Merge tag 'hwmon-for-v6.13-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git...

[linux.git] / mm / mremap.c

// SPDX-License-Identifier: GPL-2.0
/*
 *      mm/mremap.c
 *
 *      (C) Copyright 1996 Linus Torvalds
 *
 *      Address space accounting code   <alan@lxorguk.ukuu.org.uk>
 *      (C) Copyright 2002 Red Hat Inc, All Rights Reserved
 */

#include <linux/mm.h>
#include <linux/mm_inline.h>
#include <linux/hugetlb.h>
#include <linux/shm.h>
#include <linux/ksm.h>
#include <linux/mman.h>
#include <linux/swap.h>
#include <linux/capability.h>
#include <linux/fs.h>
#include <linux/swapops.h>
#include <linux/highmem.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/mmu_notifier.h>
#include <linux/uaccess.h>
#include <linux/userfaultfd_k.h>
#include <linux/mempolicy.h>

#include <asm/cacheflush.h>
#include <asm/tlb.h>
#include <asm/pgalloc.h>

#include "internal.h"

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

        pgd = pgd_offset(mm, addr);
        if (pgd_none_or_clear_bad(pgd))
                return NULL;

        p4d = p4d_offset(pgd, addr);
        if (p4d_none_or_clear_bad(p4d))
                return NULL;

        pud = pud_offset(p4d, addr);
        if (pud_none_or_clear_bad(pud))
                return NULL;

        return pud;
}

static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
{
        pud_t *pud;
        pmd_t *pmd;

        pud = get_old_pud(mm, addr);
        if (!pud)
                return NULL;

        pmd = pmd_offset(pud, addr);
        if (pmd_none(*pmd))
                return NULL;

        return pmd;
}

static pud_t *alloc_new_pud(struct mm_struct *mm, struct vm_area_struct *vma,
                            unsigned long addr)
{
        pgd_t *pgd;
        p4d_t *p4d;

        pgd = pgd_offset(mm, addr);
        p4d = p4d_alloc(mm, pgd, addr);
        if (!p4d)
                return NULL;

        return pud_alloc(mm, p4d, addr);
}

static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
                            unsigned long addr)
{
        pud_t *pud;
        pmd_t *pmd;

        pud = alloc_new_pud(mm, vma, addr);
        if (!pud)
                return NULL;

        pmd = pmd_alloc(mm, pud, addr);
        if (!pmd)
                return NULL;

        VM_BUG_ON(pmd_trans_huge(*pmd));

        return pmd;
}

static void take_rmap_locks(struct vm_area_struct *vma)
{
        if (vma->vm_file)
                i_mmap_lock_write(vma->vm_file->f_mapping);
        if (vma->anon_vma)
                anon_vma_lock_write(vma->anon_vma);
}

static void drop_rmap_locks(struct vm_area_struct *vma)
{
        if (vma->anon_vma)
                anon_vma_unlock_write(vma->anon_vma);
        if (vma->vm_file)
                i_mmap_unlock_write(vma->vm_file->f_mapping);
}

static pte_t move_soft_dirty_pte(pte_t pte)
{
        /*
         * Set soft dirty bit so we can notice
         * in userspace the ptes were moved.
         */
#ifdef CONFIG_MEM_SOFT_DIRTY
        if (pte_present(pte))
                pte = pte_mksoft_dirty(pte);
        else if (is_swap_pte(pte))
                pte = pte_swp_mksoft_dirty(pte);
#endif
        return pte;
}

static int move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
                unsigned long old_addr, unsigned long old_end,
                struct vm_area_struct *new_vma, pmd_t *new_pmd,
                unsigned long new_addr, bool need_rmap_locks)
{
        struct mm_struct *mm = vma->vm_mm;
        pte_t *old_pte, *new_pte, pte;
        pmd_t dummy_pmdval;
        spinlock_t *old_ptl, *new_ptl;
        bool force_flush = false;
        unsigned long len = old_end - old_addr;
        int err = 0;

        /*
         * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
         * locks to ensure that rmap will always observe either the old or the
         * new ptes. This is the easiest way to avoid races with
         * truncate_pagecache(), page migration, etc...
         *
         * When need_rmap_locks is false, we use other ways to avoid
         * such races:
         *
         * - During exec() shift_arg_pages(), we use a specially tagged vma
         *   which rmap call sites look for using vma_is_temporary_stack().
         *
         * - During mremap(), new_vma is often known to be placed after vma
         *   in rmap traversal order. This ensures rmap will always observe
         *   either the old pte, or the new pte, or both (the page table locks
         *   serialize access to individual ptes, but only rmap traversal
         *   order guarantees that we won't miss both the old and new ptes).
         */
        if (need_rmap_locks)
                take_rmap_locks(vma);

