#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/huge_mm.h>
#include <linux/mount.h>
#include <linux/seq_file.h>
#include <linux/highmem.h>
#include <linux/ptrace.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/mempolicy.h>
#include <linux/rmap.h>
#include <linux/swap.h>
#include <linux/swapops.h>

#include <asm/elf.h>
#include <asm/uaccess.h>
#include <asm/tlbflush.h>
#include "internal.h"

void task_mem(struct seq_file *m, struct mm_struct *mm)
{
        unsigned long data, text, lib, swap;
        unsigned long hiwater_vm, total_vm, hiwater_rss, total_rss;

        /*
         * Note: to minimize their overhead, mm maintains hiwater_vm and
         * hiwater_rss only when about to *lower* total_vm or rss.  Any
         * collector of these hiwater stats must therefore get total_vm
         * and rss too, which will usually be the higher.  Barriers? not
         * worth the effort, such snapshots can always be inconsistent.
         */
        hiwater_vm = total_vm = mm->total_vm;
        if (hiwater_vm < mm->hiwater_vm)
                hiwater_vm = mm->hiwater_vm;
        hiwater_rss = total_rss = get_mm_rss(mm);
        if (hiwater_rss < mm->hiwater_rss)
                hiwater_rss = mm->hiwater_rss;

        data = mm->total_vm - mm->shared_vm - mm->stack_vm;
        text = (PAGE_ALIGN(mm->end_code) - (mm->start_code & PAGE_MASK)) >> 10;
        lib = (mm->exec_vm << (PAGE_SHIFT-10)) - text;
        swap = get_mm_counter(mm, MM_SWAPENTS);
        seq_printf(m,
                "VmPeak:\t%8lu kB\n"
                "VmSize:\t%8lu kB\n"
                "VmLck:\t%8lu kB\n"
                "VmHWM:\t%8lu kB\n"
                "VmRSS:\t%8lu kB\n"
                "VmData:\t%8lu kB\n"
                "VmStk:\t%8lu kB\n"
                "VmExe:\t%8lu kB\n"
                "VmLib:\t%8lu kB\n"
                "VmPTE:\t%8lu kB\n"
                "VmSwap:\t%8lu kB\n",
                hiwater_vm << (PAGE_SHIFT-10),
                (total_vm - mm->reserved_vm) << (PAGE_SHIFT-10),
                mm->locked_vm << (PAGE_SHIFT-10),
                hiwater_rss << (PAGE_SHIFT-10),
                total_rss << (PAGE_SHIFT-10),
                data << (PAGE_SHIFT-10),
                mm->stack_vm << (PAGE_SHIFT-10), text, lib,
                (PTRS_PER_PTE*sizeof(pte_t)*mm->nr_ptes) >> 10,
                swap << (PAGE_SHIFT-10));
}

unsigned long task_vsize(struct mm_struct *mm)
{
        return PAGE_SIZE * mm->total_vm;
}

unsigned long task_statm(struct mm_struct *mm,
                         unsigned long *shared, unsigned long *text,
                         unsigned long *data, unsigned long *resident)
{
        *shared = get_mm_counter(mm, MM_FILEPAGES);
        *text = (PAGE_ALIGN(mm->end_code) - (mm->start_code & PAGE_MASK))
                                                                >> PAGE_SHIFT;
        *data = mm->total_vm - mm->shared_vm;
        *resident = *shared + get_mm_counter(mm, MM_ANONPAGES);
        return mm->total_vm;
}

static void pad_len_spaces(struct seq_file *m, int len)
{
        len = 25 + sizeof(void*) * 6 - len;
        if (len < 1)
                len = 1;
        seq_printf(m, "%*c", len, ' ');
}

static void vma_stop(struct proc_maps_private *priv, struct vm_area_struct *vma)
{
        if (vma && vma != priv->tail_vma) {
                struct mm_struct *mm = vma->vm_mm;
                up_read(&mm->mmap_sem);
                mmput(mm);
        }
}

static void *m_start(struct seq_file *m, loff_t *pos)
{
        struct proc_maps_private *priv = m->private;
        unsigned long last_addr = m->version;
        struct mm_struct *mm;
        struct vm_area_struct *vma, *tail_vma = NULL;
        loff_t l = *pos;

