// SPDX-License-Identifier: GPL-2.0-only
/*
 *  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 (alex@cconcepts.co.uk)
 *
 * 16.07.99  -  Support of BIGMEM added by Gerhard Wichert, Siemens AG
 *              (Gerhard.Wichert@pdb.siemens.de)
 *
 * Aug/Sep 2004 Changed to four level page tables (Andi Kleen)
 */

#include <linux/kernel_stat.h>
#include <linux/mm.h>
#include <linux/sched/mm.h>
#include <linux/sched/coredump.h>
#include <linux/sched/numa_balancing.h>
#include <linux/sched/task.h>
#include <linux/hugetlb.h>
#include <linux/mman.h>
#include <linux/swap.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/memremap.h>
#include <linux/ksm.h>
#include <linux/rmap.h>
#include <linux/export.h>
#include <linux/delayacct.h>
#include <linux/init.h>
#include <linux/pfn_t.h>
#include <linux/writeback.h>
#include <linux/memcontrol.h>
#include <linux/mmu_notifier.h>
#include <linux/swapops.h>
#include <linux/elf.h>
#include <linux/gfp.h>
#include <linux/migrate.h>
#include <linux/string.h>
#include <linux/debugfs.h>
#include <linux/userfaultfd_k.h>
#include <linux/dax.h>
#include <linux/oom.h>
#include <linux/numa.h>
#include <linux/perf_event.h>
#include <linux/ptrace.h>
#include <linux/vmalloc.h>

#include <trace/events/kmem.h>

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

#include "pgalloc-track.h"
#include "internal.h"

#if defined(LAST_CPUPID_NOT_IN_PAGE_FLAGS) && !defined(CONFIG_COMPILE_TEST)
#warning Unfortunate NUMA and NUMA Balancing config, growing page-frame for last_cpupid.
#endif

#ifndef CONFIG_NUMA
unsigned long max_mapnr;
EXPORT_SYMBOL(max_mapnr);

struct page *mem_map;
EXPORT_SYMBOL(mem_map);
#endif

/*
 * 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(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

#ifndef arch_faults_on_old_pte
static inline bool arch_faults_on_old_pte(void)
{
        /*
         * Those arches which don't have hw access flag feature need to
         * implement their own helper. By default, "true" means pagefault
         * will be hit on old pte.
         */
        return true;
}
#endif

#ifndef arch_wants_old_prefaulted_pte
static inline bool arch_wants_old_prefaulted_pte(void)
{
        /*
         * Transitioning a PTE from 'old' to 'young' can be expensive on
         * some architectures, even if it's performed in hardware. By
         * default, "false" means prefaulted entries will be 'young'.
         */
        return false;
}
#endif

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

unsigned long zero_pfn __read_mostly;
EXPORT_SYMBOL(zero_pfn);

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;
}
early_initcall(init_zero_pfn);

void mm_trace_rss_stat(struct mm_struct *mm, int member, long count)
{
        trace_rss_stat(mm, member, count);
}

#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 */

/*
 * 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);
        mm_dec_nr_ptes(tlb->mm);
}

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);
        mm_dec_nr_pmds(tlb->mm);
}

static inline void free_pud_range(struct mmu_gather *tlb, p4d_t *p4d,
                                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(p4d, 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 &= P4D_MASK;
        if (start < floor)
                return;
        if (ceiling) {
                ceiling &= P4D_MASK;
                if (!ceiling)
                        return;
        }
        if (end - 1 > ceiling - 1)
                return;

        pud = pud_offset(p4d, start);
        p4d_clear(p4d);
        pud_free_tlb(tlb, pud, start);
        mm_dec_nr_puds(tlb->mm);
}

static inline void free_p4d_range(struct mmu_gather *tlb, pgd_t *pgd,
                                unsigned long addr, unsigned long end,
                                unsigned long floor, unsigned long ceiling)
{
        p4d_t *p4d;
        unsigned long next;
        unsigned long start;

        start = addr;
        p4d = p4d_offset(pgd, addr);
        do {
                next = p4d_addr_end(addr, end);
                if (p4d_none_or_clear_bad(p4d))
                        continue;
                free_pud_range(tlb, p4d, addr, next, floor, ceiling);
        } while (p4d++, 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;

        p4d = p4d_offset(pgd, start);
        pgd_clear(pgd);
        p4d_free_tlb(tlb, p4d, start);
}

/*
 * This function frees user-level page tables of a process.
 */
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;
        /*
         * We add page table cache pages with PAGE_SIZE,
         * (see pte_free_tlb()), flush the tlb if we need
         */
        tlb_change_page_size(tlb, PAGE_SIZE);
        pgd = pgd_offset(tlb->mm, addr);
        do {
                next = pgd_addr_end(addr, end);
                if (pgd_none_or_clear_bad(pgd))
                        continue;
                free_p4d_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;
        }
}

void pmd_install(struct mm_struct *mm, pmd_t *pmd, pgtable_t *pte)
{
        spinlock_t *ptl = pmd_lock(mm, pmd);

        if (likely(pmd_none(*pmd))) {   /* Has another populated it ? */
                mm_inc_nr_ptes(mm);
                /*
                 * 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_rmb() barriers in page table walking code.
                 */
                smp_wmb(); /* Could be smp_wmb__xxx(before|after)_spin_lock */
                pmd_populate(mm, pmd, *pte);
                *pte = NULL;
        }
        spin_unlock(ptl);
}

int __pte_alloc(struct mm_struct *mm, pmd_t *pmd)
{
        pgtable_t new = pte_alloc_one(mm);
        if (!new)
                return -ENOMEM;

        pmd_install(mm, pmd, &new);
        if (new)
                pte_free(mm, new);
        return 0;
}

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

        spin_lock(&init_mm.page_table_lock);
        if (likely(pmd_none(*pmd))) {   /* Has another populated it ? */
                smp_wmb(); /* See comment in pmd_install() */
                pmd_populate_kernel(&init_mm, pmd, new);
                new = NULL;
        }
        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);
        p4d_t *p4d = p4d_offset(pgd, addr);
        pud_t *pud = pud_offset(p4d, 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) {
                        pr_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);

        pr_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, "bad pte");
        pr_alert("addr:%px vm_flags:%08lx anon_vma:%px mapping:%px index:%lx\n",
                 (void *)addr, vma->vm_flags, vma->anon_vma, mapping, index);
        pr_alert("file:%pD fault:%ps mmap:%ps readpage:%ps\n",
                 vma->vm_file,
                 vma->vm_ops ? vma->vm_ops->fault : NULL,
                 vma->vm_file ? vma->vm_file->f_op->mmap : NULL,
                 mapping ? mapping->a_ops->readpage : NULL);
        dump_stack();
        add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
}

/*
 * 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.
 *
 */
struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
                            pte_t pte)
{
        unsigned long pfn = pte_pfn(pte);

        if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL)) {
                if (likely(!pte_special(pte)))
                        goto check_pfn;
                if (vma->vm_ops && vma->vm_ops->find_special_page)
                        return vma->vm_ops->find_special_page(vma, addr);
                if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
                        return NULL;
                if (is_zero_pfn(pfn))
                        return NULL;
                if (pte_devmap(pte))
                        return NULL;

                print_bad_pte(vma, addr, pte, NULL);
                return NULL;
        }

        /* !CONFIG_ARCH_HAS_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);
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
                                pmd_t pmd)
{
        unsigned long pfn = pmd_pfn(pmd);

        /*
         * There is no pmd_special() but there may be special pmds, e.g.
         * in a direct-access (dax) mapping, so let's just replicate the
         * !CONFIG_ARCH_HAS_PTE_SPECIAL case from vm_normal_page() here.
         */
        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 (pmd_devmap(pmd))
                return NULL;
        if (is_huge_zero_pmd(pmd))
                return NULL;
        if (unlikely(pfn > highest_memmap_pfn))
                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);
}
#endif

static void restore_exclusive_pte(struct vm_area_struct *vma,
                                  struct page *page, unsigned long address,
                                  pte_t *ptep)
{
        pte_t pte;
        swp_entry_t entry;

        pte = pte_mkold(mk_pte(page, READ_ONCE(vma->vm_page_prot)));
        if (pte_swp_soft_dirty(*ptep))
                pte = pte_mksoft_dirty(pte);

        entry = pte_to_swp_entry(*ptep);
        if (pte_swp_uffd_wp(*ptep))
                pte = pte_mkuffd_wp(pte);
        else if (is_writable_device_exclusive_entry(entry))
                pte = maybe_mkwrite(pte_mkdirty(pte), vma);

        set_pte_at(vma->vm_mm, address, ptep, pte);

