#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/swap.h>
#include <linux/memremap.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/writeback.h>
#include <linux/mmu_notifier.h>
#include <linux/swapops.h>
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>

#include "internal.h"

static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
                pte_t *pte, unsigned int flags)
{
        /* No page to get reference */
        if (flags & FOLL_GET)
                return -EFAULT;

        if (flags & FOLL_TOUCH) {
                pte_t entry = *pte;

                if (flags & FOLL_WRITE)
                        entry = pte_mkdirty(entry);
                entry = pte_mkyoung(entry);

                if (!pte_same(*pte, entry)) {
                        set_pte_at(vma->vm_mm, address, pte, entry);
                        update_mmu_cache(vma, address, pte);
                }
        }

        /* Proper page table entry exists, but no corresponding struct page */
        return -EEXIST;
}

/*
 * FOLL_FORCE can write to even unwritable pte's, but only
 * after we've gone through a COW cycle and they are dirty.
 */
static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
{
        return pte_write(pte) ||
                ((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
}

/**
 * follow_page_mask - look up a page descriptor from a user-virtual address
 * @vma: vm_area_struct mapping @address
 * @address: virtual address to look up
 * @flags: flags modifying lookup behaviour
 * @page_mask: on output, *page_mask is set according to the size of the page
 *
 * @flags can have FOLL_ flags set, defined in <linux/mm.h>
 *
 * Returns the mapped (struct page *), %NULL if no mapping exists, or
 * an error pointer if there is a mapping to something not represented
 * by a page descriptor (see also vm_normal_page()).
 */
struct page *follow_page_mask(struct vm_area_struct *vma,
                              unsigned long address, unsigned int flags,
                              unsigned int *page_mask)
{
        struct dev_pagemap *pgmap = NULL;
        pgd_t *pgd;
        pud_t *pud;
        pmd_t *pmd;
        pte_t *ptep, pte;
        spinlock_t *ptl;
        struct page *page;
        struct mm_struct *mm = vma->vm_mm;

        *page_mask = 0;

        page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
        if (!IS_ERR(page)) {
                /*
                 * RHEL: BZ1268999 quick-and-dirty-fix
                 *
                 * On powerpc a race between a THP pmd clear path and
                 * follow_huge_addr() can result in follow_huge_addr()
                 * returning NULL when a THP PMD has just been cleared
                 * - usually follow_huge_addr() should return
                 * ERR_PTR(-EINVAL) on a THP PMD.  This hack avoids
                 * the BUG_ON() while waiting for a proper upstream
                 * fix.  It will mean follow_page_mask() fails, but
                 * should trigger a fall back to a faultin path which
                 * should populate the pages.
                 */
                if (page)
                        BUG_ON(flags & FOLL_GET);
                goto out;
        }

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

        pud = pud_offset(pgd, address);
        if (pud_none(*pud))
                goto no_page_table;
        if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
                page = follow_huge_pud(mm, address, pud, flags);
                if (page)
                        return page;
                goto no_page_table;
        }
        if (pud_devmap(*pud)) {
                ptl = pud_lock(mm, pud);
                page = follow_devmap_pud(vma, address, pud, flags);
                spin_unlock(ptl);
                if (page)
                        return page;
        }
        if (unlikely(pud_bad(*pud)))
                goto no_page_table;

        pmd = pmd_offset(pud, address);
        if (pmd_none(*pmd))
                goto no_page_table;
        if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) {
                page = follow_huge_pmd(mm, address, pmd, flags);
                if (page)
                        return page;
                goto no_page_table;
        }
        if ((flags & FOLL_NUMA) && pmd_numa(*pmd))
                goto no_page_table;
        if (pmd_devmap(*pmd)) {
                ptl = pmd_lock(mm, pmd);
                page = follow_devmap_pmd(vma, address, pmd, flags);
                spin_unlock(ptl);
                if (page)
                        return page;
        }
        if (pmd_trans_huge(*pmd)) {
                if (flags & FOLL_SPLIT) {
                        split_huge_page_pmd(vma, address, pmd);
                        goto split_fallthrough;
                }
                ptl = pmd_lock(mm, pmd);
                if (likely(pmd_trans_huge(*pmd))) {
                        if (unlikely(pmd_trans_splitting(*pmd))) {
                                spin_unlock(ptl);
                                wait_split_huge_page(vma->anon_vma, pmd);
                        } else {
                                page = follow_trans_huge_pmd(vma, address,
                                                             pmd, flags);
                                spin_unlock(ptl);
                                *page_mask = HPAGE_PMD_NR - 1;
                                goto out;
                        }
                } else
                        spin_unlock(ptl);
                /* fall through */
        }
split_fallthrough:
        if (unlikely(pmd_bad(*pmd)))
                goto no_page_table;