        /* Clear the per syscall fields in priv */
        priv->task = NULL;
        priv->tail_vma = NULL;

        /*
         * We remember last_addr rather than next_addr to hit with
         * mmap_cache most of the time. We have zero last_addr at
         * the beginning and also after lseek. We will have -1 last_addr
         * after the end of the vmas.
         */

        if (last_addr == -1UL)
                return NULL;

        priv->task = get_pid_task(priv->pid, PIDTYPE_PID);
        if (!priv->task)
                return ERR_PTR(-ESRCH);

        mm = mm_for_maps(priv->task);
        if (!mm || IS_ERR(mm))
                return mm;
        down_read(&mm->mmap_sem);

        tail_vma = get_gate_vma(priv->task->mm);
        priv->tail_vma = tail_vma;

        /* Start with last addr hint */
        vma = find_vma(mm, last_addr);
        if (last_addr && vma) {
                vma = vma->vm_next;
                goto out;
        }

        /*
         * Check the vma index is within the range and do
         * sequential scan until m_index.
         */
        vma = NULL;
        if ((unsigned long)l < mm->map_count) {
                vma = mm->mmap;
                while (l-- && vma)
                        vma = vma->vm_next;
                goto out;
        }

        if (l != mm->map_count)
                tail_vma = NULL; /* After gate vma */

out:
        if (vma)
                return vma;

        /* End of vmas has been reached */
        m->version = (tail_vma != NULL)? 0: -1UL;
        up_read(&mm->mmap_sem);
        mmput(mm);
        return tail_vma;
}

static void *m_next(struct seq_file *m, void *v, loff_t *pos)
{
        struct proc_maps_private *priv = m->private;
        struct vm_area_struct *vma = v;
        struct vm_area_struct *tail_vma = priv->tail_vma;

        (*pos)++;
        if (vma && (vma != tail_vma) && vma->vm_next)
                return vma->vm_next;
        vma_stop(priv, vma);
        return (vma != tail_vma)? tail_vma: NULL;
}

static void m_stop(struct seq_file *m, void *v)
{
        struct proc_maps_private *priv = m->private;
        struct vm_area_struct *vma = v;

        if (!IS_ERR(vma))
                vma_stop(priv, vma);
        if (priv->task)
                put_task_struct(priv->task);
}

static int do_maps_open(struct inode *inode, struct file *file,
                        const struct seq_operations *ops)
{
        struct proc_maps_private *priv;
        int ret = -ENOMEM;
        priv = kzalloc(sizeof(*priv), GFP_KERNEL);
        if (priv) {
                priv->pid = proc_pid(inode);
                ret = seq_open(file, ops);
                if (!ret) {
                        struct seq_file *m = file->private_data;
                        m->private = priv;
                } else {
                        kfree(priv);
                }
        }
        return ret;
}

static void show_map_vma(struct seq_file *m, struct vm_area_struct *vma)
{
        struct mm_struct *mm = vma->vm_mm;
        struct file *file = vma->vm_file;
        int flags = vma->vm_flags;
        unsigned long ino = 0;
        unsigned long long pgoff = 0;
        unsigned long start, end;
        dev_t dev = 0;
        int len;

        if (file) {
                struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
                dev = inode->i_sb->s_dev;
                ino = inode->i_ino;
                pgoff = ((loff_t)vma->vm_pgoff) << PAGE_SHIFT;
        }

        /* We don't show the stack guard page in /proc/maps */
        start = vma->vm_start;
        if (stack_guard_page_start(vma, start))
                start += PAGE_SIZE;
        end = vma->vm_end;
        if (stack_guard_page_end(vma, end))
                end -= PAGE_SIZE;

        seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu %n",
                        start,
                        end,
                        flags & VM_READ ? 'r' : '-',
                        flags & VM_WRITE ? 'w' : '-',
                        flags & VM_EXEC ? 'x' : '-',
                        flags & VM_MAYSHARE ? 's' : 'p',
                        pgoff,
                        MAJOR(dev), MINOR(dev), ino, &len);

