net/mlx5: Unregister notifier on eswitch init failure

[linux.git] / mm / mmap.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * mm/mmap.c
 *
 * Written by obz.
 *
 * Address space accounting code        <[email protected]>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/backing-dev.h>
#include <linux/mm.h>
#include <linux/mm_inline.h>
#include <linux/shm.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/syscalls.h>
#include <linux/capability.h>
#include <linux/init.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/personality.h>
#include <linux/security.h>
#include <linux/hugetlb.h>
#include <linux/shmem_fs.h>
#include <linux/profile.h>
#include <linux/export.h>
#include <linux/mount.h>
#include <linux/mempolicy.h>
#include <linux/rmap.h>
#include <linux/mmu_notifier.h>
#include <linux/mmdebug.h>
#include <linux/perf_event.h>
#include <linux/audit.h>
#include <linux/khugepaged.h>
#include <linux/uprobes.h>
#include <linux/notifier.h>
#include <linux/memory.h>
#include <linux/printk.h>
#include <linux/userfaultfd_k.h>
#include <linux/moduleparam.h>
#include <linux/pkeys.h>
#include <linux/oom.h>
#include <linux/sched/mm.h>
#include <linux/ksm.h>

#include <linux/uaccess.h>
#include <asm/cacheflush.h>
#include <asm/tlb.h>
#include <asm/mmu_context.h>

#define CREATE_TRACE_POINTS
#include <trace/events/mmap.h>

#include "internal.h"

#ifndef arch_mmap_check
#define arch_mmap_check(addr, len, flags)       (0)
#endif

#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
const int mmap_rnd_bits_min = CONFIG_ARCH_MMAP_RND_BITS_MIN;
int mmap_rnd_bits_max __ro_after_init = CONFIG_ARCH_MMAP_RND_BITS_MAX;
int mmap_rnd_bits __read_mostly = CONFIG_ARCH_MMAP_RND_BITS;
#endif
#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
const int mmap_rnd_compat_bits_min = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MIN;
const int mmap_rnd_compat_bits_max = CONFIG_ARCH_MMAP_RND_COMPAT_BITS_MAX;
int mmap_rnd_compat_bits __read_mostly = CONFIG_ARCH_MMAP_RND_COMPAT_BITS;
#endif

static bool ignore_rlimit_data;
core_param(ignore_rlimit_data, ignore_rlimit_data, bool, 0644);

/* Update vma->vm_page_prot to reflect vma->vm_flags. */
void vma_set_page_prot(struct vm_area_struct *vma)
{
        unsigned long vm_flags = vma->vm_flags;
        pgprot_t vm_page_prot;

        vm_page_prot = vm_pgprot_modify(vma->vm_page_prot, vm_flags);
        if (vma_wants_writenotify(vma, vm_page_prot)) {
                vm_flags &= ~VM_SHARED;
                vm_page_prot = vm_pgprot_modify(vm_page_prot, vm_flags);
        }
        /* remove_protection_ptes reads vma->vm_page_prot without mmap_lock */
        WRITE_ONCE(vma->vm_page_prot, vm_page_prot);
}

/*
 * check_brk_limits() - Use platform specific check of range & verify mlock
 * limits.
 * @addr: The address to check
 * @len: The size of increase.
 *
 * Return: 0 on success.
 */
static int check_brk_limits(unsigned long addr, unsigned long len)
{
        unsigned long mapped_addr;

        mapped_addr = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED);
        if (IS_ERR_VALUE(mapped_addr))
                return mapped_addr;

        return mlock_future_ok(current->mm, current->mm->def_flags, len)
                ? 0 : -EAGAIN;
}
static int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *brkvma,
                unsigned long addr, unsigned long request, unsigned long flags);
SYSCALL_DEFINE1(brk, unsigned long, brk)
{
        unsigned long newbrk, oldbrk, origbrk;
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *brkvma, *next = NULL;
        unsigned long min_brk;
        bool populate = false;
        LIST_HEAD(uf);
        struct vma_iterator vmi;

        if (mmap_write_lock_killable(mm))
                return -EINTR;

        origbrk = mm->brk;

#ifdef CONFIG_COMPAT_BRK
        /*
         * CONFIG_COMPAT_BRK can still be overridden by setting
         * randomize_va_space to 2, which will still cause mm->start_brk
         * to be arbitrarily shifted
         */
        if (current->brk_randomized)
                min_brk = mm->start_brk;
        else
                min_brk = mm->end_data;
#else
        min_brk = mm->start_brk;
#endif
        if (brk < min_brk)
                goto out;

        /*
         * Check against rlimit here. If this check is done later after the test
         * of oldbrk with newbrk then it can escape the test and let the data
         * segment grow beyond its set limit the in case where the limit is
         * not page aligned -Ram Gupta
         */
        if (check_data_rlimit(rlimit(RLIMIT_DATA), brk, mm->start_brk,
                              mm->end_data, mm->start_data))
                goto out;

        newbrk = PAGE_ALIGN(brk);
        oldbrk = PAGE_ALIGN(mm->brk);
        if (oldbrk == newbrk) {
                mm->brk = brk;
                goto success;
        }

        /* Always allow shrinking brk. */
        if (brk <= mm->brk) {
                /* Search one past newbrk */
                vma_iter_init(&vmi, mm, newbrk);
                brkvma = vma_find(&vmi, oldbrk);
                if (!brkvma || brkvma->vm_start >= oldbrk)
                        goto out; /* mapping intersects with an existing non-brk vma. */
                /*
                 * mm->brk must be protected by write mmap_lock.
                 * do_vmi_align_munmap() will drop the lock on success,  so
                 * update it before calling do_vma_munmap().
                 */
                mm->brk = brk;
                if (do_vmi_align_munmap(&vmi, brkvma, mm, newbrk, oldbrk, &uf,
                                        /* unlock = */ true))
                        goto out;

                goto success_unlocked;
        }

        if (check_brk_limits(oldbrk, newbrk - oldbrk))
                goto out;

        /*
         * Only check if the next VMA is within the stack_guard_gap of the
         * expansion area
         */
        vma_iter_init(&vmi, mm, oldbrk);
        next = vma_find(&vmi, newbrk + PAGE_SIZE + stack_guard_gap);
        if (next && newbrk + PAGE_SIZE > vm_start_gap(next))
                goto out;

        brkvma = vma_prev_limit(&vmi, mm->start_brk);
        /* Ok, looks good - let it rip. */
        if (do_brk_flags(&vmi, brkvma, oldbrk, newbrk - oldbrk, 0) < 0)
                goto out;

        mm->brk = brk;
        if (mm->def_flags & VM_LOCKED)
                populate = true;

success:
        mmap_write_unlock(mm);
success_unlocked:
        userfaultfd_unmap_complete(mm, &uf);
        if (populate)
                mm_populate(oldbrk, newbrk - oldbrk);
        return brk;

out:
        mm->brk = origbrk;
        mmap_write_unlock(mm);
        return origbrk;
}

/*
 * If a hint addr is less than mmap_min_addr change hint to be as
 * low as possible but still greater than mmap_min_addr
 */
static inline unsigned long round_hint_to_min(unsigned long hint)
{
        hint &= PAGE_MASK;
        if (((void *)hint != NULL) &&
            (hint < mmap_min_addr))
                return PAGE_ALIGN(mmap_min_addr);
        return hint;
}

bool mlock_future_ok(struct mm_struct *mm, unsigned long flags,
                        unsigned long bytes)
{
        unsigned long locked_pages, limit_pages;

        if (!(flags & VM_LOCKED) || capable(CAP_IPC_LOCK))
                return true;

        locked_pages = bytes >> PAGE_SHIFT;
        locked_pages += mm->locked_vm;

        limit_pages = rlimit(RLIMIT_MEMLOCK);
        limit_pages >>= PAGE_SHIFT;

        return locked_pages <= limit_pages;
}

static inline u64 file_mmap_size_max(struct file *file, struct inode *inode)
{
        if (S_ISREG(inode->i_mode))
                return MAX_LFS_FILESIZE;

        if (S_ISBLK(inode->i_mode))
                return MAX_LFS_FILESIZE;

        if (S_ISSOCK(inode->i_mode))
                return MAX_LFS_FILESIZE;

        /* Special "we do even unsigned file positions" case */
        if (file->f_op->fop_flags & FOP_UNSIGNED_OFFSET)
                return 0;

        /* Yes, random drivers might want more. But I'm tired of buggy drivers */
        return ULONG_MAX;
}

static inline bool file_mmap_ok(struct file *file, struct inode *inode,
                                unsigned long pgoff, unsigned long len)
{
        u64 maxsize = file_mmap_size_max(file, inode);

        if (maxsize && len > maxsize)
                return false;
        maxsize -= len;
        if (pgoff > maxsize >> PAGE_SHIFT)
                return false;
        return true;
}

/*
 * The caller must write-lock current->mm->mmap_lock.
 */
unsigned long do_mmap(struct file *file, unsigned long addr,
                        unsigned long len, unsigned long prot,
                        unsigned long flags, vm_flags_t vm_flags,
                        unsigned long pgoff, unsigned long *populate,
                        struct list_head *uf)
{
        struct mm_struct *mm = current->mm;
        int pkey = 0;

        *populate = 0;

        if (!len)
                return -EINVAL;

        /*
         * Does the application expect PROT_READ to imply PROT_EXEC?
         *
         * (the exception is when the underlying filesystem is noexec
         *  mounted, in which case we don't add PROT_EXEC.)
         */
        if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
                if (!(file && path_noexec(&file->f_path)))
                        prot |= PROT_EXEC;

        /* force arch specific MAP_FIXED handling in get_unmapped_area */
        if (flags & MAP_FIXED_NOREPLACE)
                flags |= MAP_FIXED;

        if (!(flags & MAP_FIXED))
                addr = round_hint_to_min(addr);

        /* Careful about overflows.. */
        len = PAGE_ALIGN(len);
        if (!len)
                return -ENOMEM;

        /* offset overflow? */
        if ((pgoff + (len >> PAGE_SHIFT)) < pgoff)
                return -EOVERFLOW;

        /* Too many mappings? */
        if (mm->map_count > sysctl_max_map_count)
                return -ENOMEM;

        /*
         * addr is returned from get_unmapped_area,
         * There are two cases:
         * 1> MAP_FIXED == false
         *      unallocated memory, no need to check sealing.
         * 1> MAP_FIXED == true
         *      sealing is checked inside mmap_region when
         *      do_vmi_munmap is called.
         */

        if (prot == PROT_EXEC) {
                pkey = execute_only_pkey(mm);
                if (pkey < 0)
                        pkey = 0;
        }

        /* Do simple checking here so the lower-level routines won't have
         * to. we assume access permissions have been handled by the open
         * of the memory object, so we don't do any here.
         */
        vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
                        mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;

        /* Obtain the address to map to. we verify (or select) it and ensure
         * that it represents a valid section of the address space.
         */
        addr = __get_unmapped_area(file, addr, len, pgoff, flags, vm_flags);
        if (IS_ERR_VALUE(addr))
                return addr;

        if (flags & MAP_FIXED_NOREPLACE) {
                if (find_vma_intersection(mm, addr, addr + len))
                        return -EEXIST;
        }

        if (flags & MAP_LOCKED)
                if (!can_do_mlock())
                        return -EPERM;

        if (!mlock_future_ok(mm, vm_flags, len))
                return -EAGAIN;

        if (file) {
                struct inode *inode = file_inode(file);
                unsigned long flags_mask;

                if (!file_mmap_ok(file, inode, pgoff, len))
                        return -EOVERFLOW;

                flags_mask = LEGACY_MAP_MASK;
                if (file->f_op->fop_flags & FOP_MMAP_SYNC)
                        flags_mask |= MAP_SYNC;

                switch (flags & MAP_TYPE) {
                case MAP_SHARED:
                        /*
                         * Force use of MAP_SHARED_VALIDATE with non-legacy
                         * flags. E.g. MAP_SYNC is dangerous to use with
                         * MAP_SHARED as you don't know which consistency model
                         * you will get. We silently ignore unsupported flags
                         * with MAP_SHARED to preserve backward compatibility.
                         */
                        flags &= LEGACY_MAP_MASK;
                        fallthrough;
                case MAP_SHARED_VALIDATE:
                        if (flags & ~flags_mask)
                                return -EOPNOTSUPP;
                        if (prot & PROT_WRITE) {
                                if (!(file->f_mode & FMODE_WRITE))
                                        return -EACCES;
                                if (IS_SWAPFILE(file->f_mapping->host))
                                        return -ETXTBSY;
                        }

                        /*
                         * Make sure we don't allow writing to an append-only
                         * file..
                         */
                        if (IS_APPEND(inode) && (file->f_mode & FMODE_WRITE))
                                return -EACCES;

                        vm_flags |= VM_SHARED | VM_MAYSHARE;
                        if (!(file->f_mode & FMODE_WRITE))
                                vm_flags &= ~(VM_MAYWRITE | VM_SHARED);
                        fallthrough;
                case MAP_PRIVATE:
                        if (!(file->f_mode & FMODE_READ))
                                return -EACCES;
                        if (path_noexec(&file->f_path)) {
                                if (vm_flags & VM_EXEC)
                                        return -EPERM;
                                vm_flags &= ~VM_MAYEXEC;
                        }

                        if (!file->f_op->mmap)
                                return -ENODEV;
                        if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
                                return -EINVAL;
                        break;

                default:
                        return -EINVAL;
                }
        } else {
                switch (flags & MAP_TYPE) {
                case MAP_SHARED:
                        if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
                                return -EINVAL;
                        /*
                         * Ignore pgoff.
                         */
                        pgoff = 0;
                        vm_flags |= VM_SHARED | VM_MAYSHARE;
                        break;
                case MAP_DROPPABLE:
                        if (VM_DROPPABLE == VM_NONE)
                                return -ENOTSUPP;
                        /*
                         * A locked or stack area makes no sense to be droppable.
                         *
                         * Also, since droppable pages can just go away at any time
                         * it makes no sense to copy them on fork or dump them.
                         *
                         * And don't attempt to combine with hugetlb for now.
                         */
                        if (flags & (MAP_LOCKED | MAP_HUGETLB))
                                return -EINVAL;
                        if (vm_flags & (VM_GROWSDOWN | VM_GROWSUP))
                                return -EINVAL;

                        vm_flags |= VM_DROPPABLE;

                        /*
                         * If the pages can be dropped, then it doesn't make
                         * sense to reserve them.
                         */
                        vm_flags |= VM_NORESERVE;

                        /*
                         * Likewise, they're volatile enough that they
                         * shouldn't survive forks or coredumps.
                         */
                        vm_flags |= VM_WIPEONFORK | VM_DONTDUMP;
                        fallthrough;
                case MAP_PRIVATE:
                        /*
                         * Set pgoff according to addr for anon_vma.
                         */
                        pgoff = addr >> PAGE_SHIFT;
                        break;
                default:
                        return -EINVAL;
                }
        }

        /*
         * Set 'VM_NORESERVE' if we should not account for the
         * memory use of this mapping.
         */
        if (flags & MAP_NORESERVE) {
                /* We honor MAP_NORESERVE if allowed to overcommit */
                if (sysctl_overcommit_memory != OVERCOMMIT_NEVER)
                        vm_flags |= VM_NORESERVE;

                /* hugetlb applies strict overcommit unless MAP_NORESERVE */
                if (file && is_file_hugepages(file))
                        vm_flags |= VM_NORESERVE;
        }

        addr = mmap_region(file, addr, len, vm_flags, pgoff, uf);
        if (!IS_ERR_VALUE(addr) &&
            ((vm_flags & VM_LOCKED) ||
             (flags & (MAP_POPULATE | MAP_NONBLOCK)) == MAP_POPULATE))
                *populate = len;
        return addr;
}

unsigned long ksys_mmap_pgoff(unsigned long addr, unsigned long len,
                              unsigned long prot, unsigned long flags,
                              unsigned long fd, unsigned long pgoff)
{
        struct file *file = NULL;
        unsigned long retval;

        if (!(flags & MAP_ANONYMOUS)) {
                audit_mmap_fd(fd, flags);
                file = fget(fd);
                if (!file)
                        return -EBADF;
                if (is_file_hugepages(file)) {
                        len = ALIGN(len, huge_page_size(hstate_file(file)));
                } else if (unlikely(flags & MAP_HUGETLB)) {
                        retval = -EINVAL;
                        goto out_fput;
                }
        } else if (flags & MAP_HUGETLB) {
                struct hstate *hs;

                hs = hstate_sizelog((flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
                if (!hs)
                        return -EINVAL;

                len = ALIGN(len, huge_page_size(hs));
                /*
                 * VM_NORESERVE is used because the reservations will be
                 * taken when vm_ops->mmap() is called
                 */
                file = hugetlb_file_setup(HUGETLB_ANON_FILE, len,
                                VM_NORESERVE,
                                HUGETLB_ANONHUGE_INODE,
                                (flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK);
                if (IS_ERR(file))
                        return PTR_ERR(file);
        }

        retval = vm_mmap_pgoff(file, addr, len, prot, flags, pgoff);
out_fput:
        if (file)
                fput(file);
        return retval;
}

SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
                unsigned long, prot, unsigned long, flags,
                unsigned long, fd, unsigned long, pgoff)
{
        return ksys_mmap_pgoff(addr, len, prot, flags, fd, pgoff);
}

#ifdef __ARCH_WANT_SYS_OLD_MMAP
struct mmap_arg_struct {
        unsigned long addr;
        unsigned long len;
        unsigned long prot;
        unsigned long flags;
        unsigned long fd;
        unsigned long offset;
};

SYSCALL_DEFINE1(old_mmap, struct mmap_arg_struct __user *, arg)
{
        struct mmap_arg_struct a;

        if (copy_from_user(&a, arg, sizeof(a)))
                return -EFAULT;
        if (offset_in_page(a.offset))
                return -EINVAL;

        return ksys_mmap_pgoff(a.addr, a.len, a.prot, a.flags, a.fd,
                               a.offset >> PAGE_SHIFT);
}
#endif /* __ARCH_WANT_SYS_OLD_MMAP */

/*
 * We account for memory if it's a private writeable mapping,
 * not hugepages and VM_NORESERVE wasn't set.
 */
static inline bool accountable_mapping(struct file *file, vm_flags_t vm_flags)
{
        /*
         * hugetlb has its own accounting separate from the core VM
         * VM_HUGETLB may not be set yet so we cannot check for that flag.
         */
        if (file && is_file_hugepages(file))
                return false;

        return (vm_flags & (VM_NORESERVE | VM_SHARED | VM_WRITE)) == VM_WRITE;
}

/**
 * unmapped_area() - Find an area between the low_limit and the high_limit with
 * the correct alignment and offset, all from @info. Note: current->mm is used
 * for the search.
 *
 * @info: The unmapped area information including the range [low_limit -
 * high_limit), the alignment offset and mask.
 *
 * Return: A memory address or -ENOMEM.
 */
static unsigned long unmapped_area(struct vm_unmapped_area_info *info)
{
        unsigned long length, gap;
        unsigned long low_limit, high_limit;
        struct vm_area_struct *tmp;
        VMA_ITERATOR(vmi, current->mm, 0);

        /* Adjust search length to account for worst case alignment overhead */
        length = info->length + info->align_mask + info->start_gap;
        if (length < info->length)
                return -ENOMEM;

        low_limit = info->low_limit;
        if (low_limit < mmap_min_addr)
                low_limit = mmap_min_addr;
        high_limit = info->high_limit;
retry:
        if (vma_iter_area_lowest(&vmi, low_limit, high_limit, length))
                return -ENOMEM;

        /*
         * Adjust for the gap first so it doesn't interfere with the
         * later alignment. The first step is the minimum needed to
         * fulill the start gap, the next steps is the minimum to align
         * that. It is the minimum needed to fulill both.
         */
        gap = vma_iter_addr(&vmi) + info->start_gap;
        gap += (info->align_offset - gap) & info->align_mask;
        tmp = vma_next(&vmi);
        if (tmp && (tmp->vm_flags & VM_STARTGAP_FLAGS)) { /* Avoid prev check if possible */
                if (vm_start_gap(tmp) < gap + length - 1) {
                        low_limit = tmp->vm_end;
                        vma_iter_reset(&vmi);
                        goto retry;
                }
        } else {
                tmp = vma_prev(&vmi);
                if (tmp && vm_end_gap(tmp) > gap) {
                        low_limit = vm_end_gap(tmp);
                        vma_iter_reset(&vmi);
                        goto retry;
                }
        }

        return gap;
}

/**
 * unmapped_area_topdown() - Find an area between the low_limit and the
 * high_limit with the correct alignment and offset at the highest available
 * address, all from @info. Note: current->mm is used for the search.
 *
 * @info: The unmapped area information including the range [low_limit -
 * high_limit), the alignment offset and mask.
 *
 * Return: A memory address or -ENOMEM.
 */
static unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
{
        unsigned long length, gap, gap_end;
        unsigned long low_limit, high_limit;
        struct vm_area_struct *tmp;
        VMA_ITERATOR(vmi, current->mm, 0);

        /* Adjust search length to account for worst case alignment overhead */
        length = info->length + info->align_mask + info->start_gap;
        if (length < info->length)
                return -ENOMEM;

        low_limit = info->low_limit;
        if (low_limit < mmap_min_addr)
                low_limit = mmap_min_addr;
        high_limit = info->high_limit;
retry:
        if (vma_iter_area_highest(&vmi, low_limit, high_limit, length))
                return -ENOMEM;

        gap = vma_iter_end(&vmi) - info->length;
        gap -= (gap - info->align_offset) & info->align_mask;
        gap_end = vma_iter_end(&vmi);
        tmp = vma_next(&vmi);
        if (tmp && (tmp->vm_flags & VM_STARTGAP_FLAGS)) { /* Avoid prev check if possible */
                if (vm_start_gap(tmp) < gap_end) {
                        high_limit = vm_start_gap(tmp);
                        vma_iter_reset(&vmi);
                        goto retry;
                }
        } else {
                tmp = vma_prev(&vmi);
                if (tmp && vm_end_gap(tmp) > gap) {
                        high_limit = tmp->vm_start;
                        vma_iter_reset(&vmi);
                        goto retry;
                }
        }

        return gap;
}

/*
 * Determine if the allocation needs to ensure that there is no
 * existing mapping within it's guard gaps, for use as start_gap.
 */
static inline unsigned long stack_guard_placement(vm_flags_t vm_flags)
{
        if (vm_flags & VM_SHADOW_STACK)
                return PAGE_SIZE;

        return 0;
}

/*
 * Search for an unmapped address range.
 *
 * We are looking for a range that:
 * - does not intersect with any VMA;
 * - is contained within the [low_limit, high_limit) interval;
 * - is at least the desired size.
 * - satisfies (begin_addr & align_mask) == (align_offset & align_mask)
 */
unsigned long vm_unmapped_area(struct vm_unmapped_area_info *info)
{
        unsigned long addr;

        if (info->flags & VM_UNMAPPED_AREA_TOPDOWN)
                addr = unmapped_area_topdown(info);
        else
                addr = unmapped_area(info);

        trace_vm_unmapped_area(addr, info);
        return addr;
}

/* Get an address range which is currently unmapped.
 * For shmat() with addr=0.
 *
 * Ugly calling convention alert:
 * Return value with the low bits set means error value,
 * ie
 *      if (ret & ~PAGE_MASK)
 *              error = ret;
 *
 * This function "knows" that -ENOMEM has the bits set.
 */
unsigned long
generic_get_unmapped_area(struct file *filp, unsigned long addr,
                          unsigned long len, unsigned long pgoff,
                          unsigned long flags, vm_flags_t vm_flags)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma, *prev;
        struct vm_unmapped_area_info info = {};
        const unsigned long mmap_end = arch_get_mmap_end(addr, len, flags);

        if (len > mmap_end - mmap_min_addr)
                return -ENOMEM;

        if (flags & MAP_FIXED)
                return addr;

        if (addr) {
                addr = PAGE_ALIGN(addr);
                vma = find_vma_prev(mm, addr, &prev);
                if (mmap_end - len >= addr && addr >= mmap_min_addr &&
                    (!vma || addr + len <= vm_start_gap(vma)) &&
                    (!prev || addr >= vm_end_gap(prev)))
                        return addr;
        }

        info.length = len;
        info.low_limit = mm->mmap_base;
        info.high_limit = mmap_end;
        info.start_gap = stack_guard_placement(vm_flags);
        return vm_unmapped_area(&info);
}

#ifndef HAVE_ARCH_UNMAPPED_AREA
unsigned long
arch_get_unmapped_area(struct file *filp, unsigned long addr,
                       unsigned long len, unsigned long pgoff,
                       unsigned long flags, vm_flags_t vm_flags)
{
        return generic_get_unmapped_area(filp, addr, len, pgoff, flags,
                                         vm_flags);
}
#endif

/*
 * This mmap-allocator allocates new areas top-down from below the
 * stack's low limit (the base):
 */
unsigned long
generic_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
                                  unsigned long len, unsigned long pgoff,
                                  unsigned long flags, vm_flags_t vm_flags)
{
        struct vm_area_struct *vma, *prev;
        struct mm_struct *mm = current->mm;
        struct vm_unmapped_area_info info = {};
        const unsigned long mmap_end = arch_get_mmap_end(addr, len, flags);

        /* requested length too big for entire address space */
        if (len > mmap_end - mmap_min_addr)
                return -ENOMEM;

        if (flags & MAP_FIXED)
                return addr;

        /* requesting a specific address */
        if (addr) {
                addr = PAGE_ALIGN(addr);
                vma = find_vma_prev(mm, addr, &prev);
                if (mmap_end - len >= addr && addr >= mmap_min_addr &&
                                (!vma || addr + len <= vm_start_gap(vma)) &&
                                (!prev || addr >= vm_end_gap(prev)))
                        return addr;
        }

        info.flags = VM_UNMAPPED_AREA_TOPDOWN;
        info.length = len;
        info.low_limit = PAGE_SIZE;
        info.high_limit = arch_get_mmap_base(addr, mm->mmap_base);
        info.start_gap = stack_guard_placement(vm_flags);
        addr = vm_unmapped_area(&info);

        /*
         * A failed mmap() very likely causes application failure,
         * so fall back to the bottom-up function here. This scenario
         * can happen with large stack limits and large mmap()
         * allocations.
         */
        if (offset_in_page(addr)) {
                VM_BUG_ON(addr != -ENOMEM);
                info.flags = 0;
                info.low_limit = TASK_UNMAPPED_BASE;
                info.high_limit = mmap_end;
                addr = vm_unmapped_area(&info);
        }

        return addr;
}

#ifndef HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
unsigned long
arch_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
                               unsigned long len, unsigned long pgoff,
                               unsigned long flags, vm_flags_t vm_flags)
{
        return generic_get_unmapped_area_topdown(filp, addr, len, pgoff, flags,
                                                 vm_flags);
}
#endif

unsigned long mm_get_unmapped_area_vmflags(struct mm_struct *mm, struct file *filp,
                                           unsigned long addr, unsigned long len,
                                           unsigned long pgoff, unsigned long flags,
                                           vm_flags_t vm_flags)
{
        if (test_bit(MMF_TOPDOWN, &mm->flags))
                return arch_get_unmapped_area_topdown(filp, addr, len, pgoff,
                                                      flags, vm_flags);
        return arch_get_unmapped_area(filp, addr, len, pgoff, flags, vm_flags);
}

unsigned long
__get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
                unsigned long pgoff, unsigned long flags, vm_flags_t vm_flags)
{
        unsigned long (*get_area)(struct file *, unsigned long,
                                  unsigned long, unsigned long, unsigned long)
                                  = NULL;

        unsigned long error = arch_mmap_check(addr, len, flags);
        if (error)
                return error;

        /* Careful about overflows.. */
        if (len > TASK_SIZE)
                return -ENOMEM;

        if (file) {
                if (file->f_op->get_unmapped_area)
                        get_area = file->f_op->get_unmapped_area;
        } else if (flags & MAP_SHARED) {
                /*
                 * mmap_region() will call shmem_zero_setup() to create a file,
                 * so use shmem's get_unmapped_area in case it can be huge.
                 */
                get_area = shmem_get_unmapped_area;
        }

        /* Always treat pgoff as zero for anonymous memory. */
        if (!file)
                pgoff = 0;

        if (get_area) {
                addr = get_area(file, addr, len, pgoff, flags);
        } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
                /* Ensures that larger anonymous mappings are THP aligned. */
                addr = thp_get_unmapped_area_vmflags(file, addr, len,
                                                     pgoff, flags, vm_flags);
        } else {
                addr = mm_get_unmapped_area_vmflags(current->mm, file, addr, len,
                                                    pgoff, flags, vm_flags);
        }
        if (IS_ERR_VALUE(addr))
                return addr;

        if (addr > TASK_SIZE - len)
                return -ENOMEM;
        if (offset_in_page(addr))
                return -EINVAL;

        error = security_mmap_addr(addr);
        return error ? error : addr;
}

unsigned long
mm_get_unmapped_area(struct mm_struct *mm, struct file *file,
                     unsigned long addr, unsigned long len,
                     unsigned long pgoff, unsigned long flags)
{
        if (test_bit(MMF_TOPDOWN, &mm->flags))
                return arch_get_unmapped_area_topdown(file, addr, len, pgoff, flags, 0);
        return arch_get_unmapped_area(file, addr, len, pgoff, flags, 0);
}
EXPORT_SYMBOL(mm_get_unmapped_area);

/**
 * find_vma_intersection() - Look up the first VMA which intersects the interval
 * @mm: The process address space.
 * @start_addr: The inclusive start user address.
 * @end_addr: The exclusive end user address.
 *
 * Returns: The first VMA within the provided range, %NULL otherwise.  Assumes
 * start_addr < end_addr.
 */
struct vm_area_struct *find_vma_intersection(struct mm_struct *mm,
                                             unsigned long start_addr,
                                             unsigned long end_addr)
{
        unsigned long index = start_addr;

        mmap_assert_locked(mm);
        return mt_find(&mm->mm_mt, &index, end_addr - 1);
}
EXPORT_SYMBOL(find_vma_intersection);

/**
 * find_vma() - Find the VMA for a given address, or the next VMA.
 * @mm: The mm_struct to check
 * @addr: The address
 *
 * Returns: The VMA associated with addr, or the next VMA.
 * May return %NULL in the case of no VMA at addr or above.
 */
struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
{
        unsigned long index = addr;

        mmap_assert_locked(mm);
        return mt_find(&mm->mm_mt, &index, ULONG_MAX);
}
EXPORT_SYMBOL(find_vma);

/**
 * find_vma_prev() - Find the VMA for a given address, or the next vma and
 * set %pprev to the previous VMA, if any.
 * @mm: The mm_struct to check
 * @addr: The address
 * @pprev: The pointer to set to the previous VMA
 *
 * Note that RCU lock is missing here since the external mmap_lock() is used
 * instead.
 *
 * Returns: The VMA associated with @addr, or the next vma.
 * May return %NULL in the case of no vma at addr or above.
 */
struct vm_area_struct *
find_vma_prev(struct mm_struct *mm, unsigned long addr,
                        struct vm_area_struct **pprev)
{
        struct vm_area_struct *vma;
        VMA_ITERATOR(vmi, mm, addr);

        vma = vma_iter_load(&vmi);
        *pprev = vma_prev(&vmi);
        if (!vma)
                vma = vma_next(&vmi);
        return vma;
}

/*
 * Verify that the stack growth is acceptable and
 * update accounting. This is shared with both the
 * grow-up and grow-down cases.
 */
static int acct_stack_growth(struct vm_area_struct *vma,
                             unsigned long size, unsigned long grow)
{
        struct mm_struct *mm = vma->vm_mm;
        unsigned long new_start;

        /* address space limit tests */
        if (!may_expand_vm(mm, vma->vm_flags, grow))
                return -ENOMEM;

        /* Stack limit test */
        if (size > rlimit(RLIMIT_STACK))
                return -ENOMEM;

        /* mlock limit tests */
        if (!mlock_future_ok(mm, vma->vm_flags, grow << PAGE_SHIFT))
                return -ENOMEM;

        /* Check to ensure the stack will not grow into a hugetlb-only region */
        new_start = (vma->vm_flags & VM_GROWSUP) ? vma->vm_start :
                        vma->vm_end - size;
        if (is_hugepage_only_range(vma->vm_mm, new_start, size))
                return -EFAULT;

        /*
         * Overcommit..  This must be the final test, as it will
         * update security statistics.
         */
        if (security_vm_enough_memory_mm(mm, grow))
                return -ENOMEM;

        return 0;
}

#if defined(CONFIG_STACK_GROWSUP)
/*
 * PA-RISC uses this for its stack.
 * vma is the last one with address > vma->vm_end.  Have to extend vma.
 */
static int expand_upwards(struct vm_area_struct *vma, unsigned long address)
{
        struct mm_struct *mm = vma->vm_mm;
        struct vm_area_struct *next;
        unsigned long gap_addr;
        int error = 0;
        VMA_ITERATOR(vmi, mm, vma->vm_start);

        if (!(vma->vm_flags & VM_GROWSUP))
                return -EFAULT;

        /* Guard against exceeding limits of the address space. */
        address &= PAGE_MASK;
        if (address >= (TASK_SIZE & PAGE_MASK))
                return -ENOMEM;
        address += PAGE_SIZE;

        /* Enforce stack_guard_gap */
        gap_addr = address + stack_guard_gap;

        /* Guard against overflow */
        if (gap_addr < address || gap_addr > TASK_SIZE)
                gap_addr = TASK_SIZE;

        next = find_vma_intersection(mm, vma->vm_end, gap_addr);
        if (next && vma_is_accessible(next)) {
                if (!(next->vm_flags & VM_GROWSUP))
                        return -ENOMEM;
                /* Check that both stack segments have the same anon_vma? */
        }

        if (next)
                vma_iter_prev_range_limit(&vmi, address);

        vma_iter_config(&vmi, vma->vm_start, address);
        if (vma_iter_prealloc(&vmi, vma))
                return -ENOMEM;

        /* We must make sure the anon_vma is allocated. */
        if (unlikely(anon_vma_prepare(vma))) {
                vma_iter_free(&vmi);
                return -ENOMEM;
        }

        /* Lock the VMA before expanding to prevent concurrent page faults */
        vma_start_write(vma);
        /*
         * vma->vm_start/vm_end cannot change under us because the caller
         * is required to hold the mmap_lock in read mode.  We need the
         * anon_vma lock to serialize against concurrent expand_stacks.
         */
        anon_vma_lock_write(vma->anon_vma);

        /* Somebody else might have raced and expanded it already */
        if (address > vma->vm_end) {
                unsigned long size, grow;

                size = address - vma->vm_start;
                grow = (address - vma->vm_end) >> PAGE_SHIFT;

                error = -ENOMEM;
                if (vma->vm_pgoff + (size >> PAGE_SHIFT) >= vma->vm_pgoff) {
                        error = acct_stack_growth(vma, size, grow);
                        if (!error) {
                                /*
                                 * We only hold a shared mmap_lock lock here, so
                                 * we need to protect against concurrent vma
                                 * expansions.  anon_vma_lock_write() doesn't
                                 * help here, as we don't guarantee that all
                                 * growable vmas in a mm share the same root
                                 * anon vma.  So, we reuse mm->page_table_lock
                                 * to guard against concurrent vma expansions.
                                 */
                                spin_lock(&mm->page_table_lock);
                                if (vma->vm_flags & VM_LOCKED)
                                        mm->locked_vm += grow;
                                vm_stat_account(mm, vma->vm_flags, grow);
                                anon_vma_interval_tree_pre_update_vma(vma);
                                vma->vm_end = address;
                                /* Overwrite old entry in mtree. */
                                vma_iter_store(&vmi, vma);
                                anon_vma_interval_tree_post_update_vma(vma);
                                spin_unlock(&mm->page_table_lock);

                                perf_event_mmap(vma);
                        }
                }
        }
        anon_vma_unlock_write(vma->anon_vma);
        vma_iter_free(&vmi);
        validate_mm(mm);
        return error;
}
#endif /* CONFIG_STACK_GROWSUP */

/*
 * vma is the first one with address < vma->vm_start.  Have to extend vma.
 * mmap_lock held for writing.
 */
int expand_downwards(struct vm_area_struct *vma, unsigned long address)
{
        struct mm_struct *mm = vma->vm_mm;
        struct vm_area_struct *prev;
        int error = 0;
        VMA_ITERATOR(vmi, mm, vma->vm_start);

        if (!(vma->vm_flags & VM_GROWSDOWN))
                return -EFAULT;

        address &= PAGE_MASK;
        if (address < mmap_min_addr || address < FIRST_USER_ADDRESS)
                return -EPERM;

        /* Enforce stack_guard_gap */
        prev = vma_prev(&vmi);
        /* Check that both stack segments have the same anon_vma? */
        if (prev) {
                if (!(prev->vm_flags & VM_GROWSDOWN) &&
                    vma_is_accessible(prev) &&
                    (address - prev->vm_end < stack_guard_gap))
                        return -ENOMEM;
        }

        if (prev)
                vma_iter_next_range_limit(&vmi, vma->vm_start);

        vma_iter_config(&vmi, address, vma->vm_end);
        if (vma_iter_prealloc(&vmi, vma))
                return -ENOMEM;

        /* We must make sure the anon_vma is allocated. */
        if (unlikely(anon_vma_prepare(vma))) {
                vma_iter_free(&vmi);
                return -ENOMEM;
        }

        /* Lock the VMA before expanding to prevent concurrent page faults */
        vma_start_write(vma);
        /*
         * vma->vm_start/vm_end cannot change under us because the caller
         * is required to hold the mmap_lock in read mode.  We need the
         * anon_vma lock to serialize against concurrent expand_stacks.
         */
        anon_vma_lock_write(vma->anon_vma);

        /* Somebody else might have raced and expanded it already */
        if (address < vma->vm_start) {
                unsigned long size, grow;

                size = vma->vm_end - address;
                grow = (vma->vm_start - address) >> PAGE_SHIFT;

                error = -ENOMEM;
                if (grow <= vma->vm_pgoff) {
                        error = acct_stack_growth(vma, size, grow);
                        if (!error) {
                                /*
                                 * We only hold a shared mmap_lock lock here, so
                                 * we need to protect against concurrent vma
                                 * expansions.  anon_vma_lock_write() doesn't
                                 * help here, as we don't guarantee that all
                                 * growable vmas in a mm share the same root
                                 * anon vma.  So, we reuse mm->page_table_lock
                                 * to guard against concurrent vma expansions.
                                 */
                                spin_lock(&mm->page_table_lock);
                                if (vma->vm_flags & VM_LOCKED)
                                        mm->locked_vm += grow;
                                vm_stat_account(mm, vma->vm_flags, grow);
                                anon_vma_interval_tree_pre_update_vma(vma);
                                vma->vm_start = address;
                                vma->vm_pgoff -= grow;
                                /* Overwrite old entry in mtree. */
                                vma_iter_store(&vmi, vma);
                                anon_vma_interval_tree_post_update_vma(vma);
                                spin_unlock(&mm->page_table_lock);

                                perf_event_mmap(vma);
                        }
                }
        }
        anon_vma_unlock_write(vma->anon_vma);
        vma_iter_free(&vmi);
        validate_mm(mm);
        return error;
}

/* enforced gap between the expanding stack and other mappings. */
unsigned long stack_guard_gap = 256UL<<PAGE_SHIFT;

static int __init cmdline_parse_stack_guard_gap(char *p)
{
        unsigned long val;
        char *endptr;

        val = simple_strtoul(p, &endptr, 10);
        if (!*endptr)
                stack_guard_gap = val << PAGE_SHIFT;

        return 1;
}
__setup("stack_guard_gap=", cmdline_parse_stack_guard_gap);

#ifdef CONFIG_STACK_GROWSUP
int expand_stack_locked(struct vm_area_struct *vma, unsigned long address)
{
        return expand_upwards(vma, address);
}

struct vm_area_struct *find_extend_vma_locked(struct mm_struct *mm, unsigned long addr)
{
        struct vm_area_struct *vma, *prev;

        addr &= PAGE_MASK;
        vma = find_vma_prev(mm, addr, &prev);
        if (vma && (vma->vm_start <= addr))
                return vma;
        if (!prev)
                return NULL;
        if (expand_stack_locked(prev, addr))
                return NULL;
        if (prev->vm_flags & VM_LOCKED)
                populate_vma_page_range(prev, addr, prev->vm_end, NULL);
        return prev;
}
#else
int expand_stack_locked(struct vm_area_struct *vma, unsigned long address)
{
        return expand_downwards(vma, address);
}

struct vm_area_struct *find_extend_vma_locked(struct mm_struct *mm, unsigned long addr)
{
        struct vm_area_struct *vma;
        unsigned long start;

        addr &= PAGE_MASK;
        vma = find_vma(mm, addr);
        if (!vma)
                return NULL;
        if (vma->vm_start <= addr)
                return vma;
        start = vma->vm_start;
        if (expand_stack_locked(vma, addr))
                return NULL;
        if (vma->vm_flags & VM_LOCKED)
                populate_vma_page_range(vma, addr, start, NULL);
        return vma;
}
#endif

#if defined(CONFIG_STACK_GROWSUP)

#define vma_expand_up(vma,addr) expand_upwards(vma, addr)
#define vma_expand_down(vma, addr) (-EFAULT)

#else

#define vma_expand_up(vma,addr) (-EFAULT)
#define vma_expand_down(vma, addr) expand_downwards(vma, addr)

#endif

/*
 * expand_stack(): legacy interface for page faulting. Don't use unless
 * you have to.
 *
 * This is called with the mm locked for reading, drops the lock, takes
 * the lock for writing, tries to look up a vma again, expands it if
 * necessary, and downgrades the lock to reading again.
 *
 * If no vma is found or it can't be expanded, it returns NULL and has
 * dropped the lock.
 */
struct vm_area_struct *expand_stack(struct mm_struct *mm, unsigned long addr)
{
        struct vm_area_struct *vma, *prev;

        mmap_read_unlock(mm);
        if (mmap_write_lock_killable(mm))
                return NULL;

        vma = find_vma_prev(mm, addr, &prev);
        if (vma && vma->vm_start <= addr)
                goto success;

        if (prev && !vma_expand_up(prev, addr)) {
                vma = prev;
                goto success;
        }

        if (vma && !vma_expand_down(vma, addr))
                goto success;

        mmap_write_unlock(mm);
        return NULL;

success:
        mmap_write_downgrade(mm);
        return vma;
}

/* do_munmap() - Wrapper function for non-maple tree aware do_munmap() calls.
 * @mm: The mm_struct
 * @start: The start address to munmap
 * @len: The length to be munmapped.
 * @uf: The userfaultfd list_head
 *
 * Return: 0 on success, error otherwise.
 */
int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
              struct list_head *uf)
{
        VMA_ITERATOR(vmi, mm, start);

        return do_vmi_munmap(&vmi, mm, start, len, uf, false);
}

unsigned long mmap_region(struct file *file, unsigned long addr,
                unsigned long len, vm_flags_t vm_flags, unsigned long pgoff,
                struct list_head *uf)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma = NULL;
        pgoff_t pglen = PHYS_PFN(len);
        struct vm_area_struct *merge;
        unsigned long charged = 0;
        struct vma_munmap_struct vms;
        struct ma_state mas_detach;
        struct maple_tree mt_detach;
        unsigned long end = addr + len;
        bool writable_file_mapping = false;
        int error = -ENOMEM;
        VMA_ITERATOR(vmi, mm, addr);
        VMG_STATE(vmg, mm, &vmi, addr, end, vm_flags, pgoff);

        vmg.file = file;
        /* Find the first overlapping VMA */
        vma = vma_find(&vmi, end);
        init_vma_munmap(&vms, &vmi, vma, addr, end, uf, /* unlock = */ false);
        if (vma) {
                mt_init_flags(&mt_detach, vmi.mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
                mt_on_stack(mt_detach);
                mas_init(&mas_detach, &mt_detach, /* addr = */ 0);
                /* Prepare to unmap any existing mapping in the area */
                error = vms_gather_munmap_vmas(&vms, &mas_detach);
                if (error)
                        goto gather_failed;

                vmg.next = vms.next;
                vmg.prev = vms.prev;
                vma = NULL;
        } else {
                vmg.next = vma_iter_next_rewind(&vmi, &vmg.prev);
        }

        /* Check against address space limit. */
        if (!may_expand_vm(mm, vm_flags, pglen - vms.nr_pages))
                goto abort_munmap;

        /*
         * Private writable mapping: check memory availability
         */
        if (accountable_mapping(file, vm_flags)) {
                charged = pglen;
                charged -= vms.nr_accounted;
                if (charged && security_vm_enough_memory_mm(mm, charged))
                        goto abort_munmap;

                vms.nr_accounted = 0;
                vm_flags |= VM_ACCOUNT;
                vmg.flags = vm_flags;
        }

        vma = vma_merge_new_range(&vmg);
        if (vma)
                goto expanded;
        /*
         * Determine the object being mapped and call the appropriate
         * specific mapper. the address has already been validated, but
         * not unmapped, but the maps are removed from the list.
         */
        vma = vm_area_alloc(mm);
        if (!vma)
                goto unacct_error;

        vma_iter_config(&vmi, addr, end);
        vma_set_range(vma, addr, end, pgoff);
        vm_flags_init(vma, vm_flags);
        vma->vm_page_prot = vm_get_page_prot(vm_flags);

        if (file) {
                vma->vm_file = get_file(file);
                /*
                 * call_mmap() may map PTE, so ensure there are no existing PTEs
                 * and call the vm_ops close function if one exists.
                 */
                vms_clean_up_area(&vms, &mas_detach);
                error = call_mmap(file, vma);
                if (error)
                        goto unmap_and_free_vma;

                if (vma_is_shared_maywrite(vma)) {
                        error = mapping_map_writable(file->f_mapping);
                        if (error)
                                goto close_and_free_vma;

                        writable_file_mapping = true;
                }

                /*
                 * Expansion is handled above, merging is handled below.
                 * Drivers should not alter the address of the VMA.
                 */
                error = -EINVAL;
                if (WARN_ON((addr != vma->vm_start)))
                        goto close_and_free_vma;

                vma_iter_config(&vmi, addr, end);
                /*
                 * If vm_flags changed after call_mmap(), we should try merge
                 * vma again as we may succeed this time.
                 */
                if (unlikely(vm_flags != vma->vm_flags && vmg.prev)) {
                        vmg.flags = vma->vm_flags;
                        /* If this fails, state is reset ready for a reattempt. */
                        merge = vma_merge_new_range(&vmg);

                        if (merge) {
                                /*
                                 * ->mmap() can change vma->vm_file and fput
                                 * the original file. So fput the vma->vm_file
                                 * here or we would add an extra fput for file
                                 * and cause general protection fault
                                 * ultimately.
                                 */
                                fput(vma->vm_file);
                                vm_area_free(vma);
                                vma = merge;
                                /* Update vm_flags to pick up the change. */
                                vm_flags = vma->vm_flags;
                                goto unmap_writable;
                        }
                        vma_iter_config(&vmi, addr, end);
                }

                vm_flags = vma->vm_flags;
        } else if (vm_flags & VM_SHARED) {
                error = shmem_zero_setup(vma);
                if (error)
                        goto free_vma;
        } else {
                vma_set_anonymous(vma);
        }

        if (map_deny_write_exec(vma, vma->vm_flags)) {
                error = -EACCES;
                goto close_and_free_vma;
        }

        /* Allow architectures to sanity-check the vm_flags */
        error = -EINVAL;
        if (!arch_validate_flags(vma->vm_flags))
                goto close_and_free_vma;

        error = -ENOMEM;
        if (vma_iter_prealloc(&vmi, vma))
                goto close_and_free_vma;

        /* Lock the VMA since it is modified after insertion into VMA tree */
        vma_start_write(vma);
        vma_iter_store(&vmi, vma);
        mm->map_count++;
        vma_link_file(vma);

        /*
         * vma_merge_new_range() calls khugepaged_enter_vma() too, the below
         * call covers the non-merge case.
         */
        khugepaged_enter_vma(vma, vma->vm_flags);

        /* Once vma denies write, undo our temporary denial count */
unmap_writable:
        if (writable_file_mapping)
                mapping_unmap_writable(file->f_mapping);
        file = vma->vm_file;
        ksm_add_vma(vma);
expanded:
        perf_event_mmap(vma);

        /* Unmap any existing mapping in the area */
        vms_complete_munmap_vmas(&vms, &mas_detach);

        vm_stat_account(mm, vm_flags, pglen);
        if (vm_flags & VM_LOCKED) {
                if ((vm_flags & VM_SPECIAL) || vma_is_dax(vma) ||
                                        is_vm_hugetlb_page(vma) ||
                                        vma == get_gate_vma(current->mm))
                        vm_flags_clear(vma, VM_LOCKED_MASK);
                else
                        mm->locked_vm += pglen;
        }

        if (file)
                uprobe_mmap(vma);

        /*
         * New (or expanded) vma always get soft dirty status.
         * Otherwise user-space soft-dirty page tracker won't
         * be able to distinguish situation when vma area unmapped,
         * then new mapped in-place (which must be aimed as
         * a completely new data area).
         */
        vm_flags_set(vma, VM_SOFTDIRTY);

        vma_set_page_prot(vma);

        validate_mm(mm);
        return addr;

close_and_free_vma:
        if (file && !vms.closed_vm_ops && vma->vm_ops && vma->vm_ops->close)
                vma->vm_ops->close(vma);

        if (file || vma->vm_file) {
unmap_and_free_vma:
                fput(vma->vm_file);
                vma->vm_file = NULL;

                vma_iter_set(&vmi, vma->vm_end);
                /* Undo any partial mapping done by a device driver. */
                unmap_region(&vmi.mas, vma, vmg.prev, vmg.next);
        }
        if (writable_file_mapping)
                mapping_unmap_writable(file->f_mapping);
free_vma:
        vm_area_free(vma);
unacct_error:
        if (charged)
                vm_unacct_memory(charged);

abort_munmap:
        vms_abort_munmap_vmas(&vms, &mas_detach);
gather_failed:
        validate_mm(mm);
        return error;
}

static int __vm_munmap(unsigned long start, size_t len, bool unlock)
{
        int ret;
        struct mm_struct *mm = current->mm;
        LIST_HEAD(uf);
        VMA_ITERATOR(vmi, mm, start);

        if (mmap_write_lock_killable(mm))
                return -EINTR;

        ret = do_vmi_munmap(&vmi, mm, start, len, &uf, unlock);
        if (ret || !unlock)
                mmap_write_unlock(mm);

        userfaultfd_unmap_complete(mm, &uf);
        return ret;
}

int vm_munmap(unsigned long start, size_t len)
{
        return __vm_munmap(start, len, false);
}
EXPORT_SYMBOL(vm_munmap);

SYSCALL_DEFINE2(munmap, unsigned long, addr, size_t, len)
{
        addr = untagged_addr(addr);
        return __vm_munmap(addr, len, true);
}


/*
 * Emulation of deprecated remap_file_pages() syscall.
 */
SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
                unsigned long, prot, unsigned long, pgoff, unsigned long, flags)
{

        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        unsigned long populate = 0;
        unsigned long ret = -EINVAL;
        struct file *file;

        pr_warn_once("%s (%d) uses deprecated remap_file_pages() syscall. See Documentation/mm/remap_file_pages.rst.\n",
                     current->comm, current->pid);

        if (prot)
                return ret;
        start = start & PAGE_MASK;
        size = size & PAGE_MASK;

        if (start + size <= start)
                return ret;

        /* Does pgoff wrap? */
        if (pgoff + (size >> PAGE_SHIFT) < pgoff)
                return ret;

        if (mmap_write_lock_killable(mm))
                return -EINTR;

        vma = vma_lookup(mm, start);

        if (!vma || !(vma->vm_flags & VM_SHARED))
                goto out;

        if (start + size > vma->vm_end) {
                VMA_ITERATOR(vmi, mm, vma->vm_end);
                struct vm_area_struct *next, *prev = vma;

                for_each_vma_range(vmi, next, start + size) {
                        /* hole between vmas ? */
                        if (next->vm_start != prev->vm_end)
                                goto out;

                        if (next->vm_file != vma->vm_file)
                                goto out;

                        if (next->vm_flags != vma->vm_flags)
                                goto out;

                        if (start + size <= next->vm_end)
                                break;

                        prev = next;
                }

                if (!next)
                        goto out;
        }

        prot |= vma->vm_flags & VM_READ ? PROT_READ : 0;
        prot |= vma->vm_flags & VM_WRITE ? PROT_WRITE : 0;
        prot |= vma->vm_flags & VM_EXEC ? PROT_EXEC : 0;

        flags &= MAP_NONBLOCK;
        flags |= MAP_SHARED | MAP_FIXED | MAP_POPULATE;
        if (vma->vm_flags & VM_LOCKED)
                flags |= MAP_LOCKED;

        file = get_file(vma->vm_file);
        ret = security_mmap_file(vma->vm_file, prot, flags);
        if (ret)
                goto out_fput;
        ret = do_mmap(vma->vm_file, start, size,
                        prot, flags, 0, pgoff, &populate, NULL);
out_fput:
        fput(file);
out:
        mmap_write_unlock(mm);
        if (populate)
                mm_populate(ret, populate);
        if (!IS_ERR_VALUE(ret))
                ret = 0;
        return ret;
}

/*
 * do_brk_flags() - Increase the brk vma if the flags match.
 * @vmi: The vma iterator
 * @addr: The start address
 * @len: The length of the increase
 * @vma: The vma,
 * @flags: The VMA Flags
 *
 * Extend the brk VMA from addr to addr + len.  If the VMA is NULL or the flags
 * do not match then create a new anonymous VMA.  Eventually we may be able to
 * do some brk-specific accounting here.
 */
static int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
                unsigned long addr, unsigned long len, unsigned long flags)
{
        struct mm_struct *mm = current->mm;

        /*
         * Check against address space limits by the changed size
         * Note: This happens *after* clearing old mappings in some code paths.
         */
        flags |= VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
        if (!may_expand_vm(mm, flags, len >> PAGE_SHIFT))
                return -ENOMEM;

        if (mm->map_count > sysctl_max_map_count)
                return -ENOMEM;

        if (security_vm_enough_memory_mm(mm, len >> PAGE_SHIFT))
                return -ENOMEM;

        /*
         * Expand the existing vma if possible; Note that singular lists do not
         * occur after forking, so the expand will only happen on new VMAs.
         */
        if (vma && vma->vm_end == addr) {
                VMG_STATE(vmg, mm, vmi, addr, addr + len, flags, PHYS_PFN(addr));

                vmg.prev = vma;
                vma_iter_next_range(vmi);

                if (vma_merge_new_range(&vmg))
                        goto out;
                else if (vmg_nomem(&vmg))
                        goto unacct_fail;
        }

        if (vma)
                vma_iter_next_range(vmi);
        /* create a vma struct for an anonymous mapping */
        vma = vm_area_alloc(mm);
        if (!vma)
                goto unacct_fail;

        vma_set_anonymous(vma);
        vma_set_range(vma, addr, addr + len, addr >> PAGE_SHIFT);
        vm_flags_init(vma, flags);
        vma->vm_page_prot = vm_get_page_prot(flags);
        vma_start_write(vma);
        if (vma_iter_store_gfp(vmi, vma, GFP_KERNEL))
                goto mas_store_fail;

        mm->map_count++;
        validate_mm(mm);
        ksm_add_vma(vma);
out:
        perf_event_mmap(vma);
        mm->total_vm += len >> PAGE_SHIFT;
        mm->data_vm += len >> PAGE_SHIFT;
        if (flags & VM_LOCKED)
                mm->locked_vm += (len >> PAGE_SHIFT);
        vm_flags_set(vma, VM_SOFTDIRTY);
        return 0;

mas_store_fail:
        vm_area_free(vma);
unacct_fail:
        vm_unacct_memory(len >> PAGE_SHIFT);
        return -ENOMEM;
}

int vm_brk_flags(unsigned long addr, unsigned long request, unsigned long flags)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma = NULL;
        unsigned long len;
        int ret;
        bool populate;
        LIST_HEAD(uf);
        VMA_ITERATOR(vmi, mm, addr);

        len = PAGE_ALIGN(request);
        if (len < request)
                return -ENOMEM;
        if (!len)
                return 0;

        /* Until we need other flags, refuse anything except VM_EXEC. */
        if ((flags & (~VM_EXEC)) != 0)
                return -EINVAL;

        if (mmap_write_lock_killable(mm))
                return -EINTR;

        ret = check_brk_limits(addr, len);
        if (ret)
                goto limits_failed;

        ret = do_vmi_munmap(&vmi, mm, addr, len, &uf, 0);
        if (ret)
                goto munmap_failed;

        vma = vma_prev(&vmi);
        ret = do_brk_flags(&vmi, vma, addr, len, flags);
        populate = ((mm->def_flags & VM_LOCKED) != 0);
        mmap_write_unlock(mm);
        userfaultfd_unmap_complete(mm, &uf);
        if (populate && !ret)
                mm_populate(addr, len);
        return ret;

munmap_failed:
limits_failed:
        mmap_write_unlock(mm);
        return ret;
}
EXPORT_SYMBOL(vm_brk_flags);

/* Release all mmaps. */
void exit_mmap(struct mm_struct *mm)
{
        struct mmu_gather tlb;
        struct vm_area_struct *vma;
        unsigned long nr_accounted = 0;
        VMA_ITERATOR(vmi, mm, 0);
        int count = 0;

        /* mm's last user has gone, and its about to be pulled down */
        mmu_notifier_release(mm);

        mmap_read_lock(mm);
        arch_exit_mmap(mm);

        vma = vma_next(&vmi);
        if (!vma || unlikely(xa_is_zero(vma))) {
                /* Can happen if dup_mmap() received an OOM */
                mmap_read_unlock(mm);
                mmap_write_lock(mm);
                goto destroy;
        }

        lru_add_drain();
        flush_cache_mm(mm);
        tlb_gather_mmu_fullmm(&tlb, mm);
        /* update_hiwater_rss(mm) here? but nobody should be looking */
        /* Use ULONG_MAX here to ensure all VMAs in the mm are unmapped */
        unmap_vmas(&tlb, &vmi.mas, vma, 0, ULONG_MAX, ULONG_MAX, false);
        mmap_read_unlock(mm);

        /*
         * Set MMF_OOM_SKIP to hide this task from the oom killer/reaper
         * because the memory has been already freed.
         */
        set_bit(MMF_OOM_SKIP, &mm->flags);
        mmap_write_lock(mm);
        mt_clear_in_rcu(&mm->mm_mt);
        vma_iter_set(&vmi, vma->vm_end);
        free_pgtables(&tlb, &vmi.mas, vma, FIRST_USER_ADDRESS,
                      USER_PGTABLES_CEILING, true);
        tlb_finish_mmu(&tlb);

        /*
         * Walk the list again, actually closing and freeing it, with preemption
         * enabled, without holding any MM locks besides the unreachable
         * mmap_write_lock.
         */
        vma_iter_set(&vmi, vma->vm_end);
        do {
                if (vma->vm_flags & VM_ACCOUNT)
                        nr_accounted += vma_pages(vma);
                remove_vma(vma, /* unreachable = */ true, /* closed = */ false);
                count++;
                cond_resched();
                vma = vma_next(&vmi);
        } while (vma && likely(!xa_is_zero(vma)));

        BUG_ON(count != mm->map_count);

        trace_exit_mmap(mm);
destroy:
        __mt_destroy(&mm->mm_mt);
        mmap_write_unlock(mm);
        vm_unacct_memory(nr_accounted);
}

/* Insert vm structure into process list sorted by address
 * and into the inode's i_mmap tree.  If vm_file is non-NULL
 * then i_mmap_rwsem is taken here.
 */
int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
{
        unsigned long charged = vma_pages(vma);


        if (find_vma_intersection(mm, vma->vm_start, vma->vm_end))
                return -ENOMEM;

        if ((vma->vm_flags & VM_ACCOUNT) &&
             security_vm_enough_memory_mm(mm, charged))
                return -ENOMEM;

        /*
         * The vm_pgoff of a purely anonymous vma should be irrelevant
         * until its first write fault, when page's anon_vma and index
         * are set.  But now set the vm_pgoff it will almost certainly
         * end up with (unless mremap moves it elsewhere before that
         * first wfault), so /proc/pid/maps tells a consistent story.
         *
         * By setting it to reflect the virtual start address of the
         * vma, merges and splits can happen in a seamless way, just
         * using the existing file pgoff checks and manipulations.
         * Similarly in do_mmap and in do_brk_flags.
         */
        if (vma_is_anonymous(vma)) {
                BUG_ON(vma->anon_vma);
                vma->vm_pgoff = vma->vm_start >> PAGE_SHIFT;
        }

        if (vma_link(mm, vma)) {
                if (vma->vm_flags & VM_ACCOUNT)
                        vm_unacct_memory(charged);
                return -ENOMEM;
        }

        return 0;
}

/*
 * Return true if the calling process may expand its vm space by the passed
 * number of pages
 */
bool may_expand_vm(struct mm_struct *mm, vm_flags_t flags, unsigned long npages)
{
        if (mm->total_vm + npages > rlimit(RLIMIT_AS) >> PAGE_SHIFT)
                return false;

        if (is_data_mapping(flags) &&
            mm->data_vm + npages > rlimit(RLIMIT_DATA) >> PAGE_SHIFT) {
                /* Workaround for Valgrind */
                if (rlimit(RLIMIT_DATA) == 0 &&
                    mm->data_vm + npages <= rlimit_max(RLIMIT_DATA) >> PAGE_SHIFT)
                        return true;

                pr_warn_once("%s (%d): VmData %lu exceed data ulimit %lu. Update limits%s.\n",
                             current->comm, current->pid,
                             (mm->data_vm + npages) << PAGE_SHIFT,
                             rlimit(RLIMIT_DATA),
                             ignore_rlimit_data ? "" : " or use boot option ignore_rlimit_data");

                if (!ignore_rlimit_data)
                        return false;
        }

        return true;
}

void vm_stat_account(struct mm_struct *mm, vm_flags_t flags, long npages)
{
        WRITE_ONCE(mm->total_vm, READ_ONCE(mm->total_vm)+npages);

        if (is_exec_mapping(flags))
                mm->exec_vm += npages;
        else if (is_stack_mapping(flags))
                mm->stack_vm += npages;
        else if (is_data_mapping(flags))
                mm->data_vm += npages;
}

static vm_fault_t special_mapping_fault(struct vm_fault *vmf);

/*
 * Close hook, called for unmap() and on the old vma for mremap().
 *
 * Having a close hook prevents vma merging regardless of flags.
 */
static void special_mapping_close(struct vm_area_struct *vma)
{
        const struct vm_special_mapping *sm = vma->vm_private_data;

        if (sm->close)
                sm->close(sm, vma);
}

static const char *special_mapping_name(struct vm_area_struct *vma)
{
        return ((struct vm_special_mapping *)vma->vm_private_data)->name;
}

static int special_mapping_mremap(struct vm_area_struct *new_vma)
{
        struct vm_special_mapping *sm = new_vma->vm_private_data;

        if (WARN_ON_ONCE(current->mm != new_vma->vm_mm))
                return -EFAULT;

        if (sm->mremap)
                return sm->mremap(sm, new_vma);

        return 0;
}

static int special_mapping_split(struct vm_area_struct *vma, unsigned long addr)
{
        /*
         * Forbid splitting special mappings - kernel has expectations over
         * the number of pages in mapping. Together with VM_DONTEXPAND
         * the size of vma should stay the same over the special mapping's
         * lifetime.
         */
        return -EINVAL;
}

static const struct vm_operations_struct special_mapping_vmops = {
        .close = special_mapping_close,
        .fault = special_mapping_fault,
        .mremap = special_mapping_mremap,
        .name = special_mapping_name,
        /* vDSO code relies that VVAR can't be accessed remotely */
        .access = NULL,
        .may_split = special_mapping_split,
};