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

        pte = *ptep;
        if (!pte_present(pte)) {
                swp_entry_t entry;
                /*
                 * KSM's break_ksm() relies upon recognizing a ksm page
                 * even while it is being migrated, so for that case we
                 * need migration_entry_wait().
                 */
                if (likely(!(flags & FOLL_MIGRATION)))
                        goto no_page;
                if (pte_none(pte) || pte_file(pte))
                        goto no_page;
                entry = pte_to_swp_entry(pte);
                if (!is_migration_entry(entry))
                        goto no_page;
                if (is_migration_entry(entry)) {
                        pte_unmap_unlock(ptep, ptl);
                        migration_entry_wait(mm, pmd, address);
                        goto split_fallthrough;
                }
                goto no_page;
        }
        if ((flags & FOLL_NUMA) && pte_numa(pte))
                goto no_page;
        if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags))
                goto unlock;

        page = vm_normal_page(vma, address, pte);
        if (!page && pte_devmap(pte) && (flags & FOLL_GET)) {
                /*
                 * Only return device mapping pages in the FOLL_GET case since
                 * they are only valid while holding the pgmap reference.
                 */
                pgmap = get_dev_pagemap(pte_pfn(pte), NULL);
                if (pgmap)
                        page = pte_page(pte);
                else
                        goto no_page;
        } else if (unlikely(!page)) {
                if (flags & FOLL_DUMP) {
                        /* Avoid special (like zero) pages in core dumps */
                        page = ERR_PTR(-EFAULT);
                        goto unlock;
                }

                if (is_zero_pfn(pte_pfn(pte))) {
                        page = pte_page(pte);
                } else {
                        int ret;

                        ret = follow_pfn_pte(vma, address, ptep, flags);
                        page = ERR_PTR(ret);
                        goto unlock;
                }
        }

        if (flags & FOLL_GET) {
                get_page_foll(page);

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

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

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

/**
 * __get_user_pages() - pin user pages in memory
 * @tsk:        task_struct of target task
 * @mm:         mm_struct of target mm
 * @start:      starting user address
 * @nr_pages:   number of pages from start to pin
 * @gup_flags:  flags modifying pin behaviour
 * @pages:      array that receives pointers to the pages pinned.
 *              Should be at least nr_pages long. Or NULL, if caller
 *              only intends to ensure the pages are faulted in.
 * @vmas:       array of pointers to vmas corresponding to each page.
 *              Or NULL if the caller does not require them.
 * @nonblocking: whether waiting for disk IO or mmap_sem contention
 *
 * Returns number of pages pinned. This may be fewer than the number
 * requested. If nr_pages is 0 or negative, returns 0. If no pages
 * were pinned, returns -errno. Each page returned must be released
 * with a put_page() call when it is finished with. vmas will only
 * remain valid while mmap_sem is held.
 *
 * Must be called with mmap_sem held for read or write.
 *
 * __get_user_pages walks a process's page tables and takes a reference to
 * each struct page that each user address corresponds to at a given
 * instant. That is, it takes the page that would be accessed if a user
 * thread accesses the given user virtual address at that instant.
 *
 * This does not guarantee that the page exists in the user mappings when
 * __get_user_pages returns, and there may even be a completely different
 * page there in some cases (eg. if mmapped pagecache has been invalidated
 * and subsequently re faulted). However it does guarantee that the page
 * won't be freed completely. And mostly callers simply care that the page
 * contains data that was valid *at some point in time*. Typically, an IO
 * or similar operation cannot guarantee anything stronger anyway because
 * locks can't be held over the syscall boundary.
 *
 * If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If
 * the page is written to, set_page_dirty (or set_page_dirty_lock, as
 * appropriate) must be called after the page is finished with, and
 * before put_page is called.
 *
 * If @nonblocking != NULL, __get_user_pages will not wait for disk IO
 * or mmap_sem contention, and if waiting is needed to pin all pages,
 * *@nonblocking will be set to 0.
 *
 * In most cases, get_user_pages or get_user_pages_fast should be used
 * instead of __get_user_pages. __get_user_pages should be used only if
 * you need some special @gup_flags.
 */
long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                unsigned long start, unsigned long nr_pages,
                unsigned int gup_flags, struct page **pages,
                struct vm_area_struct **vmas, int *nonblocking)
{
        long i;
        unsigned long vm_flags;
        unsigned int page_mask;
        int write = (gup_flags & FOLL_WRITE);
        int foreign = (gup_flags & FOLL_REMOTE);

        if (!nr_pages)
                return 0;

