[PATCH] Add a driver for the Technisat Skystar2 DVB card

[linux-2.6/history.git] / mm / memory.c

/*
 *  linux/mm/memory.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 */

/*
 * demand-loading started 01.12.91 - seems it is high on the list of
 * things wanted, and it should be easy to implement. - Linus
 */

/*
 * Ok, demand-loading was easy, shared pages a little bit tricker. Shared
 * pages started 02.12.91, seems to work. - Linus.
 *
 * Tested sharing by executing about 30 /bin/sh: under the old kernel it
 * would have taken more than the 6M I have free, but it worked well as
 * far as I could see.
 *
 * Also corrected some "invalidate()"s - I wasn't doing enough of them.
 */

/*
 * Real VM (paging to/from disk) started 18.12.91. Much more work and
 * thought has to go into this. Oh, well..
 * 19.12.91  -  works, somewhat. Sometimes I get faults, don't know why.
 *              Found it. Everything seems to work now.
 * 20.12.91  -  Ok, making the swap-device changeable like the root.
 */

/*
 * 05.04.94  -  Multi-page memory management added for v1.1.
 *              Idea by Alex Bligh (alex@cconcepts.co.uk)
 *
 * 16.07.99  -  Support of BIGMEM added by Gerhard Wichert, Siemens AG
 *              (Gerhard.Wichert@pdb.siemens.de)
 */

#include <linux/kernel_stat.h>
#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/mman.h>
#include <linux/swap.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/vcache.h>
#include <linux/rmap-locking.h>

#include <asm/pgalloc.h>
#include <asm/rmap.h>
#include <asm/uaccess.h>
#include <asm/tlb.h>
#include <asm/tlbflush.h>
#include <asm/pgtable.h>

#include <linux/swapops.h>

#ifndef CONFIG_DISCONTIGMEM
/* use the per-pgdat data instead for discontigmem - mbligh */
unsigned long max_mapnr;
struct page *mem_map;
#endif

unsigned long num_physpages;
void * high_memory;
struct page *highmem_start_page;

/*
 * We special-case the C-O-W ZERO_PAGE, because it's such
 * a common occurrence (no need to read the page to know
 * that it's zero - better for the cache and memory subsystem).
 */
static inline void copy_cow_page(struct page * from, struct page * to, unsigned long address)
{
        if (from == ZERO_PAGE(address)) {
                clear_user_highpage(to, address);
                return;
        }
        copy_user_highpage(to, from, address);
}

/*
 * Note: this doesn't free the actual pages themselves. That
 * has been handled earlier when unmapping all the memory regions.
 */
static inline void free_one_pmd(struct mmu_gather *tlb, pmd_t * dir)
{
        struct page *page;

        if (pmd_none(*dir))
                return;
        if (pmd_bad(*dir)) {
                pmd_ERROR(*dir);
                pmd_clear(dir);
                return;
        }
        page = pmd_page(*dir);
        pmd_clear(dir);
        pgtable_remove_rmap(page);
        pte_free_tlb(tlb, page);
}

static inline void free_one_pgd(struct mmu_gather *tlb, pgd_t * dir)
{
        int j;
        pmd_t * pmd;

        if (pgd_none(*dir))
                return;
        if (pgd_bad(*dir)) {
                pgd_ERROR(*dir);
                pgd_clear(dir);
                return;
        }
        pmd = pmd_offset(dir, 0);
        pgd_clear(dir);
        for (j = 0; j < PTRS_PER_PMD ; j++)
                free_one_pmd(tlb, pmd+j);
        pmd_free_tlb(tlb, pmd);
}

/*
 * This function clears all user-level page tables of a process - this
 * is needed by execve(), so that old pages aren't in the way.
 *
 * Must be called with pagetable lock held.
 */
void clear_page_tables(struct mmu_gather *tlb, unsigned long first, int nr)
{
        pgd_t * page_dir = tlb->mm->pgd;

        page_dir += first;
        do {
                free_one_pgd(tlb, page_dir);
                page_dir++;
        } while (--nr);
}

pte_t * pte_alloc_map(struct mm_struct *mm, pmd_t *pmd, unsigned long address)
{
        if (!pmd_present(*pmd)) {
                struct page *new;

                spin_unlock(&mm->page_table_lock);
                new = pte_alloc_one(mm, address);
                spin_lock(&mm->page_table_lock);
                if (!new)
                        return NULL;

                /*
                 * Because we dropped the lock, we should re-check the
                 * entry, as somebody else could have populated it..
                 */
                if (pmd_present(*pmd)) {
                        pte_free(new);
                        goto out;
                }
                pgtable_add_rmap(new, mm, address);
                pmd_populate(mm, pmd, new);
        }
out:
        return pte_offset_map(pmd, address);
}

pte_t * pte_alloc_kernel(struct mm_struct *mm, pmd_t *pmd, unsigned long address)
{
        if (!pmd_present(*pmd)) {
                pte_t *new;

                spin_unlock(&mm->page_table_lock);
                new = pte_alloc_one_kernel(mm, address);
                spin_lock(&mm->page_table_lock);
                if (!new)
                        return NULL;

                /*
                 * Because we dropped the lock, we should re-check the
                 * entry, as somebody else could have populated it..
                 */
                if (pmd_present(*pmd)) {
                        pte_free_kernel(new);
                        goto out;
                }
                pgtable_add_rmap(virt_to_page(new), mm, address);
                pmd_populate_kernel(mm, pmd, new);
        }
out:
        return pte_offset_kernel(pmd, address);
}
#define PTE_TABLE_MASK  ((PTRS_PER_PTE-1) * sizeof(pte_t))
#define PMD_TABLE_MASK  ((PTRS_PER_PMD-1) * sizeof(pmd_t))

/*
 * copy one vm_area from one task to the other. Assumes the page tables
 * already present in the new task to be cleared in the whole range
 * covered by this vma.
 *
 * 08Jan98 Merged into one routine from several inline routines to reduce
 *         variable count and make things faster. -jj
 *
 * dst->page_table_lock is held on entry and exit,
 * but may be dropped within pmd_alloc() and pte_alloc_map().
 */
int copy_page_range(struct mm_struct *dst, struct mm_struct *src,
                        struct vm_area_struct *vma)
{
        pgd_t * src_pgd, * dst_pgd;
        unsigned long address = vma->vm_start;
        unsigned long end = vma->vm_end;
        unsigned long cow;
        struct pte_chain *pte_chain = NULL;

        if (is_vm_hugetlb_page(vma))
                return copy_hugetlb_page_range(dst, src, vma);

        pte_chain = pte_chain_alloc(GFP_ATOMIC);
        if (!pte_chain) {
                spin_unlock(&dst->page_table_lock);
                pte_chain = pte_chain_alloc(GFP_KERNEL);
                spin_lock(&dst->page_table_lock);
                if (!pte_chain)
                        goto nomem;
        }
        
        cow = (vma->vm_flags & (VM_SHARED | VM_MAYWRITE)) == VM_MAYWRITE;
        src_pgd = pgd_offset(src, address)-1;
        dst_pgd = pgd_offset(dst, address)-1;

        for (;;) {
                pmd_t * src_pmd, * dst_pmd;

                src_pgd++; dst_pgd++;
                