        /*
         * No need to take a page reference as one was already
         * created when the swap entry was made.
         */
        if (PageAnon(page))
                page_add_anon_rmap(page, vma, address, false);
        else
                /*
                 * Currently device exclusive access only supports anonymous
                 * memory so the entry shouldn't point to a filebacked page.
                 */
                WARN_ON_ONCE(!PageAnon(page));

        if (vma->vm_flags & VM_LOCKED)
                mlock_vma_page(page);

        /*
         * No need to invalidate - it was non-present before. However
         * secondary CPUs may have mappings that need invalidating.
         */
        update_mmu_cache(vma, address, ptep);
}

/*
 * Tries to restore an exclusive pte if the page lock can be acquired without
 * sleeping.
 */
static int
try_restore_exclusive_pte(pte_t *src_pte, struct vm_area_struct *vma,
                        unsigned long addr)
{
        swp_entry_t entry = pte_to_swp_entry(*src_pte);
        struct page *page = pfn_swap_entry_to_page(entry);

        if (trylock_page(page)) {
                restore_exclusive_pte(vma, page, addr, src_pte);
                unlock_page(page);
                return 0;
        }

        return -EBUSY;
}

/*
 * 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 unsigned long
copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
                pte_t *dst_pte, pte_t *src_pte, struct vm_area_struct *dst_vma,
                struct vm_area_struct *src_vma, unsigned long addr, int *rss)
{
        unsigned long vm_flags = dst_vma->vm_flags;
        pte_t pte = *src_pte;
        struct page *page;
        swp_entry_t entry = pte_to_swp_entry(pte);

        if (likely(!non_swap_entry(entry))) {
                if (swap_duplicate(entry) < 0)
                        return -EIO;

                /* 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);
                }
                rss[MM_SWAPENTS]++;
        } else if (is_migration_entry(entry)) {
                page = pfn_swap_entry_to_page(entry);

                rss[mm_counter(page)]++;

                if (is_writable_migration_entry(entry) &&
                                is_cow_mapping(vm_flags)) {
                        /*
                         * COW mappings require pages in both
                         * parent and child to be set to read.
                         */
                        entry = make_readable_migration_entry(
                                                        swp_offset(entry));
                        pte = swp_entry_to_pte(entry);
                        if (pte_swp_soft_dirty(*src_pte))
                                pte = pte_swp_mksoft_dirty(pte);
                        if (pte_swp_uffd_wp(*src_pte))
                                pte = pte_swp_mkuffd_wp(pte);
                        set_pte_at(src_mm, addr, src_pte, pte);
                }
        } else if (is_device_private_entry(entry)) {
                page = pfn_swap_entry_to_page(entry);

                /*
                 * Update rss count even for unaddressable pages, as
                 * they should treated just like normal pages in this
                 * respect.
                 *
                 * We will likely want to have some new rss counters
                 * for unaddressable pages, at some point. But for now
                 * keep things as they are.
                 */
                get_page(page);
                rss[mm_counter(page)]++;
                page_dup_rmap(page, false);

                /*
                 * We do not preserve soft-dirty information, because so
                 * far, checkpoint/restore is the only feature that
                 * requires that. And checkpoint/restore does not work
                 * when a device driver is involved (you cannot easily
                 * save and restore device driver state).
                 */
                if (is_writable_device_private_entry(entry) &&
                    is_cow_mapping(vm_flags)) {
                        entry = make_readable_device_private_entry(
                                                        swp_offset(entry));
                        pte = swp_entry_to_pte(entry);
                        if (pte_swp_uffd_wp(*src_pte))
                                pte = pte_swp_mkuffd_wp(pte);
                        set_pte_at(src_mm, addr, src_pte, pte);
                }
        } else if (is_device_exclusive_entry(entry)) {
                /*
                 * Make device exclusive entries present by restoring the
                 * original entry then copying as for a present pte. Device
                 * exclusive entries currently only support private writable
                 * (ie. COW) mappings.
                 */
                VM_BUG_ON(!is_cow_mapping(src_vma->vm_flags));
                if (try_restore_exclusive_pte(src_pte, src_vma, addr))
                        return -EBUSY;
                return -ENOENT;
        }
        if (!userfaultfd_wp(dst_vma))
                pte = pte_swp_clear_uffd_wp(pte);
        set_pte_at(dst_mm, addr, dst_pte, pte);
        return 0;
}

/*
 * Copy a present and normal page if necessary.
 *
 * NOTE! The usual case is that this doesn't need to do
 * anything, and can just return a positive value. That
 * will let the caller know that it can just increase
 * the page refcount and re-use the pte the traditional
 * way.
 *
 * But _if_ we need to copy it because it needs to be
 * pinned in the parent (and the child should get its own
 * copy rather than just a reference to the same page),
 * we'll do that here and return zero to let the caller
 * know we're done.
 *
 * And if we need a pre-allocated page but don't yet have
 * one, return a negative error to let the preallocation
 * code know so that it can do so outside the page table
 * lock.
 */
static inline int
copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
                  pte_t *dst_pte, pte_t *src_pte, unsigned long addr, int *rss,
                  struct page **prealloc, pte_t pte, struct page *page)
{
        struct page *new_page;

        /*
         * What we want to do is to check whether this page may
         * have been pinned by the parent process.  If so,
         * instead of wrprotect the pte on both sides, we copy
         * the page immediately so that we'll always guarantee
         * the pinned page won't be randomly replaced in the
         * future.
         *
         * The page pinning checks are just "has this mm ever
         * seen pinning", along with the (inexact) check of
         * the page count. That might give false positives for
         * for pinning, but it will work correctly.
         */
        if (likely(!page_needs_cow_for_dma(src_vma, page)))
                return 1;

        new_page = *prealloc;
        if (!new_page)
                return -EAGAIN;

        /*
         * We have a prealloc page, all good!  Take it
         * over and copy the page & arm it.
         */
        *prealloc = NULL;
        copy_user_highpage(new_page, page, addr, src_vma);
        __SetPageUptodate(new_page);
        page_add_new_anon_rmap(new_page, dst_vma, addr, false);
        lru_cache_add_inactive_or_unevictable(new_page, dst_vma);
        rss[mm_counter(new_page)]++;

        /* All done, just insert the new page copy in the child */
        pte = mk_pte(new_page, dst_vma->vm_page_prot);
        pte = maybe_mkwrite(pte_mkdirty(pte), dst_vma);
        if (userfaultfd_pte_wp(dst_vma, *src_pte))
                /* Uffd-wp needs to be delivered to dest pte as well */
                pte = pte_wrprotect(pte_mkuffd_wp(pte));
        set_pte_at(dst_vma->vm_mm, addr, dst_pte, pte);
        return 0;
}

/*
 * Copy one pte.  Returns 0 if succeeded, or -EAGAIN if one preallocated page
 * is required to copy this pte.
 */
static inline int
copy_present_pte(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
                 pte_t *dst_pte, pte_t *src_pte, unsigned long addr, int *rss,
                 struct page **prealloc)
{
        struct mm_struct *src_mm = src_vma->vm_mm;
        unsigned long vm_flags = src_vma->vm_flags;
        pte_t pte = *src_pte;
        struct page *page;

        page = vm_normal_page(src_vma, addr, pte);
        if (page) {
                int retval;

                retval = copy_present_page(dst_vma, src_vma, dst_pte, src_pte,
                                           addr, rss, prealloc, pte, page);
                if (retval <= 0)
                        return retval;

                get_page(page);
                page_dup_rmap(page, false);
                rss[mm_counter(page)]++;
        }

        /*
         * If it's a COW mapping, write protect it both
         * in the parent and the child
         */
        if (is_cow_mapping(vm_flags) && pte_write(pte)) {
                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);

        if (!userfaultfd_wp(dst_vma))
                pte = pte_clear_uffd_wp(pte);

        set_pte_at(dst_vma->vm_mm, addr, dst_pte, pte);
        return 0;
}

static inline struct page *
page_copy_prealloc(struct mm_struct *src_mm, struct vm_area_struct *vma,
                   unsigned long addr)
{
        struct page *new_page;

        new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, addr);
        if (!new_page)
                return NULL;

        if (mem_cgroup_charge(page_folio(new_page), src_mm, GFP_KERNEL)) {
                put_page(new_page);
                return NULL;
        }
        cgroup_throttle_swaprate(new_page, GFP_KERNEL);

        return new_page;
}

static int
copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
               pmd_t *dst_pmd, pmd_t *src_pmd, unsigned long addr,
               unsigned long end)
{
        struct mm_struct *dst_mm = dst_vma->vm_mm;
        struct mm_struct *src_mm = src_vma->vm_mm;
        pte_t *orig_src_pte, *orig_dst_pte;
        pte_t *src_pte, *dst_pte;
        spinlock_t *src_ptl, *dst_ptl;
        int progress, ret = 0;
        int rss[NR_MM_COUNTERS];
        swp_entry_t entry = (swp_entry_t){0};
        struct page *prealloc = NULL;

again:
        progress = 0;
        init_rss_vec(rss);

        dst_pte = pte_alloc_map_lock(dst_mm, dst_pmd, addr, &dst_ptl);
        if (!dst_pte) {
                ret = -ENOMEM;
                goto out;
        }
        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;
                }
                if (unlikely(!pte_present(*src_pte))) {
                        ret = copy_nonpresent_pte(dst_mm, src_mm,
                                                  dst_pte, src_pte,
                                                  dst_vma, src_vma,
                                                  addr, rss);
                        if (ret == -EIO) {
                                entry = pte_to_swp_entry(*src_pte);
                                break;
                        } else if (ret == -EBUSY) {
                                break;
                        } else if (!ret) {
                                progress += 8;
                                continue;
                        }

