text: #ifndef _LINUX_HIGHMEM_H
  #define _LINUX_HIGHMEM_H
  
  #include <linux/fs.h>
  #include <linux/kernel.h>
  #include <linux/bug.h>
  #include <linux/mm.h>
  #include <linux/uaccess.h>
  #include <linux/hardirq.h>
  
  #include <asm/cacheflush.h>
  
  #ifndef ARCH_HAS_FLUSH_ANON_PAGE
  static inline void flush_anon_page(struct vm_area_struct *vma, struct page *page, unsigned long vmaddr)
  {
  }
  #endif
  
  #ifndef ARCH_HAS_FLUSH_KERNEL_DCACHE_PAGE
  static inline void flush_kernel_dcache_page(struct page *page)
  {
  }
  static inline void flush_kernel_vmap_range(void *vaddr, int size)
  {
  }
  static inline void invalidate_kernel_vmap_range(void *vaddr, int size)
  {
  }
  #endif
  
  #include <asm/kmap_types.h>
  
  #ifdef CONFIG_HIGHMEM
  #include <asm/highmem.h>
  
  /* declarations for linux/mm/highmem.c */
  unsigned int nr_free_highpages(void);
  extern unsigned long totalhigh_pages;
  
  void kmap_flush_unused(void);
  
  struct page *kmap_to_page(void *addr);
  
  #else /* CONFIG_HIGHMEM */
  
  static inline unsigned int nr_free_highpages(void) { return 0; }
  
  static inline struct page *kmap_to_page(void *addr)
  {
  	return virt_to_page(addr);
  }
  
  #define totalhigh_pages 0UL
  
  #ifndef ARCH_HAS_KMAP
  static inline void *kmap(struct page *page)
  {
  	might_sleep();
  	return page_address(page);
  }
  
  static inline void kunmap(struct page *page)
  {
  }
  
  static inline void *kmap_atomic(struct page *page)
  {
  	preempt_disable();
  	pagefault_disable();
  	return page_address(page);
  }
  #define kmap_atomic_prot(page, prot)	kmap_atomic(page)
  
  static inline void __kunmap_atomic(void *addr)
  {
  	pagefault_enable();
  	preempt_enable();
  }
  
  #define kmap_atomic_pfn(pfn)	kmap_atomic(pfn_to_page(pfn))
  
  #define kmap_flush_unused()	do {} while(0)
  #endif
  
  #endif /* CONFIG_HIGHMEM */
  
  #if defined(CONFIG_HIGHMEM) || defined(CONFIG_X86_32)
  
  DECLARE_PER_CPU(int, __kmap_atomic_idx);
  
  static inline int kmap_atomic_idx_push(void)
  {
  	int idx = __this_cpu_inc_return(__kmap_atomic_idx) - 1;
  
  #ifdef CONFIG_DEBUG_HIGHMEM
  	WARN_ON_ONCE(in_irq() && !irqs_disabled());
  	BUG_ON(idx >= KM_TYPE_NR);
  #endif
  	return idx;
  }
  
  static inline int kmap_atomic_idx(void)
  {
  	return __this_cpu_read(__kmap_atomic_idx) - 1;
  }
  
  static inline void kmap_atomic_idx_pop(void)
  {
  #ifdef CONFIG_DEBUG_HIGHMEM
  	int idx = __this_cpu_dec_return(__kmap_atomic_idx);
  
  	BUG_ON(idx < 0);
  #else
  	__this_cpu_dec(__kmap_atomic_idx);
  #endif
  }
  
  #endif
  
  /*
   * Prevent people trying to call kunmap_atomic() as if it were kunmap()
   * kunmap_atomic() should get the return value of kmap_atomic, not the page.
   */
  #define kunmap_atomic(addr)                                     \
  do {                                                            \
  	BUILD_BUG_ON(__same_type((addr), struct page *));       \
  	__kunmap_atomic(addr);                                  \
  } while (0)
  
  
  /* when CONFIG_HIGHMEM is not set these will be plain clear/copy_page */
  #ifndef clear_user_highpage
  static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
  {
  	void *addr = kmap_atomic(page);
  	clear_user_page(addr, vaddr, page);
  	kunmap_atomic(addr);
  }
  #endif
  