                /* copy_pmd_range */
                
                if (pgd_none(*src_pgd))
                        goto skip_copy_pmd_range;
                if (pgd_bad(*src_pgd)) {
                        pgd_ERROR(*src_pgd);
                        pgd_clear(src_pgd);
skip_copy_pmd_range:    address = (address + PGDIR_SIZE) & PGDIR_MASK;
                        if (!address || (address >= end))
                                goto out;
                        continue;
                }

                src_pmd = pmd_offset(src_pgd, address);
                dst_pmd = pmd_alloc(dst, dst_pgd, address);
                if (!dst_pmd)
                        goto nomem;

                do {
                        pte_t * src_pte, * dst_pte;
                
                        /* copy_pte_range */
                
                        if (pmd_none(*src_pmd))
                                goto skip_copy_pte_range;
                        if (pmd_bad(*src_pmd)) {
                                pmd_ERROR(*src_pmd);
                                pmd_clear(src_pmd);
skip_copy_pte_range:
                                address = (address + PMD_SIZE) & PMD_MASK;
                                if (address >= end)
                                        goto out;
                                goto cont_copy_pmd_range;
                        }

                        dst_pte = pte_alloc_map(dst, dst_pmd, address);
                        if (!dst_pte)
                                goto nomem;
                        spin_lock(&src->page_table_lock);       
                        src_pte = pte_offset_map_nested(src_pmd, address);
                        do {
                                pte_t pte = *src_pte;
                                struct page *page;
                                unsigned long pfn;

                                /* copy_one_pte */

                                if (pte_none(pte))
                                        goto cont_copy_pte_range_noset;
                                /* pte contains position in swap, so copy. */
                                if (!pte_present(pte)) {
                                        if (!pte_file(pte))
                                                swap_duplicate(pte_to_swp_entry(pte));
                                        set_pte(dst_pte, pte);
                                        goto cont_copy_pte_range_noset;
                                }
                                pfn = pte_pfn(pte);
                                /* the pte points outside of valid memory, the
                                 * mapping is assumed to be good, meaningful
                                 * and not mapped via rmap - duplicate the
                                 * mapping as is.
                                 */
                                page = NULL;
                                if (pfn_valid(pfn)) 
                                        page = pfn_to_page(pfn); 

                                if (!page || PageReserved(page)) {
                                        set_pte(dst_pte, pte);
                                        goto cont_copy_pte_range_noset;
                                }

                                /*
                                 * If it's a COW mapping, write protect it both
                                 * in the parent and the child
                                 */
                                if (cow) {
                                        ptep_set_wrprotect(src_pte);
                                        pte = *src_pte;
                                }

                                /*
                                 * If it's a shared mapping, mark it clean in
                                 * the child
                                 */
                                if (vma->vm_flags & VM_SHARED)
                                        pte = pte_mkclean(pte);
                                pte = pte_mkold(pte);
                                get_page(page);
                                dst->rss++;

                                set_pte(dst_pte, pte);
                                pte_chain = page_add_rmap(page, dst_pte,
                                                        pte_chain);
                                if (pte_chain)
                                        goto cont_copy_pte_range_noset;
                                pte_chain = pte_chain_alloc(GFP_ATOMIC);
                                if (pte_chain)
                                        goto cont_copy_pte_range_noset;

                                /*
                                 * pte_chain allocation failed, and we need to
                                 * run page reclaim.
                                 */
                                pte_unmap_nested(src_pte);
                                pte_unmap(dst_pte);
                                spin_unlock(&src->page_table_lock);     
                                spin_unlock(&dst->page_table_lock);     
                                pte_chain = pte_chain_alloc(GFP_KERNEL);
                                spin_lock(&dst->page_table_lock);       
                                if (!pte_chain)
                                        goto nomem;
                                spin_lock(&src->page_table_lock);
                                dst_pte = pte_offset_map(dst_pmd, address);
                                src_pte = pte_offset_map_nested(src_pmd,
                                                                address);
cont_copy_pte_range_noset:
                                address += PAGE_SIZE;
                                if (address >= end) {
                                        pte_unmap_nested(src_pte);
                                        pte_unmap(dst_pte);
                                        goto out_unlock;
                                }
                                src_pte++;
                                dst_pte++;
                        } while ((unsigned long)src_pte & PTE_TABLE_MASK);
                        pte_unmap_nested(src_pte-1);
                        pte_unmap(dst_pte-1);
                        spin_unlock(&src->page_table_lock);
                
cont_copy_pmd_range:
                        src_pmd++;
                        dst_pmd++;
                } while ((unsigned long)src_pmd & PMD_TABLE_MASK);
        }
out_unlock:
        spin_unlock(&src->page_table_lock);
out:
        pte_chain_free(pte_chain);
        return 0;
nomem:
        pte_chain_free(pte_chain);
        return -ENOMEM;
}

static void
zap_pte_range(struct mmu_gather *tlb, pmd_t * pmd,
                unsigned long address, unsigned long size)
{
        unsigned long offset;
        pte_t *ptep;

        if (pmd_none(*pmd))
                return;
        if (pmd_bad(*pmd)) {
                pmd_ERROR(*pmd);
                pmd_clear(pmd);
                return;
        }
        ptep = pte_offset_map(pmd, address);
        offset = address & ~PMD_MASK;
        if (offset + size > PMD_SIZE)
                size = PMD_SIZE - offset;
        size &= PAGE_MASK;
        for (offset=0; offset < size; ptep++, offset += PAGE_SIZE) {
                pte_t pte = *ptep;
                if (pte_none(pte))
                        continue;
                if (pte_present(pte)) {
                        unsigned long pfn = pte_pfn(pte);