        /*
         * We don't have to worry about the ordering of src and dst
         * pte locks because exclusive mmap_lock prevents deadlock.
         */
        old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
        if (!old_pte) {
                err = -EAGAIN;
                goto out;
        }
        /*
         * Now new_pte is none, so hpage_collapse_scan_file() path can not find
         * this by traversing file->f_mapping, so there is no concurrency with
         * retract_page_tables(). In addition, we already hold the exclusive
         * mmap_lock, so this new_pte page is stable, so there is no need to get
         * pmdval and do pmd_same() check.
         */
        new_pte = pte_offset_map_rw_nolock(mm, new_pmd, new_addr, &dummy_pmdval,
                                           &new_ptl);
        if (!new_pte) {
                pte_unmap_unlock(old_pte, old_ptl);
                err = -EAGAIN;
                goto out;
        }
        if (new_ptl != old_ptl)
                spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
        flush_tlb_batched_pending(vma->vm_mm);
        arch_enter_lazy_mmu_mode();

        for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
                                   new_pte++, new_addr += PAGE_SIZE) {
                if (pte_none(ptep_get(old_pte)))
                        continue;

                pte = ptep_get_and_clear(mm, old_addr, old_pte);
                /*
                 * If we are remapping a valid PTE, make sure
                 * to flush TLB before we drop the PTL for the
                 * PTE.
                 *
                 * NOTE! Both old and new PTL matter: the old one
                 * for racing with folio_mkclean(), the new one to
                 * make sure the physical page stays valid until
                 * the TLB entry for the old mapping has been
                 * flushed.
                 */
                if (pte_present(pte))
                        force_flush = true;
                pte = move_pte(pte, old_addr, new_addr);
                pte = move_soft_dirty_pte(pte);
                set_pte_at(mm, new_addr, new_pte, pte);
        }

        arch_leave_lazy_mmu_mode();
        if (force_flush)
                flush_tlb_range(vma, old_end - len, old_end);
        if (new_ptl != old_ptl)
                spin_unlock(new_ptl);
        pte_unmap(new_pte - 1);
        pte_unmap_unlock(old_pte - 1, old_ptl);
out:
        if (need_rmap_locks)
                drop_rmap_locks(vma);
        return err;
}

#ifndef arch_supports_page_table_move
#define arch_supports_page_table_move arch_supports_page_table_move
static inline bool arch_supports_page_table_move(void)
{
        return IS_ENABLED(CONFIG_HAVE_MOVE_PMD) ||
                IS_ENABLED(CONFIG_HAVE_MOVE_PUD);
}
#endif

#ifdef CONFIG_HAVE_MOVE_PMD
static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr,
                  unsigned long new_addr, pmd_t *old_pmd, pmd_t *new_pmd)
{
        spinlock_t *old_ptl, *new_ptl;
        struct mm_struct *mm = vma->vm_mm;
        bool res = false;
        pmd_t pmd;

        if (!arch_supports_page_table_move())
                return false;
        /*
         * The destination pmd shouldn't be established, free_pgtables()
         * should have released it.
         *
         * However, there's a case during execve() where we use mremap
         * to move the initial stack, and in that case the target area
         * may overlap the source area (always moving down).
         *
         * If everything is PMD-aligned, that works fine, as moving
         * each pmd down will clear the source pmd. But if we first
         * have a few 4kB-only pages that get moved down, and then
         * hit the "now the rest is PMD-aligned, let's do everything
         * one pmd at a time", we will still have the old (now empty
         * of any 4kB pages, but still there) PMD in the page table
         * tree.
         *
         * Warn on it once - because we really should try to figure
         * out how to do this better - but then say "I won't move
         * this pmd".
         *
         * One alternative might be to just unmap the target pmd at
         * this point, and verify that it really is empty. We'll see.
         */
        if (WARN_ON_ONCE(!pmd_none(*new_pmd)))
                return false;

        /*
         * We don't have to worry about the ordering of src and dst
         * ptlocks because exclusive mmap_lock prevents deadlock.
         */
        old_ptl = pmd_lock(vma->vm_mm, old_pmd);
        new_ptl = pmd_lockptr(mm, new_pmd);
        if (new_ptl != old_ptl)
                spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);

        pmd = *old_pmd;

        /* Racing with collapse? */
        if (unlikely(!pmd_present(pmd) || pmd_leaf(pmd)))
                goto out_unlock;
        /* Clear the pmd */
        pmd_clear(old_pmd);
        res = true;

        VM_BUG_ON(!pmd_none(*new_pmd));

        pmd_populate(mm, new_pmd, pmd_pgtable(pmd));
        flush_tlb_range(vma, old_addr, old_addr + PMD_SIZE);
out_unlock:
        if (new_ptl != old_ptl)
                spin_unlock(new_ptl);
        spin_unlock(old_ptl);

        return res;
}
#else
static inline bool move_normal_pmd(struct vm_area_struct *vma,
                unsigned long old_addr, unsigned long new_addr, pmd_t *old_pmd,
                pmd_t *new_pmd)
{
        return false;
}
#endif