                        /*
                         * Device exclusive entry restored, continue by copying
                         * the now present pte.
                         */
                        WARN_ON_ONCE(ret != -ENOENT);
                }
                /* copy_present_pte() will clear `*prealloc' if consumed */
                ret = copy_present_pte(dst_vma, src_vma, dst_pte, src_pte,
                                       addr, rss, &prealloc);
                /*
                 * If we need a pre-allocated page for this pte, drop the
                 * locks, allocate, and try again.
                 */
                if (unlikely(ret == -EAGAIN))
                        break;
                if (unlikely(prealloc)) {
                        /*
                         * pre-alloc page cannot be reused by next time so as
                         * to strictly follow mempolicy (e.g., alloc_page_vma()
                         * will allocate page according to address).  This
                         * could only happen if one pinned pte changed.
                         */
                        put_page(prealloc);
                        prealloc = NULL;
                }
                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 (ret == -EIO) {
                VM_WARN_ON_ONCE(!entry.val);
                if (add_swap_count_continuation(entry, GFP_KERNEL) < 0) {
                        ret = -ENOMEM;
                        goto out;
                }
                entry.val = 0;
        } else if (ret == -EBUSY) {
                goto out;
        } else if (ret ==  -EAGAIN) {
                prealloc = page_copy_prealloc(src_mm, src_vma, addr);
                if (!prealloc)
                        return -ENOMEM;
        } else if (ret) {
                VM_WARN_ON_ONCE(1);
        }

        /* We've captured and resolved the error. Reset, try again. */
        ret = 0;

        if (addr != end)
                goto again;
out:
        if (unlikely(prealloc))
                put_page(prealloc);
        return ret;
}

static inline int
copy_pmd_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
               pud_t *dst_pud, pud_t *src_pud, unsigned long addr,
               unsigned long end)
{
        struct mm_struct *dst_mm = dst_vma->vm_mm;
        struct mm_struct *src_mm = src_vma->vm_mm;
        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 (is_swap_pmd(*src_pmd) || pmd_trans_huge(*src_pmd)
                        || pmd_devmap(*src_pmd)) {
                        int err;
                        VM_BUG_ON_VMA(next-addr != HPAGE_PMD_SIZE, src_vma);
                        err = copy_huge_pmd(dst_mm, src_mm, dst_pmd, src_pmd,
                                            addr, dst_vma, src_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_vma, src_vma, dst_pmd, src_pmd,
                                   addr, next))
                        return -ENOMEM;
        } while (dst_pmd++, src_pmd++, addr = next, addr != end);
        return 0;
}

static inline int
copy_pud_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
               p4d_t *dst_p4d, p4d_t *src_p4d, unsigned long addr,
               unsigned long end)
{
        struct mm_struct *dst_mm = dst_vma->vm_mm;
        struct mm_struct *src_mm = src_vma->vm_mm;
        pud_t *src_pud, *dst_pud;
        unsigned long next;

        dst_pud = pud_alloc(dst_mm, dst_p4d, addr);
        if (!dst_pud)
                return -ENOMEM;
        src_pud = pud_offset(src_p4d, addr);
        do {
                next = pud_addr_end(addr, end);
                if (pud_trans_huge(*src_pud) || pud_devmap(*src_pud)) {
                        int err;

                        VM_BUG_ON_VMA(next-addr != HPAGE_PUD_SIZE, src_vma);
                        err = copy_huge_pud(dst_mm, src_mm,
                                            dst_pud, src_pud, addr, src_vma);
                        if (err == -ENOMEM)
                                return -ENOMEM;
                        if (!err)
                                continue;
                        /* fall through */
                }
                if (pud_none_or_clear_bad(src_pud))
                        continue;
                if (copy_pmd_range(dst_vma, src_vma, dst_pud, src_pud,
                                   addr, next))
                        return -ENOMEM;
        } while (dst_pud++, src_pud++, addr = next, addr != end);
        return 0;
}

static inline int
copy_p4d_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
               pgd_t *dst_pgd, pgd_t *src_pgd, unsigned long addr,
               unsigned long end)
{
        struct mm_struct *dst_mm = dst_vma->vm_mm;
        p4d_t *src_p4d, *dst_p4d;
        unsigned long next;

        dst_p4d = p4d_alloc(dst_mm, dst_pgd, addr);
        if (!dst_p4d)
                return -ENOMEM;
        src_p4d = p4d_offset(src_pgd, addr);
        do {
                next = p4d_addr_end(addr, end);
                if (p4d_none_or_clear_bad(src_p4d))
                        continue;
                if (copy_pud_range(dst_vma, src_vma, dst_p4d, src_p4d,
                                   addr, next))
                        return -ENOMEM;
        } while (dst_p4d++, src_p4d++, addr = next, addr != end);
        return 0;
}

int
copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
{
        pgd_t *src_pgd, *dst_pgd;
        unsigned long next;
        unsigned long addr = src_vma->vm_start;
        unsigned long end = src_vma->vm_end;
        struct mm_struct *dst_mm = dst_vma->vm_mm;
        struct mm_struct *src_mm = src_vma->vm_mm;
        struct mmu_notifier_range range;
        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 (!(src_vma->vm_flags & (VM_HUGETLB | VM_PFNMAP | VM_MIXEDMAP)) &&
            !src_vma->anon_vma)
                return 0;

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

        if (unlikely(src_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(src_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(src_vma->vm_flags);

        if (is_cow) {
                mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_PAGE,
                                        0, src_vma, src_mm, addr, end);
                mmu_notifier_invalidate_range_start(&range);
                /*
                 * Disabling preemption is not needed for the write side, as
                 * the read side doesn't spin, but goes to the mmap_lock.
                 *
                 * Use the raw variant of the seqcount_t write API to avoid
                 * lockdep complaining about preemptibility.
                 */
                mmap_assert_write_locked(src_mm);
                raw_write_seqcount_begin(&src_mm->write_protect_seq);
        }

        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_p4d_range(dst_vma, src_vma, dst_pgd, src_pgd,
                                            addr, next))) {
                        ret = -ENOMEM;
                        break;
                }
        } while (dst_pgd++, src_pgd++, addr = next, addr != end);

        if (is_cow) {
                raw_write_seqcount_end(&src_mm->write_protect_seq);
                mmu_notifier_invalidate_range_end(&range);
        }
        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;
        swp_entry_t entry;

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

                if (need_resched())
                        break;

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

                        page = vm_normal_page(vma, addr, ptent);
                        if (unlikely(zap_skip_check_mapping(details, page)))
                                continue;
                        ptent = ptep_get_and_clear_full(mm, addr, pte,
                                                        tlb->fullmm);
                        tlb_remove_tlb_entry(tlb, pte, addr);
                        if (unlikely(!page))
                                continue;

                        if (!PageAnon(page)) {
                                if (pte_dirty(ptent)) {
                                        force_flush = 1;
                                        set_page_dirty(page);
                                }
                                if (pte_young(ptent) &&
                                    likely(!(vma->vm_flags & VM_SEQ_READ)))
                                        mark_page_accessed(page);
                        }
                        rss[mm_counter(page)]--;
                        page_remove_rmap(page, false);
                        if (unlikely(page_mapcount(page) < 0))
                                print_bad_pte(vma, addr, ptent, page);
                        if (unlikely(__tlb_remove_page(tlb, page))) {
                                force_flush = 1;
                                addr += PAGE_SIZE;
                                break;
                        }
                        continue;
                }

                entry = pte_to_swp_entry(ptent);
                if (is_device_private_entry(entry) ||
                    is_device_exclusive_entry(entry)) {
                        struct page *page = pfn_swap_entry_to_page(entry);

                        if (unlikely(zap_skip_check_mapping(details, page)))
                                continue;
                        pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
                        rss[mm_counter(page)]--;

                        if (is_device_private_entry(entry))
                                page_remove_rmap(page, false);

                        put_page(page);
                        continue;
                }

                /* If details->check_mapping, we leave swap entries. */
                if (unlikely(details))
                        continue;

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

                        page = pfn_swap_entry_to_page(entry);
                        rss[mm_counter(page)]--;
                }
                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();