        /*
         * Print the dentry name for named mappings, and a
         * special [heap] marker for the heap:
         */
        if (file) {
                pad_len_spaces(m, len);
                seq_path(m, &file->f_path, "\n");
        } else {
                const char *name = arch_vma_name(vma);
                if (!name) {
                        if (mm) {
                                if (vma->vm_start <= mm->brk &&
                                                vma->vm_end >= mm->start_brk) {
                                        name = "[heap]";
                                } else if (vma->vm_start <= mm->start_stack &&
                                           vma->vm_end >= mm->start_stack) {
                                        name = "[stack]";
                                }
                        } else {
                                name = "[vdso]";
                        }
                }
                if (name) {
                        pad_len_spaces(m, len);
                        seq_puts(m, name);
                }
        }
        seq_putc(m, '\n');
}

static int show_map(struct seq_file *m, void *v)
{
        struct vm_area_struct *vma = v;
        struct proc_maps_private *priv = m->private;
        struct task_struct *task = priv->task;

        show_map_vma(m, vma);

        if (m->count < m->size)  /* vma is copied successfully */
                m->version = (vma != get_gate_vma(task->mm))
                        ? vma->vm_start : 0;
        return 0;
}

static const struct seq_operations proc_pid_maps_op = {
        .start  = m_start,
        .next   = m_next,
        .stop   = m_stop,
        .show   = show_map
};

static int maps_open(struct inode *inode, struct file *file)
{
        return do_maps_open(inode, file, &proc_pid_maps_op);
}

const struct file_operations proc_maps_operations = {
        .open           = maps_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = seq_release_private,
};

/*
 * Proportional Set Size(PSS): my share of RSS.
 *
 * PSS of a process is the count of pages it has in memory, where each
 * page is divided by the number of processes sharing it.  So if a
 * process has 1000 pages all to itself, and 1000 shared with one other
 * process, its PSS will be 1500.
 *
 * To keep (accumulated) division errors low, we adopt a 64bit
 * fixed-point pss counter to minimize division errors. So (pss >>
 * PSS_SHIFT) would be the real byte count.
 *
 * A shift of 12 before division means (assuming 4K page size):
 *      - 1M 3-user-pages add up to 8KB errors;
 *      - supports mapcount up to 2^24, or 16M;
 *      - supports PSS up to 2^52 bytes, or 4PB.
 */
#define PSS_SHIFT 12

#ifdef CONFIG_PROC_PAGE_MONITOR
struct mem_size_stats {
        struct vm_area_struct *vma;
        unsigned long resident;
        unsigned long shared_clean;
        unsigned long shared_dirty;
        unsigned long private_clean;
        unsigned long private_dirty;
        unsigned long referenced;
        unsigned long anonymous;
        unsigned long anonymous_thp;
        unsigned long swap;
        u64 pss;
};


static void smaps_pte_entry(pte_t ptent, unsigned long addr,
                unsigned long ptent_size, struct mm_walk *walk)
{
        struct mem_size_stats *mss = walk->private;
        struct vm_area_struct *vma = mss->vma;
        struct page *page;
        int mapcount;

        if (is_swap_pte(ptent)) {
                mss->swap += ptent_size;
                return;
        }

        if (!pte_present(ptent))
                return;

        page = vm_normal_page(vma, addr, ptent);
        if (!page)
                return;

        if (PageAnon(page))
                mss->anonymous += ptent_size;

        mss->resident += ptent_size;
        /* Accumulate the size in pages that have been accessed. */
        if (pte_young(ptent) || PageReferenced(page))
                mss->referenced += ptent_size;
        mapcount = page_mapcount(page);
        if (mapcount >= 2) {
                if (pte_dirty(ptent) || PageDirty(page))
                        mss->shared_dirty += ptent_size;
                else
                        mss->shared_clean += ptent_size;
                mss->pss += (ptent_size << PSS_SHIFT) / mapcount;
        } else {
                if (pte_dirty(ptent) || PageDirty(page))
                        mss->private_dirty += ptent_size;
                else
                        mss->private_clean += ptent_size;
                mss->pss += (ptent_size << PSS_SHIFT);
        }
}

static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
                           struct mm_walk *walk)
{
        struct mem_size_stats *mss = walk->private;
        struct vm_area_struct *vma = mss->vma;
        pte_t *pte;
        spinlock_t *ptl;

