[thirdparty/kernel/stable.git] / fs / hugetlbfs / inode.c

/*
 * hugetlbpage-backed filesystem.  Based on ramfs.
 *
 * Nadia Yvette Chambers, 2002
 *
 * Copyright (C) 2002 Linus Torvalds.
 * License: GPL
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/thread_info.h>
#include <asm/current.h>
#include <linux/falloc.h>
#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/file.h>
#include <linux/kernel.h>
#include <linux/writeback.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/capability.h>
#include <linux/ctype.h>
#include <linux/backing-dev.h>
#include <linux/hugetlb.h>
#include <linux/pagevec.h>
#include <linux/fs_parser.h>
#include <linux/mman.h>
#include <linux/slab.h>
#include <linux/dnotify.h>
#include <linux/statfs.h>
#include <linux/security.h>
#include <linux/magic.h>
#include <linux/migrate.h>
#include <linux/uio.h>

#include <linux/uaccess.h>
#include <linux/sched/mm.h>

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

static const struct address_space_operations hugetlbfs_aops;
static const struct file_operations hugetlbfs_file_operations;
static const struct inode_operations hugetlbfs_dir_inode_operations;
static const struct inode_operations hugetlbfs_inode_operations;

enum hugetlbfs_size_type { NO_SIZE, SIZE_STD, SIZE_PERCENT };

struct hugetlbfs_fs_context {
        struct hstate           *hstate;
        unsigned long long      max_size_opt;
        unsigned long long      min_size_opt;
        long                    max_hpages;
        long                    nr_inodes;
        long                    min_hpages;
        enum hugetlbfs_size_type max_val_type;
        enum hugetlbfs_size_type min_val_type;
        kuid_t                  uid;
        kgid_t                  gid;
        umode_t                 mode;
};

int sysctl_hugetlb_shm_group;

enum hugetlb_param {
        Opt_gid,
        Opt_min_size,
        Opt_mode,
        Opt_nr_inodes,
        Opt_pagesize,
        Opt_size,
        Opt_uid,
};

static const struct fs_parameter_spec hugetlb_fs_parameters[] = {
        fsparam_gid   ("gid",           Opt_gid),
        fsparam_string("min_size",      Opt_min_size),
        fsparam_u32oct("mode",          Opt_mode),
        fsparam_string("nr_inodes",     Opt_nr_inodes),
        fsparam_string("pagesize",      Opt_pagesize),
        fsparam_string("size",          Opt_size),
        fsparam_uid   ("uid",           Opt_uid),
        {}
};

/*
 * Mask used when checking the page offset value passed in via system
 * calls.  This value will be converted to a loff_t which is signed.
 * Therefore, we want to check the upper PAGE_SHIFT + 1 bits of the
 * value.  The extra bit (- 1 in the shift value) is to take the sign
 * bit into account.
 */
#define PGOFF_LOFFT_MAX \
        (((1UL << (PAGE_SHIFT + 1)) - 1) <<  (BITS_PER_LONG - (PAGE_SHIFT + 1)))

static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma)
{
        struct inode *inode = file_inode(file);
        loff_t len, vma_len;
        int ret;
        struct hstate *h = hstate_file(file);
        vm_flags_t vm_flags;

        /*
         * vma address alignment (but not the pgoff alignment) has
         * already been checked by prepare_hugepage_range.  If you add
         * any error returns here, do so after setting VM_HUGETLB, so
         * is_vm_hugetlb_page tests below unmap_region go the right
         * way when do_mmap unwinds (may be important on powerpc
         * and ia64).
         */
        vm_flags_set(vma, VM_HUGETLB | VM_DONTEXPAND);
        vma->vm_ops = &hugetlb_vm_ops;

        /*
         * page based offset in vm_pgoff could be sufficiently large to
         * overflow a loff_t when converted to byte offset.  This can
         * only happen on architectures where sizeof(loff_t) ==
         * sizeof(unsigned long).  So, only check in those instances.
         */
        if (sizeof(unsigned long) == sizeof(loff_t)) {
                if (vma->vm_pgoff & PGOFF_LOFFT_MAX)
                        return -EINVAL;
        }

        /* must be huge page aligned */
        if (vma->vm_pgoff & (~huge_page_mask(h) >> PAGE_SHIFT))
                return -EINVAL;

        vma_len = (loff_t)(vma->vm_end - vma->vm_start);
        len = vma_len + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
        /* check for overflow */
        if (len < vma_len)
                return -EINVAL;

        inode_lock(inode);
        file_accessed(file);

        ret = -ENOMEM;

        vm_flags = vma->vm_flags;
        /*
         * for SHM_HUGETLB, the pages are reserved in the shmget() call so skip
         * reserving here. Note: only for SHM hugetlbfs file, the inode
         * flag S_PRIVATE is set.
         */
        if (inode->i_flags & S_PRIVATE)
                vm_flags |= VM_NORESERVE;

        if (hugetlb_reserve_pages(inode,
                                vma->vm_pgoff >> huge_page_order(h),
                                len >> huge_page_shift(h), vma,
                                vm_flags) < 0)
                goto out;

        ret = 0;
        if (vma->vm_flags & VM_WRITE && inode->i_size < len)
                i_size_write(inode, len);
out:
        inode_unlock(inode);

        return ret;
}

/*
 * Called under mmap_write_lock(mm).
 */

unsigned long
hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
                            unsigned long len, unsigned long pgoff,
                            unsigned long flags)
{
        unsigned long addr0 = 0;
        struct hstate *h = hstate_file(file);

        if (len & ~huge_page_mask(h))
                return -EINVAL;
        if ((flags & MAP_FIXED) && (addr & ~huge_page_mask(h)))
                return -EINVAL;
        if (addr)
                addr0 = ALIGN(addr, huge_page_size(h));

        return mm_get_unmapped_area_vmflags(current->mm, file, addr0, len, pgoff,
                                            flags, 0);
}

/*
 * Someone wants to read @bytes from a HWPOISON hugetlb @folio from @offset.
 * Returns the maximum number of bytes one can read without touching the 1st raw
 * HWPOISON page.
 *
 * The implementation borrows the iteration logic from copy_page_to_iter*.
 */
static size_t adjust_range_hwpoison(struct folio *folio, size_t offset,
                size_t bytes)
{
        struct page *page;
        size_t n = 0;
        size_t res = 0;

        /* First page to start the loop. */
        page = folio_page(folio, offset / PAGE_SIZE);
        offset %= PAGE_SIZE;
        while (1) {
                if (is_raw_hwpoison_page_in_hugepage(page))
                        break;

