text: #ifndef _S390_TLB_H
  #define _S390_TLB_H
  
  /*
   * TLB flushing on s390 is complicated. The following requirement
   * from the principles of operation is the most arduous:
   *
   * "A valid table entry must not be changed while it is attached
   * to any CPU and may be used for translation by that CPU except to
   * (1) invalidate the entry by using INVALIDATE PAGE TABLE ENTRY,
   * or INVALIDATE DAT TABLE ENTRY, (2) alter bits 56-63 of a page
   * table entry, or (3) make a change by means of a COMPARE AND SWAP
   * AND PURGE instruction that purges the TLB."
   *
   * The modification of a pte of an active mm struct therefore is
   * a two step process: i) invalidate the pte, ii) store the new pte.
   * This is true for the page protection bit as well.
   * The only possible optimization is to flush at the beginning of
   * a tlb_gather_mmu cycle if the mm_struct is currently not in use.
   *
   * Pages used for the page tables is a different story. FIXME: more
   */
  
  #include <linux/mm.h>
  #include <linux/pagemap.h>
  #include <linux/swap.h>
  #include <asm/processor.h>
  #include <asm/pgalloc.h>
  #include <asm/tlbflush.h>
  
  struct mmu_gather {
  	struct mm_struct *mm;
  	struct mmu_table_batch *batch;
  	unsigned int fullmm;
  };
  
  struct mmu_table_batch {
  	struct rcu_head		rcu;
  	unsigned int		nr;
  	void			*tables[0];
  };
  
  #define MAX_TABLE_BATCH		\
  	((PAGE_SIZE - sizeof(struct mmu_table_batch)) / sizeof(void *))
  
  extern void tlb_table_flush(struct mmu_gather *tlb);
  extern void tlb_remove_table(struct mmu_gather *tlb, void *table);
  
  static inline void tlb_gather_mmu(struct mmu_gather *tlb,
  				  struct mm_struct *mm,
  				  unsigned int full_mm_flush)
  {
  	tlb->mm = mm;
  	tlb->fullmm = full_mm_flush;
  	tlb->batch = NULL;
  	if (tlb->fullmm)
  		__tlb_flush_mm(mm);
  }
  
  static inline void tlb_flush_mmu(struct mmu_gather *tlb)
  {
  	tlb_table_flush(tlb);
  }
  
  static inline void tlb_finish_mmu(struct mmu_gather *tlb,
  				  unsigned long start, unsigned long end)
  {
  	tlb_table_flush(tlb);
  }
  
  /*
   * Release the page cache reference for a pte removed by
   * tlb_ptep_clear_flush. In both flush modes the tlb for a page cache page
   * has already been freed, so just do free_page_and_swap_cache.
   */
  static inline int __tlb_remove_page(struct mmu_gather *tlb, struct page *page)
  {
  	free_page_and_swap_cache(page);
  	return 1; /* avoid calling tlb_flush_mmu */
  }
  
  static inline void tlb_remove_page(struct mmu_gather *tlb, struct page *page)
  {
  	free_page_and_swap_cache(page);
  }
  
  /*
   * pte_free_tlb frees a pte table and clears the CRSTE for the
   * page table from the tlb.
   */
  static inline void pte_free_tlb(struct mmu_gather *tlb, pgtable_t pte,
  				unsigned long address)
  {
  	if (!tlb->fullmm)
  		return page_table_free_rcu(tlb, (unsigned long *) pte);
  	page_table_free(tlb->mm, (unsigned long *) pte);
  }
  
  /*
   * pmd_free_tlb frees a pmd table and clears the CRSTE for the
   * segment table entry from the tlb.
   * If the mm uses a two level page table the single pmd is freed
   * as the pgd. pmd_free_tlb checks the asce_limit against 2GB
   * to avoid the double free of the pmd in this case.
   */
  static inline void pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd,
  				unsigned long address)
  {
  #ifdef CONFIG_64BIT
  	if (tlb->mm->context.asce_limit <= (1UL << 31))
  		return;
  	if (!tlb->fullmm)
  		return tlb_remove_table(tlb, pmd);
  	crst_table_free(tlb->mm, (unsigned long *) pmd);
  #endif
  }
  
  /*
   * pud_free_tlb frees a pud table and clears the CRSTE for the
   * region third table entry from the tlb.
   * If the mm uses a three level page table the single pud is freed
   * as the pgd. pud_free_tlb checks the asce_limit against 4TB
   * to avoid the double free of the pud in this case.
   */
  static inline void pud_free_tlb(struct mmu_gather *tlb, pud_t *pud,
  				unsigned long address)
  {
  #ifdef CONFIG_64BIT
  	if (tlb->mm->context.asce_limit <= (1UL << 42))
  		return;
  	if (!tlb->fullmm)
  		return tlb_remove_table(tlb, pud);
  	crst_table_free(tlb->mm, (unsigned long *) pud);
  #endif
  }
  
  #define tlb_start_vma(tlb, vma)			do { } while (0)
  #define tlb_end_vma(tlb, vma)			do { } while (0)
  #define tlb_remove_tlb_entry(tlb, ptep, addr)	do { } while (0)
  #define tlb_remove_pmd_tlb_entry(tlb, pmdp, addr)	do { } while (0)
  #define tlb_migrate_finish(mm)			do { } while (0)
  
  #endif /* _S390_TLB_H */
  