#if CONFIG_PGTABLE_LEVELS > 2 && defined(CONFIG_HAVE_MOVE_PUD)
static bool move_normal_pud(struct vm_area_struct *vma, unsigned long old_addr,
                  unsigned long new_addr, pud_t *old_pud, pud_t *new_pud)
{
        spinlock_t *old_ptl, *new_ptl;
        struct mm_struct *mm = vma->vm_mm;
        pud_t pud;

        if (!arch_supports_page_table_move())
                return false;
        /*
         * The destination pud shouldn't be established, free_pgtables()
         * should have released it.
         */
        if (WARN_ON_ONCE(!pud_none(*new_pud)))
                return false;

        /*
         * We don't have to worry about the ordering of src and dst
         * ptlocks because exclusive mmap_lock prevents deadlock.
         */
        old_ptl = pud_lock(vma->vm_mm, old_pud);
        new_ptl = pud_lockptr(mm, new_pud);
        if (new_ptl != old_ptl)
                spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);

        /* Clear the pud */
        pud = *old_pud;
        pud_clear(old_pud);

        VM_BUG_ON(!pud_none(*new_pud));

        pud_populate(mm, new_pud, pud_pgtable(pud));
        flush_tlb_range(vma, old_addr, old_addr + PUD_SIZE);
        if (new_ptl != old_ptl)
                spin_unlock(new_ptl);
        spin_unlock(old_ptl);

        return true;
}
#else
static inline bool move_normal_pud(struct vm_area_struct *vma,
                unsigned long old_addr, unsigned long new_addr, pud_t *old_pud,
                pud_t *new_pud)
{
        return false;
}
#endif

#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD)
static bool move_huge_pud(struct vm_area_struct *vma, unsigned long old_addr,
                          unsigned long new_addr, pud_t *old_pud, pud_t *new_pud)
{
        spinlock_t *old_ptl, *new_ptl;
        struct mm_struct *mm = vma->vm_mm;
        pud_t pud;

        /*
         * The destination pud shouldn't be established, free_pgtables()
         * should have released it.
         */
        if (WARN_ON_ONCE(!pud_none(*new_pud)))
                return false;

        /*
         * We don't have to worry about the ordering of src and dst
         * ptlocks because exclusive mmap_lock prevents deadlock.
         */
        old_ptl = pud_lock(vma->vm_mm, old_pud);
        new_ptl = pud_lockptr(mm, new_pud);
        if (new_ptl != old_ptl)
                spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);

        /* Clear the pud */
        pud = *old_pud;
        pud_clear(old_pud);

        VM_BUG_ON(!pud_none(*new_pud));

        /* Set the new pud */
        /* mark soft_ditry when we add pud level soft dirty support */
        set_pud_at(mm, new_addr, new_pud, pud);
        flush_pud_tlb_range(vma, old_addr, old_addr + HPAGE_PUD_SIZE);
        if (new_ptl != old_ptl)
                spin_unlock(new_ptl);
        spin_unlock(old_ptl);

        return true;
}
#else
static bool move_huge_pud(struct vm_area_struct *vma, unsigned long old_addr,
                          unsigned long new_addr, pud_t *old_pud, pud_t *new_pud)
{
        WARN_ON_ONCE(1);
        return false;

}
#endif

enum pgt_entry {
        NORMAL_PMD,
        HPAGE_PMD,
        NORMAL_PUD,
        HPAGE_PUD,
};

/*
 * Returns an extent of the corresponding size for the pgt_entry specified if
 * valid. Else returns a smaller extent bounded by the end of the source and
 * destination pgt_entry.
 */
static __always_inline unsigned long get_extent(enum pgt_entry entry,
                        unsigned long old_addr, unsigned long old_end,
                        unsigned long new_addr)
{
        unsigned long next, extent, mask, size;

        switch (entry) {
        case HPAGE_PMD:
        case NORMAL_PMD:
                mask = PMD_MASK;
                size = PMD_SIZE;
                break;
        case HPAGE_PUD:
        case NORMAL_PUD:
                mask = PUD_MASK;
                size = PUD_SIZE;
                break;
        default:
                BUILD_BUG();
                break;
        }

        next = (old_addr + size) & mask;
        /* even if next overflowed, extent below will be ok */
        extent = next - old_addr;
        if (extent > old_end - old_addr)
                extent = old_end - old_addr;
        next = (new_addr + size) & mask;
        if (extent > next - new_addr)
                extent = next - new_addr;
        return extent;
}

/*
 * Attempts to speedup the move by moving entry at the level corresponding to
 * pgt_entry. Returns true if the move was successful, else false.
 */
static bool move_pgt_entry(enum pgt_entry entry, struct vm_area_struct *vma,
                        unsigned long old_addr, unsigned long new_addr,
                        void *old_entry, void *new_entry, bool need_rmap_locks)
{
        bool moved = false;