        /* Do the actual TLB flush before dropping ptl */
        if (force_flush)
                tlb_flush_mmu_tlbonly(tlb);
        pte_unmap_unlock(start_pte, ptl);

        /*
         * If we forced a TLB flush (either due to running out of
         * batch buffers or because we needed to flush dirty TLB
         * entries before releasing the ptl), free the batched
         * memory too. Restart if we didn't do everything.
         */
        if (force_flush) {
                force_flush = 0;
                tlb_flush_mmu(tlb);
        }

        if (addr != end) {
                cond_resched();
                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 (is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
                        if (next - addr != HPAGE_PMD_SIZE)
                                __split_huge_pmd(vma, pmd, addr, false, NULL);
                        else if (zap_huge_pmd(tlb, vma, pmd, addr))
                                goto next;
                        /* fall through */
                } else if (details && details->single_page &&
                           PageTransCompound(details->single_page) &&
                           next - addr == HPAGE_PMD_SIZE && pmd_none(*pmd)) {
                        spinlock_t *ptl = pmd_lock(tlb->mm, pmd);
                        /*
                         * Take and drop THP pmd lock so that we cannot return
                         * prematurely, while zap_huge_pmd() has cleared *pmd,
                         * but not yet decremented compound_mapcount().
                         */
                        spin_unlock(ptl);
                }

                /*
                 * 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_lock 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, p4d_t *p4d,
                                unsigned long addr, unsigned long end,
                                struct zap_details *details)
{
        pud_t *pud;
        unsigned long next;

        pud = pud_offset(p4d, addr);
        do {
                next = pud_addr_end(addr, end);
                if (pud_trans_huge(*pud) || pud_devmap(*pud)) {
                        if (next - addr != HPAGE_PUD_SIZE) {
                                mmap_assert_locked(tlb->mm);
                                split_huge_pud(vma, pud, addr);
                        } else if (zap_huge_pud(tlb, vma, pud, addr))
                                goto next;
                        /* fall through */
                }
                if (pud_none_or_clear_bad(pud))
                        continue;
                next = zap_pmd_range(tlb, vma, pud, addr, next, details);
next:
                cond_resched();
        } while (pud++, addr = next, addr != end);

        return addr;
}

static inline unsigned long zap_p4d_range(struct mmu_gather *tlb,
                                struct vm_area_struct *vma, pgd_t *pgd,
                                unsigned long addr, unsigned long end,
                                struct zap_details *details)
{
        p4d_t *p4d;
        unsigned long next;

        p4d = p4d_offset(pgd, addr);
        do {
                next = p4d_addr_end(addr, end);
                if (p4d_none_or_clear_bad(p4d))
                        continue;
                next = zap_pud_range(tlb, vma, p4d, addr, next, details);
        } while (p4d++, addr = next, addr != end);

        return addr;
}

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;

        BUG_ON(addr >= end);
        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_p4d_range(tlb, vma, pgd, addr, next, details);
        } while (pgd++, addr = next, addr != end);
        tlb_end_vma(tlb, vma);
}


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 mmap_region. When
                         * hugetlbfs ->mmap method fails,
                         * mmap_region() 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) {
                                i_mmap_lock_write(vma->vm_file->f_mapping);
                                __unmap_hugepage_range_final(tlb, vma, start, end, NULL);
                                i_mmap_unlock_write(vma->vm_file->f_mapping);
                        }
                } else
                        unmap_page_range(tlb, vma, start, end, details);
        }
}

/**
 * unmap_vmas - unmap a range of memory covered by a list of vma's
 * @tlb: address of the caller's struct mmu_gather
 * @vma: the starting vma
 * @start_addr: virtual address at which to start unmapping
 * @end_addr: virtual address at which to end unmapping
 *
 * Unmap all pages in the vma list.
 *
 * Only addresses between `start' and `end' will be unmapped.
 *
 * The VMA list must be sorted in ascending virtual address order.
 *
 * unmap_vmas() assumes that the caller will flush the whole unmapped address
 * range after unmap_vmas() returns.  So the only responsibility here is to
 * ensure that any thus-far unmapped pages are flushed before unmap_vmas()
 * drops the lock and schedules.
 */
void unmap_vmas(struct mmu_gather *tlb,
                struct vm_area_struct *vma, unsigned long start_addr,
                unsigned long end_addr)
{
        struct mmu_notifier_range range;

        mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma, vma->vm_mm,
                                start_addr, end_addr);
        mmu_notifier_invalidate_range_start(&range);
        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(&range);
}

/**
 * zap_page_range - remove user pages in a given range
 * @vma: vm_area_struct holding the applicable pages
 * @start: starting address of pages to zap
 * @size: number of bytes to zap
 *
 * Caller must protect the VMA list
 */
void zap_page_range(struct vm_area_struct *vma, unsigned long start,
                unsigned long size)
{
        struct mmu_notifier_range range;
        struct mmu_gather tlb;

        lru_add_drain();
        mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
                                start, start + size);
        tlb_gather_mmu(&tlb, vma->vm_mm);
        update_hiwater_rss(vma->vm_mm);
        mmu_notifier_invalidate_range_start(&range);
        for ( ; vma && vma->vm_start < range.end; vma = vma->vm_next)
                unmap_single_vma(&tlb, vma, start, range.end, NULL);
        mmu_notifier_invalidate_range_end(&range);
        tlb_finish_mmu(&tlb);
}

/**
 * zap_page_range_single - remove user pages in a given range
 * @vma: vm_area_struct holding the applicable pages
 * @address: starting address of pages to zap
 * @size: number of bytes to zap
 * @details: details of shared cache invalidation
 *
 * The range must fit into one VMA.
 */
static void zap_page_range_single(struct vm_area_struct *vma, unsigned long address,
                unsigned long size, struct zap_details *details)
{
        struct mmu_notifier_range range;
        struct mmu_gather tlb;

        lru_add_drain();
        mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
                                address, address + size);
        tlb_gather_mmu(&tlb, vma->vm_mm);
        update_hiwater_rss(vma->vm_mm);
        mmu_notifier_invalidate_range_start(&range);
        unmap_single_vma(&tlb, vma, address, range.end, details);
        mmu_notifier_invalidate_range_end(&range);
        tlb_finish_mmu(&tlb);
}

/**
 * zap_vma_ptes - remove ptes mapping the vma
 * @vma: vm_area_struct holding ptes to be zapped
 * @address: starting address of pages to zap
 * @size: number of bytes to zap
 *
 * This function only unmaps ptes assigned to VM_PFNMAP vmas.
 *
 * The entire address range must be fully contained within the vma.
 *
 */
void 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;

        zap_page_range_single(vma, address, size, NULL);
}
EXPORT_SYMBOL_GPL(zap_vma_ptes);

static pmd_t *walk_to_pmd(struct mm_struct *mm, unsigned long addr)
{
        pgd_t *pgd;
        p4d_t *p4d;
        pud_t *pud;
        pmd_t *pmd;

        pgd = pgd_offset(mm, addr);
        p4d = p4d_alloc(mm, pgd, addr);
        if (!p4d)
                return NULL;
        pud = pud_alloc(mm, p4d, addr);
        if (!pud)
                return NULL;
        pmd = pmd_alloc(mm, pud, addr);
        if (!pmd)
                return NULL;

        VM_BUG_ON(pmd_trans_huge(*pmd));
        return pmd;
}

pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
                        spinlock_t **ptl)
{
        pmd_t *pmd = walk_to_pmd(mm, addr);

        if (!pmd)
                return NULL;
        return pte_alloc_map_lock(mm, pmd, addr, ptl);
}

static int validate_page_before_insert(struct page *page)
{
        if (PageAnon(page) || PageSlab(page) || page_has_type(page))
                return -EINVAL;
        flush_dcache_page(page);
        return 0;
}

static int insert_page_into_pte_locked(struct mm_struct *mm, pte_t *pte,
                        unsigned long addr, struct page *page, pgprot_t prot)
{
        if (!pte_none(*pte))
                return -EBUSY;
        /* Ok, finally just insert the thing.. */
        get_page(page);
        inc_mm_counter_fast(mm, mm_counter_file(page));
        page_add_file_rmap(page, false);
        set_pte_at(mm, addr, pte, mk_pte(page, prot));
        return 0;
}

/*
 * 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 = validate_page_before_insert(page);
        if (retval)
                goto out;
        retval = -ENOMEM;
        pte = get_locked_pte(mm, addr, &ptl);
        if (!pte)
                goto out;
        retval = insert_page_into_pte_locked(mm, pte, addr, page, prot);
        pte_unmap_unlock(pte, ptl);
out:
        return retval;
}

#ifdef pte_index
static int insert_page_in_batch_locked(struct mm_struct *mm, pte_t *pte,
                        unsigned long addr, struct page *page, pgprot_t prot)
{
        int err;

        if (!page_count(page))
                return -EINVAL;
        err = validate_page_before_insert(page);
        if (err)
                return err;
        return insert_page_into_pte_locked(mm, pte, addr, page, prot);
}

