/*
 *  linux/mm/vmalloc.c
 *
 *  Copyright (C) 1993  Linus Torvalds
 *  Support of BIGMEM added by Gerhard Wichert, Siemens AG, July 1999
 *  SMP-safe vmalloc/vfree/ioremap, Tigran Aivazian <tigran@veritas.com>, May 2000
 *  Major rework to support vmap/vunmap, Christoph Hellwig, SGI, August 2002
 *  Numa awareness, Christoph Lameter, SGI, June 2005
 */

#include <linux/mm.h>
#include <linux/module.h>
#include <linux/highmem.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/interrupt.h>

#include <linux/vmalloc.h>

#include <asm/uaccess.h>
#include <asm/tlbflush.h>


DEFINE_RWLOCK(vmlist_lock);
struct vm_struct *vmlist;

static void *__vmalloc_node(unsigned long size, gfp_t gfp_mask, pgprot_t prot,
                            int node);

static void vunmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end)
{
        pte_t *pte;

        pte = pte_offset_kernel(pmd, addr);
        do {
                pte_t ptent = ptep_get_and_clear(&init_mm, addr, pte);
                WARN_ON(!pte_none(ptent) && !pte_present(ptent));
        } while (pte++, addr += PAGE_SIZE, addr != end);
}

static inline void vunmap_pmd_range(pud_t *pud, unsigned long addr,
                                                unsigned long end)
{
        pmd_t *pmd;
        unsigned long next;

        pmd = pmd_offset(pud, addr);
        do {
                next = pmd_addr_end(addr, end);
                if (pmd_none_or_clear_bad(pmd))
                        continue;
                vunmap_pte_range(pmd, addr, next);
        } while (pmd++, addr = next, addr != end);
}

static inline void vunmap_pud_range(pgd_t *pgd, unsigned long addr,
                                                unsigned long end)
{
        pud_t *pud;
        unsigned long next;

        pud = pud_offset(pgd, addr);
        do {
                next = pud_addr_end(addr, end);
                if (pud_none_or_clear_bad(pud))
                        continue;
                vunmap_pmd_range(pud, addr, next);
        } while (pud++, addr = next, addr != end);
}

void unmap_kernel_range(unsigned long addr, unsigned long size)
{
        pgd_t *pgd;
        unsigned long next;
        unsigned long start = addr;
        unsigned long end = addr + size;

        BUG_ON(addr >= end);
        pgd = pgd_offset_k(addr);
        flush_cache_vunmap(addr, end);
        do {
                next = pgd_addr_end(addr, end);
                if (pgd_none_or_clear_bad(pgd))
                        continue;
                vunmap_pud_range(pgd, addr, next);
        } while (pgd++, addr = next, addr != end);
        flush_tlb_kernel_range(start, end);
}

static void unmap_vm_area(struct vm_struct *area)
{
        unmap_kernel_range((unsigned long)area->addr, area->size);
}

static int vmap_pte_range(pmd_t *pmd, unsigned long addr,
                        unsigned long end, pgprot_t prot, struct page ***pages)
{
        pte_t *pte;

        pte = pte_alloc_kernel(pmd, addr);
        if (!pte)
                return -ENOMEM;
        do {
                struct page *page = **pages;
                WARN_ON(!pte_none(*pte));
                if (!page)
                        return -ENOMEM;
                set_pte_at(&init_mm, addr, pte, mk_pte(page, prot));
                (*pages)++;
        } while (pte++, addr += PAGE_SIZE, addr != end);
        return 0;
}

static inline int vmap_pmd_range(pud_t *pud, unsigned long addr,
                        unsigned long end, pgprot_t prot, struct page ***pages)
{
        pmd_t *pmd;
        unsigned long next;

        pmd = pmd_alloc(&init_mm, pud, addr);
        if (!pmd)
                return -ENOMEM;
        do {
                next = pmd_addr_end(addr, end);
                if (vmap_pte_range(pmd, addr, next, prot, pages))
                        return -ENOMEM;
        } while (pmd++, addr = next, addr != end);
        return 0;
}

static inline int vmap_pud_range(pgd_t *pgd, unsigned long addr,
                        unsigned long end, pgprot_t prot, struct page ***pages)
{
        pud_t *pud;
        unsigned long next;

        pud = pud_alloc(&init_mm, pgd, addr);
        if (!pud)
                return -ENOMEM;
        do {
                next = pud_addr_end(addr, end);
                if (vmap_pmd_range(pud, addr, next, prot, pages))
                        return -ENOMEM;
        } while (pud++, addr = next, addr != end);
        return 0;
}

int map_vm_area(struct vm_struct *area, pgprot_t prot, struct page ***pages)
{
        pgd_t *pgd;
        unsigned long next;
        unsigned long addr = (unsigned long) area->addr;
        unsigned long end = addr + area->size - PAGE_SIZE;
        int err;

