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hugetlbpage.c

/*
 * 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))
                  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*/


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