/*
 * IA-32 Huge TLB Page Support for Kernel.
 *
 * 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/slab.h>
#include <linux/err.h>
#include <linux/sysctl.h>
#include <asm/mman.h>
#include <asm/tlb.h>
#include <asm/tlbflush.h>

static unsigned long page_table_shareable(struct vm_area_struct *svma,
                                struct vm_area_struct *vma,
                                unsigned long addr, pgoff_t idx)
{
        unsigned long saddr = ((idx - svma->vm_pgoff) << PAGE_SHIFT) +
                                svma->vm_start;
        unsigned long sbase = saddr & PUD_MASK;
        unsigned long s_end = sbase + PUD_SIZE;

        /*
         * match the virtual addresses, permission and the alignment of the
         * page table page.
         */
        if (pmd_index(addr) != pmd_index(saddr) ||
            vma->vm_flags != svma->vm_flags ||
            sbase < svma->vm_start || svma->vm_end < s_end)
                return 0;

        return saddr;
}

static int vma_shareable(struct vm_area_struct *vma, unsigned long addr)
{
        unsigned long base = addr & PUD_MASK;
        unsigned long end = base + PUD_SIZE;

        /*
         * check on proper vm_flags and page table alignment
         */
        if (vma->vm_flags & VM_MAYSHARE &&
            vma->vm_start <= base && end <= vma->vm_end)
                return 1;
        return 0;
}

/*
 * search for a shareable pmd page for hugetlb.
 */
static void huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud)
{
        struct vm_area_struct *vma = find_vma(mm, addr);
        struct address_space *mapping = vma->vm_file->f_mapping;
        pgoff_t idx = ((addr - vma->vm_start) >> PAGE_SHIFT) +
                        vma->vm_pgoff;
        struct prio_tree_iter iter;
        struct vm_area_struct *svma;
        unsigned long saddr;
        pte_t *spte = NULL;

        if (!vma_shareable(vma, addr))
                return;

        spin_lock(&mapping->i_mmap_lock);
        vma_prio_tree_foreach(svma, &iter, &mapping->i_mmap, idx, idx) {
                if (svma == vma)
                        continue;

                saddr = page_table_shareable(svma, vma, addr, idx);
                if (saddr) {
                        spte = huge_pte_offset(svma->vm_mm, saddr);
                        if (spte) {
                                get_page(virt_to_page(spte));
                                break;
                        }
                }
        }

        if (!spte)
                goto out;

        spin_lock(&mm->page_table_lock);
        if (pud_none(*pud))
                pud_populate(mm, pud, (unsigned long) spte & PAGE_MASK);
        else
                put_page(virt_to_page(spte));
        spin_unlock(&mm->page_table_lock);
out:
        spin_unlock(&mapping->i_mmap_lock);
}

/*
 * unmap huge page backed by shared pte.
 *
 * Hugetlb pte page is ref counted at the time of mapping.  If pte is shared
 * indicated by page_count > 1, unmap is achieved by clearing pud and
 * decrementing the ref count. If count == 1, the pte page is not shared.
 *
 * called with vma->vm_mm->page_table_lock held.
 *
 * returns: 1 successfully unmapped a shared pte page
 *          0 the underlying pte page is not shared, or it is the last user
 */
int huge_pmd_unshare(struct mm_struct *mm, unsigned long *addr, pte_t *ptep)
{
        pgd_t *pgd = pgd_offset(mm, *addr);
        pud_t *pud = pud_offset(pgd, *addr);

        BUG_ON(page_count(virt_to_page(ptep)) == 0);
        if (page_count(virt_to_page(ptep)) == 1)
                return 0;

        pud_clear(pud);
        put_page(virt_to_page(ptep));
        *addr = ALIGN(*addr, HPAGE_SIZE * PTRS_PER_PTE) - HPAGE_SIZE;
        return 1;
}

pte_t *huge_pte_alloc(struct mm_struct *mm, unsigned long addr)
{
        pgd_t *pgd;
        pud_t *pud;
        pte_t *pte = NULL;

        pgd = pgd_offset(mm, addr);
        pud = pud_alloc(mm, pgd, addr);
        if (pud) {
                if (pud_none(*pud))
                        huge_pmd_share(mm, addr, pud);
                pte = (pte_t *) pmd_alloc(mm, pud, addr);
        }
        BUG_ON(pte && !pte_none(*pte) && !pte_huge(*pte));

        return pte;
}

pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr)
{
        pgd_t *pgd;
        pud_t *pud;
        pmd_t *pmd = NULL;

        pgd = pgd_offset(mm, addr);
        if (pgd_present(*pgd)) {
                pud = pud_offset(pgd, addr);
                if (pud_present(*pud))
                        pmd = pmd_offset(pud, addr);
        }
        return (pte_t *) pmd;
}