        BUG_ON(addr >= end);
        pgd = pgd_offset_k(addr);
        do {
                next = pgd_addr_end(addr, end);
                err = vmap_pud_range(pgd, addr, next, prot, pages);
                if (err)
                        break;
        } while (pgd++, addr = next, addr != end);
        flush_cache_vmap((unsigned long) area->addr, end);
        return err;
}
EXPORT_SYMBOL_GPL(map_vm_area);

/*
 * Map a vmalloc()-space virtual address to the physical page.
 */
struct page *vmalloc_to_page(const void *vmalloc_addr)
{
        unsigned long addr = (unsigned long) vmalloc_addr;
        struct page *page = NULL;
        pgd_t *pgd = pgd_offset_k(addr);
        pud_t *pud;
        pmd_t *pmd;
        pte_t *ptep, pte;

        if (!pgd_none(*pgd)) {
                pud = pud_offset(pgd, addr);
                if (!pud_none(*pud)) {
                        pmd = pmd_offset(pud, addr);
                        if (!pmd_none(*pmd)) {
                                ptep = pte_offset_map(pmd, addr);
                                pte = *ptep;
                                if (pte_present(pte))
                                        page = pte_page(pte);
                                pte_unmap(ptep);
                        }
                }
        }
        return page;
}
EXPORT_SYMBOL(vmalloc_to_page);

/*
 * Map a vmalloc()-space virtual address to the physical page frame number.
 */
unsigned long vmalloc_to_pfn(const void *vmalloc_addr)
{
        return page_to_pfn(vmalloc_to_page(vmalloc_addr));
}
EXPORT_SYMBOL(vmalloc_to_pfn);

static struct vm_struct *__get_vm_area_node(unsigned long size, unsigned long flags,
                                            unsigned long start, unsigned long end,
                                            int node, gfp_t gfp_mask)
{
        struct vm_struct **p, *tmp, *area;
        unsigned long align = 1;
        unsigned long addr;

        BUG_ON(in_interrupt());
        if (flags & VM_IOREMAP) {
                int bit = fls(size);

                if (bit > IOREMAP_MAX_ORDER)
                        bit = IOREMAP_MAX_ORDER;
                else if (bit < PAGE_SHIFT)
                        bit = PAGE_SHIFT;

                align = 1ul << bit;
        }
        addr = ALIGN(start, align);
        size = PAGE_ALIGN(size);
        if (unlikely(!size))
                return NULL;

        area = kmalloc_node(sizeof(*area), gfp_mask & GFP_RECLAIM_MASK, node);

        if (unlikely(!area))
                return NULL;

        /*
         * We always allocate a guard page.
         */
        size += PAGE_SIZE;

        write_lock(&vmlist_lock);
        for (p = &vmlist; (tmp = *p) != NULL ;p = &tmp->next) {
                if ((unsigned long)tmp->addr < addr) {
                        if((unsigned long)tmp->addr + tmp->size >= addr)
                                addr = ALIGN(tmp->size + 
                                             (unsigned long)tmp->addr, align);
                        continue;
                }
                if ((size + addr) < addr)
                        goto out;
                if (size + addr <= (unsigned long)tmp->addr)
                        goto found;
                addr = ALIGN(tmp->size + (unsigned long)tmp->addr, align);
                if (addr > end - size)
                        goto out;
        }
        if ((size + addr) < addr)
                goto out;
        if (addr > end - size)
                goto out;

found:
        area->next = *p;
        *p = area;

        area->flags = flags;
        area->addr = (void *)addr;
        area->size = size;
        area->pages = NULL;
        area->nr_pages = 0;
        area->phys_addr = 0;
        write_unlock(&vmlist_lock);

        return area;

out:
        write_unlock(&vmlist_lock);
        kfree(area);
        if (printk_ratelimit())
                printk(KERN_WARNING "allocation failed: out of vmalloc space - use vmalloc=<size> to increase size.\n");
        return NULL;
}

struct vm_struct *__get_vm_area(unsigned long size, unsigned long flags,
                                unsigned long start, unsigned long end)
{
        return __get_vm_area_node(size, flags, start, end, -1, GFP_KERNEL);
}
EXPORT_SYMBOL_GPL(__get_vm_area);