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

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

        /*
         * If FOLL_FORCE and FOLL_NUMA are both set, handle_mm_fault
         * would be called on PROT_NONE ranges. We must never invoke
         * handle_mm_fault on PROT_NONE ranges or the NUMA hinting
         * page faults would unprotect the PROT_NONE ranges if
         * _PAGE_NUMA and _PAGE_PROTNONE are sharing the same pte/pmd
         * bitflag. So to avoid that, don't set FOLL_NUMA if
         * FOLL_FORCE is set.
         */
        if (!(gup_flags & FOLL_FORCE))
                gup_flags |= FOLL_NUMA;

        i = 0;

        do {
                struct vm_area_struct *vma;

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

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

                                page = vm_normal_page(vma, start, *pte);
                                if (!page) {
                                        if (!(gup_flags & FOLL_DUMP) &&
                                             is_zero_pfn(pte_pfn(*pte)))
                                                page = pte_page(*pte);
                                        else {
                                                pte_unmap(pte);
                                                return i ? : -EFAULT;
                                        }
                                }
                                pages[i] = page;
                                get_page(page);
                        }
                        pte_unmap(pte);
                        page_mask = 0;
                        goto next_page;
                }

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

                /*
                 * gups are always data accesses, not instruction
                 * fetches, so execute=false here
                 */
                if (!arch_vma_access_permitted(vma, write, false, foreign))
                        return i ? : -EFAULT;

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

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

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

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

                                if (foll_flags & FOLL_WRITE)
                                        fault_flags |= FAULT_FLAG_WRITE;
                                if (foll_flags & FOLL_REMOTE)
                                        fault_flags |= FAULT_FLAG_REMOTE;
                                if (nonblocking)
                                        fault_flags |= FAULT_FLAG_ALLOW_RETRY;
                                if (foll_flags & FOLL_NOWAIT)
                                        fault_flags |= (FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT);
                                if (foll_flags & FOLL_TRIED) {
                                        WARN_ON_ONCE(fault_flags &
                                                     FAULT_FLAG_ALLOW_RETRY);
                                        fault_flags |= FAULT_FLAG_TRIED;
                                }

                                ret = handle_mm_fault(vma, start,
                                                        fault_flags);

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

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

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

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

                                cond_resched();
                        }
                        if (PTR_ERR(page) == -EEXIST) {
                                /*
                                 * Proper page table entry exists, but
                                 * no corresponding struct page.
                                 */
                                goto next_page;
                        } else if (IS_ERR(page)) {
                                return i ? i : PTR_ERR(page);
                        }
                        if (pages) {
                                pages[i] = page;

                                flush_anon_page(vma, page, start);
                                flush_dcache_page(page);
                                page_mask = 0;
                        }
next_page:
                        if (vmas) {
                                vmas[i] = vma;
                                page_mask = 0;
                        }
                        page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
                        if (page_increm > nr_pages)
                                page_increm = nr_pages;
                        i += page_increm;
                        start += page_increm * PAGE_SIZE;
                        nr_pages -= page_increm;
                } while (nr_pages && start < vma->vm_end);
        } while (nr_pages);
        return i;
}
EXPORT_SYMBOL(__get_user_pages);

bool vma_permits_fault(struct vm_area_struct *vma, unsigned int fault_flags)
{
        bool write   = !!(fault_flags & FAULT_FLAG_WRITE);
        bool foreign = !!(fault_flags & FAULT_FLAG_REMOTE);
        vm_flags_t vm_flags = write ? VM_WRITE : VM_READ;

        if (!(vm_flags & vma->vm_flags))
                return false;

        /*
         * The architecture might have a hardware protection
         * mechanism other than read/write that can deny access.
         *
         * gup always represents data access, not instruction
         * fetches, so execute=false here:
         */
        if (!arch_vma_access_permitted(vma, write, false, foreign))
                return false;

        return true;
}

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

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

        if (!vma_permits_fault(vma, fault_flags))
                return -EFAULT;

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

static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
                                                struct mm_struct *mm,
                                                unsigned long start,
                                                unsigned long nr_pages,
                                                int write, int force,
                                                struct page **pages,
                                                struct vm_area_struct **vmas,
                                                int *locked, bool notify_drop,
                                                unsigned int flags)
{
        long ret, pages_done;
        bool lock_dropped;

        if (locked) {
                /* if VM_FAULT_RETRY can be returned, vmas become invalid */
                BUG_ON(vmas);
                /* check caller initialized locked */
                BUG_ON(*locked != 1);
        }

