Merge tag 'trace-printf-v6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/trace...

[drm/drm-misc.git] / mm / madvise.c

// SPDX-License-Identifier: GPL-2.0
/*
 *      linux/mm/madvise.c
 *
 * Copyright (C) 1999  Linus Torvalds
 * Copyright (C) 2002  Christoph Hellwig
 */

#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/syscalls.h>
#include <linux/mempolicy.h>
#include <linux/page-isolation.h>
#include <linux/page_idle.h>
#include <linux/userfaultfd_k.h>
#include <linux/hugetlb.h>
#include <linux/falloc.h>
#include <linux/fadvise.h>
#include <linux/sched.h>
#include <linux/sched/mm.h>
#include <linux/mm_inline.h>
#include <linux/string.h>
#include <linux/uio.h>
#include <linux/ksm.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <linux/pagewalk.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/shmem_fs.h>
#include <linux/mmu_notifier.h>

#include <asm/tlb.h>

#include "internal.h"
#include "swap.h"

/*
 * Maximum number of attempts we make to install guard pages before we give up
 * and return -ERESTARTNOINTR to have userspace try again.
 */
#define MAX_MADVISE_GUARD_RETRIES 3

struct madvise_walk_private {
        struct mmu_gather *tlb;
        bool pageout;
};

/*
 * Any behaviour which results in changes to the vma->vm_flags needs to
 * take mmap_lock for writing. Others, which simply traverse vmas, need
 * to only take it for reading.
 */
static int madvise_need_mmap_write(int behavior)
{
        switch (behavior) {
        case MADV_REMOVE:
        case MADV_WILLNEED:
        case MADV_DONTNEED:
        case MADV_DONTNEED_LOCKED:
        case MADV_COLD:
        case MADV_PAGEOUT:
        case MADV_FREE:
        case MADV_POPULATE_READ:
        case MADV_POPULATE_WRITE:
        case MADV_COLLAPSE:
        case MADV_GUARD_INSTALL:
        case MADV_GUARD_REMOVE:
                return 0;
        default:
                /* be safe, default to 1. list exceptions explicitly */
                return 1;
        }
}

#ifdef CONFIG_ANON_VMA_NAME
struct anon_vma_name *anon_vma_name_alloc(const char *name)
{
        struct anon_vma_name *anon_name;
        size_t count;

        /* Add 1 for NUL terminator at the end of the anon_name->name */
        count = strlen(name) + 1;
        anon_name = kmalloc(struct_size(anon_name, name, count), GFP_KERNEL);
        if (anon_name) {
                kref_init(&anon_name->kref);
                memcpy(anon_name->name, name, count);
        }

        return anon_name;
}

void anon_vma_name_free(struct kref *kref)
{
        struct anon_vma_name *anon_name =
                        container_of(kref, struct anon_vma_name, kref);
        kfree(anon_name);
}

struct anon_vma_name *anon_vma_name(struct vm_area_struct *vma)
{
        mmap_assert_locked(vma->vm_mm);

        return vma->anon_name;
}

/* mmap_lock should be write-locked */
static int replace_anon_vma_name(struct vm_area_struct *vma,
                                 struct anon_vma_name *anon_name)
{
        struct anon_vma_name *orig_name = anon_vma_name(vma);

        if (!anon_name) {
                vma->anon_name = NULL;
                anon_vma_name_put(orig_name);
                return 0;
        }

        if (anon_vma_name_eq(orig_name, anon_name))
                return 0;

        vma->anon_name = anon_vma_name_reuse(anon_name);
        anon_vma_name_put(orig_name);

        return 0;
}
#else /* CONFIG_ANON_VMA_NAME */
static int replace_anon_vma_name(struct vm_area_struct *vma,
                                 struct anon_vma_name *anon_name)
{
        if (anon_name)
                return -EINVAL;

        return 0;
}
#endif /* CONFIG_ANON_VMA_NAME */
/*
 * Update the vm_flags on region of a vma, splitting it or merging it as
 * necessary.  Must be called with mmap_lock held for writing;
 * Caller should ensure anon_name stability by raising its refcount even when
 * anon_name belongs to a valid vma because this function might free that vma.
 */
static int madvise_update_vma(struct vm_area_struct *vma,
                              struct vm_area_struct **prev, unsigned long start,
                              unsigned long end, unsigned long new_flags,
                              struct anon_vma_name *anon_name)
{
        struct mm_struct *mm = vma->vm_mm;
        int error;
        VMA_ITERATOR(vmi, mm, start);

        if (new_flags == vma->vm_flags && anon_vma_name_eq(anon_vma_name(vma), anon_name)) {
                *prev = vma;
                return 0;
        }

        vma = vma_modify_flags_name(&vmi, *prev, vma, start, end, new_flags,
                                    anon_name);
        if (IS_ERR(vma))
                return PTR_ERR(vma);

        *prev = vma;

        /* vm_flags is protected by the mmap_lock held in write mode. */
        vma_start_write(vma);
        vm_flags_reset(vma, new_flags);
        if (!vma->vm_file || vma_is_anon_shmem(vma)) {
                error = replace_anon_vma_name(vma, anon_name);
                if (error)
                        return error;
        }

        return 0;
}

#ifdef CONFIG_SWAP
static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
                unsigned long end, struct mm_walk *walk)
{
        struct vm_area_struct *vma = walk->private;
        struct swap_iocb *splug = NULL;
        pte_t *ptep = NULL;
        spinlock_t *ptl;
        unsigned long addr;

        for (addr = start; addr < end; addr += PAGE_SIZE) {
                pte_t pte;
                swp_entry_t entry;
                struct folio *folio;

                if (!ptep++) {
                        ptep = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
                        if (!ptep)
                                break;
                }

                pte = ptep_get(ptep);
                if (!is_swap_pte(pte))
                        continue;
                entry = pte_to_swp_entry(pte);
                if (unlikely(non_swap_entry(entry)))
                        continue;

                pte_unmap_unlock(ptep, ptl);
                ptep = NULL;

                folio = read_swap_cache_async(entry, GFP_HIGHUSER_MOVABLE,
                                             vma, addr, &splug);
                if (folio)
                        folio_put(folio);
        }

        if (ptep)
                pte_unmap_unlock(ptep, ptl);
        swap_read_unplug(splug);
        cond_resched();

        return 0;
}

static const struct mm_walk_ops swapin_walk_ops = {
        .pmd_entry              = swapin_walk_pmd_entry,
        .walk_lock              = PGWALK_RDLOCK,
};

static void shmem_swapin_range(struct vm_area_struct *vma,
                unsigned long start, unsigned long end,
                struct address_space *mapping)
{
        XA_STATE(xas, &mapping->i_pages, linear_page_index(vma, start));
        pgoff_t end_index = linear_page_index(vma, end) - 1;
        struct folio *folio;
        struct swap_iocb *splug = NULL;

        rcu_read_lock();
        xas_for_each(&xas, folio, end_index) {
                unsigned long addr;
                swp_entry_t entry;

                if (!xa_is_value(folio))
                        continue;
                entry = radix_to_swp_entry(folio);
                /* There might be swapin error entries in shmem mapping. */
                if (non_swap_entry(entry))
                        continue;

                addr = vma->vm_start +
                        ((xas.xa_index - vma->vm_pgoff) << PAGE_SHIFT);
                xas_pause(&xas);
                rcu_read_unlock();

                folio = read_swap_cache_async(entry, mapping_gfp_mask(mapping),
                                             vma, addr, &splug);
                if (folio)
                        folio_put(folio);

                rcu_read_lock();
        }
        rcu_read_unlock();
        swap_read_unplug(splug);
}
#endif          /* CONFIG_SWAP */