/**
 *      get_vm_area  -  reserve a contiguous kernel virtual area
 *      @size:          size of the area
 *      @flags:         %VM_IOREMAP for I/O mappings or VM_ALLOC
 *
 *      Search an area of @size in the kernel virtual mapping area,
 *      and reserved it for out purposes.  Returns the area descriptor
 *      on success or %NULL on failure.
 */
struct vm_struct *get_vm_area(unsigned long size, unsigned long flags)
{
        return __get_vm_area(size, flags, VMALLOC_START, VMALLOC_END);
}

struct vm_struct *get_vm_area_node(unsigned long size, unsigned long flags,
                                   int node, gfp_t gfp_mask)
{
        return __get_vm_area_node(size, flags, VMALLOC_START, VMALLOC_END, node,
                                  gfp_mask);
}

/* Caller must hold vmlist_lock */
static struct vm_struct *__find_vm_area(const void *addr)
{
        struct vm_struct *tmp;

        for (tmp = vmlist; tmp != NULL; tmp = tmp->next) {
                 if (tmp->addr == addr)
                        break;
        }

        return tmp;
}

/* Caller must hold vmlist_lock */
static struct vm_struct *__remove_vm_area(const void *addr)
{
        struct vm_struct **p, *tmp;

        for (p = &vmlist ; (tmp = *p) != NULL ;p = &tmp->next) {
                 if (tmp->addr == addr)
                         goto found;
        }
        return NULL;

found:
        unmap_vm_area(tmp);
        *p = tmp->next;

        /*
         * Remove the guard page.
         */
        tmp->size -= PAGE_SIZE;
        return tmp;
}

/**
 *      remove_vm_area  -  find and remove a continuous kernel virtual area
 *      @addr:          base address
 *
 *      Search for the kernel VM area starting at @addr, and remove it.
 *      This function returns the found VM area, but using it is NOT safe
 *      on SMP machines, except for its size or flags.
 */
struct vm_struct *remove_vm_area(const void *addr)
{
        struct vm_struct *v;
        write_lock(&vmlist_lock);
        v = __remove_vm_area(addr);
        write_unlock(&vmlist_lock);
        return v;
}

static void __vunmap(const void *addr, int deallocate_pages)
{
        struct vm_struct *area;

        if (!addr)
                return;

        if ((PAGE_SIZE-1) & (unsigned long)addr) {
                printk(KERN_ERR "Trying to vfree() bad address (%p)\n", addr);
                WARN_ON(1);
                return;
        }

        area = remove_vm_area(addr);
        if (unlikely(!area)) {
                printk(KERN_ERR "Trying to vfree() nonexistent vm area (%p)\n",
                                addr);
                WARN_ON(1);
                return;
        }

        debug_check_no_locks_freed(addr, area->size);

        if (deallocate_pages) {
                int i;

                for (i = 0; i < area->nr_pages; i++) {
                        struct page *page = area->pages[i];

                        BUG_ON(!page);
                        __free_page(page);
                }

                if (area->flags & VM_VPAGES)
                        vfree(area->pages);
                else
                        kfree(area->pages);
        }

        kfree(area);
        return;
}

/**
 *      vfree  -  release memory allocated by vmalloc()
 *      @addr:          memory base address
 *
 *      Free the virtually continuous memory area starting at @addr, as
 *      obtained from vmalloc(), vmalloc_32() or __vmalloc(). If @addr is
 *      NULL, no operation is performed.
 *
 *      Must not be called in interrupt context.
 */
void vfree(const void *addr)
{
        BUG_ON(in_interrupt());
        __vunmap(addr, 1);
}
EXPORT_SYMBOL(vfree);

/**
 *      vunmap  -  release virtual mapping obtained by vmap()
 *      @addr:          memory base address
 *
 *      Free the virtually contiguous memory area starting at @addr,
 *      which was created from the page array passed to vmap().
 *
 *      Must not be called in interrupt context.
 */
void vunmap(const void *addr)
{
        BUG_ON(in_interrupt());
        __vunmap(addr, 0);
}
EXPORT_SYMBOL(vunmap);

