mm/vmacache.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2014 Davidlohr Bueso.
   4  */
   5 #include <linux/sched/signal.h>
   6 #include <linux/sched/task.h>
   7 #include <linux/mm.h>
   8 #include <linux/vmacache.h>
   9
  10 /*
  11  * This task may be accessing a foreign mm via (for example)
  12  * get_user_pages()->find_vma().  The vmacache is task-local and this
  13  * task's vmacache pertains to a different mm (ie, its own).  There is
  14  * nothing we can do here.
  15  *
  16  * Also handle the case where a kernel thread has adopted this mm via use_mm().
  17  * That kernel thread's vmacache is not applicable to this mm.
  18  */
  19 static inline bool vmacache_valid_mm(struct mm_struct *mm)
  20 {
  21         return current->mm == mm && !(current->flags & PF_KTHREAD);
  22 }
  23
  24 void vmacache_update(unsigned long addr, struct vm_area_struct *newvma)
  25 {
  26         if (vmacache_valid_mm(newvma->vm_mm))
  27                 current->vmacache.vmas[VMACACHE_HASH(addr)] = newvma;
  28 }
  29
  30 static bool vmacache_valid(struct mm_struct *mm)
  31 {
  32         struct task_struct *curr;
  33
  34         if (!vmacache_valid_mm(mm))
  35                 return false;
  36
  37         curr = current;
  38         if (mm->vmacache_seqnum != curr->vmacache.seqnum) {
  39                 /*
  40                  * First attempt will always be invalid, initialize
  41                  * the new cache for this task here.
  42                  */
  43                 curr->vmacache.seqnum = mm->vmacache_seqnum;
  44                 vmacache_flush(curr);
  45                 return false;
  46         }
  47         return true;
  48 }
  49
  50 struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
  51 {
  52         int i;
  53
  54         count_vm_vmacache_event(VMACACHE_FIND_CALLS);
  55
  56         if (!vmacache_valid(mm))
  57                 return NULL;
  58
  59         for (i = 0; i < VMACACHE_SIZE; i++) {
  60                 struct vm_area_struct *vma = current->vmacache.vmas[i];
  61
  62                 if (!vma)
  63                         continue;
  64                 if (WARN_ON_ONCE(vma->vm_mm != mm))
  65                         break;
  66                 if (vma->vm_start <= addr && vma->vm_end > addr) {
  67                         count_vm_vmacache_event(VMACACHE_FIND_HITS);
  68                         return vma;
  69                 }
  70         }
  71
  72         return NULL;
  73 }
  74
  75 #ifndef CONFIG_MMU
  76 struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
  77                                            unsigned long start,
  78                                            unsigned long end)
  79 {
  80         int i;
  81
  82         count_vm_vmacache_event(VMACACHE_FIND_CALLS);
  83
  84         if (!vmacache_valid(mm))
  85                 return NULL;
  86
  87         for (i = 0; i < VMACACHE_SIZE; i++) {
  88                 struct vm_area_struct *vma = current->vmacache.vmas[i];
  89
  90                 if (vma && vma->vm_start == start && vma->vm_end == end) {
  91                         count_vm_vmacache_event(VMACACHE_FIND_HITS);
  92                         return vma;
  93                 }
  94         }
  95
  96         return NULL;
  97 }
  98 #endif