/*
 * Schedule all required I/O operations.  Do not wait for completion.
 */
static long madvise_willneed(struct vm_area_struct *vma,
                             struct vm_area_struct **prev,
                             unsigned long start, unsigned long end)
{
        struct mm_struct *mm = vma->vm_mm;
        struct file *file = vma->vm_file;
        loff_t offset;

        *prev = vma;
#ifdef CONFIG_SWAP
        if (!file) {
                walk_page_range(vma->vm_mm, start, end, &swapin_walk_ops, vma);
                lru_add_drain(); /* Push any new pages onto the LRU now */
                return 0;
        }

        if (shmem_mapping(file->f_mapping)) {
                shmem_swapin_range(vma, start, end, file->f_mapping);
                lru_add_drain(); /* Push any new pages onto the LRU now */
                return 0;
        }
#else
        if (!file)
                return -EBADF;
#endif

        if (IS_DAX(file_inode(file))) {
                /* no bad return value, but ignore advice */
                return 0;
        }

        /*
         * Filesystem's fadvise may need to take various locks.  We need to
         * explicitly grab a reference because the vma (and hence the
         * vma's reference to the file) can go away as soon as we drop
         * mmap_lock.
         */
        *prev = NULL;   /* tell sys_madvise we drop mmap_lock */
        get_file(file);
        offset = (loff_t)(start - vma->vm_start)
                        + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
        mmap_read_unlock(mm);
        vfs_fadvise(file, offset, end - start, POSIX_FADV_WILLNEED);
        fput(file);
        mmap_read_lock(mm);
        return 0;
}

static inline bool can_do_file_pageout(struct vm_area_struct *vma)
{
        if (!vma->vm_file)
                return false;
        /*
         * paging out pagecache only for non-anonymous mappings that correspond
         * to the files the calling process could (if tried) open for writing;
         * otherwise we'd be including shared non-exclusive mappings, which
         * opens a side channel.
         */
        return inode_owner_or_capable(&nop_mnt_idmap,
                                      file_inode(vma->vm_file)) ||
               file_permission(vma->vm_file, MAY_WRITE) == 0;
}

static inline int madvise_folio_pte_batch(unsigned long addr, unsigned long end,
                                          struct folio *folio, pte_t *ptep,
                                          pte_t pte, bool *any_young,
                                          bool *any_dirty)
{
        const fpb_t fpb_flags = FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY;
        int max_nr = (end - addr) / PAGE_SIZE;

        return folio_pte_batch(folio, addr, ptep, pte, max_nr, fpb_flags, NULL,
                               any_young, any_dirty);
}

static int madvise_cold_or_pageout_pte_range(pmd_t *pmd,
                                unsigned long addr, unsigned long end,
                                struct mm_walk *walk)
{
        struct madvise_walk_private *private = walk->private;
        struct mmu_gather *tlb = private->tlb;
        bool pageout = private->pageout;
        struct mm_struct *mm = tlb->mm;
        struct vm_area_struct *vma = walk->vma;
        pte_t *start_pte, *pte, ptent;
        spinlock_t *ptl;
        struct folio *folio = NULL;
        LIST_HEAD(folio_list);
        bool pageout_anon_only_filter;
        unsigned int batch_count = 0;
        int nr;

        if (fatal_signal_pending(current))
                return -EINTR;

        pageout_anon_only_filter = pageout && !vma_is_anonymous(vma) &&
                                        !can_do_file_pageout(vma);

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
        if (pmd_trans_huge(*pmd)) {
                pmd_t orig_pmd;
                unsigned long next = pmd_addr_end(addr, end);

                tlb_change_page_size(tlb, HPAGE_PMD_SIZE);
                ptl = pmd_trans_huge_lock(pmd, vma);
                if (!ptl)
                        return 0;

                orig_pmd = *pmd;
                if (is_huge_zero_pmd(orig_pmd))
                        goto huge_unlock;

                if (unlikely(!pmd_present(orig_pmd))) {
                        VM_BUG_ON(thp_migration_supported() &&
                                        !is_pmd_migration_entry(orig_pmd));
                        goto huge_unlock;
                }

                folio = pmd_folio(orig_pmd);

                /* Do not interfere with other mappings of this folio */
                if (folio_likely_mapped_shared(folio))
                        goto huge_unlock;

                if (pageout_anon_only_filter && !folio_test_anon(folio))
                        goto huge_unlock;

                if (next - addr != HPAGE_PMD_SIZE) {
                        int err;

                        folio_get(folio);
                        spin_unlock(ptl);
                        folio_lock(folio);
                        err = split_folio(folio);
                        folio_unlock(folio);
                        folio_put(folio);
                        if (!err)
                                goto regular_folio;
                        return 0;
                }

                if (!pageout && pmd_young(orig_pmd)) {
                        pmdp_invalidate(vma, addr, pmd);
                        orig_pmd = pmd_mkold(orig_pmd);

                        set_pmd_at(mm, addr, pmd, orig_pmd);
                        tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
                }

                folio_clear_referenced(folio);
                folio_test_clear_young(folio);
                if (folio_test_active(folio))
                        folio_set_workingset(folio);
                if (pageout) {
                        if (folio_isolate_lru(folio)) {
                                if (folio_test_unevictable(folio))
                                        folio_putback_lru(folio);
                                else
                                        list_add(&folio->lru, &folio_list);
                        }
                } else
                        folio_deactivate(folio);
huge_unlock:
                spin_unlock(ptl);
                if (pageout)
                        reclaim_pages(&folio_list);
                return 0;
        }

regular_folio:
#endif
        tlb_change_page_size(tlb, PAGE_SIZE);
restart:
        start_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
        if (!start_pte)
                return 0;
        flush_tlb_batched_pending(mm);
        arch_enter_lazy_mmu_mode();
        for (; addr < end; pte += nr, addr += nr * PAGE_SIZE) {
                nr = 1;
                ptent = ptep_get(pte);

                if (++batch_count == SWAP_CLUSTER_MAX) {
                        batch_count = 0;
                        if (need_resched()) {
                                arch_leave_lazy_mmu_mode();
                                pte_unmap_unlock(start_pte, ptl);
                                cond_resched();
                                goto restart;
                        }
                }

                if (pte_none(ptent))
                        continue;

                if (!pte_present(ptent))
                        continue;

                folio = vm_normal_folio(vma, addr, ptent);
                if (!folio || folio_is_zone_device(folio))
                        continue;