                /* Safe to read n bytes without touching HWPOISON subpage. */
                n = min(bytes, (size_t)PAGE_SIZE - offset);
                res += n;
                bytes -= n;
                if (!bytes || !n)
                        break;
                offset += n;
                if (offset == PAGE_SIZE) {
                        page = nth_page(page, 1);
                        offset = 0;
                }
        }

        return res;
}

/*
 * Support for read() - Find the page attached to f_mapping and copy out the
 * data. This provides functionality similar to filemap_read().
 */
static ssize_t hugetlbfs_read_iter(struct kiocb *iocb, struct iov_iter *to)
{
        struct file *file = iocb->ki_filp;
        struct hstate *h = hstate_file(file);
        struct address_space *mapping = file->f_mapping;
        struct inode *inode = mapping->host;
        unsigned long index = iocb->ki_pos >> huge_page_shift(h);
        unsigned long offset = iocb->ki_pos & ~huge_page_mask(h);
        unsigned long end_index;
        loff_t isize;
        ssize_t retval = 0;

        while (iov_iter_count(to)) {
                struct folio *folio;
                size_t nr, copied, want;

                /* nr is the maximum number of bytes to copy from this page */
                nr = huge_page_size(h);
                isize = i_size_read(inode);
                if (!isize)
                        break;
                end_index = (isize - 1) >> huge_page_shift(h);
                if (index > end_index)
                        break;
                if (index == end_index) {
                        nr = ((isize - 1) & ~huge_page_mask(h)) + 1;
                        if (nr <= offset)
                                break;
                }
                nr = nr - offset;

                /* Find the folio */
                folio = filemap_lock_hugetlb_folio(h, mapping, index);
                if (IS_ERR(folio)) {
                        /*
                         * We have a HOLE, zero out the user-buffer for the
                         * length of the hole or request.
                         */
                        copied = iov_iter_zero(nr, to);
                } else {
                        folio_unlock(folio);

                        if (!folio_test_hwpoison(folio))
                                want = nr;
                        else {
                                /*
                                 * Adjust how many bytes safe to read without
                                 * touching the 1st raw HWPOISON page after
                                 * offset.
                                 */
                                want = adjust_range_hwpoison(folio, offset, nr);
                                if (want == 0) {
                                        folio_put(folio);
                                        retval = -EIO;
                                        break;
                                }
                        }

                        /*
                         * We have the folio, copy it to user space buffer.
                         */
                        copied = copy_folio_to_iter(folio, offset, want, to);
                        folio_put(folio);
                }
                offset += copied;
                retval += copied;
                if (copied != nr && iov_iter_count(to)) {
                        if (!retval)
                                retval = -EFAULT;
                        break;
                }
                index += offset >> huge_page_shift(h);
                offset &= ~huge_page_mask(h);
        }
        iocb->ki_pos = ((loff_t)index << huge_page_shift(h)) + offset;
        return retval;
}

static int hugetlbfs_write_begin(const struct kiocb *iocb,
                        struct address_space *mapping,
                        loff_t pos, unsigned len,
                        struct folio **foliop, void **fsdata)
{
        return -EINVAL;
}

static int hugetlbfs_write_end(const struct kiocb *iocb,
                               struct address_space *mapping,
                               loff_t pos, unsigned len, unsigned copied,
                               struct folio *folio, void *fsdata)
{
        BUG();
        return -EINVAL;
}

static void hugetlb_delete_from_page_cache(struct folio *folio)
{
        folio_clear_dirty(folio);
        folio_clear_uptodate(folio);
        filemap_remove_folio(folio);
}

/*
 * Called with i_mmap_rwsem held for inode based vma maps.  This makes
 * sure vma (and vm_mm) will not go away.  We also hold the hugetlb fault
 * mutex for the page in the mapping.  So, we can not race with page being
 * faulted into the vma.
 */
static bool hugetlb_vma_maps_pfn(struct vm_area_struct *vma,
                                unsigned long addr, unsigned long pfn)
{
        pte_t *ptep, pte;

        ptep = hugetlb_walk(vma, addr, huge_page_size(hstate_vma(vma)));
        if (!ptep)
                return false;

        pte = huge_ptep_get(vma->vm_mm, addr, ptep);
        if (huge_pte_none(pte) || !pte_present(pte))
                return false;

        if (pte_pfn(pte) == pfn)
                return true;

        return false;
}

/*
 * Can vma_offset_start/vma_offset_end overflow on 32-bit arches?
 * No, because the interval tree returns us only those vmas
 * which overlap the truncated area starting at pgoff,
 * and no vma on a 32-bit arch can span beyond the 4GB.
 */
static unsigned long vma_offset_start(struct vm_area_struct *vma, pgoff_t start)
{
        unsigned long offset = 0;

        if (vma->vm_pgoff < start)
                offset = (start - vma->vm_pgoff) << PAGE_SHIFT;

        return vma->vm_start + offset;
}

static unsigned long vma_offset_end(struct vm_area_struct *vma, pgoff_t end)
{
        unsigned long t_end;

        if (!end)
                return vma->vm_end;

        t_end = ((end - vma->vm_pgoff) << PAGE_SHIFT) + vma->vm_start;
        if (t_end > vma->vm_end)
                t_end = vma->vm_end;
        return t_end;
}

/*
 * Called with hugetlb fault mutex held.  Therefore, no more mappings to
 * this folio can be created while executing the routine.
 */
static void hugetlb_unmap_file_folio(struct hstate *h,
                                        struct address_space *mapping,
                                        struct folio *folio, pgoff_t index)
{
        struct rb_root_cached *root = &mapping->i_mmap;
        struct hugetlb_vma_lock *vma_lock;
        unsigned long pfn = folio_pfn(folio);
        struct vm_area_struct *vma;
        unsigned long v_start;
        unsigned long v_end;
        pgoff_t start, end;

        start = index * pages_per_huge_page(h);
        end = (index + 1) * pages_per_huge_page(h);

        i_mmap_lock_write(mapping);
retry:
        vma_lock = NULL;
        vma_interval_tree_foreach(vma, root, start, end - 1) {
                v_start = vma_offset_start(vma, start);
                v_end = vma_offset_end(vma, end);

                if (!hugetlb_vma_maps_pfn(vma, v_start, pfn))
                        continue;

                if (!hugetlb_vma_trylock_write(vma)) {
                        vma_lock = vma->vm_private_data;
                        /*
                         * If we can not get vma lock, we need to drop
                         * immap_sema and take locks in order.  First,
                         * take a ref on the vma_lock structure so that
                         * we can be guaranteed it will not go away when
                         * dropping immap_sema.
                         */
                        kref_get(&vma_lock->refs);
                        break;
                }

                unmap_hugepage_range(vma, v_start, v_end, NULL,
                                     ZAP_FLAG_DROP_MARKER);
                hugetlb_vma_unlock_write(vma);
        }

        i_mmap_unlock_write(mapping);

        if (vma_lock) {
                /*
                 * Wait on vma_lock.  We know it is still valid as we have
                 * a reference.  We must 'open code' vma locking as we do
                 * not know if vma_lock is still attached to vma.
                 */
                down_write(&vma_lock->rw_sema);
                i_mmap_lock_write(mapping);

                vma = vma_lock->vma;
                if (!vma) {
                        /*
                         * If lock is no longer attached to vma, then just
                         * unlock, drop our reference and retry looking for
                         * other vmas.
                         */
                        up_write(&vma_lock->rw_sema);
                        kref_put(&vma_lock->refs, hugetlb_vma_lock_release);
                        goto retry;
                }

