)
        return -ENOMEM;

    smp_wmb(); /* See comment in __pte_alloc */

    spin_lock(&mm->page_table_lock);
    if (pgd_present(*pgd))      /* Another has populated it */
        pud_free(mm, new);
    else
        pgd_populate(mm, pgd, new);
    spin_unlock(&mm->page_table_lock);
    return 0;
}
#endif /* __PAGETABLE_PUD_FOLDED */

#ifndef __PAGETABLE_PMD_FOLDED
/*
 * Allocate page middle directory.
 * We've already handled the fast-path in-line.
 */
int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
{
    pmd_t *new = pmd_alloc_one(mm, address);
    if (!new)
        return -ENOMEM;

    smp_wmb(); /* See comment in __pte_alloc */

    spin_lock(&mm->page_table_lock);
#ifndef __ARCH_HAS_4LEVEL_HACK
    if (pud_present(*pud))      /* Another has populated it */
        pmd_free(mm, new);
    else
        pud_populate(mm, pud, new);
#else
    if (pgd_present(*pud))      /* Another has populated it */
        pmd_free(mm, new);
    else
        pgd_populate(mm, pud, new);
#endif /* __ARCH_HAS_4LEVEL_HACK */
    spin_unlock(&mm->page_table_lock);
    return 0;
}
#endif /* __PAGETABLE_PMD_FOLDED */

int make_pages_present(unsigned long addr, unsigned long end)
{
    int ret, len, write;
    struct vm_area_struct * vma;

    vma = find_vma(current->mm, addr);
    if (!vma)
        return -ENOMEM;
    /*
     * We want to touch writable mappings with a write fault in order
     * to break COW, except for shared mappings because these don't COW
     * and we would not want to dirty them for nothing.
     */
    write = (vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE;
    BUG_ON(addr >= end);
    BUG_ON(end > vma->vm_end);
    len = DIV_ROUND_UP(end, PAGE_SIZE) - addr/PAGE_SIZE;
    ret = get_user_pages(current, current->mm, addr,
            len, write, 0, NULL, NULL);
    if (ret < 0)
        return ret;
    return ret == len ? 0 : -EFAULT;
}

#if !defined(__HAVE_ARCH_GATE_AREA)

#if defined(AT_SYSINFO_EHDR)
static struct vm_area_struct gate_vma;

static int __init gate_vma_init(void)
{
    gate_vma.vm_mm = NULL;
    gate_vma.vm_start = FIXADDR_USER_START;
    gate_vma.vm_end = FIXADDR_USER_END;
    gate_vma.vm_flags = VM_READ | VM_MAYREAD | VM_EXEC | VM_MAYEXEC;
    gate_vma.vm_page_prot = __P101;

    return 0;
}
__initcall(gate_vma_init);
#endif

struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
{
#ifdef AT_SYSINFO_EHDR
    return &gate_vma;
#else
    return NULL;
#endif
}

int in_gate_area_no_mm(unsigned long addr)
{
#ifdef AT_SYSINFO_EHDR
    if ((addr >= FIXADDR_USER_START) && (addr < FIXADDR_USER_END))
        return 1;
#endif
    return 0;
}

#endif  /* __HAVE_ARCH_GATE_AREA */

static int __follow_pte(struct mm_struct *mm, unsigned long address,
        pte_t **ptepp, spinlock_t **ptlp)
{
    pgd_t *pgd;
    pud_t *pud;
    pmd_t *pmd;
    pte_t *ptep;

    pgd = pgd_offset(mm, address);
    if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
        goto out;

    pud = pud_offset(pgd, address);
    if (pud_none(*pud) || unlikely(pud_bad(*pud)))
        goto out;

    pmd = pmd_offset(pud, address);
    VM_BUG_ON(pmd_trans_huge(*pmd));
    if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
        goto out;

    /* We cannot handle huge page PFN maps. Luckily they don't exist. */
    if (pmd_huge(*pmd))
        goto out;

    ptep = pte_offset_map_lock(mm, pmd, address, ptlp);
    if (!ptep)
        goto out;
    if (!pte_present(*ptep))
        goto unlock;
    *ptepp = ptep;
    return 0;
unlock:
    pte_unmap_unlock(ptep, *ptlp);
out:
    return -EINVAL;
}

static inline int follow_pte(struct mm_struct *mm, unsigned long address,
                 pte_t **ptepp, spinlock_t **ptlp)
{
    int res;