static vm_fault_t special_mapping_fault(struct vm_fault *vmf)
{
        struct vm_area_struct *vma = vmf->vma;
        pgoff_t pgoff;
        struct page **pages;
        struct vm_special_mapping *sm = vma->vm_private_data;

        if (sm->fault)
                return sm->fault(sm, vmf->vma, vmf);

        pages = sm->pages;

        for (pgoff = vmf->pgoff; pgoff && *pages; ++pages)
                pgoff--;

        if (*pages) {
                struct page *page = *pages;
                get_page(page);
                vmf->page = page;
                return 0;
        }

        return VM_FAULT_SIGBUS;
}

static struct vm_area_struct *__install_special_mapping(
        struct mm_struct *mm,
        unsigned long addr, unsigned long len,
        unsigned long vm_flags, void *priv,
        const struct vm_operations_struct *ops)
{
        int ret;
        struct vm_area_struct *vma;

        vma = vm_area_alloc(mm);
        if (unlikely(vma == NULL))
                return ERR_PTR(-ENOMEM);

        vma_set_range(vma, addr, addr + len, 0);
        vm_flags_init(vma, (vm_flags | mm->def_flags |
                      VM_DONTEXPAND | VM_SOFTDIRTY) & ~VM_LOCKED_MASK);
        vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);

        vma->vm_ops = ops;
        vma->vm_private_data = priv;

        ret = insert_vm_struct(mm, vma);
        if (ret)
                goto out;

        vm_stat_account(mm, vma->vm_flags, len >> PAGE_SHIFT);

        perf_event_mmap(vma);

        return vma;

out:
        vm_area_free(vma);
        return ERR_PTR(ret);
}

bool vma_is_special_mapping(const struct vm_area_struct *vma,
        const struct vm_special_mapping *sm)
{
        return vma->vm_private_data == sm &&
                vma->vm_ops == &special_mapping_vmops;
}

/*
 * Called with mm->mmap_lock held for writing.
 * Insert a new vma covering the given region, with the given flags.
 * Its pages are supplied by the given array of struct page *.
 * The array can be shorter than len >> PAGE_SHIFT if it's null-terminated.
 * The region past the last page supplied will always produce SIGBUS.
 * The array pointer and the pages it points to are assumed to stay alive
 * for as long as this mapping might exist.
 */
struct vm_area_struct *_install_special_mapping(
        struct mm_struct *mm,
        unsigned long addr, unsigned long len,
        unsigned long vm_flags, const struct vm_special_mapping *spec)
{
        return __install_special_mapping(mm, addr, len, vm_flags, (void *)spec,
                                        &special_mapping_vmops);
}

/*
 * initialise the percpu counter for VM
 */
void __init mmap_init(void)
{
        int ret;

        ret = percpu_counter_init(&vm_committed_as, 0, GFP_KERNEL);
        VM_BUG_ON(ret);
}

/*
 * Initialise sysctl_user_reserve_kbytes.
 *
 * This is intended to prevent a user from starting a single memory hogging
 * process, such that they cannot recover (kill the hog) in OVERCOMMIT_NEVER
 * mode.
 *
 * The default value is min(3% of free memory, 128MB)
 * 128MB is enough to recover with sshd/login, bash, and top/kill.
 */
static int init_user_reserve(void)
{
        unsigned long free_kbytes;

        free_kbytes = K(global_zone_page_state(NR_FREE_PAGES));

        sysctl_user_reserve_kbytes = min(free_kbytes / 32, SZ_128K);
        return 0;
}
subsys_initcall(init_user_reserve);

/*
 * Initialise sysctl_admin_reserve_kbytes.
 *
 * The purpose of sysctl_admin_reserve_kbytes is to allow the sys admin
 * to log in and kill a memory hogging process.
 *
 * Systems with more than 256MB will reserve 8MB, enough to recover
 * with sshd, bash, and top in OVERCOMMIT_GUESS. Smaller systems will
 * only reserve 3% of free pages by default.
 */
static int init_admin_reserve(void)
{
        unsigned long free_kbytes;

        free_kbytes = K(global_zone_page_state(NR_FREE_PAGES));

        sysctl_admin_reserve_kbytes = min(free_kbytes / 32, SZ_8K);
        return 0;
}
subsys_initcall(init_admin_reserve);

/*
 * Reinititalise user and admin reserves if memory is added or removed.
 *
 * The default user reserve max is 128MB, and the default max for the
 * admin reserve is 8MB. These are usually, but not always, enough to
 * enable recovery from a memory hogging process using login/sshd, a shell,
 * and tools like top. It may make sense to increase or even disable the
 * reserve depending on the existence of swap or variations in the recovery
 * tools. So, the admin may have changed them.
 *
 * If memory is added and the reserves have been eliminated or increased above
 * the default max, then we'll trust the admin.
 *
 * If memory is removed and there isn't enough free memory, then we
 * need to reset the reserves.
 *
 * Otherwise keep the reserve set by the admin.
 */
static int reserve_mem_notifier(struct notifier_block *nb,
                             unsigned long action, void *data)
{
        unsigned long tmp, free_kbytes;

        switch (action) {
        case MEM_ONLINE:
                /* Default max is 128MB. Leave alone if modified by operator. */
                tmp = sysctl_user_reserve_kbytes;
                if (tmp > 0 && tmp < SZ_128K)
                        init_user_reserve();

                /* Default max is 8MB.  Leave alone if modified by operator. */
                tmp = sysctl_admin_reserve_kbytes;
                if (tmp > 0 && tmp < SZ_8K)
                        init_admin_reserve();

                break;
        case MEM_OFFLINE:
                free_kbytes = K(global_zone_page_state(NR_FREE_PAGES));

                if (sysctl_user_reserve_kbytes > free_kbytes) {
                        init_user_reserve();
                        pr_info("vm.user_reserve_kbytes reset to %lu\n",
                                sysctl_user_reserve_kbytes);
                }

                if (sysctl_admin_reserve_kbytes > free_kbytes) {
                        init_admin_reserve();
                        pr_info("vm.admin_reserve_kbytes reset to %lu\n",
                                sysctl_admin_reserve_kbytes);
                }
                break;
        default:
                break;
        }
        return NOTIFY_OK;
}

static int __meminit init_reserve_notifier(void)
{
        if (hotplug_memory_notifier(reserve_mem_notifier, DEFAULT_CALLBACK_PRI))
                pr_err("Failed registering memory add/remove notifier for admin reserve\n");

        return 0;
}
subsys_initcall(init_reserve_notifier);

/*
 * Relocate a VMA downwards by shift bytes. There cannot be any VMAs between
 * this VMA and its relocated range, which will now reside at [vma->vm_start -
 * shift, vma->vm_end - shift).
 *
 * This function is almost certainly NOT what you want for anything other than
 * early executable temporary stack relocation.
 */
int relocate_vma_down(struct vm_area_struct *vma, unsigned long shift)
{
        /*
         * The process proceeds as follows:
         *
         * 1) Use shift to calculate the new vma endpoints.
         * 2) Extend vma to cover both the old and new ranges.  This ensures the
         *    arguments passed to subsequent functions are consistent.
         * 3) Move vma's page tables to the new range.
         * 4) Free up any cleared pgd range.
         * 5) Shrink the vma to cover only the new range.
         */

        struct mm_struct *mm = vma->vm_mm;
        unsigned long old_start = vma->vm_start;
        unsigned long old_end = vma->vm_end;
        unsigned long length = old_end - old_start;
        unsigned long new_start = old_start - shift;
        unsigned long new_end = old_end - shift;
        VMA_ITERATOR(vmi, mm, new_start);
        VMG_STATE(vmg, mm, &vmi, new_start, old_end, 0, vma->vm_pgoff);
        struct vm_area_struct *next;
        struct mmu_gather tlb;

        BUG_ON(new_start > new_end);

        /*
         * ensure there are no vmas between where we want to go
         * and where we are
         */
        if (vma != vma_next(&vmi))
                return -EFAULT;

        vma_iter_prev_range(&vmi);
        /*
         * cover the whole range: [new_start, old_end)
         */
        vmg.vma = vma;
        if (vma_expand(&vmg))
                return -ENOMEM;

        /*
         * move the page tables downwards, on failure we rely on
         * process cleanup to remove whatever mess we made.
         */
        if (length != move_page_tables(vma, old_start,
                                       vma, new_start, length, false, true))
                return -ENOMEM;

        lru_add_drain();
        tlb_gather_mmu(&tlb, mm);
        next = vma_next(&vmi);
        if (new_end > old_start) {
                /*
                 * when the old and new regions overlap clear from new_end.
                 */
                free_pgd_range(&tlb, new_end, old_end, new_end,
                        next ? next->vm_start : USER_PGTABLES_CEILING);
        } else {
                /*
                 * otherwise, clean from old_start; this is done to not touch
                 * the address space in [new_end, old_start) some architectures
                 * have constraints on va-space that make this illegal (IA64) -
                 * for the others its just a little faster.
                 */
                free_pgd_range(&tlb, old_start, old_end, new_end,
                        next ? next->vm_start : USER_PGTABLES_CEILING);
        }
        tlb_finish_mmu(&tlb);

        vma_prev(&vmi);
        /* Shrink the vma to just the new range */
        return vma_shrink(&vmi, vma, new_start, new_end, vma->vm_pgoff);
}