/**
 *      vmap  -  map an array of pages into virtually contiguous space
 *      @pages:         array of page pointers
 *      @count:         number of pages to map
 *      @flags:         vm_area->flags
 *      @prot:          page protection for the mapping
 *
 *      Maps @count pages from @pages into contiguous kernel virtual
 *      space.
 */
void *vmap(struct page **pages, unsigned int count,
                unsigned long flags, pgprot_t prot)
{
        struct vm_struct *area;

        if (count > num_physpages)
                return NULL;

        area = get_vm_area((count << PAGE_SHIFT), flags);
        if (!area)
                return NULL;
        if (map_vm_area(area, prot, &pages)) {
                vunmap(area->addr);
                return NULL;
        }

        return area->addr;
}
EXPORT_SYMBOL(vmap);

static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
                                 pgprot_t prot, int node)
{
        struct page **pages;
        unsigned int nr_pages, array_size, i;

        nr_pages = (area->size - PAGE_SIZE) >> PAGE_SHIFT;
        array_size = (nr_pages * sizeof(struct page *));

        area->nr_pages = nr_pages;
        /* Please note that the recursion is strictly bounded. */
        if (array_size > PAGE_SIZE) {
                pages = __vmalloc_node(array_size, gfp_mask | __GFP_ZERO,
                                        PAGE_KERNEL, node);
                area->flags |= VM_VPAGES;
        } else {
                pages = kmalloc_node(array_size,
                                (gfp_mask & GFP_RECLAIM_MASK) | __GFP_ZERO,
                                node);
        }
        area->pages = pages;
        if (!area->pages) {
                remove_vm_area(area->addr);
                kfree(area);
                return NULL;
        }

        for (i = 0; i < area->nr_pages; i++) {
                struct page *page;

                if (node < 0)
                        page = alloc_page(gfp_mask);
                else
                        page = alloc_pages_node(node, gfp_mask, 0);

                if (unlikely(!page)) {
                        /* Successfully allocated i pages, free them in __vunmap() */
                        area->nr_pages = i;
                        goto fail;
                }
                area->pages[i] = page;
        }

        if (map_vm_area(area, prot, &pages))
                goto fail;
        return area->addr;

fail:
        vfree(area->addr);
        return NULL;
}

void *__vmalloc_area(struct vm_struct *area, gfp_t gfp_mask, pgprot_t prot)
{
        return __vmalloc_area_node(area, gfp_mask, prot, -1);
}

/**
 *      __vmalloc_node  -  allocate virtually contiguous memory
 *      @size:          allocation size
 *      @gfp_mask:      flags for the page level allocator
 *      @prot:          protection mask for the allocated pages
 *      @node:          node to use for allocation or -1
 *
 *      Allocate enough pages to cover @size from the page level
 *      allocator with @gfp_mask flags.  Map them into contiguous
 *      kernel virtual space, using a pagetable protection of @prot.
 */
static void *__vmalloc_node(unsigned long size, gfp_t gfp_mask, pgprot_t prot,
                            int node)
{
        struct vm_struct *area;

        size = PAGE_ALIGN(size);
        if (!size || (size >> PAGE_SHIFT) > num_physpages)
                return NULL;

        area = get_vm_area_node(size, VM_ALLOC, node, gfp_mask);
        if (!area)
                return NULL;

        return __vmalloc_area_node(area, gfp_mask, prot, node);
}

void *__vmalloc(unsigned long size, gfp_t gfp_mask, pgprot_t prot)
{
        return __vmalloc_node(size, gfp_mask, prot, -1);
}
EXPORT_SYMBOL(__vmalloc);

/**
 *      vmalloc  -  allocate virtually contiguous memory
 *      @size:          allocation size
 *      Allocate enough pages to cover @size from the page level
 *      allocator and map them into contiguous kernel virtual space.
 *
 *      For tight control over page level allocator and protection flags
 *      use __vmalloc() instead.
 */
void *vmalloc(unsigned long size)
{
        return __vmalloc(size, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL);
}
EXPORT_SYMBOL(vmalloc);