                        pte = ptep_get_and_clear(ptep);
                        tlb_remove_tlb_entry(tlb, ptep, address+offset);
                        if (pfn_valid(pfn)) {
                                struct page *page = pfn_to_page(pfn);
                                if (!PageReserved(page)) {
                                        if (pte_dirty(pte))
                                                set_page_dirty(page);
                                        if (page->mapping && pte_young(pte) &&
                                                        !PageSwapCache(page))
                                                mark_page_accessed(page);
                                        tlb->freed++;
                                        page_remove_rmap(page, ptep);
                                        tlb_remove_page(tlb, page);
                                }
                        }
                } else {
                        if (!pte_file(pte))
                                free_swap_and_cache(pte_to_swp_entry(pte));
                        pte_clear(ptep);
                }
        }
        pte_unmap(ptep-1);
}

static void
zap_pmd_range(struct mmu_gather *tlb, pgd_t * dir,
                unsigned long address, unsigned long size)
{
        pmd_t * pmd;
        unsigned long end;

        if (pgd_none(*dir))
                return;
        if (pgd_bad(*dir)) {
                pgd_ERROR(*dir);
                pgd_clear(dir);
                return;
        }
        pmd = pmd_offset(dir, address);
        end = address + size;
        if (end > ((address + PGDIR_SIZE) & PGDIR_MASK))
                end = ((address + PGDIR_SIZE) & PGDIR_MASK);
        do {
                zap_pte_range(tlb, pmd, address, end - address);
                address = (address + PMD_SIZE) & PMD_MASK; 
                pmd++;
        } while (address < end);
}

void unmap_page_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
                        unsigned long address, unsigned long end)
{
        pgd_t * dir;

        if (is_vm_hugetlb_page(vma)) {
                unmap_hugepage_range(vma, address, end);
                return;
        }

        BUG_ON(address >= end);

        dir = pgd_offset(vma->vm_mm, address);
        tlb_start_vma(tlb, vma);
        do {
                zap_pmd_range(tlb, dir, address, end - address);
                address = (address + PGDIR_SIZE) & PGDIR_MASK;
                dir++;
        } while (address && (address < end));
        tlb_end_vma(tlb, vma);
}

/* Dispose of an entire struct mmu_gather per rescheduling point */
#if defined(CONFIG_SMP) && defined(CONFIG_PREEMPT)
#define ZAP_BLOCK_SIZE  (FREE_PTE_NR * PAGE_SIZE)
#endif

/* For UP, 256 pages at a time gives nice low latency */
#if !defined(CONFIG_SMP) && defined(CONFIG_PREEMPT)
#define ZAP_BLOCK_SIZE  (256 * PAGE_SIZE)
#endif

/* No preempt: go for the best straight-line efficiency */
#if !defined(CONFIG_PREEMPT)
#define ZAP_BLOCK_SIZE  (~(0UL))
#endif

/**
 * unmap_vmas - unmap a range of memory covered by a list of vma's
 * @tlbp: address of the caller's struct mmu_gather
 * @mm: the controlling mm_struct
 * @vma: the starting vma
 * @start_addr: virtual address at which to start unmapping
 * @end_addr: virtual address at which to end unmapping
 * @nr_accounted: Place number of unmapped pages in vm-accountable vma's here
 *
 * Returns the number of vma's which were covered by the unmapping.
 *
 * Unmap all pages in the vma list.  Called under page_table_lock.
 *
 * We aim to not hold page_table_lock for too long (for scheduling latency
 * reasons).  So zap pages in ZAP_BLOCK_SIZE bytecounts.  This means we need to
 * return the ending mmu_gather to the caller.
 *
 * Only addresses between `start' and `end' will be unmapped.
 *
 * The VMA list must be sorted in ascending virtual address order.
 *
 * unmap_vmas() assumes that the caller will flush the whole unmapped address
 * range after unmap_vmas() returns.  So the only responsibility here is to
 * ensure that any thus-far unmapped pages are flushed before unmap_vmas()
 * drops the lock and schedules.
 */
int unmap_vmas(struct mmu_gather **tlbp, struct mm_struct *mm,
                struct vm_area_struct *vma, unsigned long start_addr,
                unsigned long end_addr, unsigned long *nr_accounted)
{
        unsigned long zap_bytes = ZAP_BLOCK_SIZE;
        unsigned long tlb_start;        /* For tlb_finish_mmu */
        int tlb_start_valid = 0;
        int ret = 0;

        if (vma) {      /* debug.  killme. */
                if (end_addr <= vma->vm_start)
                        printk("%s: end_addr(0x%08lx) <= vm_start(0x%08lx)\n",
                                __FUNCTION__, end_addr, vma->vm_start);
                if (start_addr >= vma->vm_end)
                        printk("%s: start_addr(0x%08lx) <= vm_end(0x%08lx)\n",
                                __FUNCTION__, start_addr, vma->vm_end);
        }

        for ( ; vma && vma->vm_start < end_addr; vma = vma->vm_next) {
                unsigned long start;
                unsigned long end;

                start = max(vma->vm_start, start_addr);
                if (start >= vma->vm_end)
                        continue;
                end = min(vma->vm_end, end_addr);
                if (end <= vma->vm_start)
                        continue;

                if (vma->vm_flags & VM_ACCOUNT)
                        *nr_accounted += (end - start) >> PAGE_SHIFT;

                ret++;
                while (start != end) {
                        unsigned long block;

                        if (is_vm_hugetlb_page(vma))
                                block = end - start;
                        else
                                block = min(zap_bytes, end - start);

                        if (!tlb_start_valid) {
                                tlb_start = start;
                                tlb_start_valid = 1;
                        }

                        unmap_page_range(*tlbp, vma, start, start + block);
                        start += block;
                        zap_bytes -= block;
                        if ((long)zap_bytes > 0)
                                continue;
                        if (need_resched()) {
                                tlb_finish_mmu(*tlbp, tlb_start, start);
                                cond_resched_lock(&mm->page_table_lock);
                                *tlbp = tlb_gather_mmu(mm, 0);
                                tlb_start_valid = 0;
                        }
                        zap_bytes = ZAP_BLOCK_SIZE;
                }
                if (vma->vm_next && vma->vm_next->vm_start < vma->vm_end)
                        printk("%s: VMA list is not sorted correctly!\n",
                                __FUNCTION__);          
        }
        return ret;
}