        /* See comment in move_ptes() */
        if (need_rmap_locks)
                take_rmap_locks(vma);

        switch (entry) {
        case NORMAL_PMD:
                moved = move_normal_pmd(vma, old_addr, new_addr, old_entry,
                                        new_entry);
                break;
        case NORMAL_PUD:
                moved = move_normal_pud(vma, old_addr, new_addr, old_entry,
                                        new_entry);
                break;
        case HPAGE_PMD:
                moved = IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
                        move_huge_pmd(vma, old_addr, new_addr, old_entry,
                                      new_entry);
                break;
        case HPAGE_PUD:
                moved = IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
                        move_huge_pud(vma, old_addr, new_addr, old_entry,
                                      new_entry);
                break;

        default:
                WARN_ON_ONCE(1);
                break;
        }

        if (need_rmap_locks)
                drop_rmap_locks(vma);

        return moved;
}

/*
 * A helper to check if aligning down is OK. The aligned address should fall
 * on *no mapping*. For the stack moving down, that's a special move within
 * the VMA that is created to span the source and destination of the move,
 * so we make an exception for it.
 */
static bool can_align_down(struct vm_area_struct *vma, unsigned long addr_to_align,
                            unsigned long mask, bool for_stack)
{
        unsigned long addr_masked = addr_to_align & mask;

        /*
         * If @addr_to_align of either source or destination is not the beginning
         * of the corresponding VMA, we can't align down or we will destroy part
         * of the current mapping.
         */
        if (!for_stack && vma->vm_start != addr_to_align)
                return false;

        /* In the stack case we explicitly permit in-VMA alignment. */
        if (for_stack && addr_masked >= vma->vm_start)
                return true;

        /*
         * Make sure the realignment doesn't cause the address to fall on an
         * existing mapping.
         */
        return find_vma_intersection(vma->vm_mm, addr_masked, vma->vm_start) == NULL;
}

/* Opportunistically realign to specified boundary for faster copy. */
static void try_realign_addr(unsigned long *old_addr, struct vm_area_struct *old_vma,
                             unsigned long *new_addr, struct vm_area_struct *new_vma,
                             unsigned long mask, bool for_stack)
{
        /* Skip if the addresses are already aligned. */
        if ((*old_addr & ~mask) == 0)
                return;

        /* Only realign if the new and old addresses are mutually aligned. */
        if ((*old_addr & ~mask) != (*new_addr & ~mask))
                return;

        /* Ensure realignment doesn't cause overlap with existing mappings. */
        if (!can_align_down(old_vma, *old_addr, mask, for_stack) ||
            !can_align_down(new_vma, *new_addr, mask, for_stack))
                return;

        *old_addr = *old_addr & mask;
        *new_addr = *new_addr & mask;
}

unsigned long move_page_tables(struct vm_area_struct *vma,
                unsigned long old_addr, struct vm_area_struct *new_vma,
                unsigned long new_addr, unsigned long len,
                bool need_rmap_locks, bool for_stack)
{
        unsigned long extent, old_end;
        struct mmu_notifier_range range;
        pmd_t *old_pmd, *new_pmd;
        pud_t *old_pud, *new_pud;

        if (!len)
                return 0;

        old_end = old_addr + len;

        if (is_vm_hugetlb_page(vma))
                return move_hugetlb_page_tables(vma, new_vma, old_addr,
                                                new_addr, len);

        /*
         * If possible, realign addresses to PMD boundary for faster copy.
         * Only realign if the mremap copying hits a PMD boundary.
         */
        if (len >= PMD_SIZE - (old_addr & ~PMD_MASK))
                try_realign_addr(&old_addr, vma, &new_addr, new_vma, PMD_MASK,
                                 for_stack);

        flush_cache_range(vma, old_addr, old_end);
        mmu_notifier_range_init(&range, MMU_NOTIFY_UNMAP, 0, vma->vm_mm,
                                old_addr, old_end);
        mmu_notifier_invalidate_range_start(&range);

        for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
                cond_resched();
                /*
                 * If extent is PUD-sized try to speed up the move by moving at the
                 * PUD level if possible.
                 */
                extent = get_extent(NORMAL_PUD, old_addr, old_end, new_addr);

                old_pud = get_old_pud(vma->vm_mm, old_addr);
                if (!old_pud)
                        continue;
                new_pud = alloc_new_pud(vma->vm_mm, vma, new_addr);
                if (!new_pud)
                        break;
                if (pud_trans_huge(*old_pud) || pud_devmap(*old_pud)) {
                        if (extent == HPAGE_PUD_SIZE) {
                                move_pgt_entry(HPAGE_PUD, vma, old_addr, new_addr,
                                               old_pud, new_pud, need_rmap_locks);
                                /* We ignore and continue on error? */
                                continue;
                        }
                } else if (IS_ENABLED(CONFIG_HAVE_MOVE_PUD) && extent == PUD_SIZE) {