                /*
                 * vma_lock is still attached to vma.  Check to see if vma
                 * still maps page and if so, unmap.
                 */
                v_start = vma_offset_start(vma, start);
                v_end = vma_offset_end(vma, end);
                if (hugetlb_vma_maps_pfn(vma, v_start, pfn))
                        unmap_hugepage_range(vma, v_start, v_end, NULL,
                                             ZAP_FLAG_DROP_MARKER);

                kref_put(&vma_lock->refs, hugetlb_vma_lock_release);
                hugetlb_vma_unlock_write(vma);

                goto retry;
        }
}

static void
hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end,
                      zap_flags_t zap_flags)
{
        struct vm_area_struct *vma;

        /*
         * end == 0 indicates that the entire range after start should be
         * unmapped.  Note, end is exclusive, whereas the interval tree takes
         * an inclusive "last".
         */
        vma_interval_tree_foreach(vma, root, start, end ? end - 1 : ULONG_MAX) {
                unsigned long v_start;
                unsigned long v_end;

                if (!hugetlb_vma_trylock_write(vma))
                        continue;

                v_start = vma_offset_start(vma, start);
                v_end = vma_offset_end(vma, end);

                unmap_hugepage_range(vma, v_start, v_end, NULL, zap_flags);

                /*
                 * Note that vma lock only exists for shared/non-private
                 * vmas.  Therefore, lock is not held when calling
                 * unmap_hugepage_range for private vmas.
                 */
                hugetlb_vma_unlock_write(vma);
        }
}

/*
 * Called with hugetlb fault mutex held.
 * Returns true if page was actually removed, false otherwise.
 */
static bool remove_inode_single_folio(struct hstate *h, struct inode *inode,
                                        struct address_space *mapping,
                                        struct folio *folio, pgoff_t index,
                                        bool truncate_op)
{
        bool ret = false;

        /*
         * If folio is mapped, it was faulted in after being
         * unmapped in caller.  Unmap (again) while holding
         * the fault mutex.  The mutex will prevent faults
         * until we finish removing the folio.
         */
        if (unlikely(folio_mapped(folio)))
                hugetlb_unmap_file_folio(h, mapping, folio, index);

        folio_lock(folio);
        /*
         * We must remove the folio from page cache before removing
         * the region/ reserve map (hugetlb_unreserve_pages).  In
         * rare out of memory conditions, removal of the region/reserve
         * map could fail.  Correspondingly, the subpool and global
         * reserve usage count can need to be adjusted.
         */
        VM_BUG_ON_FOLIO(folio_test_hugetlb_restore_reserve(folio), folio);
        hugetlb_delete_from_page_cache(folio);
        ret = true;
        if (!truncate_op) {
                if (unlikely(hugetlb_unreserve_pages(inode, index,
                                                        index + 1, 1)))
                        hugetlb_fix_reserve_counts(inode);
        }

        folio_unlock(folio);
        return ret;
}

/*
 * remove_inode_hugepages handles two distinct cases: truncation and hole
 * punch.  There are subtle differences in operation for each case.
 *
 * truncation is indicated by end of range being LLONG_MAX
 *      In this case, we first scan the range and release found pages.
 *      After releasing pages, hugetlb_unreserve_pages cleans up region/reserve
 *      maps and global counts.  Page faults can race with truncation.
 *      During faults, hugetlb_no_page() checks i_size before page allocation,
 *      and again after obtaining page table lock.  It will 'back out'
 *      allocations in the truncated range.
 * hole punch is indicated if end is not LLONG_MAX
 *      In the hole punch case we scan the range and release found pages.
 *      Only when releasing a page is the associated region/reserve map
 *      deleted.  The region/reserve map for ranges without associated
 *      pages are not modified.  Page faults can race with hole punch.
 *      This is indicated if we find a mapped page.
 * Note: If the passed end of range value is beyond the end of file, but
 * not LLONG_MAX this routine still performs a hole punch operation.
 */
static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
                                   loff_t lend)
{
        struct hstate *h = hstate_inode(inode);
        struct address_space *mapping = &inode->i_data;
        const pgoff_t end = lend >> PAGE_SHIFT;
        struct folio_batch fbatch;
        pgoff_t next, index;
        int i, freed = 0;
        bool truncate_op = (lend == LLONG_MAX);

        folio_batch_init(&fbatch);
        next = lstart >> PAGE_SHIFT;
        while (filemap_get_folios(mapping, &next, end - 1, &fbatch)) {
                for (i = 0; i < folio_batch_count(&fbatch); ++i) {
                        struct folio *folio = fbatch.folios[i];
                        u32 hash = 0;

                        index = folio->index >> huge_page_order(h);
                        hash = hugetlb_fault_mutex_hash(mapping, index);
                        mutex_lock(&hugetlb_fault_mutex_table[hash]);

                        /*
                         * Remove folio that was part of folio_batch.
                         */
                        if (remove_inode_single_folio(h, inode, mapping, folio,
                                                        index, truncate_op))
                                freed++;

                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                }
                folio_batch_release(&fbatch);
                cond_resched();
        }

        if (truncate_op)
                (void)hugetlb_unreserve_pages(inode,
                                lstart >> huge_page_shift(h),
                                LONG_MAX, freed);
}

static void hugetlbfs_evict_inode(struct inode *inode)
{
        struct resv_map *resv_map;

        trace_hugetlbfs_evict_inode(inode);
        remove_inode_hugepages(inode, 0, LLONG_MAX);

        /*
         * Get the resv_map from the address space embedded in the inode.
         * This is the address space which points to any resv_map allocated
         * at inode creation time.  If this is a device special inode,
         * i_mapping may not point to the original address space.
         */
        resv_map = (struct resv_map *)(&inode->i_data)->i_private_data;
        /* Only regular and link inodes have associated reserve maps */
        if (resv_map)
                resv_map_release(&resv_map->refs);
        clear_inode(inode);
}

static void hugetlb_vmtruncate(struct inode *inode, loff_t offset)
{
        pgoff_t pgoff;
        struct address_space *mapping = inode->i_mapping;
        struct hstate *h = hstate_inode(inode);