#if 0   /* This is just for testing */
struct page *
follow_huge_addr(struct mm_struct *mm, unsigned long address, int write)
{
        unsigned long start = address;
        int length = 1;
        int nr;
        struct page *page;
        struct vm_area_struct *vma;

        vma = find_vma(mm, addr);
        if (!vma || !is_vm_hugetlb_page(vma))
                return ERR_PTR(-EINVAL);

        pte = huge_pte_offset(mm, address);

        /* 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));

        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)
{
        return NULL;
}

#else

struct page *
follow_huge_addr(struct mm_struct *mm, unsigned long address, int write)
{
        return ERR_PTR(-EINVAL);
}

int pmd_huge(pmd_t pmd)
{
        return !!(pmd_val(pmd) & _PAGE_PSE);
}

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

        page = pte_page(*(pte_t *)pmd);
        if (page)
                page += ((address & ~HPAGE_MASK) >> PAGE_SHIFT);
        return page;
}
#endif

/* x86_64 also uses this file */

#ifdef HAVE_ARCH_HUGETLB_UNMAPPED_AREA
static unsigned long hugetlb_get_unmapped_area_bottomup(struct file *file,
                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 > mm->cached_hole_size) {
                start_addr = mm->free_area_cache;
        } else {
                start_addr = TASK_UNMAPPED_BASE;
                mm->cached_hole_size = 0;
        }

full_search:
        addr = ALIGN(start_addr, HPAGE_SIZE);

        for (vma = find_vma(mm, addr); ; vma = vma->vm_next) {
                /* At this point:  (!vma || addr < vma->vm_end). */
                if (TASK_SIZE - len < addr) {
                        /*
                         * Start a new search - just in case we missed
                         * some holes.
                         */
                        if (start_addr != TASK_UNMAPPED_BASE) {
                                start_addr = TASK_UNMAPPED_BASE;
                                mm->cached_hole_size = 0;
                                goto full_search;
                        }
                        return -ENOMEM;
                }
                if (!vma || addr + len <= vma->vm_start) {
                        mm->free_area_cache = addr + len;
                        return addr;
                }
                if (addr + mm->cached_hole_size < vma->vm_start)
                        mm->cached_hole_size = vma->vm_start - addr;
                addr = ALIGN(vma->vm_end, HPAGE_SIZE);
        }
}

static unsigned long hugetlb_get_unmapped_area_topdown(struct file *file,
                unsigned long addr0, unsigned long len,
                unsigned long pgoff, unsigned long flags)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma, *prev_vma;
        unsigned long base = mm->mmap_base, addr = addr0;
        unsigned long largest_hole = mm->cached_hole_size;
        int first_time = 1;

        /* don't allow allocations above current base */
        if (mm->free_area_cache > base)
                mm->free_area_cache = base;

        if (len <= largest_hole) {
                largest_hole = 0;
                mm->free_area_cache  = base;
        }
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) & HPAGE_MASK;
        do {
                /*
                 * 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 */
                        mm->cached_hole_size = largest_hole;
                        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;
                                mm->cached_hole_size = largest_hole;
                        }
                }

                /* remember the largest hole we saw so far */
                if (addr + largest_hole < vma->vm_start)
                        largest_hole = vma->vm_start - addr;

                /* try just below the current vma->vm_start */
                addr = (vma->vm_start - len) & HPAGE_MASK;
        } 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;
                largest_hole = 0;
                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;
        mm->cached_hole_size = ~0UL;
        addr = hugetlb_get_unmapped_area_bottomup(file, addr0,
                        len, pgoff, flags);

        /*
         * Restore the topdown base:
         */
        mm->free_area_cache = base;
        mm->cached_hole_size = ~0UL;

        return addr;
}

unsigned long
hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
                unsigned long len, unsigned long pgoff, unsigned long flags)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;

        if (len & ~HPAGE_MASK)
                return -EINVAL;
        if (len > TASK_SIZE)
                return -ENOMEM;

        if (flags & MAP_FIXED) {
                if (prepare_hugepage_range(addr, len, pgoff))
                        return -EINVAL;
                return addr;
        }

        if (addr) {
                addr = ALIGN(addr, HPAGE_SIZE);
                vma = find_vma(mm, addr);
                if (TASK_SIZE - len >= addr &&
                    (!vma || addr + len <= vma->vm_start))
                        return addr;
        }
        if (mm->get_unmapped_area == arch_get_unmapped_area)
                return hugetlb_get_unmapped_area_bottomup(file, addr, len,
                                pgoff, flags);
        else
                return hugetlb_get_unmapped_area_topdown(file, addr, len,
                                pgoff, flags);
}

#endif /*HAVE_ARCH_HUGETLB_UNMAPPED_AREA*/