                /*
                 * If we encounter a large folio, only split it if it is not
                 * fully mapped within the range we are operating on. Otherwise
                 * leave it as is so that it can be swapped out whole. If we
                 * fail to split a folio, leave it in place and advance to the
                 * next pte in the range.
                 */
                if (folio_test_large(folio)) {
                        bool any_young;

                        nr = madvise_folio_pte_batch(addr, end, folio, pte,
                                                     ptent, &any_young, NULL);
                        if (any_young)
                                ptent = pte_mkyoung(ptent);

                        if (nr < folio_nr_pages(folio)) {
                                int err;

                                if (folio_likely_mapped_shared(folio))
                                        continue;
                                if (pageout_anon_only_filter && !folio_test_anon(folio))
                                        continue;
                                if (!folio_trylock(folio))
                                        continue;
                                folio_get(folio);
                                arch_leave_lazy_mmu_mode();
                                pte_unmap_unlock(start_pte, ptl);
                                start_pte = NULL;
                                err = split_folio(folio);
                                folio_unlock(folio);
                                folio_put(folio);
                                start_pte = pte =
                                        pte_offset_map_lock(mm, pmd, addr, &ptl);
                                if (!start_pte)
                                        break;
                                arch_enter_lazy_mmu_mode();
                                if (!err)
                                        nr = 0;
                                continue;
                        }
                }

                /*
                 * Do not interfere with other mappings of this folio and
                 * non-LRU folio. If we have a large folio at this point, we
                 * know it is fully mapped so if its mapcount is the same as its
                 * number of pages, it must be exclusive.
                 */
                if (!folio_test_lru(folio) ||
                    folio_mapcount(folio) != folio_nr_pages(folio))
                        continue;

                if (pageout_anon_only_filter && !folio_test_anon(folio))
                        continue;

                if (!pageout && pte_young(ptent)) {
                        clear_young_dirty_ptes(vma, addr, pte, nr,
                                               CYDP_CLEAR_YOUNG);
                        tlb_remove_tlb_entries(tlb, pte, nr, addr);
                }

                /*
                 * We are deactivating a folio for accelerating reclaiming.
                 * VM couldn't reclaim the folio unless we clear PG_young.
                 * As a side effect, it makes confuse idle-page tracking
                 * because they will miss recent referenced history.
                 */
                folio_clear_referenced(folio);
                folio_test_clear_young(folio);
                if (folio_test_active(folio))
                        folio_set_workingset(folio);
                if (pageout) {
                        if (folio_isolate_lru(folio)) {
                                if (folio_test_unevictable(folio))
                                        folio_putback_lru(folio);
                                else
                                        list_add(&folio->lru, &folio_list);
                        }
                } else
                        folio_deactivate(folio);
        }

        if (start_pte) {
                arch_leave_lazy_mmu_mode();
                pte_unmap_unlock(start_pte, ptl);
        }
        if (pageout)
                reclaim_pages(&folio_list);
        cond_resched();

        return 0;
}

static const struct mm_walk_ops cold_walk_ops = {
        .pmd_entry = madvise_cold_or_pageout_pte_range,
        .walk_lock = PGWALK_RDLOCK,
};

static void madvise_cold_page_range(struct mmu_gather *tlb,
                             struct vm_area_struct *vma,
                             unsigned long addr, unsigned long end)
{
        struct madvise_walk_private walk_private = {
                .pageout = false,
                .tlb = tlb,
        };

        tlb_start_vma(tlb, vma);
        walk_page_range(vma->vm_mm, addr, end, &cold_walk_ops, &walk_private);
        tlb_end_vma(tlb, vma);
}

static inline bool can_madv_lru_vma(struct vm_area_struct *vma)
{
        return !(vma->vm_flags & (VM_LOCKED|VM_PFNMAP|VM_HUGETLB));
}

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

        *prev = vma;
        if (!can_madv_lru_vma(vma))
                return -EINVAL;

        lru_add_drain();
        tlb_gather_mmu(&tlb, mm);
        madvise_cold_page_range(&tlb, vma, start_addr, end_addr);
        tlb_finish_mmu(&tlb);

        return 0;
}

static void madvise_pageout_page_range(struct mmu_gather *tlb,
                             struct vm_area_struct *vma,
                             unsigned long addr, unsigned long end)
{
        struct madvise_walk_private walk_private = {
                .pageout = true,
                .tlb = tlb,
        };

        tlb_start_vma(tlb, vma);
        walk_page_range(vma->vm_mm, addr, end, &cold_walk_ops, &walk_private);
        tlb_end_vma(tlb, vma);
}

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

        *prev = vma;
        if (!can_madv_lru_vma(vma))
                return -EINVAL;

        /*
         * If the VMA belongs to a private file mapping, there can be private
         * dirty pages which can be paged out if even this process is neither
         * owner nor write capable of the file. We allow private file mappings
         * further to pageout dirty anon pages.
         */
        if (!vma_is_anonymous(vma) && (!can_do_file_pageout(vma) &&
                                (vma->vm_flags & VM_MAYSHARE)))
                return 0;

        lru_add_drain();
        tlb_gather_mmu(&tlb, mm);
        madvise_pageout_page_range(&tlb, vma, start_addr, end_addr);
        tlb_finish_mmu(&tlb);

        return 0;
}

static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr,
                                unsigned long end, struct mm_walk *walk)

{
        const cydp_t cydp_flags = CYDP_CLEAR_YOUNG | CYDP_CLEAR_DIRTY;
        struct mmu_gather *tlb = walk->private;
        struct mm_struct *mm = tlb->mm;
        struct vm_area_struct *vma = walk->vma;
        spinlock_t *ptl;
        pte_t *start_pte, *pte, ptent;
        struct folio *folio;
        int nr_swap = 0;
        unsigned long next;
        int nr, max_nr;

        next = pmd_addr_end(addr, end);
        if (pmd_trans_huge(*pmd))
                if (madvise_free_huge_pmd(tlb, vma, pmd, addr, next))
                        return 0;

        tlb_change_page_size(tlb, PAGE_SIZE);
        start_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
        if (!start_pte)
                return 0;
        flush_tlb_batched_pending(mm);
        arch_enter_lazy_mmu_mode();
        for (; addr != end; pte += nr, addr += PAGE_SIZE * nr) {
                nr = 1;
                ptent = ptep_get(pte);

                if (pte_none(ptent))
                        continue;
                /*
                 * If the pte has swp_entry, just clear page table to
                 * prevent swap-in which is more expensive rather than
                 * (page allocation + zeroing).
                 */
                if (!pte_present(ptent)) {
                        swp_entry_t entry;

                        entry = pte_to_swp_entry(ptent);
                        if (!non_swap_entry(entry)) {
                                max_nr = (end - addr) / PAGE_SIZE;
                                nr = swap_pte_batch(pte, max_nr, ptent);
                                nr_swap -= nr;
                                free_swap_and_cache_nr(entry, nr);
                                clear_not_present_full_ptes(mm, addr, pte, nr, tlb->fullmm);
                        } else if (is_hwpoison_entry(entry) ||
                                   is_poisoned_swp_entry(entry)) {
                                pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
                        }
                        continue;
                }

                folio = vm_normal_folio(vma, addr, ptent);
                if (!folio || folio_is_zone_device(folio))
                        continue;