    /* (void) is needed to make gcc happy */
    (void) __cond_lock(*ptlp,
               !(res = __follow_pte(mm, address, ptepp, ptlp)));
    return res;
}

int follow_pfn(struct vm_area_struct *vma, unsigned long address,
    unsigned long *pfn)
{
    int ret = -EINVAL;
    spinlock_t *ptl;
    pte_t *ptep;

    if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
        return ret;

    ret = follow_pte(vma->vm_mm, address, &ptep, &ptl);
    if (ret)
        return ret;
    *pfn = pte_pfn(*ptep);
    pte_unmap_unlock(ptep, ptl);
    return 0;
}
EXPORT_SYMBOL(follow_pfn);

#ifdef CONFIG_HAVE_IOREMAP_PROT
int follow_phys(struct vm_area_struct *vma,
        unsigned long address, unsigned int flags,
        unsigned long *prot, resource_size_t *phys)
{
    int ret = -EINVAL;
    pte_t *ptep, pte;
    spinlock_t *ptl;

    if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
        goto out;

    if (follow_pte(vma->vm_mm, address, &ptep, &ptl))
        goto out;
    pte = *ptep;

    if ((flags & FOLL_WRITE) && !pte_write(pte))
        goto unlock;

    *prot = pgprot_val(pte_pgprot(pte));
    *phys = (resource_size_t)pte_pfn(pte) << PAGE_SHIFT;

    ret = 0;
unlock:
    pte_unmap_unlock(ptep, ptl);
out:
    return ret;
}

int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
            void *buf, int len, int write)
{
    resource_size_t phys_addr;
    unsigned long prot = 0;
    void __iomem *maddr;
    int offset = addr & (PAGE_SIZE-1);

    if (follow_phys(vma, addr, write, &prot, &phys_addr))
        return -EINVAL;

    maddr = ioremap_prot(phys_addr, PAGE_SIZE, prot);
    if (write)
        memcpy_toio(maddr + offset, buf, len);
    else
        memcpy_fromio(buf, maddr + offset, len);
    iounmap(maddr);

    return len;
}
#endif

/*
 * Access another process' address space as given in mm.  If non-NULL, use the
 * given task for page fault accounting.
 */
static int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
        unsigned long addr, void *buf, int len, int write)
{
    struct vm_area_struct *vma;
    void *old_buf = buf;

    down_read(&mm->mmap_sem);
    /* ignore errors, just check how much was successfully transferred */
    while (len) {
        int bytes, ret, offset;
        void *maddr;
        struct page *page = NULL;

        ret = get_user_pages(tsk, mm, addr, 1,
                write, 1, &page, &vma);
        if (ret <= 0) {
            /*
             * Check if this is a VM_IO | VM_PFNMAP VMA, which
             * we can access using slightly different code.
             */
#ifdef CONFIG_HAVE_IOREMAP_PROT
            vma = find_vma(mm, addr);
            if (!vma || vma->vm_start > addr)
                break;
            if (vma->vm_ops && vma->vm_ops->access)
                ret = vma->vm_ops->access(vma, addr, buf,
                              len, write);
            if (ret <= 0)
#endif
                break;
            bytes = ret;
        } else {
            bytes = len;
            offset = addr & (PAGE_SIZE-1);
            if (bytes > PAGE_SIZE-offset)
                bytes = PAGE_SIZE-offset;

            maddr = kmap(page);
            if (write) {
                copy_to_user_page(vma, page, addr,
                          maddr + offset, buf, bytes);
                set_page_dirty_lock(page);
            } else {
                copy_from_user_page(vma, page, addr,
                            buf, maddr + offset, bytes);
            }
            kunmap(page);
            page_cache_release(page);
        }
        len -= bytes;
        buf += bytes;
        addr += bytes;
    }
    up_read(&mm->mmap_sem);

    return buf - old_buf;
}

int access_remote_vm(struct mm_struct *mm, unsigned long addr,
        void *buf, int len, int write)
{
    return __access_remote_vm(NULL, mm, addr, buf, len, write);
}

