Linux-2.6.12-rc2

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / arch / ppc64 / mm / hugetlbpage.c

/*
 * PPC64 (POWER4) Huge TLB Page Support for Kernel.
 *
 * Copyright (C) 2003 David Gibson, IBM Corporation.
 *
 * Based on the IA-32 version:
 * Copyright (C) 2002, Rohit Seth <rohit.seth@intel.com>
 */

#include <linux/init.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/pagemap.h>
#include <linux/smp_lock.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/sysctl.h>
#include <asm/mman.h>
#include <asm/pgalloc.h>
#include <asm/tlb.h>
#include <asm/tlbflush.h>
#include <asm/mmu_context.h>
#include <asm/machdep.h>
#include <asm/cputable.h>
#include <asm/tlb.h>

#include <linux/sysctl.h>

#define HUGEPGDIR_SHIFT         (HPAGE_SHIFT + PAGE_SHIFT - 3)
#define HUGEPGDIR_SIZE          (1UL << HUGEPGDIR_SHIFT)
#define HUGEPGDIR_MASK          (~(HUGEPGDIR_SIZE-1))

#define HUGEPTE_INDEX_SIZE      9
#define HUGEPGD_INDEX_SIZE      10

#define PTRS_PER_HUGEPTE        (1 << HUGEPTE_INDEX_SIZE)
#define PTRS_PER_HUGEPGD        (1 << HUGEPGD_INDEX_SIZE)

static inline int hugepgd_index(unsigned long addr)
{
        return (addr & ~REGION_MASK) >> HUGEPGDIR_SHIFT;
}

static pgd_t *hugepgd_offset(struct mm_struct *mm, unsigned long addr)
{
        int index;

        if (! mm->context.huge_pgdir)
                return NULL;


        index = hugepgd_index(addr);
        BUG_ON(index >= PTRS_PER_HUGEPGD);
        return mm->context.huge_pgdir + index;
}

static inline pte_t *hugepte_offset(pgd_t *dir, unsigned long addr)
{
        int index;

        if (pgd_none(*dir))
                return NULL;

        index = (addr >> HPAGE_SHIFT) % PTRS_PER_HUGEPTE;
        return (pte_t *)pgd_page(*dir) + index;
}

static pgd_t *hugepgd_alloc(struct mm_struct *mm, unsigned long addr)
{
        BUG_ON(! in_hugepage_area(mm->context, addr));

        if (! mm->context.huge_pgdir) {
                pgd_t *new;
                spin_unlock(&mm->page_table_lock);
                /* Don't use pgd_alloc(), because we want __GFP_REPEAT */
                new = kmem_cache_alloc(zero_cache, GFP_KERNEL | __GFP_REPEAT);
                BUG_ON(memcmp(new, empty_zero_page, PAGE_SIZE));
                spin_lock(&mm->page_table_lock);

                /*
                 * Because we dropped the lock, we should re-check the
                 * entry, as somebody else could have populated it..
                 */
                if (mm->context.huge_pgdir)
                        pgd_free(new);
                else
                        mm->context.huge_pgdir = new;
        }
        return hugepgd_offset(mm, addr);
}

static pte_t *hugepte_alloc(struct mm_struct *mm, pgd_t *dir,
                            unsigned long addr)
{
        if (! pgd_present(*dir)) {
                pte_t *new;

                spin_unlock(&mm->page_table_lock);
                new = kmem_cache_alloc(zero_cache, GFP_KERNEL | __GFP_REPEAT);
                BUG_ON(memcmp(new, empty_zero_page, PAGE_SIZE));
                spin_lock(&mm->page_table_lock);
                /*
                 * Because we dropped the lock, we should re-check the
                 * entry, as somebody else could have populated it..
                 */
                if (pgd_present(*dir)) {
                        if (new)
                                kmem_cache_free(zero_cache, new);
                } else {
                        struct page *ptepage;

                        if (! new)
                                return NULL;
                        ptepage = virt_to_page(new);
                        ptepage->mapping = (void *) mm;
                        ptepage->index = addr & HUGEPGDIR_MASK;
                        pgd_populate(mm, dir, new);
                }
        }

        return hugepte_offset(dir, addr);
}

static pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr)
{
        pgd_t *pgd;