/* insert_pages() amortizes the cost of spinlock operations
 * when inserting pages in a loop. Arch *must* define pte_index.
 */
static int insert_pages(struct vm_area_struct *vma, unsigned long addr,
                        struct page **pages, unsigned long *num, pgprot_t prot)
{
        pmd_t *pmd = NULL;
        pte_t *start_pte, *pte;
        spinlock_t *pte_lock;
        struct mm_struct *const mm = vma->vm_mm;
        unsigned long curr_page_idx = 0;
        unsigned long remaining_pages_total = *num;
        unsigned long pages_to_write_in_pmd;
        int ret;
more:
        ret = -EFAULT;
        pmd = walk_to_pmd(mm, addr);
        if (!pmd)
                goto out;

        pages_to_write_in_pmd = min_t(unsigned long,
                remaining_pages_total, PTRS_PER_PTE - pte_index(addr));

        /* Allocate the PTE if necessary; takes PMD lock once only. */
        ret = -ENOMEM;
        if (pte_alloc(mm, pmd))
                goto out;

        while (pages_to_write_in_pmd) {
                int pte_idx = 0;
                const int batch_size = min_t(int, pages_to_write_in_pmd, 8);

                start_pte = pte_offset_map_lock(mm, pmd, addr, &pte_lock);
                for (pte = start_pte; pte_idx < batch_size; ++pte, ++pte_idx) {
                        int err = insert_page_in_batch_locked(mm, pte,
                                addr, pages[curr_page_idx], prot);
                        if (unlikely(err)) {
                                pte_unmap_unlock(start_pte, pte_lock);
                                ret = err;
                                remaining_pages_total -= pte_idx;
                                goto out;
                        }
                        addr += PAGE_SIZE;
                        ++curr_page_idx;
                }
                pte_unmap_unlock(start_pte, pte_lock);
                pages_to_write_in_pmd -= batch_size;
                remaining_pages_total -= batch_size;
        }
        if (remaining_pages_total)
                goto more;
        ret = 0;
out:
        *num = remaining_pages_total;
        return ret;
}
#endif  /* ifdef pte_index */

/**
 * vm_insert_pages - insert multiple pages into user vma, batching the pmd lock.
 * @vma: user vma to map to
 * @addr: target start user address of these pages
 * @pages: source kernel pages
 * @num: in: number of pages to map. out: number of pages that were *not*
 * mapped. (0 means all pages were successfully mapped).
 *
 * Preferred over vm_insert_page() when inserting multiple pages.
 *
 * In case of error, we may have mapped a subset of the provided
 * pages. It is the caller's responsibility to account for this case.
 *
 * The same restrictions apply as in vm_insert_page().
 */
int vm_insert_pages(struct vm_area_struct *vma, unsigned long addr,
                        struct page **pages, unsigned long *num)
{
#ifdef pte_index
        const unsigned long end_addr = addr + (*num * PAGE_SIZE) - 1;

        if (addr < vma->vm_start || end_addr >= vma->vm_end)
                return -EFAULT;
        if (!(vma->vm_flags & VM_MIXEDMAP)) {
                BUG_ON(mmap_read_trylock(vma->vm_mm));
                BUG_ON(vma->vm_flags & VM_PFNMAP);
                vma->vm_flags |= VM_MIXEDMAP;
        }
        /* Defer page refcount checking till we're about to map that page. */
        return insert_pages(vma, addr, pages, num, vma->vm_page_prot);
#else
        unsigned long idx = 0, pgcount = *num;
        int err = -EINVAL;

        for (; idx < pgcount; ++idx) {
                err = vm_insert_page(vma, addr + (PAGE_SIZE * idx), pages[idx]);
                if (err)
                        break;
        }
        *num = pgcount - idx;
        return err;
#endif  /* ifdef pte_index */
}
EXPORT_SYMBOL(vm_insert_pages);

/**
 * vm_insert_page - insert single page into user vma
 * @vma: user vma to map to
 * @addr: target user address of this page
 * @page: source kernel page
 *
 * This allows drivers to insert individual pages they've allocated
 * into a user vma.
 *
 * The page has to be a nice clean _individual_ kernel allocation.
 * If you allocate a compound page, you need to have marked it as
 * such (__GFP_COMP), or manually just split the page up yourself
 * (see split_page()).
 *
 * NOTE! Traditionally this was done with "remap_pfn_range()" which
 * took an arbitrary page protection parameter. This doesn't allow
 * that. Your vma protection will have to be set up correctly, which
 * means that if you want a shared writable mapping, you'd better
 * ask for a shared writable mapping!
 *
 * The page does not need to be reserved.
 *
 * Usually this function is called from f_op->mmap() handler
 * under mm->mmap_lock write-lock, so it can change vma->vm_flags.
 * Caller must set VM_MIXEDMAP on vma if it wants to call this
 * function from other places, for example from page-fault handler.
 *
 * Return: %0 on success, negative error code otherwise.
 */
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(mmap_read_trylock(vma->vm_mm));
                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);

/*
 * __vm_map_pages - maps range of kernel pages into user vma
 * @vma: user vma to map to
 * @pages: pointer to array of source kernel pages
 * @num: number of pages in page array
 * @offset: user's requested vm_pgoff
 *
 * This allows drivers to map range of kernel pages into a user vma.
 *
 * Return: 0 on success and error code otherwise.
 */
static int __vm_map_pages(struct vm_area_struct *vma, struct page **pages,
                                unsigned long num, unsigned long offset)
{
        unsigned long count = vma_pages(vma);
        unsigned long uaddr = vma->vm_start;
        int ret, i;

        /* Fail if the user requested offset is beyond the end of the object */
        if (offset >= num)
                return -ENXIO;

        /* Fail if the user requested size exceeds available object size */
        if (count > num - offset)
                return -ENXIO;

        for (i = 0; i < count; i++) {
                ret = vm_insert_page(vma, uaddr, pages[offset + i]);
                if (ret < 0)
                        return ret;
                uaddr += PAGE_SIZE;
        }

        return 0;
}

/**
 * vm_map_pages - maps range of kernel pages starts with non zero offset
 * @vma: user vma to map to
 * @pages: pointer to array of source kernel pages
 * @num: number of pages in page array
 *
 * Maps an object consisting of @num pages, catering for the user's
 * requested vm_pgoff
 *
 * If we fail to insert any page into the vma, the function will return
 * immediately leaving any previously inserted pages present.  Callers
 * from the mmap handler may immediately return the error as their caller
 * will destroy the vma, removing any successfully inserted pages. Other
 * callers should make their own arrangements for calling unmap_region().
 *
 * Context: Process context. Called by mmap handlers.
 * Return: 0 on success and error code otherwise.
 */
int vm_map_pages(struct vm_area_struct *vma, struct page **pages,
                                unsigned long num)
{
        return __vm_map_pages(vma, pages, num, vma->vm_pgoff);
}
EXPORT_SYMBOL(vm_map_pages);

/**
 * vm_map_pages_zero - map range of kernel pages starts with zero offset
 * @vma: user vma to map to
 * @pages: pointer to array of source kernel pages

 * @num: number of pages in page array
 *
 * Similar to vm_map_pages(), except that it explicitly sets the offset
 * to 0. This function is intended for the drivers that did not consider
 * vm_pgoff.
 *
 * Context: Process context. Called by mmap handlers.
 * Return: 0 on success and error code otherwise.
 */
int vm_map_pages_zero(struct vm_area_struct *vma, struct page **pages,
                                unsigned long num)
{
        return __vm_map_pages(vma, pages, num, 0);
}
EXPORT_SYMBOL(vm_map_pages_zero);

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

        pte = get_locked_pte(mm, addr, &ptl);
        if (!pte)
                return VM_FAULT_OOM;
        if (!pte_none(*pte)) {
                if (mkwrite) {
                        /*
                         * For read faults on private mappings the PFN passed
                         * in may not match the PFN we have mapped if the
                         * mapped PFN is a writeable COW page.  In the mkwrite
                         * case we are creating a writable PTE for a shared
                         * mapping and we expect the PFNs to match. If they
                         * don't match, we are likely racing with block
                         * allocation and mapping invalidation so just skip the
                         * update.
                         */
                        if (pte_pfn(*pte) != pfn_t_to_pfn(pfn)) {
                                WARN_ON_ONCE(!is_zero_pfn(pte_pfn(*pte)));
                                goto out_unlock;
                        }
                        entry = pte_mkyoung(*pte);
                        entry = maybe_mkwrite(pte_mkdirty(entry), vma);
                        if (ptep_set_access_flags(vma, addr, pte, entry, 1))
                                update_mmu_cache(vma, addr, pte);
                }
                goto out_unlock;
        }