                        if (move_pgt_entry(NORMAL_PUD, vma, old_addr, new_addr,
                                           old_pud, new_pud, true))
                                continue;
                }

                extent = get_extent(NORMAL_PMD, old_addr, old_end, new_addr);
                old_pmd = get_old_pmd(vma->vm_mm, old_addr);
                if (!old_pmd)
                        continue;
                new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
                if (!new_pmd)
                        break;
again:
                if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd) ||
                    pmd_devmap(*old_pmd)) {
                        if (extent == HPAGE_PMD_SIZE &&
                            move_pgt_entry(HPAGE_PMD, vma, old_addr, new_addr,
                                           old_pmd, new_pmd, need_rmap_locks))
                                continue;
                        split_huge_pmd(vma, old_pmd, old_addr);
                } else if (IS_ENABLED(CONFIG_HAVE_MOVE_PMD) &&
                           extent == PMD_SIZE) {
                        /*
                         * If the extent is PMD-sized, try to speed the move by
                         * moving at the PMD level if possible.
                         */
                        if (move_pgt_entry(NORMAL_PMD, vma, old_addr, new_addr,
                                           old_pmd, new_pmd, true))
                                continue;
                }
                if (pmd_none(*old_pmd))
                        continue;
                if (pte_alloc(new_vma->vm_mm, new_pmd))
                        break;
                if (move_ptes(vma, old_pmd, old_addr, old_addr + extent,
                              new_vma, new_pmd, new_addr, need_rmap_locks) < 0)
                        goto again;
        }

        mmu_notifier_invalidate_range_end(&range);

        /*
         * Prevent negative return values when {old,new}_addr was realigned
         * but we broke out of the above loop for the first PMD itself.
         */
        if (old_addr < old_end - len)
                return 0;

        return len + old_addr - old_end;        /* how much done */
}

static unsigned long move_vma(struct vm_area_struct *vma,
                unsigned long old_addr, unsigned long old_len,
                unsigned long new_len, unsigned long new_addr,
                bool *locked, unsigned long flags,
                struct vm_userfaultfd_ctx *uf, struct list_head *uf_unmap)
{
        long to_account = new_len - old_len;
        struct mm_struct *mm = vma->vm_mm;
        struct vm_area_struct *new_vma;
        unsigned long vm_flags = vma->vm_flags;
        unsigned long new_pgoff;
        unsigned long moved_len;
        unsigned long account_start = 0;
        unsigned long account_end = 0;
        unsigned long hiwater_vm;
        int err = 0;
        bool need_rmap_locks;
        struct vma_iterator vmi;

        /*
         * We'd prefer to avoid failure later on in do_munmap:
         * which may split one vma into three before unmapping.
         */
        if (mm->map_count >= sysctl_max_map_count - 3)
                return -ENOMEM;

        if (unlikely(flags & MREMAP_DONTUNMAP))
                to_account = new_len;

        if (vma->vm_ops && vma->vm_ops->may_split) {
                if (vma->vm_start != old_addr)
                        err = vma->vm_ops->may_split(vma, old_addr);
                if (!err && vma->vm_end != old_addr + old_len)
                        err = vma->vm_ops->may_split(vma, old_addr + old_len);
                if (err)
                        return err;
        }

        /*
         * Advise KSM to break any KSM pages in the area to be moved:
         * it would be confusing if they were to turn up at the new
         * location, where they happen to coincide with different KSM
         * pages recently unmapped.  But leave vma->vm_flags as it was,
         * so KSM can come around to merge on vma and new_vma afterwards.
         */
        err = ksm_madvise(vma, old_addr, old_addr + old_len,
                                                MADV_UNMERGEABLE, &vm_flags);
        if (err)
                return err;

        if (vm_flags & VM_ACCOUNT) {
                if (security_vm_enough_memory_mm(mm, to_account >> PAGE_SHIFT))
                        return -ENOMEM;
        }

        vma_start_write(vma);
        new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
        new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
                           &need_rmap_locks);
        if (!new_vma) {
                if (vm_flags & VM_ACCOUNT)
                        vm_unacct_memory(to_account >> PAGE_SHIFT);
                return -ENOMEM;
        }

        moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
                                     need_rmap_locks, false);
        if (moved_len < old_len) {
                err = -ENOMEM;
        } else if (vma->vm_ops && vma->vm_ops->mremap) {
                err = vma->vm_ops->mremap(new_vma);
        }

        if (unlikely(err)) {
                /*
                 * On error, move entries back from new area to old,
                 * which will succeed since page tables still there,
                 * and then proceed to unmap new area instead of old.
                 */
                move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
                                 true, false);
                vma = new_vma;
                old_len = new_len;
                old_addr = new_addr;
                new_addr = err;
        } else {
                mremap_userfaultfd_prep(new_vma, uf);
        }

        if (is_vm_hugetlb_page(vma)) {
                clear_vma_resv_huge_pages(vma);
        }