        BUG_ON(! in_hugepage_area(mm->context, addr));

        pgd = hugepgd_offset(mm, addr);
        if (! pgd)
                return NULL;

        return hugepte_offset(pgd, addr);
}

static pte_t *huge_pte_alloc(struct mm_struct *mm, unsigned long addr)
{
        pgd_t *pgd;

        BUG_ON(! in_hugepage_area(mm->context, addr));

        pgd = hugepgd_alloc(mm, addr);
        if (! pgd)
                return NULL;

        return hugepte_alloc(mm, pgd, addr);
}

static void set_huge_pte(struct mm_struct *mm, struct vm_area_struct *vma,
                         unsigned long addr, struct page *page,
                         pte_t *ptep, int write_access)
{
        pte_t entry;

        add_mm_counter(mm, rss, HPAGE_SIZE / PAGE_SIZE);
        if (write_access) {
                entry =
                    pte_mkwrite(pte_mkdirty(mk_pte(page, vma->vm_page_prot)));
        } else {
                entry = pte_wrprotect(mk_pte(page, vma->vm_page_prot));
        }
        entry = pte_mkyoung(entry);
        entry = pte_mkhuge(entry);

        set_pte_at(mm, addr, ptep, entry);
}

/*
 * This function checks for proper alignment of input addr and len parameters.
 */
int is_aligned_hugepage_range(unsigned long addr, unsigned long len)
{
        if (len & ~HPAGE_MASK)
                return -EINVAL;
        if (addr & ~HPAGE_MASK)
                return -EINVAL;
        if (! (within_hugepage_low_range(addr, len)
               || within_hugepage_high_range(addr, len)) )
                return -EINVAL;
        return 0;
}

static void flush_segments(void *parm)
{
        u16 segs = (unsigned long) parm;
        unsigned long i;

        asm volatile("isync" : : : "memory");

        for (i = 0; i < 16; i++) {
                if (! (segs & (1U << i)))
                        continue;
                asm volatile("slbie %0" : : "r" (i << SID_SHIFT));
        }

        asm volatile("isync" : : : "memory");
}

static int prepare_low_seg_for_htlb(struct mm_struct *mm, unsigned long seg)
{
        unsigned long start = seg << SID_SHIFT;
        unsigned long end = (seg+1) << SID_SHIFT;
        struct vm_area_struct *vma;
        unsigned long addr;
        struct mmu_gather *tlb;

        BUG_ON(seg >= 16);

        /* Check no VMAs are in the region */
        vma = find_vma(mm, start);
        if (vma && (vma->vm_start < end))
                return -EBUSY;

        /* Clean up any leftover PTE pages in the region */
        spin_lock(&mm->page_table_lock);
        tlb = tlb_gather_mmu(mm, 0);
        for (addr = start; addr < end; addr += PMD_SIZE) {
                pgd_t *pgd = pgd_offset(mm, addr);
                pmd_t *pmd;
                struct page *page;
                pte_t *pte;
                int i;

                if (pgd_none(*pgd))
                        continue;
                pmd = pmd_offset(pgd, addr);
                if (!pmd || pmd_none(*pmd))
                        continue;
                if (pmd_bad(*pmd)) {
                        pmd_ERROR(*pmd);
                        pmd_clear(pmd);
                        continue;
                }
                pte = (pte_t *)pmd_page_kernel(*pmd);
                /* No VMAs, so there should be no PTEs, check just in case. */
                for (i = 0; i < PTRS_PER_PTE; i++) {
                        BUG_ON(!pte_none(*pte));
                        pte++;
                }
                page = pmd_page(*pmd);
                pmd_clear(pmd);
                mm->nr_ptes--;
                dec_page_state(nr_page_table_pages);
                pte_free_tlb(tlb, page);
        }
        tlb_finish_mmu(tlb, start, end);
        spin_unlock(&mm->page_table_lock);

        return 0;
}

static int open_low_hpage_segs(struct mm_struct *mm, u16 newsegs)
{
        unsigned long i;

        newsegs &= ~(mm->context.htlb_segs);
        if (! newsegs)
                return 0; /* The segments we want are already open */

        for (i = 0; i < 16; i++)
                if ((1 << i) & newsegs)
                        if (prepare_low_seg_for_htlb(mm, i) != 0)
                                return -EBUSY;

        mm->context.htlb_segs |= newsegs;