/**
 * zap_page_range - remove user pages in a given range
 * @vma: vm_area_struct holding the applicable pages
 * @address: starting address of pages to zap
 * @size: number of bytes to zap
 */
void zap_page_range(struct vm_area_struct *vma,
                        unsigned long address, unsigned long size)
{
        struct mm_struct *mm = vma->vm_mm;
        struct mmu_gather *tlb;
        unsigned long end = address + size;
        unsigned long nr_accounted = 0;

        might_sleep();

        if (is_vm_hugetlb_page(vma)) {
                zap_hugepage_range(vma, address, size);
                return;
        }

        lru_add_drain();
        spin_lock(&mm->page_table_lock);
        tlb = tlb_gather_mmu(mm, 0);
        unmap_vmas(&tlb, mm, vma, address, end, &nr_accounted);
        tlb_finish_mmu(tlb, address, end);
        spin_unlock(&mm->page_table_lock);
}

/*
 * Do a quick page-table lookup for a single page.
 * mm->page_table_lock must be held.
 */
struct page *
follow_page(struct mm_struct *mm, unsigned long address, int write) 
{
        pgd_t *pgd;
        pmd_t *pmd;
        pte_t *ptep, pte;
        unsigned long pfn;
        struct vm_area_struct *vma;

        vma = hugepage_vma(mm, address);
        if (vma)
                return follow_huge_addr(mm, vma, address, write);

        pgd = pgd_offset(mm, address);
        if (pgd_none(*pgd) || pgd_bad(*pgd))
                goto out;

        pmd = pmd_offset(pgd, address);
        if (pmd_none(*pmd))
                goto out;
        if (pmd_huge(*pmd))
                return follow_huge_pmd(mm, address, pmd, write);
        if (pmd_bad(*pmd))
                goto out;

        ptep = pte_offset_map(pmd, address);
        if (!ptep)
                goto out;

        pte = *ptep;
        pte_unmap(ptep);
        if (pte_present(pte)) {
                if (!write || (pte_write(pte) && pte_dirty(pte))) {
                        pfn = pte_pfn(pte);
                        if (pfn_valid(pfn))
                                return pfn_to_page(pfn);
                }
        }

out:
        return NULL;
}

/* 
 * Given a physical address, is there a useful struct page pointing to
 * it?  This may become more complex in the future if we start dealing
 * with IO-aperture pages for direct-IO.
 */

static inline struct page *get_page_map(struct page *page)
{
        if (!pfn_valid(page_to_pfn(page)))
                return 0;
        return page;
}


int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                unsigned long start, int len, int write, int force,
                struct page **pages, struct vm_area_struct **vmas)
{
        int i;
        unsigned int flags;

        /* 
         * Require read or write permissions.
         * If 'force' is set, we only require the "MAY" flags.
         */
        flags = write ? (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
        flags &= force ? (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
        i = 0;

        do {
                struct vm_area_struct * vma;

                vma = find_extend_vma(mm, start);

#ifdef FIXADDR_USER_START
                if (!vma &&
                    start >= FIXADDR_USER_START && start < FIXADDR_USER_END) {
                        static struct vm_area_struct fixmap_vma = {
                                /* Catch users - if there are any valid
                                   ones, we can make this be "&init_mm" or
                                   something.  */
                                .vm_mm = NULL,
                                .vm_start = FIXADDR_USER_START,
                                .vm_end = FIXADDR_USER_END,
                                .vm_page_prot = PAGE_READONLY,
                                .vm_flags = VM_READ | VM_EXEC,
                        };
                        unsigned long pg = start & PAGE_MASK;
                        pgd_t *pgd;
                        pmd_t *pmd;
                        pte_t *pte;
                        if (write) /* user fixmap pages are read-only */
                                return i ? : -EFAULT;
                        pgd = pgd_offset_k(pg);
                        if (!pgd)
                                return i ? : -EFAULT;
                        pmd = pmd_offset(pgd, pg);
                        if (!pmd)
                                return i ? : -EFAULT;
                        pte = pte_offset_kernel(pmd, pg);
                        if (!pte || !pte_present(*pte))
                                return i ? : -EFAULT;
                        if (pages) {
                                pages[i] = pte_page(*pte);
                                get_page(pages[i]);
                        }
                        if (vmas)
                                vmas[i] = &fixmap_vma;
                        i++;
                        start += PAGE_SIZE;
                        len--;
                        continue;
                }
#endif

                if (!vma || (pages && (vma->vm_flags & VM_IO))
                                || !(flags & vma->vm_flags))
                        return i ? : -EFAULT;

                if (is_vm_hugetlb_page(vma)) {
                        i = follow_hugetlb_page(mm, vma, pages, vmas,
                                                &start, &len, i);
                        continue;
                }
                spin_lock(&mm->page_table_lock);
                do {
                        struct page *map;
                        while (!(map = follow_page(mm, start, write))) {
                                spin_unlock(&mm->page_table_lock);
                                switch (handle_mm_fault(mm,vma,start,write)) {
                                case VM_FAULT_MINOR:
                                        tsk->min_flt++;
                                        break;
                                case VM_FAULT_MAJOR:
                                        tsk->maj_flt++;
                                        break;
                                case VM_FAULT_SIGBUS:
                                        return i ? i : -EFAULT;
                                case VM_FAULT_OOM:
                                        return i ? i : -ENOMEM;
                                default:
                                        BUG();
                                }
                                spin_lock(&mm->page_table_lock);
                        }
                        if (pages) {
                                pages[i] = get_page_map(map);
                                if (!pages[i]) {
                                        spin_unlock(&mm->page_table_lock);
                                        while (i--)
                                                page_cache_release(pages[i]);
                                        i = -EFAULT;
                                        goto out;
                                }
                                flush_dcache_page(pages[i]);
                                if (!PageReserved(pages[i]))
                                        page_cache_get(pages[i]);
                        }
                        if (vmas)
                                vmas[i] = vma;
                        i++;
                        start += PAGE_SIZE;
                        len--;
                } while(len && start < vma->vm_end);
                spin_unlock(&mm->page_table_lock);
        } while(len);
out:
        return i;
}

static void zeromap_pte_range(pte_t * pte, unsigned long address,
                                     unsigned long size, pgprot_t prot)
{
        unsigned long end;

        address &= ~PMD_MASK;
        end = address + size;
        if (end > PMD_SIZE)
                end = PMD_SIZE;
        do {
                pte_t zero_pte = pte_wrprotect(mk_pte(ZERO_PAGE(address), prot));
                BUG_ON(!pte_none(*pte));
                set_pte(pte, zero_pte);
                address += PAGE_SIZE;
                pte++;
        } while (address && (address < end));
}

static inline int zeromap_pmd_range(struct mm_struct *mm, pmd_t * pmd, unsigned long address,
                                    unsigned long size, pgprot_t prot)
{
        unsigned long end;