        /* Conceal VM_ACCOUNT so old reservation is not undone */
        if (vm_flags & VM_ACCOUNT && !(flags & MREMAP_DONTUNMAP)) {
                vm_flags_clear(vma, VM_ACCOUNT);
                if (vma->vm_start < old_addr)
                        account_start = vma->vm_start;
                if (vma->vm_end > old_addr + old_len)
                        account_end = vma->vm_end;
        }

        /*
         * If we failed to move page tables we still do total_vm increment
         * since do_munmap() will decrement it by old_len == new_len.
         *
         * Since total_vm is about to be raised artificially high for a
         * moment, we need to restore high watermark afterwards: if stats
         * are taken meanwhile, total_vm and hiwater_vm appear too high.
         * If this were a serious issue, we'd add a flag to do_munmap().
         */
        hiwater_vm = mm->hiwater_vm;
        vm_stat_account(mm, vma->vm_flags, new_len >> PAGE_SHIFT);

        /* Tell pfnmap has moved from this vma */
        if (unlikely(vma->vm_flags & VM_PFNMAP))
                untrack_pfn_clear(vma);

        if (unlikely(!err && (flags & MREMAP_DONTUNMAP))) {
                /* We always clear VM_LOCKED[ONFAULT] on the old vma */
                vm_flags_clear(vma, VM_LOCKED_MASK);

                /*
                 * anon_vma links of the old vma is no longer needed after its page
                 * table has been moved.
                 */
                if (new_vma != vma && vma->vm_start == old_addr &&
                        vma->vm_end == (old_addr + old_len))
                        unlink_anon_vmas(vma);

                /* Because we won't unmap we don't need to touch locked_vm */
                return new_addr;
        }

        vma_iter_init(&vmi, mm, old_addr);
        if (do_vmi_munmap(&vmi, mm, old_addr, old_len, uf_unmap, false) < 0) {
                /* OOM: unable to split vma, just get accounts right */
                if (vm_flags & VM_ACCOUNT && !(flags & MREMAP_DONTUNMAP))
                        vm_acct_memory(old_len >> PAGE_SHIFT);
                account_start = account_end = 0;
        }

        if (vm_flags & VM_LOCKED) {
                mm->locked_vm += new_len >> PAGE_SHIFT;
                *locked = true;
        }

        mm->hiwater_vm = hiwater_vm;

        /* Restore VM_ACCOUNT if one or two pieces of vma left */
        if (account_start) {
                vma = vma_prev(&vmi);
                vm_flags_set(vma, VM_ACCOUNT);
        }

        if (account_end) {
                vma = vma_next(&vmi);
                vm_flags_set(vma, VM_ACCOUNT);
        }

        return new_addr;
}

/*
 * resize_is_valid() - Ensure the vma can be resized to the new length at the give
 * address.
 *
 * @vma: The vma to resize
 * @addr: The old address
 * @old_len: The current size
 * @new_len: The desired size
 * @flags: The vma flags
 *
 * Return 0 on success, error otherwise.
 */
static int resize_is_valid(struct vm_area_struct *vma, unsigned long addr,
        unsigned long old_len, unsigned long new_len, unsigned long flags)
{
        struct mm_struct *mm = current->mm;
        unsigned long pgoff;

        /*
         * !old_len is a special case where an attempt is made to 'duplicate'
         * a mapping.  This makes no sense for private mappings as it will
         * instead create a fresh/new mapping unrelated to the original.  This
         * is contrary to the basic idea of mremap which creates new mappings
         * based on the original.  There are no known use cases for this
         * behavior.  As a result, fail such attempts.
         */
        if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
                pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap.  This is not supported.\n", current->comm, current->pid);
                return -EINVAL;
        }

        if ((flags & MREMAP_DONTUNMAP) &&
                        (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)))
                return -EINVAL;

        /* We can't remap across vm area boundaries */
        if (old_len > vma->vm_end - addr)
                return -EFAULT;

        if (new_len == old_len)
                return 0;