  #ifndef __HAVE_ARCH_ALLOC_ZEROED_USER_HIGHPAGE
  /**
   * __alloc_zeroed_user_highpage - Allocate a zeroed HIGHMEM page for a VMA with caller-specified movable GFP flags
   * @movableflags: The GFP flags related to the pages future ability to move like __GFP_MOVABLE
   * @vma: The VMA the page is to be allocated for
   * @vaddr: The virtual address the page will be inserted into
   *
   * This function will allocate a page for a VMA but the caller is expected
   * to specify via movableflags whether the page will be movable in the
   * future or not
   *
   * An architecture may override this function by defining
   * __HAVE_ARCH_ALLOC_ZEROED_USER_HIGHPAGE and providing their own
   * implementation.
   */
  static inline struct page *
  __alloc_zeroed_user_highpage(gfp_t movableflags,
  			struct vm_area_struct *vma,
  			unsigned long vaddr)
  {
  	struct page *page = alloc_page_vma(GFP_HIGHUSER | movableflags,
  			vma, vaddr);
  
  	if (page)
  		clear_user_highpage(page, vaddr);
  
  	return page;
  }
  #endif
  
  /**
   * alloc_zeroed_user_highpage_movable - Allocate a zeroed HIGHMEM page for
   *					a VMA that the caller knows can move
   * @vma: The VMA the page is to be allocated for
   * @vaddr: The virtual address the page will be inserted into
   *
   * This function will allocate a page for a VMA that the caller knows will
   * be able to migrate in the future using move_pages() or reclaimed
   */
  static inline struct page *
  alloc_zeroed_user_highpage_movable(struct vm_area_struct *vma,
  				   unsigned long vaddr)
  {
  	return __alloc_zeroed_user_highpage(__GFP_MOVABLE, vma, vaddr);
  }
  
  static inline struct page *
  alloc_zeroed_user_highpage(gfp_t gfp, struct vm_area_struct *vma,
  			   unsigned long vaddr)
  {
  	return __alloc_zeroed_user_highpage(gfp, vma, vaddr);
  }
  
  static inline void clear_highpage(struct page *page)
  {
  	void *kaddr = kmap_atomic(page);
  	clear_page(kaddr);
  	kunmap_atomic(kaddr);
  }
  
  static inline void zero_user_segments(struct page *page,
  	unsigned start1, unsigned end1,
  	unsigned start2, unsigned end2)
  {
  	void *kaddr = kmap_atomic(page);
  
  	BUG_ON(end1 > PAGE_SIZE || end2 > PAGE_SIZE);
  
  	if (end1 > start1)
  		memset(kaddr + start1, 0, end1 - start1);
  
  	if (end2 > start2)
  		memset(kaddr + start2, 0, end2 - start2);
  
  	kunmap_atomic(kaddr);
  	flush_dcache_page(page);
  }
  
  static inline void zero_user_segment(struct page *page,
  	unsigned start, unsigned end)
  {
  	zero_user_segments(page, start, end, 0, 0);
  }
  
  static inline void zero_user(struct page *page,
  	unsigned start, unsigned size)
  {
  	zero_user_segments(page, start, start + size, 0, 0);
  }
  
  #ifndef __HAVE_ARCH_COPY_USER_HIGHPAGE
  
  static inline void copy_user_highpage(struct page *to, struct page *from,
  	unsigned long vaddr, struct vm_area_struct *vma)
  {
  	char *vfrom, *vto;
  
  	vfrom = kmap_atomic(from);
  	vto = kmap_atomic(to);
  	copy_user_page(vto, vfrom, vaddr, to);
  	kunmap_atomic(vto);
  	kunmap_atomic(vfrom);
  }
  
  #endif
  
  static inline void copy_highpage(struct page *to, struct page *from)
  {
  	char *vfrom, *vto;
  
  	vfrom = kmap_atomic(from);
  	vto = kmap_atomic(to);
  	copy_page(vto, vfrom);
  	kunmap_atomic(vto);
  	kunmap_atomic(vfrom);
  }
  
  #endif /* _LINUX_HIGHMEM_H */
  