        address &= ~PGDIR_MASK;
        end = address + size;
        if (end > PGDIR_SIZE)
                end = PGDIR_SIZE;
        do {
                pte_t * pte = pte_alloc_map(mm, pmd, address);
                if (!pte)
                        return -ENOMEM;
                zeromap_pte_range(pte, address, end - address, prot);
                pte_unmap(pte);
                address = (address + PMD_SIZE) & PMD_MASK;
                pmd++;
        } while (address && (address < end));
        return 0;
}

int zeromap_page_range(struct vm_area_struct *vma, unsigned long address, unsigned long size, pgprot_t prot)
{
        int error = 0;
        pgd_t * dir;
        unsigned long beg = address;
        unsigned long end = address + size;
        struct mm_struct *mm = vma->vm_mm;

        dir = pgd_offset(mm, address);
        flush_cache_range(vma, beg, end);
        if (address >= end)
                BUG();

        spin_lock(&mm->page_table_lock);
        do {
                pmd_t *pmd = pmd_alloc(mm, dir, address);
                error = -ENOMEM;
                if (!pmd)
                        break;
                error = zeromap_pmd_range(mm, pmd, address, end - address, prot);
                if (error)
                        break;
                address = (address + PGDIR_SIZE) & PGDIR_MASK;
                dir++;
        } while (address && (address < end));
        flush_tlb_range(vma, beg, end);
        spin_unlock(&mm->page_table_lock);
        return error;
}

/*
 * maps a range of physical memory into the requested pages. the old
 * mappings are removed. any references to nonexistent pages results
 * in null mappings (currently treated as "copy-on-access")
 */
static inline void remap_pte_range(pte_t * pte, unsigned long address, unsigned long size,
        unsigned long phys_addr, pgprot_t prot)
{
        unsigned long end;
        unsigned long pfn;

        address &= ~PMD_MASK;
        end = address + size;
        if (end > PMD_SIZE)
                end = PMD_SIZE;
        pfn = phys_addr >> PAGE_SHIFT;
        do {
                BUG_ON(!pte_none(*pte));
                if (!pfn_valid(pfn) || PageReserved(pfn_to_page(pfn)))
                        set_pte(pte, pfn_pte(pfn, prot));
                address += PAGE_SIZE;
                pfn++;
                pte++;
        } while (address && (address < end));
}

static inline int remap_pmd_range(struct mm_struct *mm, pmd_t * pmd, unsigned long address, unsigned long size,
        unsigned long phys_addr, pgprot_t prot)
{
        unsigned long base, end;

        base = address & PGDIR_MASK;
        address &= ~PGDIR_MASK;
        end = address + size;
        if (end > PGDIR_SIZE)
                end = PGDIR_SIZE;
        phys_addr -= address;
        do {
                pte_t * pte = pte_alloc_map(mm, pmd, base + address);
                if (!pte)
                        return -ENOMEM;
                remap_pte_range(pte, base + address, end - address, address + phys_addr, prot);
                pte_unmap(pte);
                address = (address + PMD_SIZE) & PMD_MASK;
                pmd++;
        } while (address && (address < end));
        return 0;
}

/*  Note: this is only safe if the mm semaphore is held when called. */
int remap_page_range(struct vm_area_struct *vma, unsigned long from, unsigned long phys_addr, unsigned long size, pgprot_t prot)
{
        int error = 0;
        pgd_t * dir;
        unsigned long beg = from;
        unsigned long end = from + size;
        struct mm_struct *mm = vma->vm_mm;

        phys_addr -= from;
        dir = pgd_offset(mm, from);
        flush_cache_range(vma, beg, end);
        if (from >= end)
                BUG();

        spin_lock(&mm->page_table_lock);
        do {
                pmd_t *pmd = pmd_alloc(mm, dir, from);
                error = -ENOMEM;
                if (!pmd)
                        break;
                error = remap_pmd_range(mm, pmd, from, end - from, phys_addr + from, prot);
                if (error)
                        break;
                from = (from + PGDIR_SIZE) & PGDIR_MASK;
                dir++;
        } while (from && (from < end));
        flush_tlb_range(vma, beg, end);
        spin_unlock(&mm->page_table_lock);
        return error;
}

/*
 * Establish a new mapping:
 *  - flush the old one
 *  - update the page tables
 *  - inform the TLB about the new one
 *
 * We hold the mm semaphore for reading and vma->vm_mm->page_table_lock
 */
static inline void establish_pte(struct vm_area_struct * vma, unsigned long address, pte_t *page_table, pte_t entry)
{
        set_pte(page_table, entry);
        flush_tlb_page(vma, address);
        update_mmu_cache(vma, address, entry);
}

/*
 * We hold the mm semaphore for reading and vma->vm_mm->page_table_lock
 */
static inline void break_cow(struct vm_area_struct * vma, struct page * new_page, unsigned long address, 
                pte_t *page_table)
{
        invalidate_vcache(address, vma->vm_mm, new_page);
        flush_cache_page(vma, address);
        establish_pte(vma, address, page_table, pte_mkwrite(pte_mkdirty(mk_pte(new_page, vma->vm_page_prot))));
}

/*
 * This routine handles present pages, when users try to write
 * to a shared page. It is done by copying the page to a new address
 * and decrementing the shared-page counter for the old page.
 *
 * Goto-purists beware: the only reason for goto's here is that it results
 * in better assembly code.. The "default" path will see no jumps at all.
 *
 * Note that this routine assumes that the protection checks have been
 * done by the caller (the low-level page fault routine in most cases).
 * Thus we can safely just mark it writable once we've done any necessary
 * COW.
 *
 * We also mark the page dirty at this point even though the page will
 * change only once the write actually happens. This avoids a few races,
 * and potentially makes it more efficient.
 *
 * We hold the mm semaphore and the page_table_lock on entry and exit
 * with the page_table_lock released.
 */
static int do_wp_page(struct mm_struct *mm, struct vm_area_struct * vma,
        unsigned long address, pte_t *page_table, pmd_t *pmd, pte_t pte)
{
        struct page *old_page, *new_page;
        unsigned long pfn = pte_pfn(pte);
        struct pte_chain *pte_chain = NULL;
        int ret;

        if (unlikely(!pfn_valid(pfn))) {
                /*
                 * This should really halt the system so it can be debugged or
                 * at least the kernel stops what it's doing before it corrupts
                 * data, but for the moment just pretend this is OOM.
                 */
                pte_unmap(page_table);
                printk(KERN_ERR "do_wp_page: bogus page at address %08lx\n",
                                address);
                goto oom;
        }
        old_page = pfn_to_page(pfn);

        if (!TestSetPageLocked(old_page)) {
                int reuse = can_share_swap_page(old_page);
                unlock_page(old_page);
                if (reuse) {
                        flush_cache_page(vma, address);
                        establish_pte(vma, address, page_table,
                                pte_mkyoung(pte_mkdirty(pte_mkwrite(pte))));
                        pte_unmap(page_table);
                        ret = VM_FAULT_MINOR;
                        goto out;
                }
        }
        pte_unmap(page_table);