        /* Need to be careful about a growing mapping */
        pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
        pgoff += vma->vm_pgoff;
        if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
                return -EINVAL;

        if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
                return -EFAULT;

        if (!mlock_future_ok(mm, vma->vm_flags, new_len - old_len))
                return -EAGAIN;

        if (!may_expand_vm(mm, vma->vm_flags,
                                (new_len - old_len) >> PAGE_SHIFT))
                return -ENOMEM;

        return 0;
}

/*
 * mremap_to() - remap a vma to a new location
 * @addr: The old address
 * @old_len: The old size
 * @new_addr: The target address
 * @new_len: The new size
 * @locked: If the returned vma is locked (VM_LOCKED)
 * @flags: the mremap flags
 * @uf: The mremap userfaultfd context
 * @uf_unmap_early: The userfaultfd unmap early context
 * @uf_unmap: The userfaultfd unmap context
 *
 * Returns: The new address of the vma or an error.
 */
static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
                unsigned long new_addr, unsigned long new_len, bool *locked,
                unsigned long flags, struct vm_userfaultfd_ctx *uf,
                struct list_head *uf_unmap_early,
                struct list_head *uf_unmap)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        unsigned long ret;
        unsigned long map_flags = 0;

        if (offset_in_page(new_addr))
                return -EINVAL;

        if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
                return -EINVAL;

        /* Ensure the old/new locations do not overlap */
        if (addr + old_len > new_addr && new_addr + new_len > addr)
                return -EINVAL;

        /*
         * move_vma() need us to stay 4 maps below the threshold, otherwise
         * it will bail out at the very beginning.
         * That is a problem if we have already unmaped the regions here
         * (new_addr, and old_addr), because userspace will not know the
         * state of the vma's after it gets -ENOMEM.
         * So, to avoid such scenario we can pre-compute if the whole
         * operation has high chances to success map-wise.
         * Worst-scenario case is when both vma's (new_addr and old_addr) get
         * split in 3 before unmapping it.
         * That means 2 more maps (1 for each) to the ones we already hold.
         * Check whether current map count plus 2 still leads us to 4 maps below
         * the threshold, otherwise return -ENOMEM here to be more safe.
         */
        if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
                return -ENOMEM;

        if (flags & MREMAP_FIXED) {
                /*
                 * In mremap_to().
                 * VMA is moved to dst address, and munmap dst first.
                 * do_munmap will check if dst is sealed.
                 */
                ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
                if (ret)
                        return ret;
        }

        if (old_len > new_len) {
                ret = do_munmap(mm, addr+new_len, old_len - new_len, uf_unmap);
                if (ret)
                        return ret;
                old_len = new_len;
        }

        vma = vma_lookup(mm, addr);
        if (!vma)
                return -EFAULT;

        ret = resize_is_valid(vma, addr, old_len, new_len, flags);
        if (ret)
                return ret;

        /* MREMAP_DONTUNMAP expands by old_len since old_len == new_len */
        if (flags & MREMAP_DONTUNMAP &&
                !may_expand_vm(mm, vma->vm_flags, old_len >> PAGE_SHIFT)) {
                return -ENOMEM;
        }

        if (flags & MREMAP_FIXED)
                map_flags |= MAP_FIXED;

        if (vma->vm_flags & VM_MAYSHARE)
                map_flags |= MAP_SHARED;

        ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
                                ((addr - vma->vm_start) >> PAGE_SHIFT),
                                map_flags);
        if (IS_ERR_VALUE(ret))
                return ret;

        /* We got a new mapping */
        if (!(flags & MREMAP_FIXED))
                new_addr = ret;

        return move_vma(vma, addr, old_len, new_len, new_addr, locked, flags,
                        uf, uf_unmap);
}

static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
{
        unsigned long end = vma->vm_end + delta;

        if (end < vma->vm_end) /* overflow */
                return 0;
        if (find_vma_intersection(vma->vm_mm, vma->vm_end, end))
                return 0;
        if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
                              0, MAP_FIXED) & ~PAGE_MASK)
                return 0;
        return 1;
}

/*
 * Expand (or shrink) an existing mapping, potentially moving it at the
 * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
 *
 * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
 * This option implies MREMAP_MAYMOVE.
 */
SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
                unsigned long, new_len, unsigned long, flags,
                unsigned long, new_addr)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        unsigned long ret = -EINVAL;
        bool locked = false;
        struct vm_userfaultfd_ctx uf = NULL_VM_UFFD_CTX;
        LIST_HEAD(uf_unmap_early);
        LIST_HEAD(uf_unmap);

        /*
         * There is a deliberate asymmetry here: we strip the pointer tag
         * from the old address but leave the new address alone. This is
         * for consistency with mmap(), where we prevent the creation of
         * aliasing mappings in userspace by leaving the tag bits of the
         * mapping address intact. A non-zero tag will cause the subsequent
         * range checks to reject the address as invalid.
         *
         * See Documentation/arch/arm64/tagged-address-abi.rst for more
         * information.
         */
        addr = untagged_addr(addr);

        if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE | MREMAP_DONTUNMAP))
                return ret;

        if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
                return ret;

        /*
         * MREMAP_DONTUNMAP is always a move and it does not allow resizing
         * in the process.
         */
        if (flags & MREMAP_DONTUNMAP &&
                        (!(flags & MREMAP_MAYMOVE) || old_len != new_len))
                return ret;


        if (offset_in_page(addr))
                return ret;

        old_len = PAGE_ALIGN(old_len);
        new_len = PAGE_ALIGN(new_len);