        /* Ok, finally just insert the thing.. */
        if (pfn_t_devmap(pfn))
                entry = pte_mkdevmap(pfn_t_pte(pfn, prot));
        else
                entry = pte_mkspecial(pfn_t_pte(pfn, prot));

        if (mkwrite) {
                entry = pte_mkyoung(entry);
                entry = maybe_mkwrite(pte_mkdirty(entry), vma);
        }

        set_pte_at(mm, addr, pte, entry);
        update_mmu_cache(vma, addr, pte); /* XXX: why not for insert_page? */

out_unlock:
        pte_unmap_unlock(pte, ptl);
        return VM_FAULT_NOPAGE;
}

/**
 * vmf_insert_pfn_prot - insert single pfn into user vma with specified pgprot
 * @vma: user vma to map to
 * @addr: target user address of this page
 * @pfn: source kernel pfn
 * @pgprot: pgprot flags for the inserted page
 *
 * This is exactly like vmf_insert_pfn(), except that it allows drivers
 * to override pgprot on a per-page basis.
 *
 * This only makes sense for IO mappings, and it makes no sense for
 * COW mappings.  In general, using multiple vmas is preferable;
 * vmf_insert_pfn_prot should only be used if using multiple VMAs is
 * impractical.
 *
 * See vmf_insert_mixed_prot() for a discussion of the implication of using
 * a value of @pgprot different from that of @vma->vm_page_prot.
 *
 * Context: Process context.  May allocate using %GFP_KERNEL.
 * Return: vm_fault_t value.
 */
vm_fault_t vmf_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr,
                        unsigned long pfn, pgprot_t pgprot)
{
        /*
         * 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 VM_FAULT_SIGBUS;

        if (!pfn_modify_allowed(pfn, pgprot))
                return VM_FAULT_SIGBUS;

        track_pfn_insert(vma, &pgprot, __pfn_to_pfn_t(pfn, PFN_DEV));

        return insert_pfn(vma, addr, __pfn_to_pfn_t(pfn, PFN_DEV), pgprot,
                        false);
}
EXPORT_SYMBOL(vmf_insert_pfn_prot);

/**
 * vmf_insert_pfn - insert single pfn into user vma
 * @vma: user vma to map to
 * @addr: target user address of this page
 * @pfn: source kernel pfn
 *
 * Similar to vm_insert_page, this allows drivers to insert individual pages
 * they've allocated into a user vma. Same comments apply.
 *
 * This function should only be called from a vm_ops->fault handler, and
 * in that case the handler should return the result of this function.
 *
 * vma cannot be a COW mapping.
 *
 * As this is called only for pages that do not currently exist, we
 * do not need to flush old virtual caches or the TLB.
 *
 * Context: Process context.  May allocate using %GFP_KERNEL.
 * Return: vm_fault_t value.
 */
vm_fault_t vmf_insert_pfn(struct vm_area_struct *vma, unsigned long addr,
                        unsigned long pfn)
{
        return vmf_insert_pfn_prot(vma, addr, pfn, vma->vm_page_prot);
}
EXPORT_SYMBOL(vmf_insert_pfn);

static bool vm_mixed_ok(struct vm_area_struct *vma, pfn_t pfn)
{
        /* these checks mirror the abort conditions in vm_normal_page */
        if (vma->vm_flags & VM_MIXEDMAP)
                return true;
        if (pfn_t_devmap(pfn))
                return true;
        if (pfn_t_special(pfn))
                return true;
        if (is_zero_pfn(pfn_t_to_pfn(pfn)))
                return true;
        return false;
}

static vm_fault_t __vm_insert_mixed(struct vm_area_struct *vma,
                unsigned long addr, pfn_t pfn, pgprot_t pgprot,
                bool mkwrite)
{
        int err;

        BUG_ON(!vm_mixed_ok(vma, pfn));

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

        track_pfn_insert(vma, &pgprot, pfn);

        if (!pfn_modify_allowed(pfn_t_to_pfn(pfn), pgprot))
                return VM_FAULT_SIGBUS;

        /*
         * 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 (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL) &&
            !pfn_t_devmap(pfn) && pfn_t_valid(pfn)) {
                struct page *page;

                /*
                 * At this point we are committed to insert_page()
                 * regardless of whether the caller specified flags that
                 * result in pfn_t_has_page() == false.
                 */
                page = pfn_to_page(pfn_t_to_pfn(pfn));
                err = insert_page(vma, addr, page, pgprot);
        } else {
                return insert_pfn(vma, addr, pfn, pgprot, mkwrite);
        }

        if (err == -ENOMEM)
                return VM_FAULT_OOM;
        if (err < 0 && err != -EBUSY)
                return VM_FAULT_SIGBUS;

        return VM_FAULT_NOPAGE;
}

/**
 * vmf_insert_mixed_prot - insert single pfn into user vma with specified pgprot
 * @vma: user vma to map to
 * @addr: target user address of this page
 * @pfn: source kernel pfn
 * @pgprot: pgprot flags for the inserted page
 *
 * This is exactly like vmf_insert_mixed(), except that it allows drivers
 * to override pgprot on a per-page basis.
 *
 * Typically this function should be used by drivers to set caching- and
 * encryption bits different than those of @vma->vm_page_prot, because
 * the caching- or encryption mode may not be known at mmap() time.
 * This is ok as long as @vma->vm_page_prot is not used by the core vm
 * to set caching and encryption bits for those vmas (except for COW pages).
 * This is ensured by core vm only modifying these page table entries using
 * functions that don't touch caching- or encryption bits, using pte_modify()
 * if needed. (See for example mprotect()).
 * Also when new page-table entries are created, this is only done using the
 * fault() callback, and never using the value of vma->vm_page_prot,
 * except for page-table entries that point to anonymous pages as the result
 * of COW.
 *
 * Context: Process context.  May allocate using %GFP_KERNEL.
 * Return: vm_fault_t value.
 */
vm_fault_t vmf_insert_mixed_prot(struct vm_area_struct *vma, unsigned long addr,
                                 pfn_t pfn, pgprot_t pgprot)
{
        return __vm_insert_mixed(vma, addr, pfn, pgprot, false);
}
EXPORT_SYMBOL(vmf_insert_mixed_prot);

vm_fault_t vmf_insert_mixed(struct vm_area_struct *vma, unsigned long addr,
                pfn_t pfn)
{
        return __vm_insert_mixed(vma, addr, pfn, vma->vm_page_prot, false);
}
EXPORT_SYMBOL(vmf_insert_mixed);

/*
 *  If the insertion of PTE failed because someone else already added a
 *  different entry in the mean time, we treat that as success as we assume
 *  the same entry was actually inserted.
 */
vm_fault_t vmf_insert_mixed_mkwrite(struct vm_area_struct *vma,
                unsigned long addr, pfn_t pfn)
{
        return __vm_insert_mixed(vma, addr, pfn, vma->vm_page_prot, true);
}
EXPORT_SYMBOL(vmf_insert_mixed_mkwrite);

/*
 * 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, *mapped_pte;
        spinlock_t *ptl;
        int err = 0;

        mapped_pte = pte = pte_alloc_map_lock(mm, pmd, addr, &ptl);
        if (!pte)
                return -ENOMEM;
        arch_enter_lazy_mmu_mode();
        do {
                BUG_ON(!pte_none(*pte));
                if (!pfn_modify_allowed(pfn, prot)) {
                        err = -EACCES;
                        break;
                }
                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(mapped_pte, ptl);
        return err;
}

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;
        int err;

        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);
                err = remap_pte_range(mm, pmd, addr, next,
                                pfn + (addr >> PAGE_SHIFT), prot);
                if (err)
                        return err;
        } while (pmd++, addr = next, addr != end);
        return 0;
}

static inline int remap_pud_range(struct mm_struct *mm, p4d_t *p4d,
                        unsigned long addr, unsigned long end,
                        unsigned long pfn, pgprot_t prot)
{
        pud_t *pud;
        unsigned long next;
        int err;

        pfn -= addr >> PAGE_SHIFT;
        pud = pud_alloc(mm, p4d, addr);
        if (!pud)
                return -ENOMEM;
        do {
                next = pud_addr_end(addr, end);
                err = remap_pmd_range(mm, pud, addr, next,
                                pfn + (addr >> PAGE_SHIFT), prot);
                if (err)
                        return err;
        } while (pud++, addr = next, addr != end);
        return 0;
}

static inline int remap_p4d_range(struct mm_struct *mm, pgd_t *pgd,
                        unsigned long addr, unsigned long end,
                        unsigned long pfn, pgprot_t prot)
{
        p4d_t *p4d;
        unsigned long next;
        int err;

        pfn -= addr >> PAGE_SHIFT;
        p4d = p4d_alloc(mm, pgd, addr);
        if (!p4d)
                return -ENOMEM;
        do {
                next = p4d_addr_end(addr, end);
                err = remap_pud_range(mm, p4d, addr, next,
                                pfn + (addr >> PAGE_SHIFT), prot);
                if (err)
                        return err;
        } while (p4d++, addr = next, addr != end);
        return 0;
}