        BUG_ON(offset & ~huge_page_mask(h));
        pgoff = offset >> PAGE_SHIFT;

        i_size_write(inode, offset);
        i_mmap_lock_write(mapping);
        if (!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root))
                hugetlb_vmdelete_list(&mapping->i_mmap, pgoff, 0,
                                      ZAP_FLAG_DROP_MARKER);
        i_mmap_unlock_write(mapping);
        remove_inode_hugepages(inode, offset, LLONG_MAX);
}

static void hugetlbfs_zero_partial_page(struct hstate *h,
                                        struct address_space *mapping,
                                        loff_t start,
                                        loff_t end)
{
        pgoff_t idx = start >> huge_page_shift(h);
        struct folio *folio;

        folio = filemap_lock_hugetlb_folio(h, mapping, idx);
        if (IS_ERR(folio))
                return;

        start = start & ~huge_page_mask(h);
        end = end & ~huge_page_mask(h);
        if (!end)
                end = huge_page_size(h);

        folio_zero_segment(folio, (size_t)start, (size_t)end);

        folio_unlock(folio);
        folio_put(folio);
}

static long hugetlbfs_punch_hole(struct inode *inode, loff_t offset, loff_t len)
{
        struct hugetlbfs_inode_info *info = HUGETLBFS_I(inode);
        struct address_space *mapping = inode->i_mapping;
        struct hstate *h = hstate_inode(inode);
        loff_t hpage_size = huge_page_size(h);
        loff_t hole_start, hole_end;

        /*
         * hole_start and hole_end indicate the full pages within the hole.
         */
        hole_start = round_up(offset, hpage_size);
        hole_end = round_down(offset + len, hpage_size);

        inode_lock(inode);

        /* protected by i_rwsem */
        if (info->seals & (F_SEAL_WRITE | F_SEAL_FUTURE_WRITE)) {
                inode_unlock(inode);
                return -EPERM;
        }

        i_mmap_lock_write(mapping);

        /* If range starts before first full page, zero partial page. */
        if (offset < hole_start)
                hugetlbfs_zero_partial_page(h, mapping,
                                offset, min(offset + len, hole_start));

        /* Unmap users of full pages in the hole. */
        if (hole_end > hole_start) {
                if (!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root))
                        hugetlb_vmdelete_list(&mapping->i_mmap,
                                              hole_start >> PAGE_SHIFT,
                                              hole_end >> PAGE_SHIFT, 0);
        }

        /* If range extends beyond last full page, zero partial page. */
        if ((offset + len) > hole_end && (offset + len) > hole_start)
                hugetlbfs_zero_partial_page(h, mapping,
                                hole_end, offset + len);

        i_mmap_unlock_write(mapping);

        /* Remove full pages from the file. */
        if (hole_end > hole_start)
                remove_inode_hugepages(inode, hole_start, hole_end);

        inode_unlock(inode);

        return 0;
}

static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
                                loff_t len)
{
        struct inode *inode = file_inode(file);
        struct hugetlbfs_inode_info *info = HUGETLBFS_I(inode);
        struct address_space *mapping = inode->i_mapping;
        struct hstate *h = hstate_inode(inode);
        struct vm_area_struct pseudo_vma;
        struct mm_struct *mm = current->mm;
        loff_t hpage_size = huge_page_size(h);
        unsigned long hpage_shift = huge_page_shift(h);
        pgoff_t start, index, end;
        int error;
        u32 hash;

        if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
                return -EOPNOTSUPP;

        if (mode & FALLOC_FL_PUNCH_HOLE) {
                error = hugetlbfs_punch_hole(inode, offset, len);
                goto out_nolock;
        }

        /*
         * Default preallocate case.
         * For this range, start is rounded down and end is rounded up
         * as well as being converted to page offsets.
         */
        start = offset >> hpage_shift;
        end = (offset + len + hpage_size - 1) >> hpage_shift;

        inode_lock(inode);

        /* We need to check rlimit even when FALLOC_FL_KEEP_SIZE */
        error = inode_newsize_ok(inode, offset + len);
        if (error)
                goto out;

        if ((info->seals & F_SEAL_GROW) && offset + len > inode->i_size) {
                error = -EPERM;
                goto out;
        }

        /*
         * Initialize a pseudo vma as this is required by the huge page
         * allocation routines.
         */
        vma_init(&pseudo_vma, mm);
        vm_flags_init(&pseudo_vma, VM_HUGETLB | VM_MAYSHARE | VM_SHARED);
        pseudo_vma.vm_file = file;

        for (index = start; index < end; index++) {
                /*
                 * This is supposed to be the vaddr where the page is being
                 * faulted in, but we have no vaddr here.
                 */
                struct folio *folio;
                unsigned long addr;

                cond_resched();

                /*
                 * fallocate(2) manpage permits EINTR; we may have been
                 * interrupted because we are using up too much memory.
                 */
                if (signal_pending(current)) {
                        error = -EINTR;
                        break;
                }

                /* addr is the offset within the file (zero based) */
                addr = index * hpage_size;

                /* mutex taken here, fault path and hole punch */
                hash = hugetlb_fault_mutex_hash(mapping, index);
                mutex_lock(&hugetlb_fault_mutex_table[hash]);

                /* See if already present in mapping to avoid alloc/free */
                folio = filemap_get_folio(mapping, index << huge_page_order(h));
                if (!IS_ERR(folio)) {
                        folio_put(folio);
                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                        continue;
                }

                /*
                 * Allocate folio without setting the avoid_reserve argument.
                 * There certainly are no reserves associated with the
                 * pseudo_vma.  However, there could be shared mappings with
                 * reserves for the file at the inode level.  If we fallocate
                 * folios in these areas, we need to consume the reserves
                 * to keep reservation accounting consistent.
                 */
                folio = alloc_hugetlb_folio(&pseudo_vma, addr, false);
                if (IS_ERR(folio)) {
                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                        error = PTR_ERR(folio);
                        goto out;
                }
                folio_zero_user(folio, addr);
                __folio_mark_uptodate(folio);
                error = hugetlb_add_to_page_cache(folio, mapping, index);
                if (unlikely(error)) {
                        restore_reserve_on_error(h, &pseudo_vma, addr, folio);
                        folio_put(folio);
                        mutex_unlock(&hugetlb_fault_mutex_table[hash]);
                        goto out;
                }

                mutex_unlock(&hugetlb_fault_mutex_table[hash]);

                folio_set_hugetlb_migratable(folio);
                /*
                 * folio_unlock because locked by hugetlb_add_to_page_cache()
                 * folio_put() due to reference from alloc_hugetlb_folio()
                 */
                folio_unlock(folio);
                folio_put(folio);
        }

        if (!(mode & FALLOC_FL_KEEP_SIZE) && offset + len > inode->i_size)
                i_size_write(inode, offset + len);
        inode_set_ctime_current(inode);
out:
        inode_unlock(inode);

out_nolock:
        trace_hugetlbfs_fallocate(inode, mode, offset, len, error);
        return error;
}

static int hugetlbfs_setattr(struct mnt_idmap *idmap,
                             struct dentry *dentry, struct iattr *attr)
{
        struct inode *inode = d_inode(dentry);
        struct hstate *h = hstate_inode(inode);
        int error;
        unsigned int ia_valid = attr->ia_valid;
        struct hugetlbfs_inode_info *info = HUGETLBFS_I(inode);