                /*
                 * If we encounter a large folio, only split it if it is not
                 * fully mapped within the range we are operating on. Otherwise
                 * leave it as is so that it can be marked as lazyfree. If we
                 * fail to split a folio, leave it in place and advance to the
                 * next pte in the range.
                 */
                if (folio_test_large(folio)) {
                        bool any_young, any_dirty;

                        nr = madvise_folio_pte_batch(addr, end, folio, pte,
                                                     ptent, &any_young, &any_dirty);

                        if (nr < folio_nr_pages(folio)) {
                                int err;

                                if (folio_likely_mapped_shared(folio))
                                        continue;
                                if (!folio_trylock(folio))
                                        continue;
                                folio_get(folio);
                                arch_leave_lazy_mmu_mode();
                                pte_unmap_unlock(start_pte, ptl);
                                start_pte = NULL;
                                err = split_folio(folio);
                                folio_unlock(folio);
                                folio_put(folio);
                                pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
                                start_pte = pte;
                                if (!start_pte)
                                        break;
                                arch_enter_lazy_mmu_mode();
                                if (!err)
                                        nr = 0;
                                continue;
                        }

                        if (any_young)
                                ptent = pte_mkyoung(ptent);
                        if (any_dirty)
                                ptent = pte_mkdirty(ptent);
                }

                if (folio_test_swapcache(folio) || folio_test_dirty(folio)) {
                        if (!folio_trylock(folio))
                                continue;
                        /*
                         * If we have a large folio at this point, we know it is
                         * fully mapped so if its mapcount is the same as its
                         * number of pages, it must be exclusive.
                         */
                        if (folio_mapcount(folio) != folio_nr_pages(folio)) {
                                folio_unlock(folio);
                                continue;
                        }

                        if (folio_test_swapcache(folio) &&
                            !folio_free_swap(folio)) {
                                folio_unlock(folio);
                                continue;
                        }

                        folio_clear_dirty(folio);
                        folio_unlock(folio);
                }

                if (pte_young(ptent) || pte_dirty(ptent)) {
                        clear_young_dirty_ptes(vma, addr, pte, nr, cydp_flags);
                        tlb_remove_tlb_entries(tlb, pte, nr, addr);
                }
                folio_mark_lazyfree(folio);
        }

        if (nr_swap)
                add_mm_counter(mm, MM_SWAPENTS, nr_swap);
        if (start_pte) {
                arch_leave_lazy_mmu_mode();
                pte_unmap_unlock(start_pte, ptl);
        }
        cond_resched();

        return 0;
}

static const struct mm_walk_ops madvise_free_walk_ops = {
        .pmd_entry              = madvise_free_pte_range,
        .walk_lock              = PGWALK_RDLOCK,
};

static int madvise_free_single_vma(struct vm_area_struct *vma,
                        unsigned long start_addr, unsigned long end_addr)
{
        struct mm_struct *mm = vma->vm_mm;
        struct mmu_notifier_range range;
        struct mmu_gather tlb;

        /* MADV_FREE works for only anon vma at the moment */
        if (!vma_is_anonymous(vma))
                return -EINVAL;

        range.start = max(vma->vm_start, start_addr);
        if (range.start >= vma->vm_end)
                return -EINVAL;
        range.end = min(vma->vm_end, end_addr);
        if (range.end <= vma->vm_start)
                return -EINVAL;
        mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
                                range.start, range.end);

        lru_add_drain();
        tlb_gather_mmu(&tlb, mm);
        update_hiwater_rss(mm);

        mmu_notifier_invalidate_range_start(&range);
        tlb_start_vma(&tlb, vma);
        walk_page_range(vma->vm_mm, range.start, range.end,
                        &madvise_free_walk_ops, &tlb);
        tlb_end_vma(&tlb, vma);
        mmu_notifier_invalidate_range_end(&range);
        tlb_finish_mmu(&tlb);

        return 0;
}

/*
 * Application no longer needs these pages.  If the pages are dirty,
 * it's OK to just throw them away.  The app will be more careful about
 * data it wants to keep.  Be sure to free swap resources too.  The
 * zap_page_range_single call sets things up for shrink_active_list to actually
 * free these pages later if no one else has touched them in the meantime,
 * although we could add these pages to a global reuse list for
 * shrink_active_list to pick up before reclaiming other pages.
 *
 * NB: This interface discards data rather than pushes it out to swap,
 * as some implementations do.  This has performance implications for
 * applications like large transactional databases which want to discard
 * pages in anonymous maps after committing to backing store the data
 * that was kept in them.  There is no reason to write this data out to
 * the swap area if the application is discarding it.
 *
 * An interface that causes the system to free clean pages and flush
 * dirty pages is already available as msync(MS_INVALIDATE).
 */
static long madvise_dontneed_single_vma(struct vm_area_struct *vma,
                                        unsigned long start, unsigned long end)
{
        zap_page_range_single(vma, start, end - start, NULL);
        return 0;
}

static bool madvise_dontneed_free_valid_vma(struct vm_area_struct *vma,
                                            unsigned long start,
                                            unsigned long *end,
                                            int behavior)
{
        if (!is_vm_hugetlb_page(vma)) {
                unsigned int forbidden = VM_PFNMAP;

                if (behavior != MADV_DONTNEED_LOCKED)
                        forbidden |= VM_LOCKED;

                return !(vma->vm_flags & forbidden);
        }

        if (behavior != MADV_DONTNEED && behavior != MADV_DONTNEED_LOCKED)
                return false;
        if (start & ~huge_page_mask(hstate_vma(vma)))
                return false;

        /*
         * Madvise callers expect the length to be rounded up to PAGE_SIZE
         * boundaries, and may be unaware that this VMA uses huge pages.
         * Avoid unexpected data loss by rounding down the number of
         * huge pages freed.
         */
        *end = ALIGN_DOWN(*end, huge_page_size(hstate_vma(vma)));

        return true;
}

static long madvise_dontneed_free(struct vm_area_struct *vma,
                                  struct vm_area_struct **prev,
                                  unsigned long start, unsigned long end,
                                  int behavior)
{
        struct mm_struct *mm = vma->vm_mm;

