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    /*
     *  mm/pgtable-generic.c
     *
     *  Generic pgtable methods declared in asm-generic/pgtable.h
     *
     *  Copyright (C) 2010  Linus Torvalds
     */
    
    #include <linux/pagemap.h>
    #include <asm/tlb.h>
    #include <asm-generic/pgtable.h>
    
    /*
     * If a p?d_bad entry is found while walking page tables, report
     * the error, before resetting entry to p?d_none.  Usually (but
     * very seldom) called out from the p?d_none_or_clear_bad macros.
     */
    
    void pgd_clear_bad(pgd_t *pgd)
    {
    	pgd_ERROR(*pgd);
    	pgd_clear(pgd);
    }
    
    void pud_clear_bad(pud_t *pud)
    {
    	pud_ERROR(*pud);
    	pud_clear(pud);
    }
    
    void pmd_clear_bad(pmd_t *pmd)
    {
    	pmd_ERROR(*pmd);
    	pmd_clear(pmd);
    }
    
    #ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
    /*
     * Only sets the access flags (dirty, accessed), as well as write 
     * permission. Furthermore, we know it always gets set to a "more
     * permissive" setting, which allows most architectures to optimize
     * this. We return whether the PTE actually changed, which in turn
     * instructs the caller to do things like update__mmu_cache.  This
     * used to be done in the caller, but sparc needs minor faults to
     * force that call on sun4c so we changed this macro slightly
     */
    int ptep_set_access_flags(struct vm_area_struct *vma,
    			  unsigned long address, pte_t *ptep,
    			  pte_t entry, int dirty)
    {
    	int changed = !pte_same(*ptep, entry);
    	if (changed) {
    		set_pte_at(vma->vm_mm, address, ptep, entry);
    		flush_tlb_fix_spurious_fault(vma, address);
    	}
    	return changed;
    }
    #endif
    
    #ifndef __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH
    int ptep_clear_flush_young(struct vm_area_struct *vma,
    			   unsigned long address, pte_t *ptep)
    {
    	int young;
    	young = ptep_test_and_clear_young(vma, address, ptep);
    	if (young)
    		flush_tlb_page(vma, address);
    	return young;
    }
    #endif
    
    #ifndef __HAVE_ARCH_PTEP_CLEAR_FLUSH
    pte_t ptep_clear_flush(struct vm_area_struct *vma, unsigned long address,
    		       pte_t *ptep)
    {
    	struct mm_struct *mm = (vma)->vm_mm;
    	pte_t pte;
    	pte = ptep_get_and_clear(mm, address, ptep);
    	if (pte_accessible(mm, pte))
    		flush_tlb_page(vma, address);
    	return pte;
    }
    #endif
    
    #ifdef CONFIG_TRANSPARENT_HUGEPAGE
    
    #ifndef __HAVE_ARCH_PMDP_SET_ACCESS_FLAGS
    int pmdp_set_access_flags(struct vm_area_struct *vma,
    			  unsigned long address, pmd_t *pmdp,
    			  pmd_t entry, int dirty)
    {
    	int changed = !pmd_same(*pmdp, entry);
    	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
    	if (changed) {
    		set_pmd_at(vma->vm_mm, address, pmdp, entry);
    		flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
    	}
    	return changed;
    }
    #endif
    
    #ifndef __HAVE_ARCH_PMDP_CLEAR_YOUNG_FLUSH
    int pmdp_clear_flush_young(struct vm_area_struct *vma,
    			   unsigned long address, pmd_t *pmdp)
    {
    	int young;
    	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
    	young = pmdp_test_and_clear_young(vma, address, pmdp);
    	if (young)
    		flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
    	return young;
    }
    #endif
    
    #ifndef __HAVE_ARCH_PMDP_HUGE_CLEAR_FLUSH
    pmd_t pmdp_huge_clear_flush(struct vm_area_struct *vma, unsigned long address,
    			    pmd_t *pmdp)
    {
    	pmd_t pmd;
    	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
    	VM_BUG_ON(!pmd_trans_huge(*pmdp) && !pmd_devmap(*pmdp));
    	pmd = pmdp_huge_get_and_clear(vma->vm_mm, address, pmdp);
    	flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
    	return pmd;
    }
    #endif
    
    #ifndef __HAVE_ARCH_PGTABLE_DEPOSIT
    void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp,
    				pgtable_t pgtable)
    {
    	assert_spin_locked(pmd_lockptr(mm, pmdp));
    
    	/* FIFO */
    	if (!pmd_huge_pte(mm, pmdp))
    		INIT_LIST_HEAD(&pgtable->lru);
    	else
    		list_add(&pgtable->lru, &pmd_huge_pte(mm, pmdp)->lru);
    	pmd_huge_pte(mm, pmdp) = pgtable;
    }
    #endif
    
    #ifndef __HAVE_ARCH_PGTABLE_WITHDRAW
    /* no "address" argument so destroys page coloring of some arch */
    pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp)
    {
    	pgtable_t pgtable;
    
    	assert_spin_locked(pmd_lockptr(mm, pmdp));
    
    	/* FIFO */
    	pgtable = pmd_huge_pte(mm, pmdp);
    	pmd_huge_pte(mm, pmdp) = list_first_entry_or_null(&pgtable->lru,
    							  struct page, lru);
    	if (pmd_huge_pte(mm, pmdp))
    		list_del(&pgtable->lru);
    	return pgtable;
    }
    #endif
    
    #ifndef __HAVE_ARCH_PMDP_INVALIDATE
    void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
    		     pmd_t *pmdp)
    {
    	pmd_t entry = *pmdp;
    	set_pmd_at(vma->vm_mm, address, pmdp, pmd_mknotpresent(entry));
    	flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
    }
    #endif
    
    #ifndef pmdp_collapse_flush
    pmd_t pmdp_collapse_flush(struct vm_area_struct *vma, unsigned long address,
    			  pmd_t *pmdp)
    {
    	/*
    	 * pmd and hugepage pte format are same. So we could
    	 * use the same function.
    	 */
    	pmd_t pmd;
    
    	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
    	VM_BUG_ON(pmd_trans_huge(*pmdp));
    	pmd = pmdp_huge_get_and_clear(vma->vm_mm, address, pmdp);
    
    	/* collapse entails shooting down ptes not pmd */
    	flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
    	return pmd;
    }
    #endif
    #endif /* CONFIG_TRANSPARENT_HUGEPAGE */