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

        pages_done = 0;
        lock_dropped = false;
        for (;;) {
                ret = __get_user_pages(tsk, mm, start, nr_pages, flags, pages,
                                       vmas, locked);
                if (!locked)
                        /* VM_FAULT_RETRY couldn't trigger, bypass */
                        return ret;

                /* VM_FAULT_RETRY cannot return errors */
                if (!*locked) {
                        BUG_ON(ret < 0);
                        BUG_ON(ret >= nr_pages);
                }

                if (!pages)
                        /* If it's a prefault don't insist harder */
                        return ret;

                if (ret > 0) {
                        nr_pages -= ret;
                        pages_done += ret;
                        if (!nr_pages)
                                break;
                }
                if (*locked) {
                        /* VM_FAULT_RETRY didn't trigger */
                        if (!pages_done)
                                pages_done = ret;
                        break;
                }
                /* VM_FAULT_RETRY triggered, so seek to the faulting offset */
                pages += ret;
                start += ret << PAGE_SHIFT;

                /*
                 * Repeat on the address that fired VM_FAULT_RETRY
                 * without FAULT_FLAG_ALLOW_RETRY but with
                 * FAULT_FLAG_TRIED.
                 */
                *locked = 1;
                lock_dropped = true;
                down_read(&mm->mmap_sem);
                ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
                                       pages, NULL, NULL);
                if (ret != 1) {
                        BUG_ON(ret > 1);
                        if (!pages_done)
                                pages_done = ret;
                        break;
                }
                nr_pages--;
                pages_done++;
                if (!nr_pages)
                        break;
                pages++;
                start += PAGE_SIZE;
        }
        if (notify_drop && lock_dropped && *locked) {
                /*
                 * We must let the caller know we temporarily dropped the lock
                 * and so the critical section protected by it was lost.
                 */
                up_read(&mm->mmap_sem);
                *locked = 0;
        }
        return pages_done;
}

/*
 * We can leverage the VM_FAULT_RETRY functionality in the page fault
 * paths better by using either get_user_pages_locked() or
 * get_user_pages_unlocked().
 *
 * get_user_pages_locked() is suitable to replace the form:
 *
 *      down_read(&mm->mmap_sem);
 *      do_something()
 *      get_user_pages(tsk, mm, ..., pages, NULL);
 *      up_read(&mm->mmap_sem);
 *
 *  to:
 *
 *      int locked = 1;
 *      down_read(&mm->mmap_sem);
 *      do_something()
 *      get_user_pages_locked(tsk, mm, ..., pages, &locked);
 *      if (locked)
 *          up_read(&mm->mmap_sem);
 */
long get_user_pages_locked(struct task_struct *tsk, struct mm_struct *mm,
                           unsigned long start, unsigned long nr_pages,
                           int write, int force, struct page **pages,
                           int *locked)
{
        return __get_user_pages_locked(tsk, mm, start, nr_pages, write, force,
                                       pages, NULL, locked, true, FOLL_TOUCH);
}
EXPORT_SYMBOL(get_user_pages_locked);

/*
 * Same as get_user_pages_unlocked(...., FOLL_TOUCH) but it allows to
 * pass additional gup_flags as last parameter (like FOLL_HWPOISON).
 *
 * NOTE: here FOLL_TOUCH is not set implicitly and must be set by the
 * caller if required (just like with __get_user_pages). "FOLL_GET",
 * "FOLL_WRITE" and "FOLL_FORCE" are set implicitly as needed
 * according to the parameters "pages", "write", "force"
 * respectively.
 */
__always_inline long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
                                               unsigned long start, unsigned long nr_pages,
                                               int write, int force, struct page **pages,
                                               unsigned int gup_flags)
{
        long ret;
        int locked = 1;
        down_read(&mm->mmap_sem);
        ret = __get_user_pages_locked(tsk, mm, start, nr_pages, write, force,
                                      pages, NULL, &locked, false, gup_flags);
        if (locked)
                up_read(&mm->mmap_sem);
        return ret;
}
EXPORT_SYMBOL(__get_user_pages_unlocked);

/*
 * get_user_pages_unlocked() is suitable to replace the form:
 *
 *      down_read(&mm->mmap_sem);
 *      get_user_pages(tsk, mm, ..., pages, NULL);
 *      up_read(&mm->mmap_sem);
 *
 *  with:
 *
 *      get_user_pages_unlocked(tsk, mm, ..., pages);
 *
 * It is functionally equivalent to get_user_pages_fast so
 * get_user_pages_fast should be used instead, if the two parameters
 * "tsk" and "mm" are respectively equal to current and current->mm,
 * or if "force" shall be set to 1 (get_user_pages_fast misses the
 * "force" parameter).
 */
long get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
                             unsigned long start, unsigned long nr_pages,
                             int write, int force, struct page **pages)
{
        return __get_user_pages_unlocked(tsk, mm, start, nr_pages, write,
                                         force, pages, FOLL_TOUCH);
}
EXPORT_SYMBOL(get_user_pages_unlocked);