        spin_lock(&walk->mm->page_table_lock);
        if (pmd_trans_huge(*pmd)) {
                if (pmd_trans_splitting(*pmd)) {
                        spin_unlock(&walk->mm->page_table_lock);
                        wait_split_huge_page(vma->anon_vma, pmd);
                } else {
                        smaps_pte_entry(*(pte_t *)pmd, addr,
                                        HPAGE_PMD_SIZE, walk);
                        spin_unlock(&walk->mm->page_table_lock);
                        mss->anonymous_thp += HPAGE_PMD_SIZE;
                        return 0;
                }
        } else {
                spin_unlock(&walk->mm->page_table_lock);
        }
        /*
         * The mmap_sem held all the way back in m_start() is what
         * keeps khugepaged out of here and from collapsing things
         * in here.
         */
        pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
        for (; addr != end; pte++, addr += PAGE_SIZE)
                smaps_pte_entry(*pte, addr, PAGE_SIZE, walk);
        pte_unmap_unlock(pte - 1, ptl);
        cond_resched();
        return 0;
}

static int show_smap(struct seq_file *m, void *v)
{
        struct proc_maps_private *priv = m->private;
        struct task_struct *task = priv->task;
        struct vm_area_struct *vma = v;
        struct mem_size_stats mss;
        struct mm_walk smaps_walk = {
                .pmd_entry = smaps_pte_range,
                .mm = vma->vm_mm,
                .private = &mss,
        };

        memset(&mss, 0, sizeof mss);
        mss.vma = vma;
        /* mmap_sem is held in m_start */
        if (vma->vm_mm && !is_vm_hugetlb_page(vma))
                walk_page_range(vma->vm_start, vma->vm_end, &smaps_walk);

        show_map_vma(m, vma);

        seq_printf(m,
                   "Size:           %8lu kB\n"
                   "Rss:            %8lu kB\n"
                   "Pss:            %8lu kB\n"
                   "Shared_Clean:   %8lu kB\n"
                   "Shared_Dirty:   %8lu kB\n"
                   "Private_Clean:  %8lu kB\n"
                   "Private_Dirty:  %8lu kB\n"
                   "Referenced:     %8lu kB\n"
                   "Anonymous:      %8lu kB\n"
                   "AnonHugePages:  %8lu kB\n"
                   "Swap:           %8lu kB\n"
                   "KernelPageSize: %8lu kB\n"
                   "MMUPageSize:    %8lu kB\n"
                   "Locked:         %8lu kB\n",
                   (vma->vm_end - vma->vm_start) >> 10,
                   mss.resident >> 10,
                   (unsigned long)(mss.pss >> (10 + PSS_SHIFT)),
                   mss.shared_clean  >> 10,
                   mss.shared_dirty  >> 10,
                   mss.private_clean >> 10,
                   mss.private_dirty >> 10,
                   mss.referenced >> 10,
                   mss.anonymous >> 10,
                   mss.anonymous_thp >> 10,
                   mss.swap >> 10,
                   vma_kernel_pagesize(vma) >> 10,
                   vma_mmu_pagesize(vma) >> 10,
                   (vma->vm_flags & VM_LOCKED) ?
                        (unsigned long)(mss.pss >> (10 + PSS_SHIFT)) : 0);

        if (m->count < m->size)  /* vma is copied successfully */
                m->version = (vma != get_gate_vma(task->mm))
                        ? vma->vm_start : 0;
        return 0;
}

static const struct seq_operations proc_pid_smaps_op = {
        .start  = m_start,
        .next   = m_next,
        .stop   = m_stop,
        .show   = show_smap
};

static int smaps_open(struct inode *inode, struct file *file)
{
        return do_maps_open(inode, file, &proc_pid_smaps_op);
}

const struct file_operations proc_smaps_operations = {
        .open           = smaps_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = seq_release_private,
};

static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
                                unsigned long end, struct mm_walk *walk)
{
        struct vm_area_struct *vma = walk->private;
        pte_t *pte, ptent;
        spinlock_t *ptl;
        struct page *page;

        split_huge_page_pmd(walk->mm, pmd);

        pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
        for (; addr != end; pte++, addr += PAGE_SIZE) {
                ptent = *pte;
                if (!pte_present(ptent))
                        continue;

                page = vm_normal_page(vma, addr, ptent);
                if (!page)
                        continue;