        *prev = vma;
        if (!madvise_dontneed_free_valid_vma(vma, start, &end, behavior))
                return -EINVAL;

        if (start == end)
                return 0;

        if (!userfaultfd_remove(vma, start, end)) {
                *prev = NULL; /* mmap_lock has been dropped, prev is stale */

                mmap_read_lock(mm);
                vma = vma_lookup(mm, start);
                if (!vma)
                        return -ENOMEM;
                /*
                 * Potential end adjustment for hugetlb vma is OK as
                 * the check below keeps end within vma.
                 */
                if (!madvise_dontneed_free_valid_vma(vma, start, &end,
                                                     behavior))
                        return -EINVAL;
                if (end > vma->vm_end) {
                        /*
                         * Don't fail if end > vma->vm_end. If the old
                         * vma was split while the mmap_lock was
                         * released the effect of the concurrent
                         * operation may not cause madvise() to
                         * have an undefined result. There may be an
                         * adjacent next vma that we'll walk
                         * next. userfaultfd_remove() will generate an
                         * UFFD_EVENT_REMOVE repetition on the
                         * end-vma->vm_end range, but the manager can
                         * handle a repetition fine.
                         */
                        end = vma->vm_end;
                }
                VM_WARN_ON(start >= end);
        }

        if (behavior == MADV_DONTNEED || behavior == MADV_DONTNEED_LOCKED)
                return madvise_dontneed_single_vma(vma, start, end);
        else if (behavior == MADV_FREE)
                return madvise_free_single_vma(vma, start, end);
        else
                return -EINVAL;
}

static long madvise_populate(struct mm_struct *mm, unsigned long start,
                unsigned long end, int behavior)
{
        const bool write = behavior == MADV_POPULATE_WRITE;
        int locked = 1;
        long pages;

        while (start < end) {
                /* Populate (prefault) page tables readable/writable. */
                pages = faultin_page_range(mm, start, end, write, &locked);
                if (!locked) {
                        mmap_read_lock(mm);
                        locked = 1;
                }
                if (pages < 0) {
                        switch (pages) {
                        case -EINTR:
                                return -EINTR;
                        case -EINVAL: /* Incompatible mappings / permissions. */
                                return -EINVAL;
                        case -EHWPOISON:
                                return -EHWPOISON;
                        case -EFAULT: /* VM_FAULT_SIGBUS or VM_FAULT_SIGSEGV */
                                return -EFAULT;
                        default:
                                pr_warn_once("%s: unhandled return value: %ld\n",
                                             __func__, pages);
                                fallthrough;
                        case -ENOMEM: /* No VMA or out of memory. */
                                return -ENOMEM;
                        }
                }
                start += pages * PAGE_SIZE;
        }
        return 0;
}

/*
 * Application wants to free up the pages and associated backing store.
 * This is effectively punching a hole into the middle of a file.
 */
static long madvise_remove(struct vm_area_struct *vma,
                                struct vm_area_struct **prev,
                                unsigned long start, unsigned long end)
{
        loff_t offset;
        int error;
        struct file *f;
        struct mm_struct *mm = vma->vm_mm;

        *prev = NULL;   /* tell sys_madvise we drop mmap_lock */

        if (vma->vm_flags & VM_LOCKED)
                return -EINVAL;

        f = vma->vm_file;

        if (!f || !f->f_mapping || !f->f_mapping->host) {
                        return -EINVAL;
        }

        if (!vma_is_shared_maywrite(vma))
                return -EACCES;

        offset = (loff_t)(start - vma->vm_start)
                        + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);

        /*
         * Filesystem's fallocate may need to take i_rwsem.  We need to
         * explicitly grab a reference because the vma (and hence the
         * vma's reference to the file) can go away as soon as we drop
         * mmap_lock.
         */
        get_file(f);
        if (userfaultfd_remove(vma, start, end)) {
                /* mmap_lock was not released by userfaultfd_remove() */
                mmap_read_unlock(mm);
        }
        error = vfs_fallocate(f,
                                FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
                                offset, end - start);
        fput(f);
        mmap_read_lock(mm);
        return error;
}

static bool is_valid_guard_vma(struct vm_area_struct *vma, bool allow_locked)
{
        vm_flags_t disallowed = VM_SPECIAL | VM_HUGETLB;

        /*
         * A user could lock after setting a guard range but that's fine, as
         * they'd not be able to fault in. The issue arises when we try to zap
         * existing locked VMAs. We don't want to do that.
         */
        if (!allow_locked)
                disallowed |= VM_LOCKED;

        if (!vma_is_anonymous(vma))
                return false;

        if ((vma->vm_flags & (VM_MAYWRITE | disallowed)) != VM_MAYWRITE)
                return false;

        return true;
}

static bool is_guard_pte_marker(pte_t ptent)
{
        return is_pte_marker(ptent) &&
                is_guard_swp_entry(pte_to_swp_entry(ptent));
}

static int guard_install_pud_entry(pud_t *pud, unsigned long addr,
                                   unsigned long next, struct mm_walk *walk)
{
        pud_t pudval = pudp_get(pud);

        /* If huge return >0 so we abort the operation + zap. */
        return pud_trans_huge(pudval) || pud_devmap(pudval);
}

static int guard_install_pmd_entry(pmd_t *pmd, unsigned long addr,
                                   unsigned long next, struct mm_walk *walk)
{
        pmd_t pmdval = pmdp_get(pmd);

        /* If huge return >0 so we abort the operation + zap. */
        return pmd_trans_huge(pmdval) || pmd_devmap(pmdval);
}

static int guard_install_pte_entry(pte_t *pte, unsigned long addr,
                                   unsigned long next, struct mm_walk *walk)
{
        pte_t pteval = ptep_get(pte);
        unsigned long *nr_pages = (unsigned long *)walk->private;

        /* If there is already a guard page marker, we have nothing to do. */
        if (is_guard_pte_marker(pteval)) {
                (*nr_pages)++;

                return 0;
        }

        /* If populated return >0 so we abort the operation + zap. */
        return 1;
}

static int guard_install_set_pte(unsigned long addr, unsigned long next,
                                 pte_t *ptep, struct mm_walk *walk)
{
        unsigned long *nr_pages = (unsigned long *)walk->private;

        /* Simply install a PTE marker, this causes segfault on access. */
        *ptep = make_pte_marker(PTE_MARKER_GUARD);
        (*nr_pages)++;

        return 0;
}

static const struct mm_walk_ops guard_install_walk_ops = {
        .pud_entry              = guard_install_pud_entry,
        .pmd_entry              = guard_install_pmd_entry,
        .pte_entry              = guard_install_pte_entry,
        .install_pte            = guard_install_set_pte,
        .walk_lock              = PGWALK_RDLOCK,
};

static long madvise_guard_install(struct vm_area_struct *vma,
                                 struct vm_area_struct **prev,
                                 unsigned long start, unsigned long end)
{
        long err;
        int i;

        *prev = vma;
        if (!is_valid_guard_vma(vma, /* allow_locked = */false))
                return -EINVAL;

        /*
         * If we install guard markers, then the range is no longer
         * empty from a page table perspective and therefore it's
         * appropriate to have an anon_vma.
         *
         * This ensures that on fork, we copy page tables correctly.
         */
        err = anon_vma_prepare(vma);
        if (err)
                return err;

        /*
         * Optimistically try to install the guard marker pages first. If any
         * non-guard pages are encountered, give up and zap the range before
         * trying again.
         *
         * We try a few times before giving up and releasing back to userland to
         * loop around, releasing locks in the process to avoid contention. This
         * would only happen if there was a great many racing page faults.
         *
         * In most cases we should simply install the guard markers immediately
         * with no zap or looping.
         */
        for (i = 0; i < MAX_MADVISE_GUARD_RETRIES; i++) {
                unsigned long nr_pages = 0;