/*
 * Variant of remap_pfn_range that does not call track_pfn_remap.  The caller
 * must have pre-validated the caching bits of the pgprot_t.
 */
int remap_pfn_range_notrack(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;

        if (WARN_ON_ONCE(!PAGE_ALIGNED(addr)))
                return -EINVAL;

        /*
         * 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;
        }

        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_p4d_range(mm, pgd, addr, next,
                                pfn + (addr >> PAGE_SHIFT), prot);
                if (err)
                        return err;
        } while (pgd++, addr = next, addr != end);

        return 0;
}

/**
 * remap_pfn_range - remap kernel memory to userspace
 * @vma: user vma to map to
 * @addr: target page aligned user address to start at
 * @pfn: page frame number of kernel physical memory address
 * @size: size of mapping area
 * @prot: page protection flags for this mapping
 *
 * Note: this is only safe if the mm semaphore is held when called.
 *
 * Return: %0 on success, negative error code otherwise.
 */
int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
                    unsigned long pfn, unsigned long size, pgprot_t prot)
{
        int err;

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

        err = remap_pfn_range_notrack(vma, addr, pfn, size, prot);
        if (err)
                untrack_pfn(vma, pfn, PAGE_ALIGN(size));
        return err;
}
EXPORT_SYMBOL(remap_pfn_range);

/**
 * vm_iomap_memory - remap memory to userspace
 * @vma: user vma to map to
 * @start: start of the physical memory to be mapped
 * @len: size of area
 *
 * This is a simplified io_remap_pfn_range() for common driver use. The
 * driver just needs to give us the physical memory range to be mapped,
 * we'll figure out the rest from the vma information.
 *
 * NOTE! Some drivers might want to tweak vma->vm_page_prot first to get
 * whatever write-combining details or similar.
 *
 * Return: %0 on success, negative error code otherwise.
 */
int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len)
{
        unsigned long vm_len, pfn, pages;

        /* Check that the physical memory area passed in looks valid */
        if (start + len < start)
                return -EINVAL;
        /*
         * You *really* shouldn't map things that aren't page-aligned,
         * but we've historically allowed it because IO memory might
         * just have smaller alignment.
         */
        len += start & ~PAGE_MASK;
        pfn = start >> PAGE_SHIFT;
        pages = (len + ~PAGE_MASK) >> PAGE_SHIFT;
        if (pfn + pages < pfn)
                return -EINVAL;

        /* We start the mapping 'vm_pgoff' pages into the area */
        if (vma->vm_pgoff > pages)
                return -EINVAL;
        pfn += vma->vm_pgoff;
        pages -= vma->vm_pgoff;

        /* Can we fit all of the mapping? */
        vm_len = vma->vm_end - vma->vm_start;
        if (vm_len >> PAGE_SHIFT > pages)
                return -EINVAL;

        /* Ok, let it rip */
        return io_remap_pfn_range(vma, vma->vm_start, pfn, vm_len, vma->vm_page_prot);
}
EXPORT_SYMBOL(vm_iomap_memory);

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, bool create,
                                     pgtbl_mod_mask *mask)
{
        pte_t *pte, *mapped_pte;
        int err = 0;
        spinlock_t *ptl;

        if (create) {
                mapped_pte = pte = (mm == &init_mm) ?
                        pte_alloc_kernel_track(pmd, addr, mask) :
                        pte_alloc_map_lock(mm, pmd, addr, &ptl);
                if (!pte)
                        return -ENOMEM;
        } else {
                mapped_pte = pte = (mm == &init_mm) ?
                        pte_offset_kernel(pmd, addr) :
                        pte_offset_map_lock(mm, pmd, addr, &ptl);
        }

        BUG_ON(pmd_huge(*pmd));

        arch_enter_lazy_mmu_mode();

        if (fn) {
                do {
                        if (create || !pte_none(*pte)) {
                                err = fn(pte++, addr, data);
                                if (err)
                                        break;
                        }
                } while (addr += PAGE_SIZE, addr != end);
        }
        *mask |= PGTBL_PTE_MODIFIED;

        arch_leave_lazy_mmu_mode();

        if (mm != &init_mm)
                pte_unmap_unlock(mapped_pte, 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, bool create,
                                     pgtbl_mod_mask *mask)
{
        pmd_t *pmd;
        unsigned long next;
        int err = 0;

        BUG_ON(pud_huge(*pud));

        if (create) {
                pmd = pmd_alloc_track(mm, pud, addr, mask);
                if (!pmd)
                        return -ENOMEM;
        } else {
                pmd = pmd_offset(pud, addr);
        }
        do {
                next = pmd_addr_end(addr, end);
                if (pmd_none(*pmd) && !create)
                        continue;
                if (WARN_ON_ONCE(pmd_leaf(*pmd)))
                        return -EINVAL;
                if (!pmd_none(*pmd) && WARN_ON_ONCE(pmd_bad(*pmd))) {
                        if (!create)
                                continue;
                        pmd_clear_bad(pmd);
                }
                err = apply_to_pte_range(mm, pmd, addr, next,
                                         fn, data, create, mask);
                if (err)
                        break;
        } while (pmd++, addr = next, addr != end);

        return err;
}

static int apply_to_pud_range(struct mm_struct *mm, p4d_t *p4d,
                                     unsigned long addr, unsigned long end,
                                     pte_fn_t fn, void *data, bool create,
                                     pgtbl_mod_mask *mask)
{
        pud_t *pud;
        unsigned long next;
        int err = 0;

        if (create) {
                pud = pud_alloc_track(mm, p4d, addr, mask);
                if (!pud)
                        return -ENOMEM;
        } else {
                pud = pud_offset(p4d, addr);
        }
        do {
                next = pud_addr_end(addr, end);
                if (pud_none(*pud) && !create)
                        continue;
                if (WARN_ON_ONCE(pud_leaf(*pud)))
                        return -EINVAL;
                if (!pud_none(*pud) && WARN_ON_ONCE(pud_bad(*pud))) {
                        if (!create)
                                continue;
                        pud_clear_bad(pud);
                }
                err = apply_to_pmd_range(mm, pud, addr, next,
                                         fn, data, create, mask);
                if (err)
                        break;
        } while (pud++, addr = next, addr != end);

        return err;
}

static int apply_to_p4d_range(struct mm_struct *mm, pgd_t *pgd,
                                     unsigned long addr, unsigned long end,
                                     pte_fn_t fn, void *data, bool create,
                                     pgtbl_mod_mask *mask)
{
        p4d_t *p4d;
        unsigned long next;
        int err = 0;

        if (create) {
                p4d = p4d_alloc_track(mm, pgd, addr, mask);
                if (!p4d)
                        return -ENOMEM;
        } else {
                p4d = p4d_offset(pgd, addr);
        }
        do {
                next = p4d_addr_end(addr, end);
                if (p4d_none(*p4d) && !create)
                        continue;
                if (WARN_ON_ONCE(p4d_leaf(*p4d)))
                        return -EINVAL;
                if (!p4d_none(*p4d) && WARN_ON_ONCE(p4d_bad(*p4d))) {
                        if (!create)
                                continue;
                        p4d_clear_bad(p4d);
                }
                err = apply_to_pud_range(mm, p4d, addr, next,
                                         fn, data, create, mask);
                if (err)
                        break;
        } while (p4d++, addr = next, addr != end);

        return err;
}

static int __apply_to_page_range(struct mm_struct *mm, unsigned long addr,
                                 unsigned long size, pte_fn_t fn,
                                 void *data, bool create)
{
        pgd_t *pgd;
        unsigned long start = addr, next;
        unsigned long end = addr + size;
        pgtbl_mod_mask mask = 0;
        int err = 0;

        if (WARN_ON(addr >= end))
                return -EINVAL;

        pgd = pgd_offset(mm, addr);
        do {
                next = pgd_addr_end(addr, end);
                if (pgd_none(*pgd) && !create)
                        continue;
                if (WARN_ON_ONCE(pgd_leaf(*pgd)))
                        return -EINVAL;
                if (!pgd_none(*pgd) && WARN_ON_ONCE(pgd_bad(*pgd))) {
                        if (!create)
                                continue;
                        pgd_clear_bad(pgd);
                }
                err = apply_to_p4d_range(mm, pgd, addr, next,
                                         fn, data, create, &mask);
                if (err)
                        break;
        } while (pgd++, addr = next, addr != end);

        if (mask & ARCH_PAGE_TABLE_SYNC_MASK)
                arch_sync_kernel_mappings(start, start + size);