                /* Clear accessed and referenced bits. */
                ptep_test_and_clear_young(vma, addr, pte);
                ClearPageReferenced(page);
        }
        pte_unmap_unlock(pte - 1, ptl);
        cond_resched();
        return 0;
}

#define CLEAR_REFS_ALL 1
#define CLEAR_REFS_ANON 2
#define CLEAR_REFS_MAPPED 3

static ssize_t clear_refs_write(struct file *file, const char __user *buf,
                                size_t count, loff_t *ppos)
{
        struct task_struct *task;
        char buffer[PROC_NUMBUF];
        struct mm_struct *mm;
        struct vm_area_struct *vma;
        long type;

        memset(buffer, 0, sizeof(buffer));
        if (count > sizeof(buffer) - 1)
                count = sizeof(buffer) - 1;
        if (copy_from_user(buffer, buf, count))
                return -EFAULT;
        if (strict_strtol(strstrip(buffer), 10, &type))
                return -EINVAL;
        if (type < CLEAR_REFS_ALL || type > CLEAR_REFS_MAPPED)
                return -EINVAL;
        task = get_proc_task(file->f_path.dentry->d_inode);
        if (!task)
                return -ESRCH;
        mm = get_task_mm(task);
        if (mm) {
                struct mm_walk clear_refs_walk = {
                        .pmd_entry = clear_refs_pte_range,
                        .mm = mm,
                };
                down_read(&mm->mmap_sem);
                for (vma = mm->mmap; vma; vma = vma->vm_next) {
                        clear_refs_walk.private = vma;
                        if (is_vm_hugetlb_page(vma))
                                continue;
                        /*
                         * Writing 1 to /proc/pid/clear_refs affects all pages.
                         *
                         * Writing 2 to /proc/pid/clear_refs only affects
                         * Anonymous pages.
                         *
                         * Writing 3 to /proc/pid/clear_refs only affects file
                         * mapped pages.
                         */
                        if (type == CLEAR_REFS_ANON && vma->vm_file)
                                continue;
                        if (type == CLEAR_REFS_MAPPED && !vma->vm_file)
                                continue;
                        walk_page_range(vma->vm_start, vma->vm_end,
                                        &clear_refs_walk);
                }
                flush_tlb_mm(mm);
                up_read(&mm->mmap_sem);
                mmput(mm);
        }
        put_task_struct(task);

        return count;
}

const struct file_operations proc_clear_refs_operations = {
        .write          = clear_refs_write,
        .llseek         = noop_llseek,
};

struct pagemapread {
        int pos, len;
        u64 *buffer;
};

#define PM_ENTRY_BYTES      sizeof(u64)
#define PM_STATUS_BITS      3
#define PM_STATUS_OFFSET    (64 - PM_STATUS_BITS)
#define PM_STATUS_MASK      (((1LL << PM_STATUS_BITS) - 1) << PM_STATUS_OFFSET)
#define PM_STATUS(nr)       (((nr) << PM_STATUS_OFFSET) & PM_STATUS_MASK)
#define PM_PSHIFT_BITS      6
#define PM_PSHIFT_OFFSET    (PM_STATUS_OFFSET - PM_PSHIFT_BITS)
#define PM_PSHIFT_MASK      (((1LL << PM_PSHIFT_BITS) - 1) << PM_PSHIFT_OFFSET)
#define PM_PSHIFT(x)        (((u64) (x) << PM_PSHIFT_OFFSET) & PM_PSHIFT_MASK)
#define PM_PFRAME_MASK      ((1LL << PM_PSHIFT_OFFSET) - 1)
#define PM_PFRAME(x)        ((x) & PM_PFRAME_MASK)