/*
 * Access another process' address space.
 * Source/target buffer must be kernel space,
 * Do not walk the page table directly, use get_user_pages
 */
int access_process_vm(struct task_struct *tsk, unsigned long addr,
        void *buf, int len, int write)
{
    struct mm_struct *mm;
    int ret;

    mm = get_task_mm(tsk);
    if (!mm)
        return 0;

    ret = __access_remote_vm(tsk, mm, addr, buf, len, write);
    mmput(mm);

    return ret;
}

/*
 * Print the name of a VMA.
 */
void print_vma_addr(char *prefix, unsigned long ip)
{
    struct mm_struct *mm = current->mm;
    struct vm_area_struct *vma;

    /*
     * Do not print if we are in atomic
     * contexts (in exception stacks, etc.):
     */
    if (preempt_count())
        return;

    down_read(&mm->mmap_sem);
    vma = find_vma(mm, ip);
    if (vma && vma->vm_file) {
        struct file *f = vma->vm_file;
        char *buf = (char *)__get_free_page(GFP_KERNEL);
        if (buf) {
            char *p, *s;

            p = d_path(&f->f_path, buf, PAGE_SIZE);
            if (IS_ERR(p))
                p = "?";
            s = strrchr(p, '/');
            if (s)
                p = s+1;
            printk("%s%s[%lx+%lx]", prefix, p,
                    vma->vm_start,
                    vma->vm_end - vma->vm_start);
            free_page((unsigned long)buf);
        }
    }
    up_read(&mm->mmap_sem);
}

#ifdef CONFIG_PROVE_LOCKING
void might_fault(void)
{
    /*
     * Some code (nfs/sunrpc) uses socket ops on kernel memory while
     * holding the mmap_sem, this is safe because kernel memory doesn't
     * get paged out, therefore we'll never actually fault, and the
     * below annotations will generate false positives.
     */
    if (segment_eq(get_fs(), KERNEL_DS))
        return;

    might_sleep();
    /*
     * it would be nicer only to annotate paths which are not under
     * pagefault_disable, however that requires a larger audit and
     * providing helpers like get_user_atomic.
     */
    if (!in_atomic() && current->mm)
        might_lock_read(&current->mm->mmap_sem);
}
EXPORT_SYMBOL(might_fault);
#endif

#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
static void clear_gigantic_page(struct page *page,
                unsigned long addr,
                unsigned int pages_per_huge_page)
{
    int i;
    struct page *p = page;

    might_sleep();
    for (i = 0; i < pages_per_huge_page;
         i++, p = mem_map_next(p, page, i)) {
        cond_resched();
        clear_user_highpage(p, addr + i * PAGE_SIZE);
    }
}
void clear_huge_page(struct page *page,
             unsigned long addr, unsigned int pages_per_huge_page)
{
    int i;

    if (unlikely(pages_per_huge_page > MAX_ORDER_NR_PAGES)) {
        clear_gigantic_page(page, addr, pages_per_huge_page);
        return;
    }

    might_sleep();
    for (i = 0; i < pages_per_huge_page; i++) {
        cond_resched();
        clear_user_highpage(page + i, addr + i * PAGE_SIZE);
    }
}

static void copy_user_gigantic_page(struct page *dst, struct page *src,
                    unsigned long addr,
                    struct vm_area_struct *vma,
                    unsigned int pages_per_huge_page)
{
    int i;
    struct page *dst_base = dst;
    struct page *src_base = src;

    for (i = 0; i < pages_per_huge_page; ) {
        cond_resched();
        copy_user_highpage(dst, src, addr + i*PAGE_SIZE, vma);

        i++;
        dst = mem_map_next(dst, dst_base, i);
        src = mem_map_next(src, src_base, i);
    }
}

void copy_user_huge_page(struct page *dst, struct page *src,
             unsigned long addr, struct vm_area_struct *vma,
             unsigned int pages_per_huge_page)
{
    int i;

    if (unlikely(pages_per_huge_page > MAX_ORDER_NR_PAGES)) {
        copy_user_gigantic_page(dst, src, addr, vma,
                    pages_per_huge_page);
        return;
    }

    might_sleep();
    for (i = 0; i < pages_per_huge_page; i++) {
        cond_resched();
        copy_user_highpage(dst + i, src + i, addr + i*PAGE_SIZE, vma);
    }
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */