mm/vmacache.c

   1 /*
   2  * Copyright (C) 2014 Davidlohr Bueso.
   3  */
   4 #include <linux/sched.h>
   5 #include <linux/mm.h>
   6 #include <linux/vmacache.h>
   7
   8 /*
   9  * This task may be accessing a foreign mm via (for example)
  10  * get_user_pages()->find_vma().  The vmacache is task-local and this
  11  * task's vmacache pertains to a different mm (ie, its own).  There is
  12  * nothing we can do here.
  13  *
  14  * Also handle the case where a kernel thread has adopted this mm via use_mm().
  15  * That kernel thread's vmacache is not applicable to this mm.
  16  */
  17 static inline bool vmacache_valid_mm(struct mm_struct *mm)
  18 {
  19         return current->mm == mm && !(current->flags & PF_KTHREAD);
  20 }
  21
  22 void vmacache_update(unsigned long addr, struct vm_area_struct *newvma)
  23 {
  24         if (vmacache_valid_mm(newvma->vm_mm))
  25                 current->vmacache[VMACACHE_HASH(addr)] = newvma;
  26 }
  27
  28 static bool vmacache_valid(struct mm_struct *mm)
  29 {
  30         struct task_struct *curr;
  31
  32         if (!vmacache_valid_mm(mm))
  33                 return false;
  34
  35         curr = current;
  36         if (mm->vmacache_seqnum != curr->vmacache_seqnum) {
  37                 /*
  38                  * First attempt will always be invalid, initialize
  39                  * the new cache for this task here.
  40                  */
  41                 curr->vmacache_seqnum = mm->vmacache_seqnum;
  42                 vmacache_flush(curr);
  43                 return false;
  44         }
  45         return true;
  46 }
  47
  48 struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
  49 {
  50         int i;
  51
  52         if (!vmacache_valid(mm))
  53                 return NULL;
  54
  55         count_vm_vmacache_event(VMACACHE_FIND_CALLS);
  56
  57         for (i = 0; i < VMACACHE_SIZE; i++) {
  58                 struct vm_area_struct *vma = current->vmacache[i];
  59
  60                 if (!vma)
  61                         continue;
  62                 if (WARN_ON_ONCE(vma->vm_mm != mm))
  63                         break;
  64                 if (vma->vm_start <= addr && vma->vm_end > addr) {
  65                         count_vm_vmacache_event(VMACACHE_FIND_HITS);
  66                         return vma;
  67                 }
  68         }
  69
  70         return NULL;
  71 }
  72
  73 #ifndef CONFIG_MMU
  74 struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
  75                                            unsigned long start,
  76                                            unsigned long end)
  77 {
  78         int i;
  79
  80         if (!vmacache_valid(mm))
  81                 return NULL;
  82
  83         count_vm_vmacache_event(VMACACHE_FIND_CALLS);
  84
  85         for (i = 0; i < VMACACHE_SIZE; i++) {
  86                 struct vm_area_struct *vma = current->vmacache[i];
  87
  88                 if (vma && vma->vm_start == start && vma->vm_end == end) {
  89                         count_vm_vmacache_event(VMACACHE_FIND_HITS);
  90                         return vma;
  91                 }
  92         }
  93
  94         return NULL;
  95 }
  96 #endif