        /*
         * Ok, we need to copy. Oh, well..
         */
        page_cache_get(old_page);
        spin_unlock(&mm->page_table_lock);

        pte_chain = pte_chain_alloc(GFP_KERNEL);
        if (!pte_chain)
                goto no_mem;
        new_page = alloc_page(GFP_HIGHUSER);
        if (!new_page)
                goto no_mem;
        copy_cow_page(old_page,new_page,address);

        /*
         * Re-check the pte - we dropped the lock
         */
        spin_lock(&mm->page_table_lock);
        page_table = pte_offset_map(pmd, address);
        if (pte_same(*page_table, pte)) {
                if (PageReserved(old_page))
                        ++mm->rss;
                page_remove_rmap(old_page, page_table);
                break_cow(vma, new_page, address, page_table);
                pte_chain = page_add_rmap(new_page, page_table, pte_chain);
                lru_cache_add_active(new_page);

                /* Free the old page.. */
                new_page = old_page;
        }
        pte_unmap(page_table);
        page_cache_release(new_page);
        page_cache_release(old_page);
        ret = VM_FAULT_MINOR;
        goto out;

no_mem:
        page_cache_release(old_page);
oom:
        ret = VM_FAULT_OOM;
out:
        spin_unlock(&mm->page_table_lock);
        pte_chain_free(pte_chain);
        return ret;
}

static void vmtruncate_list(struct list_head *head, unsigned long pgoff)
{
        unsigned long start, end, len, diff;
        struct vm_area_struct *vma;
        struct list_head *curr;

        list_for_each(curr, head) {
                vma = list_entry(curr, struct vm_area_struct, shared);
                start = vma->vm_start;
                end = vma->vm_end;
                len = end - start;

                /* mapping wholly truncated? */
                if (vma->vm_pgoff >= pgoff) {
                        zap_page_range(vma, start, len);
                        continue;
                }

                /* mapping wholly unaffected? */
                len = len >> PAGE_SHIFT;
                diff = pgoff - vma->vm_pgoff;
                if (diff >= len)
                        continue;

                /* Ok, partially affected.. */
                start += diff << PAGE_SHIFT;
                len = (len - diff) << PAGE_SHIFT;
                zap_page_range(vma, start, len);
        }
}

/*
 * Handle all mappings that got truncated by a "truncate()"
 * system call.
 *
 * NOTE! We have to be ready to update the memory sharing
 * between the file and the memory map for a potential last
 * incomplete page.  Ugly, but necessary.
 */
int vmtruncate(struct inode * inode, loff_t offset)
{
        unsigned long pgoff;
        struct address_space *mapping = inode->i_mapping;
        unsigned long limit;

        if (inode->i_size < offset)
                goto do_expand;
        i_size_write(inode, offset);
        pgoff = (offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
        down(&mapping->i_shared_sem);
        if (unlikely(!list_empty(&mapping->i_mmap)))
                vmtruncate_list(&mapping->i_mmap, pgoff);
        if (unlikely(!list_empty(&mapping->i_mmap_shared)))
                vmtruncate_list(&mapping->i_mmap_shared, pgoff);
        up(&mapping->i_shared_sem);
        truncate_inode_pages(mapping, offset);
        goto out_truncate;

do_expand:
        limit = current->rlim[RLIMIT_FSIZE].rlim_cur;
        if (limit != RLIM_INFINITY && offset > limit)
                goto out_sig;
        if (offset > inode->i_sb->s_maxbytes)
                goto out;
        i_size_write(inode, offset);

out_truncate:
        if (inode->i_op && inode->i_op->truncate)
                inode->i_op->truncate(inode);
        return 0;
out_sig:
        send_sig(SIGXFSZ, current, 0);
out:
        return -EFBIG;
}

/* 
 * Primitive swap readahead code. We simply read an aligned block of
 * (1 << page_cluster) entries in the swap area. This method is chosen
 * because it doesn't cost us any seek time.  We also make sure to queue
 * the 'original' request together with the readahead ones...  
 */
void swapin_readahead(swp_entry_t entry)
{
        int i, num;
        struct page *new_page;
        unsigned long offset;

        /*
         * Get the number of handles we should do readahead io to.
         */
        num = valid_swaphandles(entry, &offset);
        for (i = 0; i < num; offset++, i++) {
                /* Ok, do the async read-ahead now */
                new_page = read_swap_cache_async(swp_entry(swp_type(entry),
                                                offset));
                if (!new_page)
                        break;
                page_cache_release(new_page);
        }
        lru_add_drain();        /* Push any new pages onto the LRU now */
}

/*
 * We hold the mm semaphore and the page_table_lock on entry and
 * should release the pagetable lock on exit..
 */
static int do_swap_page(struct mm_struct * mm,
        struct vm_area_struct * vma, unsigned long address,
        pte_t *page_table, pmd_t *pmd, pte_t orig_pte, int write_access)
{
        struct page *page;
        swp_entry_t entry = pte_to_swp_entry(orig_pte);
        pte_t pte;
        int ret = VM_FAULT_MINOR;
        struct pte_chain *pte_chain = NULL;

        pte_unmap(page_table);
        spin_unlock(&mm->page_table_lock);
        page = lookup_swap_cache(entry);
        if (!page) {
                swapin_readahead(entry);
                page = read_swap_cache_async(entry);
                if (!page) {
                        /*
                         * Back out if somebody else faulted in this pte while
                         * we released the page table lock.
                         */
                        spin_lock(&mm->page_table_lock);
                        page_table = pte_offset_map(pmd, address);
                        if (pte_same(*page_table, orig_pte))
                                ret = VM_FAULT_OOM;
                        else
                                ret = VM_FAULT_MINOR;
                        pte_unmap(page_table);
                        spin_unlock(&mm->page_table_lock);
                        goto out;
                }

                /* Had to read the page from swap area: Major fault */
                ret = VM_FAULT_MAJOR;
                inc_page_state(pgmajfault);
        }

        mark_page_accessed(page);
        pte_chain = pte_chain_alloc(GFP_KERNEL);
        if (!pte_chain) {
                ret = -ENOMEM;
                goto out;
        }
        lock_page(page);