        /* update the paca copy of the context struct */
        get_paca()->context = mm->context;

        /* the context change must make it to memory before the flush,
         * so that further SLB misses do the right thing. */
        mb();
        on_each_cpu(flush_segments, (void *)(unsigned long)newsegs, 0, 1);

        return 0;
}

int prepare_hugepage_range(unsigned long addr, unsigned long len)
{
        if (within_hugepage_high_range(addr, len))
                return 0;
        else if ((addr < 0x100000000UL) && ((addr+len) < 0x100000000UL)) {
                int err;
                /* Yes, we need both tests, in case addr+len overflows
                 * 64-bit arithmetic */
                err = open_low_hpage_segs(current->mm,
                                          LOW_ESID_MASK(addr, len));
                if (err)
                        printk(KERN_DEBUG "prepare_hugepage_range(%lx, %lx)"
                               " failed (segs: 0x%04hx)\n", addr, len,
                               LOW_ESID_MASK(addr, len));
                return err;
        }

        return -EINVAL;
}

int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
                        struct vm_area_struct *vma)
{
        pte_t *src_pte, *dst_pte, entry;
        struct page *ptepage;
        unsigned long addr = vma->vm_start;
        unsigned long end = vma->vm_end;
        int err = -ENOMEM;

        while (addr < end) {
                dst_pte = huge_pte_alloc(dst, addr);
                if (!dst_pte)
                        goto out;

                src_pte = huge_pte_offset(src, addr);
                entry = *src_pte;
                
                ptepage = pte_page(entry);
                get_page(ptepage);
                add_mm_counter(dst, rss, HPAGE_SIZE / PAGE_SIZE);
                set_pte_at(dst, addr, dst_pte, entry);

                addr += HPAGE_SIZE;
        }

        err = 0;
 out:
        return err;
}

int
follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
                    struct page **pages, struct vm_area_struct **vmas,
                    unsigned long *position, int *length, int i)
{
        unsigned long vpfn, vaddr = *position;
        int remainder = *length;

        WARN_ON(!is_vm_hugetlb_page(vma));

        vpfn = vaddr/PAGE_SIZE;
        while (vaddr < vma->vm_end && remainder) {
                if (pages) {
                        pte_t *pte;
                        struct page *page;

                        pte = huge_pte_offset(mm, vaddr);

                        /* hugetlb should be locked, and hence, prefaulted */
                        WARN_ON(!pte || pte_none(*pte));

                        page = &pte_page(*pte)[vpfn % (HPAGE_SIZE/PAGE_SIZE)];

                        WARN_ON(!PageCompound(page));

                        get_page(page);
                        pages[i] = page;
                }

                if (vmas)
                        vmas[i] = vma;

                vaddr += PAGE_SIZE;
                ++vpfn;
                --remainder;
                ++i;
        }

        *length = remainder;
        *position = vaddr;

        return i;
}

struct page *
follow_huge_addr(struct mm_struct *mm, unsigned long address, int write)
{
        pte_t *ptep;
        struct page *page;

        if (! in_hugepage_area(mm->context, address))
                return ERR_PTR(-EINVAL);

        ptep = huge_pte_offset(mm, address);
        page = pte_page(*ptep);
        if (page)
                page += (address % HPAGE_SIZE) / PAGE_SIZE;

        return page;
}

int pmd_huge(pmd_t pmd)
{
        return 0;
}

struct page *
follow_huge_pmd(struct mm_struct *mm, unsigned long address,
                pmd_t *pmd, int write)
{
        BUG();
        return NULL;
}

void unmap_hugepage_range(struct vm_area_struct *vma,
                          unsigned long start, unsigned long end)
{
        struct mm_struct *mm = vma->vm_mm;
        unsigned long addr;
        pte_t *ptep;
        struct page *page;

