/*
   * Copyright (C) 2014 Davidlohr Bueso.
   */
  #include <linux/sched.h>
  #include <linux/mm.h>
  #include <linux/vmacache.h>
  
  /*
   * Flush vma caches for threads that share a given mm.
   *
   * The operation is safe because the caller holds the mmap_sem
   * exclusively and other threads accessing the vma cache will
   * have mmap_sem held at least for read, so no extra locking
   * is required to maintain the vma cache.
   */
  void vmacache_flush_all(struct mm_struct *mm)
  {
  	struct task_struct *g, *p;

  	count_vm_vmacache_event(VMACACHE_FULL_FLUSHES);

  	/*
  	 * Single threaded tasks need not iterate the entire
  	 * list of process. We can avoid the flushing as well
  	 * since the mm's seqnum was increased and don't have
  	 * to worry about other threads' seqnum. Current's
  	 * flush will occur upon the next lookup.
  	 */
  	if (atomic_read(&mm->mm_users) == 1)
  		return;

  	rcu_read_lock();
  	for_each_process_thread(g, p) {
  		/*
  		 * Only flush the vmacache pointers as the
  		 * mm seqnum is already set and curr's will
  		 * be set upon invalidation when the next
  		 * lookup is done.
  		 */
  		if (mm == p->mm)
  			vmacache_flush(p);
  	}
  	rcu_read_unlock();
  }
  
  /*
   * This task may be accessing a foreign mm via (for example)
   * get_user_pages()->find_vma().  The vmacache is task-local and this
   * task's vmacache pertains to a different mm (ie, its own).  There is
   * nothing we can do here.
   *
   * Also handle the case where a kernel thread has adopted this mm via use_mm().
   * That kernel thread's vmacache is not applicable to this mm.
   */

  static inline bool vmacache_valid_mm(struct mm_struct *mm)

  {
  	return current->mm == mm && !(current->flags & PF_KTHREAD);
  }
  
  void vmacache_update(unsigned long addr, struct vm_area_struct *newvma)
  {
  	if (vmacache_valid_mm(newvma->vm_mm))
  		current->vmacache[VMACACHE_HASH(addr)] = newvma;
  }
  
  static bool vmacache_valid(struct mm_struct *mm)
  {
  	struct task_struct *curr;
  
  	if (!vmacache_valid_mm(mm))
  		return false;
  
  	curr = current;
  	if (mm->vmacache_seqnum != curr->vmacache_seqnum) {
  		/*
  		 * First attempt will always be invalid, initialize
  		 * the new cache for this task here.
  		 */
  		curr->vmacache_seqnum = mm->vmacache_seqnum;
  		vmacache_flush(curr);
  		return false;
  	}
  	return true;
  }
  
  struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
  {
  	int i;

  	count_vm_vmacache_event(VMACACHE_FIND_CALLS);

  	if (!vmacache_valid(mm))
  		return NULL;
  
  	for (i = 0; i < VMACACHE_SIZE; i++) {
  		struct vm_area_struct *vma = current->vmacache[i];

  		if (!vma)
  			continue;
  		if (WARN_ON_ONCE(vma->vm_mm != mm))
  			break;

  		if (vma->vm_start <= addr && vma->vm_end > addr) {
  			count_vm_vmacache_event(VMACACHE_FIND_HITS);

  			return vma;

  		}

  	}
  
  	return NULL;
  }
  
  #ifndef CONFIG_MMU
  struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
  					   unsigned long start,
  					   unsigned long end)
  {
  	int i;

  	count_vm_vmacache_event(VMACACHE_FIND_CALLS);

  	if (!vmacache_valid(mm))
  		return NULL;
  
  	for (i = 0; i < VMACACHE_SIZE; i++) {
  		struct vm_area_struct *vma = current->vmacache[i];

  		if (vma && vma->vm_start == start && vma->vm_end == end) {
  			count_vm_vmacache_event(VMACACHE_FIND_HITS);

  			return vma;

  		}

  	}
  
  	return NULL;
  }
  #endif