        error = setattr_prepare(idmap, dentry, attr);
        if (error)
                return error;

        trace_hugetlbfs_setattr(inode, dentry, attr);

        if (ia_valid & ATTR_SIZE) {
                loff_t oldsize = inode->i_size;
                loff_t newsize = attr->ia_size;

                if (newsize & ~huge_page_mask(h))
                        return -EINVAL;
                /* protected by i_rwsem */
                if ((newsize < oldsize && (info->seals & F_SEAL_SHRINK)) ||
                    (newsize > oldsize && (info->seals & F_SEAL_GROW)))
                        return -EPERM;
                hugetlb_vmtruncate(inode, newsize);
        }

        setattr_copy(idmap, inode, attr);
        mark_inode_dirty(inode);
        return 0;
}

static struct inode *hugetlbfs_get_root(struct super_block *sb,
                                        struct hugetlbfs_fs_context *ctx)
{
        struct inode *inode;

        inode = new_inode(sb);
        if (inode) {
                inode->i_ino = get_next_ino();
                inode->i_mode = S_IFDIR | ctx->mode;
                inode->i_uid = ctx->uid;
                inode->i_gid = ctx->gid;
                simple_inode_init_ts(inode);
                inode->i_op = &hugetlbfs_dir_inode_operations;
                inode->i_fop = &simple_dir_operations;
                /* directory inodes start off with i_nlink == 2 (for "." entry) */
                inc_nlink(inode);
                lockdep_annotate_inode_mutex_key(inode);
        }
        return inode;
}

/*
 * Hugetlbfs is not reclaimable; therefore its i_mmap_rwsem will never
 * be taken from reclaim -- unlike regular filesystems. This needs an
 * annotation because huge_pmd_share() does an allocation under hugetlb's
 * i_mmap_rwsem.
 */
static struct lock_class_key hugetlbfs_i_mmap_rwsem_key;

static struct inode *hugetlbfs_get_inode(struct super_block *sb,
                                        struct mnt_idmap *idmap,
                                        struct inode *dir,
                                        umode_t mode, dev_t dev)
{
        struct inode *inode;
        struct resv_map *resv_map = NULL;

        /*
         * Reserve maps are only needed for inodes that can have associated
         * page allocations.
         */
        if (S_ISREG(mode) || S_ISLNK(mode)) {
                resv_map = resv_map_alloc();
                if (!resv_map)
                        return NULL;
        }

        inode = new_inode(sb);
        if (inode) {
                struct hugetlbfs_inode_info *info = HUGETLBFS_I(inode);

                inode->i_ino = get_next_ino();
                inode_init_owner(idmap, inode, dir, mode);
                lockdep_set_class(&inode->i_mapping->i_mmap_rwsem,
                                &hugetlbfs_i_mmap_rwsem_key);
                inode->i_mapping->a_ops = &hugetlbfs_aops;
                simple_inode_init_ts(inode);
                inode->i_mapping->i_private_data = resv_map;
                info->seals = F_SEAL_SEAL;
                switch (mode & S_IFMT) {
                default:
                        init_special_inode(inode, mode, dev);
                        break;
                case S_IFREG:
                        inode->i_op = &hugetlbfs_inode_operations;
                        inode->i_fop = &hugetlbfs_file_operations;
                        break;
                case S_IFDIR:
                        inode->i_op = &hugetlbfs_dir_inode_operations;
                        inode->i_fop = &simple_dir_operations;

                        /* directory inodes start off with i_nlink == 2 (for "." entry) */
                        inc_nlink(inode);
                        break;
                case S_IFLNK:
                        inode->i_op = &page_symlink_inode_operations;
                        inode_nohighmem(inode);
                        break;
                }
                lockdep_annotate_inode_mutex_key(inode);
                trace_hugetlbfs_alloc_inode(inode, dir, mode);
        } else {
                if (resv_map)
                        kref_put(&resv_map->refs, resv_map_release);
        }

        return inode;
}

/*
 * File creation. Allocate an inode, and we're done..
 */
static int hugetlbfs_mknod(struct mnt_idmap *idmap, struct inode *dir,
                           struct dentry *dentry, umode_t mode, dev_t dev)
{
        struct inode *inode;

        inode = hugetlbfs_get_inode(dir->i_sb, idmap, dir, mode, dev);
        if (!inode)
                return -ENOSPC;
        inode_set_mtime_to_ts(dir, inode_set_ctime_current(dir));
        d_instantiate(dentry, inode);
        dget(dentry);/* Extra count - pin the dentry in core */
        return 0;
}

static struct dentry *hugetlbfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
                                      struct dentry *dentry, umode_t mode)
{
        int retval = hugetlbfs_mknod(idmap, dir, dentry,
                                     mode | S_IFDIR, 0);
        if (!retval)
                inc_nlink(dir);
        return ERR_PTR(retval);
}

static int hugetlbfs_create(struct mnt_idmap *idmap,
                            struct inode *dir, struct dentry *dentry,
                            umode_t mode, bool excl)
{
        return hugetlbfs_mknod(idmap, dir, dentry, mode | S_IFREG, 0);
}

static int hugetlbfs_tmpfile(struct mnt_idmap *idmap,
                             struct inode *dir, struct file *file,
                             umode_t mode)
{
        struct inode *inode;

        inode = hugetlbfs_get_inode(dir->i_sb, idmap, dir, mode | S_IFREG, 0);
        if (!inode)
                return -ENOSPC;
        inode_set_mtime_to_ts(dir, inode_set_ctime_current(dir));
        d_tmpfile(file, inode);
        return finish_open_simple(file, 0);
}

static int hugetlbfs_symlink(struct mnt_idmap *idmap,
                             struct inode *dir, struct dentry *dentry,
                             const char *symname)
{
        const umode_t mode = S_IFLNK|S_IRWXUGO;
        struct inode *inode;
        int error = -ENOSPC;

        inode = hugetlbfs_get_inode(dir->i_sb, idmap, dir, mode, 0);
        if (inode) {
                int l = strlen(symname)+1;
                error = page_symlink(inode, symname, l);
                if (!error) {
                        d_instantiate(dentry, inode);
                        dget(dentry);
                } else
                        iput(inode);
        }
        inode_set_mtime_to_ts(dir, inode_set_ctime_current(dir));

        return error;
}

#ifdef CONFIG_MIGRATION
static int hugetlbfs_migrate_folio(struct address_space *mapping,
                                struct folio *dst, struct folio *src,
                                enum migrate_mode mode)
{
        int rc;

        rc = migrate_huge_page_move_mapping(mapping, dst, src);
        if (rc != MIGRATEPAGE_SUCCESS)
                return rc;

        if (hugetlb_folio_subpool(src)) {
                hugetlb_set_folio_subpool(dst,
                                        hugetlb_folio_subpool(src));
                hugetlb_set_folio_subpool(src, NULL);
        }

        folio_migrate_flags(dst, src);

        return MIGRATEPAGE_SUCCESS;
}
#else
#define hugetlbfs_migrate_folio NULL
#endif

static int hugetlbfs_error_remove_folio(struct address_space *mapping,
                                struct folio *folio)
{
        return 0;
}