        /*
         * Back out if somebody else faulted in this pte while we
         * released the page table lock.
         */
        spin_lock(&mm->page_table_lock);
        page_table = pte_offset_map(pmd, address);
        if (!pte_same(*page_table, orig_pte)) {
                pte_unmap(page_table);
                spin_unlock(&mm->page_table_lock);
                unlock_page(page);
                page_cache_release(page);
                ret = VM_FAULT_MINOR;
                goto out;
        }

        /* The page isn't present yet, go ahead with the fault. */
                
        swap_free(entry);
        if (vm_swap_full())
                remove_exclusive_swap_page(page);

        mm->rss++;
        pte = mk_pte(page, vma->vm_page_prot);
        if (write_access && can_share_swap_page(page))
                pte = pte_mkdirty(pte_mkwrite(pte));
        unlock_page(page);

        flush_icache_page(vma, page);
        set_pte(page_table, pte);
        pte_chain = page_add_rmap(page, page_table, pte_chain);

        /* No need to invalidate - it was non-present before */
        update_mmu_cache(vma, address, pte);
        pte_unmap(page_table);
        spin_unlock(&mm->page_table_lock);
out:
        pte_chain_free(pte_chain);
        return ret;
}

/*
 * We are called with the MM semaphore and page_table_lock
 * spinlock held to protect against concurrent faults in
 * multithreaded programs. 
 */
static int
do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
                pte_t *page_table, pmd_t *pmd, int write_access,
                unsigned long addr)
{
        pte_t entry;
        struct page * page = ZERO_PAGE(addr);
        struct pte_chain *pte_chain;
        int ret;

        pte_chain = pte_chain_alloc(GFP_ATOMIC);
        if (!pte_chain) {
                pte_unmap(page_table);
                spin_unlock(&mm->page_table_lock);
                pte_chain = pte_chain_alloc(GFP_KERNEL);
                if (!pte_chain)
                        goto no_mem;
                spin_lock(&mm->page_table_lock);
                page_table = pte_offset_map(pmd, addr);
        }
                
        /* Read-only mapping of ZERO_PAGE. */
        entry = pte_wrprotect(mk_pte(ZERO_PAGE(addr), vma->vm_page_prot));

        /* ..except if it's a write access */
        if (write_access) {
                /* Allocate our own private page. */
                pte_unmap(page_table);
                spin_unlock(&mm->page_table_lock);

                page = alloc_page(GFP_HIGHUSER);
                if (!page)
                        goto no_mem;
                clear_user_highpage(page, addr);

                spin_lock(&mm->page_table_lock);
                page_table = pte_offset_map(pmd, addr);

                if (!pte_none(*page_table)) {
                        pte_unmap(page_table);
                        page_cache_release(page);
                        spin_unlock(&mm->page_table_lock);
                        ret = VM_FAULT_MINOR;
                        goto out;
                }
                mm->rss++;
                entry = pte_mkwrite(pte_mkdirty(mk_pte(page, vma->vm_page_prot)));
                lru_cache_add_active(page);
                mark_page_accessed(page);
        }

        set_pte(page_table, entry);
        /* ignores ZERO_PAGE */
        pte_chain = page_add_rmap(page, page_table, pte_chain);
        pte_unmap(page_table);

        /* No need to invalidate - it was non-present before */
        update_mmu_cache(vma, addr, entry);
        spin_unlock(&mm->page_table_lock);
        ret = VM_FAULT_MINOR;
        goto out;

no_mem:
        ret = VM_FAULT_OOM;
out:
        pte_chain_free(pte_chain);
        return ret;
}

/*
 * do_no_page() tries to create a new page mapping. It aggressively
 * tries to share with existing pages, but makes a separate copy if
 * the "write_access" parameter is true in order to avoid the next
 * page fault.
 *
 * As this is called only for pages that do not currently exist, we
 * do not need to flush old virtual caches or the TLB.
 *
 * This is called with the MM semaphore held and the page table
 * spinlock held. Exit with the spinlock released.
 */
static int
do_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
        unsigned long address, int write_access, pte_t *page_table, pmd_t *pmd)
{
        struct page * new_page;
        pte_t entry;
        struct pte_chain *pte_chain;
        int ret;

        if (!vma->vm_ops || !vma->vm_ops->nopage)
                return do_anonymous_page(mm, vma, page_table,
                                        pmd, write_access, address);
        pte_unmap(page_table);
        spin_unlock(&mm->page_table_lock);

        new_page = vma->vm_ops->nopage(vma, address & PAGE_MASK, 0);

        /* no page was available -- either SIGBUS or OOM */
        if (new_page == NOPAGE_SIGBUS)
                return VM_FAULT_SIGBUS;
        if (new_page == NOPAGE_OOM)
                return VM_FAULT_OOM;

        pte_chain = pte_chain_alloc(GFP_KERNEL);
        if (!pte_chain)
                goto oom;

        /*
         * Should we do an early C-O-W break?
         */
        if (write_access && !(vma->vm_flags & VM_SHARED)) {
                struct page * page = alloc_page(GFP_HIGHUSER);
                if (!page) {
                        page_cache_release(new_page);
                        goto oom;
                }
                copy_user_highpage(page, new_page, address);
                page_cache_release(new_page);
                lru_cache_add_active(page);
                new_page = page;
        }

        spin_lock(&mm->page_table_lock);
        page_table = pte_offset_map(pmd, address);

        /*
         * This silly early PAGE_DIRTY setting removes a race
         * due to the bad i386 page protection. But it's valid
         * for other architectures too.
         *
         * Note that if write_access is true, we either now have
         * an exclusive copy of the page, or this is a shared mapping,
         * so we can make it writable and dirty to avoid having to
         * handle that later.
         */
        /* Only go through if we didn't race with anybody else... */
        if (pte_none(*page_table)) {
                ++mm->rss;
                flush_icache_page(vma, new_page);
                entry = mk_pte(new_page, vma->vm_page_prot);
                if (write_access)
                        entry = pte_mkwrite(pte_mkdirty(entry));
                set_pte(page_table, entry);
                pte_chain = page_add_rmap(new_page, page_table, pte_chain);
                pte_unmap(page_table);
        } else {
                /* One of our sibling threads was faster, back out. */
                pte_unmap(page_table);
                page_cache_release(new_page);
                spin_unlock(&mm->page_table_lock);
                ret = VM_FAULT_MINOR;
                goto out;
        }

