text: // SPDX-License-Identifier: GPL-2.0
  /*
   * Copyright (C) 2014 Davidlohr Bueso.
   */
  #include <linux/sched/signal.h>
  #include <linux/sched/task.h>
  #include <linux/mm.h>
  #include <linux/vmacache.h>
  #include <asm/pgtable.h>
  
  /*
   * Hash based on the pmd of addr if configured with MMU, which provides a good
   * hit rate for workloads with spatial locality.  Otherwise, use pages.
   */
  #ifdef CONFIG_MMU
  #define VMACACHE_SHIFT	PMD_SHIFT
  #else
  #define VMACACHE_SHIFT	PAGE_SHIFT
  #endif
  #define VMACACHE_HASH(addr) ((addr >> VMACACHE_SHIFT) & VMACACHE_MASK)
  
  /*
   * 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.vmas[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 idx = VMACACHE_HASH(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.vmas[idx];
  
  		if (vma) {
  #ifdef CONFIG_DEBUG_VM_VMACACHE
  			if (WARN_ON_ONCE(vma->vm_mm != mm))
  				break;
  #endif
  			if (vma->vm_start <= addr && vma->vm_end > addr) {
  				count_vm_vmacache_event(VMACACHE_FIND_HITS);
  				return vma;
  			}
  		}
  		if (++idx == VMACACHE_SIZE)
  			idx = 0;
  	}
  
  	return NULL;
  }
  
  #ifndef CONFIG_MMU
  struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
  					   unsigned long start,
  					   unsigned long end)
  {
  	int idx = VMACACHE_HASH(start);
  	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.vmas[idx];
  
  		if (vma && vma->vm_start == start && vma->vm_end == end) {
  			count_vm_vmacache_event(VMACACHE_FIND_HITS);
  			return vma;
  		}
  		if (++idx == VMACACHE_SIZE)
  			idx = 0;
  	}
  
  	return NULL;
  }
  #endif
  