/*
 * Display the mount options in /proc/mounts.
 */
static int hugetlbfs_show_options(struct seq_file *m, struct dentry *root)
{
        struct hugetlbfs_sb_info *sbinfo = HUGETLBFS_SB(root->d_sb);
        struct hugepage_subpool *spool = sbinfo->spool;
        unsigned long hpage_size = huge_page_size(sbinfo->hstate);
        unsigned hpage_shift = huge_page_shift(sbinfo->hstate);
        char mod;

        if (!uid_eq(sbinfo->uid, GLOBAL_ROOT_UID))
                seq_printf(m, ",uid=%u",
                           from_kuid_munged(&init_user_ns, sbinfo->uid));
        if (!gid_eq(sbinfo->gid, GLOBAL_ROOT_GID))
                seq_printf(m, ",gid=%u",
                           from_kgid_munged(&init_user_ns, sbinfo->gid));
        if (sbinfo->mode != 0755)
                seq_printf(m, ",mode=%o", sbinfo->mode);
        if (sbinfo->max_inodes != -1)
                seq_printf(m, ",nr_inodes=%lu", sbinfo->max_inodes);

        hpage_size /= 1024;
        mod = 'K';
        if (hpage_size >= 1024) {
                hpage_size /= 1024;
                mod = 'M';
        }
        seq_printf(m, ",pagesize=%lu%c", hpage_size, mod);
        if (spool) {
                if (spool->max_hpages != -1)
                        seq_printf(m, ",size=%llu",
                                   (unsigned long long)spool->max_hpages << hpage_shift);
                if (spool->min_hpages != -1)
                        seq_printf(m, ",min_size=%llu",
                                   (unsigned long long)spool->min_hpages << hpage_shift);
        }
        return 0;
}

static int hugetlbfs_statfs(struct dentry *dentry, struct kstatfs *buf)
{
        struct hugetlbfs_sb_info *sbinfo = HUGETLBFS_SB(dentry->d_sb);
        struct hstate *h = hstate_inode(d_inode(dentry));
        u64 id = huge_encode_dev(dentry->d_sb->s_dev);

        buf->f_fsid = u64_to_fsid(id);
        buf->f_type = HUGETLBFS_MAGIC;
        buf->f_bsize = huge_page_size(h);
        if (sbinfo) {
                spin_lock(&sbinfo->stat_lock);
                /* If no limits set, just report 0 or -1 for max/free/used
                 * blocks, like simple_statfs() */
                if (sbinfo->spool) {
                        long free_pages;

                        spin_lock_irq(&sbinfo->spool->lock);
                        buf->f_blocks = sbinfo->spool->max_hpages;
                        free_pages = sbinfo->spool->max_hpages
                                - sbinfo->spool->used_hpages;
                        buf->f_bavail = buf->f_bfree = free_pages;
                        spin_unlock_irq(&sbinfo->spool->lock);
                        buf->f_files = sbinfo->max_inodes;
                        buf->f_ffree = sbinfo->free_inodes;
                }
                spin_unlock(&sbinfo->stat_lock);
        }
        buf->f_namelen = NAME_MAX;
        return 0;
}

static void hugetlbfs_put_super(struct super_block *sb)
{
        struct hugetlbfs_sb_info *sbi = HUGETLBFS_SB(sb);

        if (sbi) {
                sb->s_fs_info = NULL;

                if (sbi->spool)
                        hugepage_put_subpool(sbi->spool);

                kfree(sbi);
        }
}

static inline int hugetlbfs_dec_free_inodes(struct hugetlbfs_sb_info *sbinfo)
{
        if (sbinfo->free_inodes >= 0) {
                spin_lock(&sbinfo->stat_lock);
                if (unlikely(!sbinfo->free_inodes)) {
                        spin_unlock(&sbinfo->stat_lock);
                        return 0;
                }
                sbinfo->free_inodes--;
                spin_unlock(&sbinfo->stat_lock);
        }

        return 1;
}

static void hugetlbfs_inc_free_inodes(struct hugetlbfs_sb_info *sbinfo)
{
        if (sbinfo->free_inodes >= 0) {
                spin_lock(&sbinfo->stat_lock);
                sbinfo->free_inodes++;
                spin_unlock(&sbinfo->stat_lock);
        }
}


static struct kmem_cache *hugetlbfs_inode_cachep;

static struct inode *hugetlbfs_alloc_inode(struct super_block *sb)
{
        struct hugetlbfs_sb_info *sbinfo = HUGETLBFS_SB(sb);
        struct hugetlbfs_inode_info *p;

        if (unlikely(!hugetlbfs_dec_free_inodes(sbinfo)))
                return NULL;
        p = alloc_inode_sb(sb, hugetlbfs_inode_cachep, GFP_KERNEL);
        if (unlikely(!p)) {
                hugetlbfs_inc_free_inodes(sbinfo);
                return NULL;
        }
        return &p->vfs_inode;
}

static void hugetlbfs_free_inode(struct inode *inode)
{
        trace_hugetlbfs_free_inode(inode);
        kmem_cache_free(hugetlbfs_inode_cachep, HUGETLBFS_I(inode));
}

static void hugetlbfs_destroy_inode(struct inode *inode)
{
        hugetlbfs_inc_free_inodes(HUGETLBFS_SB(inode->i_sb));
}

static const struct address_space_operations hugetlbfs_aops = {
        .write_begin    = hugetlbfs_write_begin,
        .write_end      = hugetlbfs_write_end,
        .dirty_folio    = noop_dirty_folio,
        .migrate_folio  = hugetlbfs_migrate_folio,
        .error_remove_folio     = hugetlbfs_error_remove_folio,
};


static void init_once(void *foo)
{
        struct hugetlbfs_inode_info *ei = foo;

        inode_init_once(&ei->vfs_inode);
}

static const struct file_operations hugetlbfs_file_operations = {
        .read_iter              = hugetlbfs_read_iter,
        .mmap                   = hugetlbfs_file_mmap,
        .fsync                  = noop_fsync,
        .get_unmapped_area      = hugetlb_get_unmapped_area,
        .llseek                 = default_llseek,
        .fallocate              = hugetlbfs_fallocate,
        .fop_flags              = FOP_HUGE_PAGES,
};

static const struct inode_operations hugetlbfs_dir_inode_operations = {
        .create         = hugetlbfs_create,
        .lookup         = simple_lookup,
        .link           = simple_link,
        .unlink         = simple_unlink,
        .symlink        = hugetlbfs_symlink,
        .mkdir          = hugetlbfs_mkdir,
        .rmdir          = simple_rmdir,
        .mknod          = hugetlbfs_mknod,
        .rename         = simple_rename,
        .setattr        = hugetlbfs_setattr,
        .tmpfile        = hugetlbfs_tmpfile,
};

static const struct inode_operations hugetlbfs_inode_operations = {
        .setattr        = hugetlbfs_setattr,
};

static const struct super_operations hugetlbfs_ops = {
        .alloc_inode    = hugetlbfs_alloc_inode,
        .free_inode     = hugetlbfs_free_inode,
        .destroy_inode  = hugetlbfs_destroy_inode,
        .evict_inode    = hugetlbfs_evict_inode,
        .statfs         = hugetlbfs_statfs,
        .put_super      = hugetlbfs_put_super,
        .show_options   = hugetlbfs_show_options,
};