        /* no need to invalidate: a not-present page shouldn't be cached */
        update_mmu_cache(vma, address, entry);
        spin_unlock(&mm->page_table_lock);
        ret = VM_FAULT_MAJOR;
        goto out;
oom:
        ret = VM_FAULT_OOM;
out:
        pte_chain_free(pte_chain);
        return ret;
}

/*
 * Fault of a previously existing named mapping. Repopulate the pte
 * from the encoded file_pte if possible. This enables swappable
 * nonlinear vmas.
 */
static int do_file_page(struct mm_struct * mm, struct vm_area_struct * vma,
        unsigned long address, int write_access, pte_t *pte, pmd_t *pmd)
{
        unsigned long pgoff;
        int err;

        BUG_ON(!vma->vm_ops || !vma->vm_ops->nopage);
        /*
         * Fall back to the linear mapping if the fs does not support
         * ->populate:
         */
        if (!vma->vm_ops || !vma->vm_ops->populate || 
                        (write_access && !(vma->vm_flags & VM_SHARED))) {
                pte_clear(pte);
                return do_no_page(mm, vma, address, write_access, pte, pmd);
        }

        pgoff = pte_to_pgoff(*pte);

        pte_unmap(pte);
        spin_unlock(&mm->page_table_lock);

        err = vma->vm_ops->populate(vma, address & PAGE_MASK, PAGE_SIZE, vma->vm_page_prot, pgoff, 0);
        if (err == -ENOMEM)
                return VM_FAULT_OOM;
        if (err)
                return VM_FAULT_SIGBUS;
        return VM_FAULT_MAJOR;
}

/*
 * These routines also need to handle stuff like marking pages dirty
 * and/or accessed for architectures that don't do it in hardware (most
 * RISC architectures).  The early dirtying is also good on the i386.
 *
 * There is also a hook called "update_mmu_cache()" that architectures
 * with external mmu caches can use to update those (ie the Sparc or
 * PowerPC hashed page tables that act as extended TLBs).
 *
 * Note the "page_table_lock". It is to protect against kswapd removing
 * pages from under us. Note that kswapd only ever _removes_ pages, never
 * adds them. As such, once we have noticed that the page is not present,
 * we can drop the lock early.
 *
 * The adding of pages is protected by the MM semaphore (which we hold),
 * so we don't need to worry about a page being suddenly been added into
 * our VM.
 *
 * We enter with the pagetable spinlock held, we are supposed to
 * release it when done.
 */
static inline int handle_pte_fault(struct mm_struct *mm,
        struct vm_area_struct * vma, unsigned long address,
        int write_access, pte_t *pte, pmd_t *pmd)
{
        pte_t entry;

        entry = *pte;
        if (!pte_present(entry)) {
                /*
                 * If it truly wasn't present, we know that kswapd
                 * and the PTE updates will not touch it later. So
                 * drop the lock.
                 */
                if (pte_none(entry))
                        return do_no_page(mm, vma, address, write_access, pte, pmd);
                if (pte_file(entry))
                        return do_file_page(mm, vma, address, write_access, pte, pmd);
                return do_swap_page(mm, vma, address, pte, pmd, entry, write_access);
        }

        if (write_access) {
                if (!pte_write(entry))
                        return do_wp_page(mm, vma, address, pte, pmd, entry);

                entry = pte_mkdirty(entry);
        }
        entry = pte_mkyoung(entry);
        establish_pte(vma, address, pte, entry);
        pte_unmap(pte);
        spin_unlock(&mm->page_table_lock);
        return VM_FAULT_MINOR;
}

/*
 * By the time we get here, we already hold the mm semaphore
 */
int handle_mm_fault(struct mm_struct *mm, struct vm_area_struct * vma,
        unsigned long address, int write_access)
{
        pgd_t *pgd;
        pmd_t *pmd;

        __set_current_state(TASK_RUNNING);
        pgd = pgd_offset(mm, address);

        inc_page_state(pgfault);

        if (is_vm_hugetlb_page(vma))
                return VM_FAULT_SIGBUS; /* mapping truncation does this. */

        /*
         * We need the page table lock to synchronize with kswapd
         * and the SMP-safe atomic PTE updates.
         */
        spin_lock(&mm->page_table_lock);
        pmd = pmd_alloc(mm, pgd, address);

        if (pmd) {
                pte_t * pte = pte_alloc_map(mm, pmd, address);
                if (pte)
                        return handle_pte_fault(mm, vma, address, write_access, pte, pmd);
        }
        spin_unlock(&mm->page_table_lock);
        return VM_FAULT_OOM;
}

/*
 * Allocate page middle directory.
 *
 * We've already handled the fast-path in-line, and we own the
 * page table lock.
 *
 * On a two-level page table, this ends up actually being entirely
 * optimized away.
 */
pmd_t *__pmd_alloc(struct mm_struct *mm, pgd_t *pgd, unsigned long address)
{
        pmd_t *new;

        spin_unlock(&mm->page_table_lock);
        new = pmd_alloc_one(mm, address);
        spin_lock(&mm->page_table_lock);
        if (!new)
                return NULL;

        /*
         * Because we dropped the lock, we should re-check the
         * entry, as somebody else could have populated it..
         */
        if (pgd_present(*pgd)) {
                pmd_free(new);
                goto out;
        }
        pgd_populate(mm, pgd, new);
out:
        return pmd_offset(pgd, address);
}

int make_pages_present(unsigned long addr, unsigned long end)
{
        int ret, len, write;
        struct vm_area_struct * vma;

        vma = find_vma(current->mm, addr);
        write = (vma->vm_flags & VM_WRITE) != 0;
        if (addr >= end)
                BUG();
        if (end > vma->vm_end)
                BUG();
        len = (end+PAGE_SIZE-1)/PAGE_SIZE-addr/PAGE_SIZE;
        ret = get_user_pages(current, current->mm, addr,
                        len, write, 0, NULL, NULL);
        return ret == len ? 0 : -1;
}

/* 
 * Map a vmalloc()-space virtual address to the physical page.
 */
struct page * vmalloc_to_page(void * vmalloc_addr)
{
        unsigned long addr = (unsigned long) vmalloc_addr;
        struct page *page = NULL;
        pgd_t *pgd = pgd_offset_k(addr);
        pmd_t *pmd;
        pte_t *ptep, pte;
  
        if (!pgd_none(*pgd)) {
                pmd = pmd_offset(pgd, addr);
                if (!pmd_none(*pmd)) {
                        preempt_disable();
                        ptep = pte_offset_map(pmd, addr);
                        pte = *ptep;
                        if (pte_present(pte))
                                page = pte_page(pte);
                        pte_unmap(ptep);
                        preempt_enable();
                }
        }
        return page;
}