                /* Returns < 0 on error, == 0 if success, > 0 if zap needed. */
                err = walk_page_range_mm(vma->vm_mm, start, end,
                                         &guard_install_walk_ops, &nr_pages);
                if (err < 0)
                        return err;

                if (err == 0) {
                        unsigned long nr_expected_pages = PHYS_PFN(end - start);

                        VM_WARN_ON(nr_pages != nr_expected_pages);
                        return 0;
                }

                /*
                 * OK some of the range have non-guard pages mapped, zap
                 * them. This leaves existing guard pages in place.
                 */
                zap_page_range_single(vma, start, end - start, NULL);
        }

        /*
         * We were unable to install the guard pages due to being raced by page
         * faults. This should not happen ordinarily. We return to userspace and
         * immediately retry, relieving lock contention.
         */
        return restart_syscall();
}

static int guard_remove_pud_entry(pud_t *pud, unsigned long addr,
                                  unsigned long next, struct mm_walk *walk)
{
        pud_t pudval = pudp_get(pud);

        /* If huge, cannot have guard pages present, so no-op - skip. */
        if (pud_trans_huge(pudval) || pud_devmap(pudval))
                walk->action = ACTION_CONTINUE;

        return 0;
}

static int guard_remove_pmd_entry(pmd_t *pmd, unsigned long addr,
                                  unsigned long next, struct mm_walk *walk)
{
        pmd_t pmdval = pmdp_get(pmd);

        /* If huge, cannot have guard pages present, so no-op - skip. */
        if (pmd_trans_huge(pmdval) || pmd_devmap(pmdval))
                walk->action = ACTION_CONTINUE;

        return 0;
}

static int guard_remove_pte_entry(pte_t *pte, unsigned long addr,
                                  unsigned long next, struct mm_walk *walk)
{
        pte_t ptent = ptep_get(pte);

        if (is_guard_pte_marker(ptent)) {
                /* Simply clear the PTE marker. */
                pte_clear_not_present_full(walk->mm, addr, pte, false);
                update_mmu_cache(walk->vma, addr, pte);
        }

        return 0;
}

static const struct mm_walk_ops guard_remove_walk_ops = {
        .pud_entry              = guard_remove_pud_entry,
        .pmd_entry              = guard_remove_pmd_entry,
        .pte_entry              = guard_remove_pte_entry,
        .walk_lock              = PGWALK_RDLOCK,
};

static long madvise_guard_remove(struct vm_area_struct *vma,
                                 struct vm_area_struct **prev,
                                 unsigned long start, unsigned long end)
{
        *prev = vma;
        /*
         * We're ok with removing guards in mlock()'d ranges, as this is a
         * non-destructive action.
         */
        if (!is_valid_guard_vma(vma, /* allow_locked = */true))
                return -EINVAL;

        return walk_page_range(vma->vm_mm, start, end,
                               &guard_remove_walk_ops, NULL);
}

/*
 * Apply an madvise behavior to a region of a vma.  madvise_update_vma
 * will handle splitting a vm area into separate areas, each area with its own
 * behavior.
 */
static int madvise_vma_behavior(struct vm_area_struct *vma,
                                struct vm_area_struct **prev,
                                unsigned long start, unsigned long end,
                                unsigned long behavior)
{
        int error;
        struct anon_vma_name *anon_name;
        unsigned long new_flags = vma->vm_flags;

        if (unlikely(!can_modify_vma_madv(vma, behavior)))
                return -EPERM;

        switch (behavior) {
        case MADV_REMOVE:
                return madvise_remove(vma, prev, start, end);
        case MADV_WILLNEED:
                return madvise_willneed(vma, prev, start, end);
        case MADV_COLD:
                return madvise_cold(vma, prev, start, end);
        case MADV_PAGEOUT:
                return madvise_pageout(vma, prev, start, end);
        case MADV_FREE:
        case MADV_DONTNEED:
        case MADV_DONTNEED_LOCKED:
                return madvise_dontneed_free(vma, prev, start, end, behavior);
        case MADV_NORMAL:
                new_flags = new_flags & ~VM_RAND_READ & ~VM_SEQ_READ;
                break;
        case MADV_SEQUENTIAL:
                new_flags = (new_flags & ~VM_RAND_READ) | VM_SEQ_READ;
                break;
        case MADV_RANDOM:
                new_flags = (new_flags & ~VM_SEQ_READ) | VM_RAND_READ;
                break;
        case MADV_DONTFORK:
                new_flags |= VM_DONTCOPY;
                break;
        case MADV_DOFORK:
                if (vma->vm_flags & VM_IO)
                        return -EINVAL;
                new_flags &= ~VM_DONTCOPY;
                break;
        case MADV_WIPEONFORK:
                /* MADV_WIPEONFORK is only supported on anonymous memory. */
                if (vma->vm_file || vma->vm_flags & VM_SHARED)
                        return -EINVAL;
                new_flags |= VM_WIPEONFORK;
                break;
        case MADV_KEEPONFORK:
                if (vma->vm_flags & VM_DROPPABLE)
                        return -EINVAL;
                new_flags &= ~VM_WIPEONFORK;
                break;
        case MADV_DONTDUMP:
                new_flags |= VM_DONTDUMP;
                break;
        case MADV_DODUMP:
                if ((!is_vm_hugetlb_page(vma) && new_flags & VM_SPECIAL) ||
                    (vma->vm_flags & VM_DROPPABLE))
                        return -EINVAL;
                new_flags &= ~VM_DONTDUMP;
                break;
        case MADV_MERGEABLE:
        case MADV_UNMERGEABLE:
                error = ksm_madvise(vma, start, end, behavior, &new_flags);
                if (error)
                        goto out;
                break;
        case MADV_HUGEPAGE:
        case MADV_NOHUGEPAGE:
                error = hugepage_madvise(vma, &new_flags, behavior);
                if (error)
                        goto out;
                break;
        case MADV_COLLAPSE:
                return madvise_collapse(vma, prev, start, end);
        case MADV_GUARD_INSTALL:
                return madvise_guard_install(vma, prev, start, end);
        case MADV_GUARD_REMOVE:
                return madvise_guard_remove(vma, prev, start, end);
        }

        anon_name = anon_vma_name(vma);
        anon_vma_name_get(anon_name);
        error = madvise_update_vma(vma, prev, start, end, new_flags,
                                   anon_name);
        anon_vma_name_put(anon_name);

out:
        /*
         * madvise() returns EAGAIN if kernel resources, such as
         * slab, are temporarily unavailable.
         */
        if (error == -ENOMEM)
                error = -EAGAIN;
        return error;
}

#ifdef CONFIG_MEMORY_FAILURE
/*
 * Error injection support for memory error handling.
 */
static int madvise_inject_error(int behavior,
                unsigned long start, unsigned long end)
{
        unsigned long size;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;


        for (; start < end; start += size) {
                unsigned long pfn;
                struct page *page;
                int ret;

                ret = get_user_pages_fast(start, 1, 0, &page);
                if (ret != 1)
                        return ret;
                pfn = page_to_pfn(page);