/*
 * Convert size option passed from command line to number of huge pages
 * in the pool specified by hstate.  Size option could be in bytes
 * (val_type == SIZE_STD) or percentage of the pool (val_type == SIZE_PERCENT).
 */
static long
hugetlbfs_size_to_hpages(struct hstate *h, unsigned long long size_opt,
                         enum hugetlbfs_size_type val_type)
{
        if (val_type == NO_SIZE)
                return -1;

        if (val_type == SIZE_PERCENT) {
                size_opt <<= huge_page_shift(h);
                size_opt *= h->max_huge_pages;
                do_div(size_opt, 100);
        }

        size_opt >>= huge_page_shift(h);
        return size_opt;
}

/*
 * Parse one mount parameter.
 */
static int hugetlbfs_parse_param(struct fs_context *fc, struct fs_parameter *param)
{
        struct hugetlbfs_fs_context *ctx = fc->fs_private;
        struct fs_parse_result result;
        struct hstate *h;
        char *rest;
        unsigned long ps;
        int opt;

        opt = fs_parse(fc, hugetlb_fs_parameters, param, &result);
        if (opt < 0)
                return opt;

        switch (opt) {
        case Opt_uid:
                ctx->uid = result.uid;
                return 0;

        case Opt_gid:
                ctx->gid = result.gid;
                return 0;

        case Opt_mode:
                ctx->mode = result.uint_32 & 01777U;
                return 0;

        case Opt_size:
                /* memparse() will accept a K/M/G without a digit */
                if (!param->string || !isdigit(param->string[0]))
                        goto bad_val;
                ctx->max_size_opt = memparse(param->string, &rest);
                ctx->max_val_type = SIZE_STD;
                if (*rest == '%')
                        ctx->max_val_type = SIZE_PERCENT;
                return 0;

        case Opt_nr_inodes:
                /* memparse() will accept a K/M/G without a digit */
                if (!param->string || !isdigit(param->string[0]))
                        goto bad_val;
                ctx->nr_inodes = memparse(param->string, &rest);
                return 0;

        case Opt_pagesize:
                ps = memparse(param->string, &rest);
                h = size_to_hstate(ps);
                if (!h) {
                        pr_err("Unsupported page size %lu MB\n", ps / SZ_1M);
                        return -EINVAL;
                }
                ctx->hstate = h;
                return 0;

        case Opt_min_size:
                /* memparse() will accept a K/M/G without a digit */
                if (!param->string || !isdigit(param->string[0]))
                        goto bad_val;
                ctx->min_size_opt = memparse(param->string, &rest);
                ctx->min_val_type = SIZE_STD;
                if (*rest == '%')
                        ctx->min_val_type = SIZE_PERCENT;
                return 0;

        default:
                return -EINVAL;
        }

bad_val:
        return invalfc(fc, "Bad value '%s' for mount option '%s'\n",
                      param->string, param->key);
}

/*
 * Validate the parsed options.
 */
static int hugetlbfs_validate(struct fs_context *fc)
{
        struct hugetlbfs_fs_context *ctx = fc->fs_private;

        /*
         * Use huge page pool size (in hstate) to convert the size
         * options to number of huge pages.  If NO_SIZE, -1 is returned.
         */
        ctx->max_hpages = hugetlbfs_size_to_hpages(ctx->hstate,
                                                   ctx->max_size_opt,
                                                   ctx->max_val_type);
        ctx->min_hpages = hugetlbfs_size_to_hpages(ctx->hstate,
                                                   ctx->min_size_opt,
                                                   ctx->min_val_type);

        /*
         * If max_size was specified, then min_size must be smaller
         */
        if (ctx->max_val_type > NO_SIZE &&
            ctx->min_hpages > ctx->max_hpages) {
                pr_err("Minimum size can not be greater than maximum size\n");
                return -EINVAL;
        }

        return 0;
}

static int
hugetlbfs_fill_super(struct super_block *sb, struct fs_context *fc)
{
        struct hugetlbfs_fs_context *ctx = fc->fs_private;
        struct hugetlbfs_sb_info *sbinfo;

        sbinfo = kmalloc(sizeof(struct hugetlbfs_sb_info), GFP_KERNEL);
        if (!sbinfo)
                return -ENOMEM;
        sb->s_fs_info = sbinfo;
        spin_lock_init(&sbinfo->stat_lock);
        sbinfo->hstate          = ctx->hstate;
        sbinfo->max_inodes      = ctx->nr_inodes;
        sbinfo->free_inodes     = ctx->nr_inodes;
        sbinfo->spool           = NULL;
        sbinfo->uid             = ctx->uid;
        sbinfo->gid             = ctx->gid;
        sbinfo->mode            = ctx->mode;

        /*
         * Allocate and initialize subpool if maximum or minimum size is
         * specified.  Any needed reservations (for minimum size) are taken
         * when the subpool is created.
         */
        if (ctx->max_hpages != -1 || ctx->min_hpages != -1) {
                sbinfo->spool = hugepage_new_subpool(ctx->hstate,
                                                     ctx->max_hpages,
                                                     ctx->min_hpages);
                if (!sbinfo->spool)
                        goto out_free;
        }
        sb->s_maxbytes = MAX_LFS_FILESIZE;
        sb->s_blocksize = huge_page_size(ctx->hstate);
        sb->s_blocksize_bits = huge_page_shift(ctx->hstate);
        sb->s_magic = HUGETLBFS_MAGIC;
        sb->s_op = &hugetlbfs_ops;
        sb->s_d_flags = DCACHE_DONTCACHE;
        sb->s_time_gran = 1;