        /*
         * We allow a zero old-len as a special case
         * for DOS-emu "duplicate shm area" thing. But
         * a zero new-len is nonsensical.
         */
        if (!new_len)
                return ret;

        if (mmap_write_lock_killable(current->mm))
                return -EINTR;
        vma = vma_lookup(mm, addr);
        if (!vma) {
                ret = -EFAULT;
                goto out;
        }

        /* Don't allow remapping vmas when they have already been sealed */
        if (!can_modify_vma(vma)) {
                ret = -EPERM;
                goto out;
        }

        if (is_vm_hugetlb_page(vma)) {
                struct hstate *h __maybe_unused = hstate_vma(vma);

                old_len = ALIGN(old_len, huge_page_size(h));
                new_len = ALIGN(new_len, huge_page_size(h));

                /* addrs must be huge page aligned */
                if (addr & ~huge_page_mask(h))
                        goto out;
                if (new_addr & ~huge_page_mask(h))
                        goto out;

                /*
                 * Don't allow remap expansion, because the underlying hugetlb
                 * reservation is not yet capable to handle split reservation.
                 */
                if (new_len > old_len)
                        goto out;
        }

        if (flags & (MREMAP_FIXED | MREMAP_DONTUNMAP)) {
                ret = mremap_to(addr, old_len, new_addr, new_len,
                                &locked, flags, &uf, &uf_unmap_early,
                                &uf_unmap);
                goto out;
        }

        /*
         * Always allow a shrinking remap: that just unmaps
         * the unnecessary pages..
         * do_vmi_munmap does all the needed commit accounting, and
         * unlocks the mmap_lock if so directed.
         */
        if (old_len >= new_len) {
                VMA_ITERATOR(vmi, mm, addr + new_len);

                if (old_len == new_len) {
                        ret = addr;
                        goto out;
                }

                ret = do_vmi_munmap(&vmi, mm, addr + new_len, old_len - new_len,
                                    &uf_unmap, true);
                if (ret)
                        goto out;

                ret = addr;
                goto out_unlocked;
        }

        /*
         * Ok, we need to grow..
         */
        ret = resize_is_valid(vma, addr, old_len, new_len, flags);
        if (ret)
                goto out;

        /* old_len exactly to the end of the area..
         */
        if (old_len == vma->vm_end - addr) {
                unsigned long delta = new_len - old_len;

                /* can we just expand the current mapping? */
                if (vma_expandable(vma, delta)) {
                        long pages = delta >> PAGE_SHIFT;
                        VMA_ITERATOR(vmi, mm, vma->vm_end);
                        long charged = 0;

                        if (vma->vm_flags & VM_ACCOUNT) {
                                if (security_vm_enough_memory_mm(mm, pages)) {
                                        ret = -ENOMEM;
                                        goto out;
                                }
                                charged = pages;
                        }

                        /*
                         * Function vma_merge_extend() is called on the
                         * extension we are adding to the already existing vma,
                         * vma_merge_extend() will merge this extension with the
                         * already existing vma (expand operation itself) and
                         * possibly also with the next vma if it becomes
                         * adjacent to the expanded vma and otherwise
                         * compatible.
                         */
                        vma = vma_merge_extend(&vmi, vma, delta);
                        if (!vma) {
                                vm_unacct_memory(charged);
                                ret = -ENOMEM;
                                goto out;
                        }

                        vm_stat_account(mm, vma->vm_flags, pages);
                        if (vma->vm_flags & VM_LOCKED) {
                                mm->locked_vm += pages;
                                locked = true;
                                new_addr = addr;
                        }
                        ret = addr;
                        goto out;
                }
        }

        /*
         * We weren't able to just expand or shrink the area,
         * we need to create a new one and move it..
         */
        ret = -ENOMEM;
        if (flags & MREMAP_MAYMOVE) {
                unsigned long map_flags = 0;
                if (vma->vm_flags & VM_MAYSHARE)
                        map_flags |= MAP_SHARED;

                new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
                                        vma->vm_pgoff +
                                        ((addr - vma->vm_start) >> PAGE_SHIFT),
                                        map_flags);
                if (IS_ERR_VALUE(new_addr)) {
                        ret = new_addr;
                        goto out;
                }

                ret = move_vma(vma, addr, old_len, new_len, new_addr,
                               &locked, flags, &uf, &uf_unmap);
        }
out:
        if (offset_in_page(ret))
                locked = false;
        mmap_write_unlock(current->mm);
        if (locked && new_len > old_len)
                mm_populate(new_addr + old_len, new_len - old_len);
out_unlocked:
        userfaultfd_unmap_complete(mm, &uf_unmap_early);
        mremap_userfaultfd_complete(&uf, addr, ret, old_len);
        userfaultfd_unmap_complete(mm, &uf_unmap);
        return ret;
}