#define PM_PRESENT          PM_STATUS(4LL)
#define PM_SWAP             PM_STATUS(2LL)
#define PM_NOT_PRESENT      PM_PSHIFT(PAGE_SHIFT)
#define PM_END_OF_BUFFER    1

static int add_to_pagemap(unsigned long addr, u64 pfn,
                          struct pagemapread *pm)
{
        pm->buffer[pm->pos++] = pfn;
        if (pm->pos >= pm->len)
                return PM_END_OF_BUFFER;
        return 0;
}

static int pagemap_pte_hole(unsigned long start, unsigned long end,
                                struct mm_walk *walk)
{
        struct pagemapread *pm = walk->private;
        unsigned long addr;
        int err = 0;
        for (addr = start; addr < end; addr += PAGE_SIZE) {
                err = add_to_pagemap(addr, PM_NOT_PRESENT, pm);
                if (err)
                        break;
        }
        return err;
}

static u64 swap_pte_to_pagemap_entry(pte_t pte)
{
        swp_entry_t e = pte_to_swp_entry(pte);
        return swp_type(e) | (swp_offset(e) << MAX_SWAPFILES_SHIFT);
}

static u64 pte_to_pagemap_entry(pte_t pte)
{
        u64 pme = 0;
        if (is_swap_pte(pte))
                pme = PM_PFRAME(swap_pte_to_pagemap_entry(pte))
                        | PM_PSHIFT(PAGE_SHIFT) | PM_SWAP;
        else if (pte_present(pte))
                pme = PM_PFRAME(pte_pfn(pte))
                        | PM_PSHIFT(PAGE_SHIFT) | PM_PRESENT;
        return pme;
}

static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
                             struct mm_walk *walk)
{
        struct vm_area_struct *vma;
        struct pagemapread *pm = walk->private;
        pte_t *pte;
        int err = 0;

        split_huge_page_pmd(walk->mm, pmd);

        /* find the first VMA at or above 'addr' */
        vma = find_vma(walk->mm, addr);
        for (; addr != end; addr += PAGE_SIZE) {
                u64 pfn = PM_NOT_PRESENT;

                /* check to see if we've left 'vma' behind
                 * and need a new, higher one */
                if (vma && (addr >= vma->vm_end))
                        vma = find_vma(walk->mm, addr);

                /* check that 'vma' actually covers this address,
                 * and that it isn't a huge page vma */
                if (vma && (vma->vm_start <= addr) &&
                    !is_vm_hugetlb_page(vma)) {
                        pte = pte_offset_map(pmd, addr);
                        pfn = pte_to_pagemap_entry(*pte);
                        /* unmap before userspace copy */
                        pte_unmap(pte);
                }
                err = add_to_pagemap(addr, pfn, pm);
                if (err)
                        return err;
        }

        cond_resched();

        return err;
}

#ifdef CONFIG_HUGETLB_PAGE
static u64 huge_pte_to_pagemap_entry(pte_t pte, int offset)
{
        u64 pme = 0;
        if (pte_present(pte))
                pme = PM_PFRAME(pte_pfn(pte) + offset)
                        | PM_PSHIFT(PAGE_SHIFT) | PM_PRESENT;
        return pme;
}

/* This function walks within one hugetlb entry in the single call */
static int pagemap_hugetlb_range(pte_t *pte, unsigned long hmask,
                                 unsigned long addr, unsigned long end,
                                 struct mm_walk *walk)
{
        struct pagemapread *pm = walk->private;
        int err = 0;
        u64 pfn;

        for (; addr != end; addr += PAGE_SIZE) {
                int offset = (addr & ~hmask) >> PAGE_SHIFT;
                pfn = huge_pte_to_pagemap_entry(*pte, offset);
                err = add_to_pagemap(addr, pfn, pm);
                if (err)
                        return err;
        }

        cond_resched();