        WARN_ON(!is_vm_hugetlb_page(vma));
        BUG_ON((start % HPAGE_SIZE) != 0);
        BUG_ON((end % HPAGE_SIZE) != 0);

        for (addr = start; addr < end; addr += HPAGE_SIZE) {
                pte_t pte;

                ptep = huge_pte_offset(mm, addr);
                if (!ptep || pte_none(*ptep))
                        continue;

                pte = *ptep;
                page = pte_page(pte);
                pte_clear(mm, addr, ptep);

                put_page(page);
        }
        add_mm_counter(mm, rss, -((end - start) >> PAGE_SHIFT));
        flush_tlb_pending();
}

void hugetlb_free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *prev,
                           unsigned long start, unsigned long end)
{
        /* Because the huge pgtables are only 2 level, they can take
         * at most around 4M, much less than one hugepage which the
         * process is presumably entitled to use.  So we don't bother
         * freeing up the pagetables on unmap, and wait until
         * destroy_context() to clean up the lot. */
}

int hugetlb_prefault(struct address_space *mapping, struct vm_area_struct *vma)
{
        struct mm_struct *mm = current->mm;
        unsigned long addr;
        int ret = 0;

        WARN_ON(!is_vm_hugetlb_page(vma));
        BUG_ON((vma->vm_start % HPAGE_SIZE) != 0);
        BUG_ON((vma->vm_end % HPAGE_SIZE) != 0);

        spin_lock(&mm->page_table_lock);
        for (addr = vma->vm_start; addr < vma->vm_end; addr += HPAGE_SIZE) {
                unsigned long idx;
                pte_t *pte = huge_pte_alloc(mm, addr);
                struct page *page;

                if (!pte) {
                        ret = -ENOMEM;
                        goto out;
                }
                if (! pte_none(*pte))
                        continue;

                idx = ((addr - vma->vm_start) >> HPAGE_SHIFT)
                        + (vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT));
                page = find_get_page(mapping, idx);
                if (!page) {
                        /* charge the fs quota first */
                        if (hugetlb_get_quota(mapping)) {
                                ret = -ENOMEM;
                                goto out;
                        }
                        page = alloc_huge_page();
                        if (!page) {
                                hugetlb_put_quota(mapping);
                                ret = -ENOMEM;
                                goto out;
                        }
                        ret = add_to_page_cache(page, mapping, idx, GFP_ATOMIC);
                        if (! ret) {
                                unlock_page(page);
                        } else {
                                hugetlb_put_quota(mapping);
                                free_huge_page(page);
                                goto out;
                        }
                }
                set_huge_pte(mm, vma, addr, page, pte, vma->vm_flags & VM_WRITE);
        }
out:
        spin_unlock(&mm->page_table_lock);
        return ret;
}

/* Because we have an exclusive hugepage region which lies within the
 * normal user address space, we have to take special measures to make
 * non-huge mmap()s evade the hugepage reserved regions. */
unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
                                     unsigned long len, unsigned long pgoff,
                                     unsigned long flags)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        unsigned long start_addr;

        if (len > TASK_SIZE)
                return -ENOMEM;

        if (addr) {
                addr = PAGE_ALIGN(addr);
                vma = find_vma(mm, addr);
                if (((TASK_SIZE - len) >= addr)
                    && (!vma || (addr+len) <= vma->vm_start)
                    && !is_hugepage_only_range(mm, addr,len))
                        return addr;
        }
        start_addr = addr = mm->free_area_cache;

full_search:
        vma = find_vma(mm, addr);
        while (TASK_SIZE - len >= addr) {
                BUG_ON(vma && (addr >= vma->vm_end));

                if (touches_hugepage_low_range(mm, addr, len)) {
                        addr = ALIGN(addr+1, 1<<SID_SHIFT);
                        vma = find_vma(mm, addr);
                        continue;
                }
                if (touches_hugepage_high_range(addr, len)) {
                        addr = TASK_HPAGE_END;
                        vma = find_vma(mm, addr);
                        continue;
                }
                if (!vma || addr + len <= vma->vm_start) {
                        /*
                         * Remember the place where we stopped the search:
                         */
                        mm->free_area_cache = addr + len;
                        return addr;
                }
                addr = vma->vm_end;
                vma = vma->vm_next;
        }

        /* Make sure we didn't miss any holes */
        if (start_addr != TASK_UNMAPPED_BASE) {
                start_addr = addr = TASK_UNMAPPED_BASE;
                goto full_search;
        }
        return -ENOMEM;
}

/*
 * This mmap-allocator allocates new areas top-down from below the
 * stack's low limit (the base):
 *
 * Because we have an exclusive hugepage region which lies within the
 * normal user address space, we have to take special measures to make
 * non-huge mmap()s evade the hugepage reserved regions.
 */
unsigned long
arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
                          const unsigned long len, const unsigned long pgoff,
                          const unsigned long flags)
{
        struct vm_area_struct *vma, *prev_vma;
        struct mm_struct *mm = current->mm;
        unsigned long base = mm->mmap_base, addr = addr0;
        int first_time = 1;

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

        /* dont allow allocations above current base */
        if (mm->free_area_cache > base)
                mm->free_area_cache = base;

        /* requesting a specific address */
        if (addr) {
                addr = PAGE_ALIGN(addr);
                vma = find_vma(mm, addr);
                if (TASK_SIZE - len >= addr &&
                                (!vma || addr + len <= vma->vm_start)
                                && !is_hugepage_only_range(mm, addr,len))
                        return addr;
        }

try_again:
        /* make sure it can fit in the remaining address space */
        if (mm->free_area_cache < len)
                goto fail;

        /* either no address requested or cant fit in requested address hole */
        addr = (mm->free_area_cache - len) & PAGE_MASK;
        do {
hugepage_recheck:
                if (touches_hugepage_low_range(mm, addr, len)) {
                        addr = (addr & ((~0) << SID_SHIFT)) - len;
                        goto hugepage_recheck;
                } else if (touches_hugepage_high_range(addr, len)) {
                        addr = TASK_HPAGE_BASE - len;
                }

                /*
                 * Lookup failure means no vma is above this address,
                 * i.e. return with success:
                 */
                if (!(vma = find_vma_prev(mm, addr, &prev_vma)))
                        return addr;

                /*
                 * new region fits between prev_vma->vm_end and
                 * vma->vm_start, use it:
                 */
                if (addr+len <= vma->vm_start &&
                                (!prev_vma || (addr >= prev_vma->vm_end)))
                        /* remember the address as a hint for next time */
                        return (mm->free_area_cache = addr);
                else
                        /* pull free_area_cache down to the first hole */
                        if (mm->free_area_cache == vma->vm_end)
                                mm->free_area_cache = vma->vm_start;

                /* try just below the current vma->vm_start */
                addr = vma->vm_start-len;
        } while (len <= vma->vm_start);

fail:
        /*
         * if hint left us with no space for the requested
         * mapping then try again:
         */
        if (first_time) {
                mm->free_area_cache = base;
                first_time = 0;
                goto try_again;
        }
        /*
         * A failed mmap() very likely causes application failure,
         * so fall back to the bottom-up function here. This scenario
         * can happen with large stack limits and large mmap()
         * allocations.
         */
        mm->free_area_cache = TASK_UNMAPPED_BASE;
        addr = arch_get_unmapped_area(filp, addr0, len, pgoff, flags);
        /*
         * Restore the topdown base:
         */
        mm->free_area_cache = base;

        return addr;
}

static unsigned long htlb_get_low_area(unsigned long len, u16 segmask)
{
        unsigned long addr = 0;
        struct vm_area_struct *vma;

        vma = find_vma(current->mm, addr);
        while (addr + len <= 0x100000000UL) {
                BUG_ON(vma && (addr >= vma->vm_end)); /* invariant */