        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)
{
        return __apply_to_page_range(mm, addr, size, fn, data, true);
}
EXPORT_SYMBOL_GPL(apply_to_page_range);

/*
 * Scan a region of virtual memory, calling a provided function on
 * each leaf page table where it exists.
 *
 * Unlike apply_to_page_range, this does _not_ fill in page tables
 * where they are absent.
 */
int apply_to_existing_page_range(struct mm_struct *mm, unsigned long addr,
                                 unsigned long size, pte_fn_t fn, void *data)
{
        return __apply_to_page_range(mm, addr, size, fn, data, false);
}
EXPORT_SYMBOL_GPL(apply_to_existing_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 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 vm_fault *vmf)
{
        int same = 1;
#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPTION)
        if (sizeof(pte_t) > sizeof(unsigned long)) {
                spinlock_t *ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
                spin_lock(ptl);
                same = pte_same(*vmf->pte, vmf->orig_pte);
                spin_unlock(ptl);
        }
#endif
        pte_unmap(vmf->pte);
        vmf->pte = NULL;
        return same;
}

static inline bool cow_user_page(struct page *dst, struct page *src,
                                 struct vm_fault *vmf)
{
        bool ret;
        void *kaddr;
        void __user *uaddr;
        bool locked = false;
        struct vm_area_struct *vma = vmf->vma;
        struct mm_struct *mm = vma->vm_mm;
        unsigned long addr = vmf->address;

        if (likely(src)) {
                copy_user_highpage(dst, src, addr, vma);
                return true;
        }

        /*
         * 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.
         */
        kaddr = kmap_atomic(dst);
        uaddr = (void __user *)(addr & PAGE_MASK);

        /*
         * On architectures with software "accessed" bits, we would
         * take a double page fault, so mark it accessed here.
         */
        if (arch_faults_on_old_pte() && !pte_young(vmf->orig_pte)) {
                pte_t entry;

                vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);
                locked = true;
                if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) {
                        /*
                         * Other thread has already handled the fault
                         * and update local tlb only
                         */
                        update_mmu_tlb(vma, addr, vmf->pte);
                        ret = false;
                        goto pte_unlock;
                }

                entry = pte_mkyoung(vmf->orig_pte);
                if (ptep_set_access_flags(vma, addr, vmf->pte, entry, 0))
                        update_mmu_cache(vma, addr, vmf->pte);
        }

        /*
         * 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)) {
                if (locked)
                        goto warn;

                /* Re-validate under PTL if the page is still mapped */
                vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);
                locked = true;
                if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) {
                        /* The PTE changed under us, update local tlb */
                        update_mmu_tlb(vma, addr, vmf->pte);
                        ret = false;
                        goto pte_unlock;
                }

                /*
                 * The same page can be mapped back since last copy attempt.
                 * Try to copy again under PTL.
                 */
                if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
                        /*
                         * Give a warn in case there can be some obscure
                         * use-case
                         */
warn:
                        WARN_ON_ONCE(1);
                        clear_page(kaddr);
                }
        }

        ret = true;

pte_unlock:
        if (locked)
                pte_unmap_unlock(vmf->pte, vmf->ptl);
        kunmap_atomic(kaddr);
        flush_dcache_page(dst);

        return ret;
}

static gfp_t __get_fault_gfp_mask(struct vm_area_struct *vma)
{
        struct file *vm_file = vma->vm_file;

        if (vm_file)
                return mapping_gfp_mask(vm_file->f_mapping) | __GFP_FS | __GFP_IO;

        /*
         * Special mappings (e.g. VDSO) do not have any file so fake
         * a default GFP_KERNEL for them.
         */
        return GFP_KERNEL;
}

/*
 * 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.
 */
static vm_fault_t do_page_mkwrite(struct vm_fault *vmf)
{
        vm_fault_t ret;
        struct page *page = vmf->page;
        unsigned int old_flags = vmf->flags;

        vmf->flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;

        if (vmf->vma->vm_file &&
            IS_SWAPFILE(vmf->vma->vm_file->f_mapping->host))
                return VM_FAULT_SIGBUS;

        ret = vmf->vma->vm_ops->page_mkwrite(vmf);
        /* Restore original flags so that caller is not surprised */
        vmf->flags = old_flags;
        if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE)))
                return ret;
        if (unlikely(!(ret & VM_FAULT_LOCKED))) {
                lock_page(page);
                if (!page->mapping) {
                        unlock_page(page);
                        return 0; /* retry */
                }
                ret |= VM_FAULT_LOCKED;
        } else
                VM_BUG_ON_PAGE(!PageLocked(page), page);
        return ret;
}

/*
 * Handle dirtying of a page in shared file mapping on a write fault.
 *
 * The function expects the page to be locked and unlocks it.
 */
static vm_fault_t fault_dirty_shared_page(struct vm_fault *vmf)
{
        struct vm_area_struct *vma = vmf->vma;
        struct address_space *mapping;
        struct page *page = vmf->page;
        bool dirtied;
        bool page_mkwrite = vma->vm_ops && vma->vm_ops->page_mkwrite;

        dirtied = set_page_dirty(page);
        VM_BUG_ON_PAGE(PageAnon(page), page);
        /*
         * Take a local copy of the address_space - page.mapping may be zeroed
         * by truncate after unlock_page().   The address_space itself remains
         * pinned by vma->vm_file's reference.  We rely on unlock_page()'s
         * release semantics to prevent the compiler from undoing this copying.
         */
        mapping = page_rmapping(page);
        unlock_page(page);

        if (!page_mkwrite)
                file_update_time(vma->vm_file);

        /*
         * Throttle page dirtying rate down to writeback speed.
         *
         * mapping may be NULL here because some device drivers do not
         * set page.mapping but still dirty their pages
         *
         * Drop the mmap_lock before waiting on IO, if we can. The file
         * is pinning the mapping, as per above.
         */
        if ((dirtied || page_mkwrite) && mapping) {
                struct file *fpin;

                fpin = maybe_unlock_mmap_for_io(vmf, NULL);
                balance_dirty_pages_ratelimited(mapping);
                if (fpin) {
                        fput(fpin);
                        return VM_FAULT_RETRY;
                }
        }

        return 0;
}

/*
 * Handle write page faults for pages that can be reused in the current vma
 *
 * This can happen either due to the mapping being with the VM_SHARED flag,
 * or due to us being the last reference standing to the page. In either
 * case, all we need to do here is to mark the page as writable and update
 * any related book-keeping.
 */
static inline void wp_page_reuse(struct vm_fault *vmf)
        __releases(vmf->ptl)
{
        struct vm_area_struct *vma = vmf->vma;
        struct page *page = vmf->page;
        pte_t entry;
        /*
         * Clear the pages cpupid information as the existing
         * information potentially belongs to a now completely
         * unrelated process.
         */
        if (page)
                page_cpupid_xchg_last(page, (1 << LAST_CPUPID_SHIFT) - 1);

        flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
        entry = pte_mkyoung(vmf->orig_pte);
        entry = maybe_mkwrite(pte_mkdirty(entry), vma);
        if (ptep_set_access_flags(vma, vmf->address, vmf->pte, entry, 1))
                update_mmu_cache(vma, vmf->address, vmf->pte);
        pte_unmap_unlock(vmf->pte, vmf->ptl);
        count_vm_event(PGREUSE);
}

/*
 * Handle the case of a page which we actually need to copy to a new page.
 *
 * Called with mmap_lock locked and the old page referenced, but
 * without the ptl held.
 *
 * High level logic flow:
 *
 * - Allocate a page, copy the content of the old page to the new one.
 * - Handle book keeping and accounting - cgroups, mmu-notifiers, etc.
 * - Take the PTL. If the pte changed, bail out and release the allocated page
 * - If the pte is still the way we remember it, update the page table and all
 *   relevant references. This includes dropping the reference the page-table
 *   held to the old page, as well as updating the rmap.
 * - In any case, unlock the PTL and drop the reference we took to the old page.
 */
static vm_fault_t wp_page_copy(struct vm_fault *vmf)
{
        struct vm_area_struct *vma = vmf->vma;
        struct mm_struct *mm = vma->vm_mm;
        struct page *old_page = vmf->page;
        struct page *new_page = NULL;
        pte_t entry;
        int page_copied = 0;
        struct mmu_notifier_range range;

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

        if (is_zero_pfn(pte_pfn(vmf->orig_pte))) {
                new_page = alloc_zeroed_user_highpage_movable(vma,
                                                              vmf->address);
                if (!new_page)
                        goto oom;
        } else {
                new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma,
                                vmf->address);
                if (!new_page)
                        goto oom;

                if (!cow_user_page(new_page, old_page, vmf)) {
                        /*
                         * COW failed, if the fault was solved by other,
                         * it's fine. If not, userspace would re-fault on
                         * the same address and we will handle the fault
                         * from the second attempt.
                         */