        return err;
}
#endif /* HUGETLB_PAGE */

/*
 * /proc/pid/pagemap - an array mapping virtual pages to pfns
 *
 * For each page in the address space, this file contains one 64-bit entry
 * consisting of the following:
 *
 * Bits 0-55  page frame number (PFN) if present
 * Bits 0-4   swap type if swapped
 * Bits 5-55  swap offset if swapped
 * Bits 55-60 page shift (page size = 1<<page shift)
 * Bit  61    reserved for future use
 * Bit  62    page swapped
 * Bit  63    page present
 *
 * If the page is not present but in swap, then the PFN contains an
 * encoding of the swap file number and the page's offset into the
 * swap. Unmapped pages return a null PFN. This allows determining
 * precisely which pages are mapped (or in swap) and comparing mapped
 * pages between processes.
 *
 * Efficient users of this interface will use /proc/pid/maps to
 * determine which areas of memory are actually mapped and llseek to
 * skip over unmapped regions.
 */
#define PAGEMAP_WALK_SIZE       (PMD_SIZE)
#define PAGEMAP_WALK_MASK       (PMD_MASK)
static ssize_t pagemap_read(struct file *file, char __user *buf,
                            size_t count, loff_t *ppos)
{
        struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
        struct mm_struct *mm;
        struct pagemapread pm;
        int ret = -ESRCH;
        struct mm_walk pagemap_walk = {};
        unsigned long src;
        unsigned long svpfn;
        unsigned long start_vaddr;
        unsigned long end_vaddr;
        int copied = 0;

        if (!task)
                goto out;

        mm = mm_for_maps(task);
        ret = PTR_ERR(mm);
        if (!mm || IS_ERR(mm))
                goto out_task;

        ret = -EINVAL;
        /* file position must be aligned */
        if ((*ppos % PM_ENTRY_BYTES) || (count % PM_ENTRY_BYTES))
                goto out_task;

        ret = 0;

        if (!count)
                goto out_task;

        pm.len = PM_ENTRY_BYTES * (PAGEMAP_WALK_SIZE >> PAGE_SHIFT);
        pm.buffer = kmalloc(pm.len, GFP_TEMPORARY);
        ret = -ENOMEM;
        if (!pm.buffer)
                goto out_mm;

        pagemap_walk.pmd_entry = pagemap_pte_range;
        pagemap_walk.pte_hole = pagemap_pte_hole;
#ifdef CONFIG_HUGETLB_PAGE
        pagemap_walk.hugetlb_entry = pagemap_hugetlb_range;
#endif
        pagemap_walk.mm = mm;
        pagemap_walk.private = &pm;

        src = *ppos;
        svpfn = src / PM_ENTRY_BYTES;
        start_vaddr = svpfn << PAGE_SHIFT;
        end_vaddr = TASK_SIZE_OF(task);

        /* watch out for wraparound */
        if (svpfn > TASK_SIZE_OF(task) >> PAGE_SHIFT)
                start_vaddr = end_vaddr;

        /*
         * The odds are that this will stop walking way
         * before end_vaddr, because the length of the
         * user buffer is tracked in "pm", and the walk
         * will stop when we hit the end of the buffer.
         */
        ret = 0;
        while (count && (start_vaddr < end_vaddr)) {
                int len;
                unsigned long end;

                pm.pos = 0;
                end = (start_vaddr + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK;
                /* overflow ? */
                if (end < start_vaddr || end > end_vaddr)
                        end = end_vaddr;
                down_read(&mm->mmap_sem);
                ret = walk_page_range(start_vaddr, end, &pagemap_walk);
                up_read(&mm->mmap_sem);
                start_vaddr = end;

                len = min(count, PM_ENTRY_BYTES * pm.pos);
                if (copy_to_user(buf, pm.buffer, len)) {
                        ret = -EFAULT;
                        goto out_free;
                }
                copied += len;
                buf += len;
                count -= len;
        }
        *ppos += copied;
        if (!ret || ret == PM_END_OF_BUFFER)
                ret = copied;

out_free:
        kfree(pm.buffer);
out_mm:
        mmput(mm);
out_task:
        put_task_struct(task);
out:
        return ret;
}

const struct file_operations proc_pagemap_operations = {
        .llseek         = mem_lseek, /* borrow this */
        .read           = pagemap_read,
};
#endif /* CONFIG_PROC_PAGE_MONITOR */

#ifdef CONFIG_NUMA
extern int show_numa_map(struct seq_file *m, void *v);

static const struct seq_operations proc_pid_numa_maps_op = {
        .start  = m_start,
        .next   = m_next,
        .stop   = m_stop,
        .show   = show_numa_map,
};

static int numa_maps_open(struct inode *inode, struct file *file)
{
        return do_maps_open(inode, file, &proc_pid_numa_maps_op);
}

const struct file_operations proc_numa_maps_operations = {
        .open           = numa_maps_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = seq_release_private,
};
#endif