                if (! __within_hugepage_low_range(addr, len, segmask)) {
                        addr = ALIGN(addr+1, 1<<SID_SHIFT);
                        vma = find_vma(current->mm, addr);
                        continue;
                }

                if (!vma || (addr + len) <= vma->vm_start)
                        return addr;
                addr = ALIGN(vma->vm_end, HPAGE_SIZE);
                /* Depending on segmask this might not be a confirmed
                 * hugepage region, so the ALIGN could have skipped
                 * some VMAs */
                vma = find_vma(current->mm, addr);
        }

        return -ENOMEM;
}

static unsigned long htlb_get_high_area(unsigned long len)
{
        unsigned long addr = TASK_HPAGE_BASE;
        struct vm_area_struct *vma;

        vma = find_vma(current->mm, addr);
        for (vma = find_vma(current->mm, addr);
             addr + len <= TASK_HPAGE_END;
             vma = vma->vm_next) {
                BUG_ON(vma && (addr >= vma->vm_end)); /* invariant */
                BUG_ON(! within_hugepage_high_range(addr, len));

                if (!vma || (addr + len) <= vma->vm_start)
                        return addr;
                addr = ALIGN(vma->vm_end, HPAGE_SIZE);
                /* Because we're in a hugepage region, this alignment
                 * should not skip us over any VMAs */
        }

        return -ENOMEM;
}

unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
                                        unsigned long len, unsigned long pgoff,
                                        unsigned long flags)
{
        if (len & ~HPAGE_MASK)
                return -EINVAL;

        if (!cpu_has_feature(CPU_FTR_16M_PAGE))
                return -EINVAL;

        if (test_thread_flag(TIF_32BIT)) {
                int lastshift = 0;
                u16 segmask, cursegs = current->mm->context.htlb_segs;

                /* First see if we can do the mapping in the existing
                 * low hpage segments */
                addr = htlb_get_low_area(len, cursegs);
                if (addr != -ENOMEM)
                        return addr;

                for (segmask = LOW_ESID_MASK(0x100000000UL-len, len);
                     ! lastshift; segmask >>=1) {
                        if (segmask & 1)
                                lastshift = 1;

                        addr = htlb_get_low_area(len, cursegs | segmask);
                        if ((addr != -ENOMEM)
                            && open_low_hpage_segs(current->mm, segmask) == 0)
                                return addr;
                }
                printk(KERN_DEBUG "hugetlb_get_unmapped_area() unable to open"
                       " enough segments\n");
                return -ENOMEM;
        } else {
                return htlb_get_high_area(len);
        }
}

void hugetlb_mm_free_pgd(struct mm_struct *mm)
{
        int i;
        pgd_t *pgdir;

        spin_lock(&mm->page_table_lock);

        pgdir = mm->context.huge_pgdir;
        if (! pgdir)
                goto out;

        mm->context.huge_pgdir = NULL;

        /* cleanup any hugepte pages leftover */
        for (i = 0; i < PTRS_PER_HUGEPGD; i++) {
                pgd_t *pgd = pgdir + i;

                if (! pgd_none(*pgd)) {
                        pte_t *pte = (pte_t *)pgd_page(*pgd);
                        struct page *ptepage = virt_to_page(pte);

                        ptepage->mapping = NULL;

                        BUG_ON(memcmp(pte, empty_zero_page, PAGE_SIZE));
                        kmem_cache_free(zero_cache, pte);
                }
                pgd_clear(pgd);
        }

        BUG_ON(memcmp(pgdir, empty_zero_page, PAGE_SIZE));
        kmem_cache_free(zero_cache, pgdir);

 out:
        spin_unlock(&mm->page_table_lock);
}

int hash_huge_page(struct mm_struct *mm, unsigned long access,
                   unsigned long ea, unsigned long vsid, int local)
{
        pte_t *ptep;
        unsigned long va, vpn;
        pte_t old_pte, new_pte;
        unsigned long hpteflags, prpn;
        long slot;
        int err = 1;

        spin_lock(&mm->page_table_lock);

        ptep = huge_pte_offset(mm, ea);