/*
 * get_user_pages_remote() - pin user pages in memory
 * @tsk:        the task_struct to use for page fault accounting, or
 *              NULL if faults are not to be recorded.
 * @mm:         mm_struct of target mm
 * @start:      starting user address
 * @nr_pages:   number of pages from start to pin
 * @write:      whether pages will be written to by the caller
 * @force:      whether to force write access even if user mapping is
 *              readonly. This will result in the page being COWed even
 *              in MAP_SHARED mappings. You do not want this.
 * @pages:      array that receives pointers to the pages pinned.
 *              Should be at least nr_pages long. Or NULL, if caller
 *              only intends to ensure the pages are faulted in.
 * @vmas:       array of pointers to vmas corresponding to each page.
 *              Or NULL if the caller does not require them.
 *
 * Returns number of pages pinned. This may be fewer than the number
 * requested. If nr_pages is 0 or negative, returns 0. If no pages
 * were pinned, returns -errno. Each page returned must be released
 * with a put_page() call when it is finished with. vmas will only
 * remain valid while mmap_sem is held.
 *
 * Must be called with mmap_sem held for read or write.
 *
 * get_user_pages walks a process's page tables and takes a reference to
 * each struct page that each user address corresponds to at a given
 * instant. That is, it takes the page that would be accessed if a user
 * thread accesses the given user virtual address at that instant.
 *
 * This does not guarantee that the page exists in the user mappings when
 * get_user_pages returns, and there may even be a completely different
 * page there in some cases (eg. if mmapped pagecache has been invalidated
 * and subsequently re faulted). However it does guarantee that the page
 * won't be freed completely. And mostly callers simply care that the page
 * contains data that was valid *at some point in time*. Typically, an IO
 * or similar operation cannot guarantee anything stronger anyway because
 * locks can't be held over the syscall boundary.
 *
 * If write=0, the page must not be written to. If the page is written to,
 * set_page_dirty (or set_page_dirty_lock, as appropriate) must be called
 * after the page is finished with, and before put_page is called.
 *
 * get_user_pages is typically used for fewer-copy IO operations, to get a
 * handle on the memory by some means other than accesses via the user virtual
 * addresses. The pages may be submitted for DMA to devices or accessed via
 * their kernel linear mapping (via the kmap APIs). Care should be taken to
 * use the correct cache flushing APIs.
 *
 * See also get_user_pages_fast, for performance critical applications.
 *
 * get_user_pages should be phased out in favor of
 * get_user_pages_locked|unlocked or get_user_pages_fast. Nothing
 * should use get_user_pages because it cannot pass
 * FAULT_FLAG_ALLOW_RETRY to handle_mm_fault.
 */
long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
                unsigned long start, unsigned long nr_pages,
                int write, int force, struct page **pages,
                struct vm_area_struct **vmas)
{
        return __get_user_pages_locked(tsk, mm, start, nr_pages, write, force,
                                       pages, vmas, NULL, false,
                                       FOLL_TOUCH | FOLL_REMOTE);
}
EXPORT_SYMBOL(get_user_pages_remote);

/*
 * This is the same as get_user_pages_remote() for the time
 * being.
 */
long get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                unsigned long start, unsigned long nr_pages,
                int write, int force, struct page **pages,
                struct vm_area_struct **vmas)
{
        return __get_user_pages_locked(tsk, mm, start, nr_pages,
                                       write, force, pages, vmas, NULL, false,
                                       FOLL_TOUCH);
}
EXPORT_SYMBOL(get_user_pages);

/**
 * get_dump_page() - pin user page in memory while writing it to core dump
 * @addr: user address
 *
 * Returns struct page pointer of user page pinned for dump,
 * to be freed afterwards by page_cache_release() or put_page().
 *
 * Returns NULL on any kind of failure - a hole must then be inserted into
 * the corefile, to preserve alignment with its headers; and also returns
 * NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
 * allowing a hole to be left in the corefile to save diskspace.
 *
 * Called without mmap_sem, but after all other threads have been killed.
 */
#ifdef CONFIG_ELF_CORE
struct page *get_dump_page(unsigned long addr)
{
        struct vm_area_struct *vma;
        struct page *page;

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