/**
 * vmalloc_user - allocate zeroed virtually contiguous memory for userspace
 * @size: allocation size
 *
 * The resulting memory area is zeroed so it can be mapped to userspace
 * without leaking data.
 */
void *vmalloc_user(unsigned long size)
{
        struct vm_struct *area;
        void *ret;

        ret = __vmalloc(size, GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO, PAGE_KERNEL);
        if (ret) {
                write_lock(&vmlist_lock);
                area = __find_vm_area(ret);
                area->flags |= VM_USERMAP;
                write_unlock(&vmlist_lock);
        }
        return ret;
}
EXPORT_SYMBOL(vmalloc_user);

/**
 *      vmalloc_node  -  allocate memory on a specific node
 *      @size:          allocation size
 *      @node:          numa node
 *
 *      Allocate enough pages to cover @size from the page level
 *      allocator and map them into contiguous kernel virtual space.
 *
 *      For tight control over page level allocator and protection flags
 *      use __vmalloc() instead.
 */
void *vmalloc_node(unsigned long size, int node)
{
        return __vmalloc_node(size, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL, node);
}
EXPORT_SYMBOL(vmalloc_node);

#ifndef PAGE_KERNEL_EXEC
# define PAGE_KERNEL_EXEC PAGE_KERNEL
#endif

/**
 *      vmalloc_exec  -  allocate virtually contiguous, executable memory
 *      @size:          allocation size
 *
 *      Kernel-internal function to allocate enough pages to cover @size
 *      the page level allocator and map them into contiguous and
 *      executable kernel virtual space.
 *
 *      For tight control over page level allocator and protection flags
 *      use __vmalloc() instead.
 */

void *vmalloc_exec(unsigned long size)
{
        return __vmalloc(size, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL_EXEC);
}

#if defined(CONFIG_64BIT) && defined(CONFIG_ZONE_DMA32)
#define GFP_VMALLOC32 GFP_DMA32 | GFP_KERNEL
#elif defined(CONFIG_64BIT) && defined(CONFIG_ZONE_DMA)
#define GFP_VMALLOC32 GFP_DMA | GFP_KERNEL
#else
#define GFP_VMALLOC32 GFP_KERNEL
#endif

/**
 *      vmalloc_32  -  allocate virtually contiguous memory (32bit addressable)
 *      @size:          allocation size
 *
 *      Allocate enough 32bit PA addressable pages to cover @size from the
 *      page level allocator and map them into contiguous kernel virtual space.
 */
void *vmalloc_32(unsigned long size)
{
        return __vmalloc(size, GFP_VMALLOC32, PAGE_KERNEL);
}
EXPORT_SYMBOL(vmalloc_32);

/**
 * vmalloc_32_user - allocate zeroed virtually contiguous 32bit memory
 *      @size:          allocation size
 *
 * The resulting memory area is 32bit addressable and zeroed so it can be
 * mapped to userspace without leaking data.
 */
void *vmalloc_32_user(unsigned long size)
{
        struct vm_struct *area;
        void *ret;

        ret = __vmalloc(size, GFP_VMALLOC32 | __GFP_ZERO, PAGE_KERNEL);
        if (ret) {
                write_lock(&vmlist_lock);
                area = __find_vm_area(ret);
                area->flags |= VM_USERMAP;
                write_unlock(&vmlist_lock);
        }
        return ret;
}
EXPORT_SYMBOL(vmalloc_32_user);

long vread(char *buf, char *addr, unsigned long count)
{
        struct vm_struct *tmp;
        char *vaddr, *buf_start = buf;
        unsigned long n;

        /* Don't allow overflow */
        if ((unsigned long) addr + count < count)
                count = -(unsigned long) addr;

        read_lock(&vmlist_lock);
        for (tmp = vmlist; tmp; tmp = tmp->next) {
                vaddr = (char *) tmp->addr;
                if (addr >= vaddr + tmp->size - PAGE_SIZE)
                        continue;
                while (addr < vaddr) {
                        if (count == 0)
                                goto finished;
                        *buf = '\0';
                        buf++;
                        addr++;
                        count--;
                }
                n = vaddr + tmp->size - PAGE_SIZE - addr;
                do {
                        if (count == 0)
                                goto finished;
                        *buf = *addr;
                        buf++;
                        addr++;
                        count--;
                } while (--n > 0);
        }
finished:
        read_unlock(&vmlist_lock);
        return buf - buf_start;
}

long vwrite(char *buf, char *addr, unsigned long count)
{
        struct vm_struct *tmp;
        char *vaddr, *buf_start = buf;
        unsigned long n;