        /*
         * Due to the special and limited functionality of hugetlbfs, it does
         * not work well as a stacking filesystem.
         */
        sb->s_stack_depth = FILESYSTEM_MAX_STACK_DEPTH;
        sb->s_root = d_make_root(hugetlbfs_get_root(sb, ctx));
        if (!sb->s_root)
                goto out_free;
        return 0;
out_free:
        kfree(sbinfo->spool);
        kfree(sbinfo);
        return -ENOMEM;
}

static int hugetlbfs_get_tree(struct fs_context *fc)
{
        int err = hugetlbfs_validate(fc);
        if (err)
                return err;
        return get_tree_nodev(fc, hugetlbfs_fill_super);
}

static void hugetlbfs_fs_context_free(struct fs_context *fc)
{
        kfree(fc->fs_private);
}

static const struct fs_context_operations hugetlbfs_fs_context_ops = {
        .free           = hugetlbfs_fs_context_free,
        .parse_param    = hugetlbfs_parse_param,
        .get_tree       = hugetlbfs_get_tree,
};

static int hugetlbfs_init_fs_context(struct fs_context *fc)
{
        struct hugetlbfs_fs_context *ctx;

        ctx = kzalloc(sizeof(struct hugetlbfs_fs_context), GFP_KERNEL);
        if (!ctx)
                return -ENOMEM;

        ctx->max_hpages = -1; /* No limit on size by default */
        ctx->nr_inodes  = -1; /* No limit on number of inodes by default */
        ctx->uid        = current_fsuid();
        ctx->gid        = current_fsgid();
        ctx->mode       = 0755;
        ctx->hstate     = &default_hstate;
        ctx->min_hpages = -1; /* No default minimum size */
        ctx->max_val_type = NO_SIZE;
        ctx->min_val_type = NO_SIZE;
        fc->fs_private = ctx;
        fc->ops = &hugetlbfs_fs_context_ops;
        return 0;
}

static struct file_system_type hugetlbfs_fs_type = {
        .name                   = "hugetlbfs",
        .init_fs_context        = hugetlbfs_init_fs_context,
        .parameters             = hugetlb_fs_parameters,
        .kill_sb                = kill_litter_super,
        .fs_flags               = FS_ALLOW_IDMAP,
};

static struct vfsmount *hugetlbfs_vfsmount[HUGE_MAX_HSTATE];

static int can_do_hugetlb_shm(void)
{
        kgid_t shm_group;
        shm_group = make_kgid(&init_user_ns, sysctl_hugetlb_shm_group);
        return capable(CAP_IPC_LOCK) || in_group_p(shm_group);
}

static int get_hstate_idx(int page_size_log)
{
        struct hstate *h = hstate_sizelog(page_size_log);

        if (!h)
                return -1;
        return hstate_index(h);
}

/*
 * Note that size should be aligned to proper hugepage size in caller side,
 * otherwise hugetlb_reserve_pages reserves one less hugepages than intended.
 */
struct file *hugetlb_file_setup(const char *name, size_t size,
                                vm_flags_t acctflag, int creat_flags,
                                int page_size_log)
{
        struct inode *inode;
        struct vfsmount *mnt;
        int hstate_idx;
        struct file *file;

        hstate_idx = get_hstate_idx(page_size_log);
        if (hstate_idx < 0)
                return ERR_PTR(-ENODEV);

        mnt = hugetlbfs_vfsmount[hstate_idx];
        if (!mnt)
                return ERR_PTR(-ENOENT);

        if (creat_flags == HUGETLB_SHMFS_INODE && !can_do_hugetlb_shm()) {
                struct ucounts *ucounts = current_ucounts();

                if (user_shm_lock(size, ucounts)) {
                        pr_warn_once("%s (%d): Using mlock ulimits for SHM_HUGETLB is obsolete\n",
                                current->comm, current->pid);
                        user_shm_unlock(size, ucounts);
                }
                return ERR_PTR(-EPERM);
        }

        file = ERR_PTR(-ENOSPC);
        /* hugetlbfs_vfsmount[] mounts do not use idmapped mounts.  */
        inode = hugetlbfs_get_inode(mnt->mnt_sb, &nop_mnt_idmap, NULL,
                                    S_IFREG | S_IRWXUGO, 0);
        if (!inode)
                goto out;
        if (creat_flags == HUGETLB_SHMFS_INODE)
                inode->i_flags |= S_PRIVATE;

        inode->i_size = size;
        clear_nlink(inode);

        if (hugetlb_reserve_pages(inode, 0,
                        size >> huge_page_shift(hstate_inode(inode)), NULL,
                        acctflag) < 0)
                file = ERR_PTR(-ENOMEM);
        else
                file = alloc_file_pseudo(inode, mnt, name, O_RDWR,
                                        &hugetlbfs_file_operations);
        if (!IS_ERR(file))
                return file;

        iput(inode);
out:
        return file;
}

static struct vfsmount *__init mount_one_hugetlbfs(struct hstate *h)
{
        struct fs_context *fc;
        struct vfsmount *mnt;

        fc = fs_context_for_mount(&hugetlbfs_fs_type, SB_KERNMOUNT);
        if (IS_ERR(fc)) {
                mnt = ERR_CAST(fc);
        } else {
                struct hugetlbfs_fs_context *ctx = fc->fs_private;
                ctx->hstate = h;
                mnt = fc_mount_longterm(fc);
                put_fs_context(fc);
        }
        if (IS_ERR(mnt))
                pr_err("Cannot mount internal hugetlbfs for page size %luK",
                       huge_page_size(h) / SZ_1K);
        return mnt;
}

static int __init init_hugetlbfs_fs(void)
{
        struct vfsmount *mnt;
        struct hstate *h;
        int error;
        int i;

        if (!hugepages_supported()) {
                pr_info("disabling because there are no supported hugepage sizes\n");
                return -ENOTSUPP;
        }

        error = -ENOMEM;
        hugetlbfs_inode_cachep = kmem_cache_create("hugetlbfs_inode_cache",
                                        sizeof(struct hugetlbfs_inode_info),
                                        0, SLAB_ACCOUNT, init_once);
        if (hugetlbfs_inode_cachep == NULL)
                goto out;

        error = register_filesystem(&hugetlbfs_fs_type);
        if (error)
                goto out_free;

        /* default hstate mount is required */
        mnt = mount_one_hugetlbfs(&default_hstate);
        if (IS_ERR(mnt)) {
                error = PTR_ERR(mnt);
                goto out_unreg;
        }
        hugetlbfs_vfsmount[default_hstate_idx] = mnt;

        /* other hstates are optional */
        i = 0;
        for_each_hstate(h) {
                if (i == default_hstate_idx) {
                        i++;
                        continue;
                }

                mnt = mount_one_hugetlbfs(h);
                if (IS_ERR(mnt))
                        hugetlbfs_vfsmount[i] = NULL;
                else
                        hugetlbfs_vfsmount[i] = mnt;
                i++;
        }

        return 0;

 out_unreg:
        (void)unregister_filesystem(&hugetlbfs_fs_type);
 out_free:
        kmem_cache_destroy(hugetlbfs_inode_cachep);
 out:
        return error;
}
fs_initcall(init_hugetlbfs_fs)