                /*
                 * When soft offlining hugepages, after migrating the page
                 * we dissolve it, therefore in the second loop "page" will
                 * no longer be a compound page.
                 */
                size = page_size(compound_head(page));

                if (behavior == MADV_SOFT_OFFLINE) {
                        pr_info("Soft offlining pfn %#lx at process virtual address %#lx\n",
                                 pfn, start);
                        ret = soft_offline_page(pfn, MF_COUNT_INCREASED);
                } else {
                        pr_info("Injecting memory failure for pfn %#lx at process virtual address %#lx\n",
                                 pfn, start);
                        ret = memory_failure(pfn, MF_ACTION_REQUIRED | MF_COUNT_INCREASED | MF_SW_SIMULATED);
                        if (ret == -EOPNOTSUPP)
                                ret = 0;
                }

                if (ret)
                        return ret;
        }

        return 0;
}
#endif

static bool
madvise_behavior_valid(int behavior)
{
        switch (behavior) {
        case MADV_DOFORK:
        case MADV_DONTFORK:
        case MADV_NORMAL:
        case MADV_SEQUENTIAL:
        case MADV_RANDOM:
        case MADV_REMOVE:
        case MADV_WILLNEED:
        case MADV_DONTNEED:
        case MADV_DONTNEED_LOCKED:
        case MADV_FREE:
        case MADV_COLD:
        case MADV_PAGEOUT:
        case MADV_POPULATE_READ:
        case MADV_POPULATE_WRITE:
#ifdef CONFIG_KSM
        case MADV_MERGEABLE:
        case MADV_UNMERGEABLE:
#endif
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
        case MADV_HUGEPAGE:
        case MADV_NOHUGEPAGE:
        case MADV_COLLAPSE:
#endif
        case MADV_DONTDUMP:
        case MADV_DODUMP:
        case MADV_WIPEONFORK:
        case MADV_KEEPONFORK:
        case MADV_GUARD_INSTALL:
        case MADV_GUARD_REMOVE:
#ifdef CONFIG_MEMORY_FAILURE
        case MADV_SOFT_OFFLINE:
        case MADV_HWPOISON:
#endif
                return true;

        default:
                return false;
        }
}

/* Can we invoke process_madvise() on a remote mm for the specified behavior? */
static bool process_madvise_remote_valid(int behavior)
{
        switch (behavior) {
        case MADV_COLD:
        case MADV_PAGEOUT:
        case MADV_WILLNEED:
        case MADV_COLLAPSE:
                return true;
        default:
                return false;
        }
}

/*
 * Walk the vmas in range [start,end), and call the visit function on each one.
 * The visit function will get start and end parameters that cover the overlap
 * between the current vma and the original range.  Any unmapped regions in the
 * original range will result in this function returning -ENOMEM while still
 * calling the visit function on all of the existing vmas in the range.
 * Must be called with the mmap_lock held for reading or writing.
 */
static
int madvise_walk_vmas(struct mm_struct *mm, unsigned long start,
                      unsigned long end, unsigned long arg,
                      int (*visit)(struct vm_area_struct *vma,
                                   struct vm_area_struct **prev, unsigned long start,
                                   unsigned long end, unsigned long arg))
{
        struct vm_area_struct *vma;
        struct vm_area_struct *prev;
        unsigned long tmp;
        int unmapped_error = 0;

        /*
         * If the interval [start,end) covers some unmapped address
         * ranges, just ignore them, but return -ENOMEM at the end.
         * - different from the way of handling in mlock etc.
         */
        vma = find_vma_prev(mm, start, &prev);
        if (vma && start > vma->vm_start)
                prev = vma;

        for (;;) {
                int error;

                /* Still start < end. */
                if (!vma)
                        return -ENOMEM;

                /* Here start < (end|vma->vm_end). */
                if (start < vma->vm_start) {
                        unmapped_error = -ENOMEM;
                        start = vma->vm_start;
                        if (start >= end)
                                break;
                }

                /* Here vma->vm_start <= start < (end|vma->vm_end) */
                tmp = vma->vm_end;
                if (end < tmp)
                        tmp = end;

                /* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
                error = visit(vma, &prev, start, tmp, arg);
                if (error)
                        return error;
                start = tmp;
                if (prev && start < prev->vm_end)
                        start = prev->vm_end;
                if (start >= end)
                        break;
                if (prev)
                        vma = find_vma(mm, prev->vm_end);
                else    /* madvise_remove dropped mmap_lock */
                        vma = find_vma(mm, start);
        }

        return unmapped_error;
}

#ifdef CONFIG_ANON_VMA_NAME
static int madvise_vma_anon_name(struct vm_area_struct *vma,
                                 struct vm_area_struct **prev,
                                 unsigned long start, unsigned long end,
                                 unsigned long anon_name)
{
        int error;

        /* Only anonymous mappings can be named */
        if (vma->vm_file && !vma_is_anon_shmem(vma))
                return -EBADF;

        error = madvise_update_vma(vma, prev, start, end, vma->vm_flags,
                                   (struct anon_vma_name *)anon_name);

        /*
         * madvise() returns EAGAIN if kernel resources, such as
         * slab, are temporarily unavailable.
         */
        if (error == -ENOMEM)
                error = -EAGAIN;
        return error;
}

int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
                          unsigned long len_in, struct anon_vma_name *anon_name)
{
        unsigned long end;
        unsigned long len;

        if (start & ~PAGE_MASK)
                return -EINVAL;
        len = (len_in + ~PAGE_MASK) & PAGE_MASK;

        /* Check to see whether len was rounded up from small -ve to zero */
        if (len_in && !len)
                return -EINVAL;

        end = start + len;
        if (end < start)
                return -EINVAL;

        if (end == start)
                return 0;