        /* Don't allow overflow */
        if ((unsigned long) addr + count < count)
                count = -(unsigned long) addr;

        read_lock(&vmlist_lock);
        for (tmp = vmlist; tmp; tmp = tmp->next) {
                vaddr = (char *) tmp->addr;
                if (addr >= vaddr + tmp->size - PAGE_SIZE)
                        continue;
                while (addr < vaddr) {
                        if (count == 0)
                                goto finished;
                        buf++;
                        addr++;
                        count--;
                }
                n = vaddr + tmp->size - PAGE_SIZE - addr;
                do {
                        if (count == 0)
                                goto finished;
                        *addr = *buf;
                        buf++;
                        addr++;
                        count--;
                } while (--n > 0);
        }
finished:
        read_unlock(&vmlist_lock);
        return buf - buf_start;
}

/**
 *      remap_vmalloc_range  -  map vmalloc pages to userspace
 *      @vma:           vma to cover (map full range of vma)
 *      @addr:          vmalloc memory
 *      @pgoff:         number of pages into addr before first page to map
 *
 *      Returns:        0 for success, -Exxx on failure
 *
 *      This function checks that addr is a valid vmalloc'ed area, and
 *      that it is big enough to cover the vma. Will return failure if
 *      that criteria isn't met.
 *
 *      Similar to remap_pfn_range() (see mm/memory.c)
 */
int remap_vmalloc_range(struct vm_area_struct *vma, void *addr,
                                                unsigned long pgoff)
{
        struct vm_struct *area;
        unsigned long uaddr = vma->vm_start;
        unsigned long usize = vma->vm_end - vma->vm_start;
        int ret;

        if ((PAGE_SIZE-1) & (unsigned long)addr)
                return -EINVAL;

        read_lock(&vmlist_lock);
        area = __find_vm_area(addr);
        if (!area)
                goto out_einval_locked;

        if (!(area->flags & VM_USERMAP))
                goto out_einval_locked;

        if (usize + (pgoff << PAGE_SHIFT) > area->size - PAGE_SIZE)
                goto out_einval_locked;
        read_unlock(&vmlist_lock);

        addr += pgoff << PAGE_SHIFT;
        do {
                struct page *page = vmalloc_to_page(addr);
                ret = vm_insert_page(vma, uaddr, page);
                if (ret)
                        return ret;

                uaddr += PAGE_SIZE;
                addr += PAGE_SIZE;
                usize -= PAGE_SIZE;
        } while (usize > 0);

        /* Prevent "things" like memory migration? VM_flags need a cleanup... */
        vma->vm_flags |= VM_RESERVED;

        return ret;

out_einval_locked:
        read_unlock(&vmlist_lock);
        return -EINVAL;
}
EXPORT_SYMBOL(remap_vmalloc_range);

/*
 * Implement a stub for vmalloc_sync_all() if the architecture chose not to
 * have one.
 */
void  __attribute__((weak)) vmalloc_sync_all(void)
{
}


static int f(pte_t *pte, pgtable_t table, unsigned long addr, void *data)
{
        /* apply_to_page_range() does all the hard work. */
        return 0;
}

/**
 *      alloc_vm_area - allocate a range of kernel address space
 *      @size:          size of the area
 *
 *      Returns:        NULL on failure, vm_struct on success
 *
 *      This function reserves a range of kernel address space, and
 *      allocates pagetables to map that range.  No actual mappings
 *      are created.  If the kernel address space is not shared
 *      between processes, it syncs the pagetable across all
 *      processes.
 */
struct vm_struct *alloc_vm_area(size_t size)
{
        struct vm_struct *area;

        area = get_vm_area(size, VM_IOREMAP);
        if (area == NULL)
                return NULL;

        /*
         * This ensures that page tables are constructed for this region
         * of kernel virtual address space and mapped into init_mm.
         */
        if (apply_to_page_range(&init_mm, (unsigned long)area->addr,
                                area->size, f, NULL)) {
                free_vm_area(area);
                return NULL;
        }

        /* Make sure the pagetables are constructed in process kernel
           mappings */
        vmalloc_sync_all();

        return area;
}
EXPORT_SYMBOL_GPL(alloc_vm_area);

void free_vm_area(struct vm_struct *area)
{
        struct vm_struct *ret;
        ret = remove_vm_area(area->addr);
        BUG_ON(ret != area);
        kfree(area);
}
EXPORT_SYMBOL_GPL(free_vm_area);