        /* Search the Linux page table for a match with va */
        va = (vsid << 28) | (ea & 0x0fffffff);
        vpn = va >> HPAGE_SHIFT;

        /*
         * If no pte found or not present, send the problem up to
         * do_page_fault
         */
        if (unlikely(!ptep || pte_none(*ptep)))
                goto out;

/*      BUG_ON(pte_bad(*ptep)); */

        /* 
         * Check the user's access rights to the page.  If access should be
         * prevented then send the problem up to do_page_fault.
         */
        if (unlikely(access & ~pte_val(*ptep)))
                goto out;
        /*
         * At this point, we have a pte (old_pte) which can be used to build
         * or update an HPTE. There are 2 cases:
         *
         * 1. There is a valid (present) pte with no associated HPTE (this is 
         *      the most common case)
         * 2. There is a valid (present) pte with an associated HPTE. The
         *      current values of the pp bits in the HPTE prevent access
         *      because we are doing software DIRTY bit management and the
         *      page is currently not DIRTY. 
         */


        old_pte = *ptep;
        new_pte = old_pte;

        hpteflags = 0x2 | (! (pte_val(new_pte) & _PAGE_RW));
        /* _PAGE_EXEC -> HW_NO_EXEC since it's inverted */
        hpteflags |= ((pte_val(new_pte) & _PAGE_EXEC) ? 0 : HW_NO_EXEC);

        /* Check if pte already has an hpte (case 2) */
        if (unlikely(pte_val(old_pte) & _PAGE_HASHPTE)) {
                /* There MIGHT be an HPTE for this pte */
                unsigned long hash, slot;

                hash = hpt_hash(vpn, 1);
                if (pte_val(old_pte) & _PAGE_SECONDARY)
                        hash = ~hash;
                slot = (hash & htab_hash_mask) * HPTES_PER_GROUP;
                slot += (pte_val(old_pte) & _PAGE_GROUP_IX) >> 12;

                if (ppc_md.hpte_updatepp(slot, hpteflags, va, 1, local) == -1)
                        pte_val(old_pte) &= ~_PAGE_HPTEFLAGS;
        }

        if (likely(!(pte_val(old_pte) & _PAGE_HASHPTE))) {
                unsigned long hash = hpt_hash(vpn, 1);
                unsigned long hpte_group;

                prpn = pte_pfn(old_pte);

repeat:
                hpte_group = ((hash & htab_hash_mask) *
                              HPTES_PER_GROUP) & ~0x7UL;

                /* Update the linux pte with the HPTE slot */
                pte_val(new_pte) &= ~_PAGE_HPTEFLAGS;
                pte_val(new_pte) |= _PAGE_HASHPTE;

                /* Add in WIMG bits */
                /* XXX We should store these in the pte */
                hpteflags |= _PAGE_COHERENT;

                slot = ppc_md.hpte_insert(hpte_group, va, prpn, 0,
                                          hpteflags, 0, 1);

                /* Primary is full, try the secondary */
                if (unlikely(slot == -1)) {
                        pte_val(new_pte) |= _PAGE_SECONDARY;
                        hpte_group = ((~hash & htab_hash_mask) *
                                      HPTES_PER_GROUP) & ~0x7UL; 
                        slot = ppc_md.hpte_insert(hpte_group, va, prpn,
                                                  1, hpteflags, 0, 1);
                        if (slot == -1) {
                                if (mftb() & 0x1)
                                        hpte_group = ((hash & htab_hash_mask) * HPTES_PER_GROUP) & ~0x7UL;

                                ppc_md.hpte_remove(hpte_group);
                                goto repeat;
                        }
                }

                if (unlikely(slot == -2))
                        panic("hash_huge_page: pte_insert failed\n");

                pte_val(new_pte) |= (slot<<12) & _PAGE_GROUP_IX;

                /* 
                 * No need to use ldarx/stdcx here because all who
                 * might be updating the pte will hold the
                 * page_table_lock
                 */
                *ptep = new_pte;
        }

        err = 0;

 out:
        spin_unlock(&mm->page_table_lock);

        return err;
}