        return madvise_walk_vmas(mm, start, end, (unsigned long)anon_name,
                                 madvise_vma_anon_name);
}
#endif /* CONFIG_ANON_VMA_NAME */
/*
 * The madvise(2) system call.
 *
 * Applications can use madvise() to advise the kernel how it should
 * handle paging I/O in this VM area.  The idea is to help the kernel
 * use appropriate read-ahead and caching techniques.  The information
 * provided is advisory only, and can be safely disregarded by the
 * kernel without affecting the correct operation of the application.
 *
 * behavior values:
 *  MADV_NORMAL - the default behavior is to read clusters.  This
 *              results in some read-ahead and read-behind.
 *  MADV_RANDOM - the system should read the minimum amount of data
 *              on any access, since it is unlikely that the appli-
 *              cation will need more than what it asks for.
 *  MADV_SEQUENTIAL - pages in the given range will probably be accessed
 *              once, so they can be aggressively read ahead, and
 *              can be freed soon after they are accessed.
 *  MADV_WILLNEED - the application is notifying the system to read
 *              some pages ahead.
 *  MADV_DONTNEED - the application is finished with the given range,
 *              so the kernel can free resources associated with it.
 *  MADV_FREE - the application marks pages in the given range as lazy free,
 *              where actual purges are postponed until memory pressure happens.
 *  MADV_REMOVE - the application wants to free up the given range of
 *              pages and associated backing store.
 *  MADV_DONTFORK - omit this area from child's address space when forking:
 *              typically, to avoid COWing pages pinned by get_user_pages().
 *  MADV_DOFORK - cancel MADV_DONTFORK: no longer omit this area when forking.
 *  MADV_WIPEONFORK - present the child process with zero-filled memory in this
 *              range after a fork.
 *  MADV_KEEPONFORK - undo the effect of MADV_WIPEONFORK
 *  MADV_HWPOISON - trigger memory error handler as if the given memory range
 *              were corrupted by unrecoverable hardware memory failure.
 *  MADV_SOFT_OFFLINE - try to soft-offline the given range of memory.
 *  MADV_MERGEABLE - the application recommends that KSM try to merge pages in
 *              this area with pages of identical content from other such areas.
 *  MADV_UNMERGEABLE- cancel MADV_MERGEABLE: no longer merge pages with others.
 *  MADV_HUGEPAGE - the application wants to back the given range by transparent
 *              huge pages in the future. Existing pages might be coalesced and
 *              new pages might be allocated as THP.
 *  MADV_NOHUGEPAGE - mark the given range as not worth being backed by
 *              transparent huge pages so the existing pages will not be
 *              coalesced into THP and new pages will not be allocated as THP.
 *  MADV_COLLAPSE - synchronously coalesce pages into new THP.
 *  MADV_DONTDUMP - the application wants to prevent pages in the given range
 *              from being included in its core dump.
 *  MADV_DODUMP - cancel MADV_DONTDUMP: no longer exclude from core dump.
 *  MADV_COLD - the application is not expected to use this memory soon,
 *              deactivate pages in this range so that they can be reclaimed
 *              easily if memory pressure happens.
 *  MADV_PAGEOUT - the application is not expected to use this memory soon,
 *              page out the pages in this range immediately.
 *  MADV_POPULATE_READ - populate (prefault) page tables readable by
 *              triggering read faults if required
 *  MADV_POPULATE_WRITE - populate (prefault) page tables writable by
 *              triggering write faults if required
 *
 * return values:
 *  zero    - success
 *  -EINVAL - start + len < 0, start is not page-aligned,
 *              "behavior" is not a valid value, or application
 *              is attempting to release locked or shared pages,
 *              or the specified address range includes file, Huge TLB,
 *              MAP_SHARED or VMPFNMAP range.
 *  -ENOMEM - addresses in the specified range are not currently
 *              mapped, or are outside the AS of the process.
 *  -EIO    - an I/O error occurred while paging in data.
 *  -EBADF  - map exists, but area maps something that isn't a file.
 *  -EAGAIN - a kernel resource was temporarily unavailable.
 *  -EPERM  - memory is sealed.
 */
int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int behavior)
{
        unsigned long end;
        int error;
        int write;
        size_t len;
        struct blk_plug plug;

        if (!madvise_behavior_valid(behavior))
                return -EINVAL;

        if (!PAGE_ALIGNED(start))
                return -EINVAL;
        len = PAGE_ALIGN(len_in);

        /* Check to see whether len was rounded up from small -ve to zero */
        if (len_in && !len)
                return -EINVAL;

        end = start + len;
        if (end < start)
                return -EINVAL;

        if (end == start)
                return 0;

#ifdef CONFIG_MEMORY_FAILURE
        if (behavior == MADV_HWPOISON || behavior == MADV_SOFT_OFFLINE)
                return madvise_inject_error(behavior, start, start + len_in);
#endif

        write = madvise_need_mmap_write(behavior);
        if (write) {
                if (mmap_write_lock_killable(mm))
                        return -EINTR;
        } else {
                mmap_read_lock(mm);
        }

        start = untagged_addr_remote(mm, start);
        end = start + len;

        blk_start_plug(&plug);
        switch (behavior) {
        case MADV_POPULATE_READ:
        case MADV_POPULATE_WRITE:
                error = madvise_populate(mm, start, end, behavior);
                break;
        default:
                error = madvise_walk_vmas(mm, start, end, behavior,
                                          madvise_vma_behavior);
                break;
        }
        blk_finish_plug(&plug);

        if (write)
                mmap_write_unlock(mm);
        else
                mmap_read_unlock(mm);

        return error;
}

SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
{
        return do_madvise(current->mm, start, len_in, behavior);
}

/* Perform an madvise operation over a vector of addresses and lengths. */
static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter,
                              int behavior)
{
        ssize_t ret = 0;
        size_t total_len;

        total_len = iov_iter_count(iter);

        while (iov_iter_count(iter)) {
                ret = do_madvise(mm, (unsigned long)iter_iov_addr(iter),
                                 iter_iov_len(iter), behavior);
                /*
                 * An madvise operation is attempting to restart the syscall,
                 * but we cannot proceed as it would not be correct to repeat
                 * the operation in aggregate, and would be surprising to the
                 * user.
                 *
                 * As we have already dropped locks, it is safe to just loop and
                 * try again. We check for fatal signals in case we need exit
                 * early anyway.
                 */
                if (ret == -ERESTARTNOINTR) {
                        if (fatal_signal_pending(current)) {
                                ret = -EINTR;
                                break;
                        }
                        continue;
                }
                if (ret < 0)
                        break;
                iov_iter_advance(iter, iter_iov_len(iter));
        }

        ret = (total_len - iov_iter_count(iter)) ? : ret;

        return ret;
}

SYSCALL_DEFINE5(process_madvise, int, pidfd, const struct iovec __user *, vec,
                size_t, vlen, int, behavior, unsigned int, flags)
{
        ssize_t ret;
        struct iovec iovstack[UIO_FASTIOV];
        struct iovec *iov = iovstack;
        struct iov_iter iter;
        struct task_struct *task;
        struct mm_struct *mm;
        unsigned int f_flags;

        if (flags != 0) {
                ret = -EINVAL;
                goto out;
        }

        ret = import_iovec(ITER_DEST, vec, vlen, ARRAY_SIZE(iovstack), &iov, &iter);
        if (ret < 0)
                goto out;

        task = pidfd_get_task(pidfd, &f_flags);
        if (IS_ERR(task)) {
                ret = PTR_ERR(task);
                goto free_iov;
        }

        /* Require PTRACE_MODE_READ to avoid leaking ASLR metadata. */
        mm = mm_access(task, PTRACE_MODE_READ_FSCREDS);
        if (IS_ERR(mm)) {
                ret = PTR_ERR(mm);
                goto release_task;
        }

        /*
         * We need only perform this check if we are attempting to manipulate a
         * remote process's address space.
         */
        if (mm != current->mm && !process_madvise_remote_valid(behavior)) {
                ret = -EINVAL;
                goto release_mm;
        }

        /*
         * Require CAP_SYS_NICE for influencing process performance. Note that
         * only non-destructive hints are currently supported for remote
         * processes.
         */
        if (mm != current->mm && !capable(CAP_SYS_NICE)) {
                ret = -EPERM;
                goto release_mm;
        }

        ret = vector_madvise(mm, &iter, behavior);

release_mm:
        mmput(mm);
release_task:
        put_task_struct(task);
free_iov:
        kfree(iov);
out:
        return ret;
}