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 #include <asm/pgtable.h>
  10
  11 /*
  12  * Hash based on the pmd of addr if configured with MMU, which provides a good
  13  * hit rate for workloads with spatial locality.  Otherwise, use pages.
  14  */
  15 #ifdef CONFIG_MMU
  16 #define VMACACHE_SHIFT  PMD_SHIFT
  17 #else
  18 #define VMACACHE_SHIFT  PAGE_SHIFT
  19 #endif
  20 #define VMACACHE_HASH(addr) ((addr >> VMACACHE_SHIFT) & VMACACHE_MASK)
  21
  22 /*
  23  * This task may be accessing a foreign mm via (for example)
  24  * get_user_pages()->find_vma().  The vmacache is task-local and this
  25  * task's vmacache pertains to a different mm (ie, its own).  There is
  26  * nothing we can do here.
  27  *
  28  * Also handle the case where a kernel thread has adopted this mm via use_mm().
  29  * That kernel thread's vmacache is not applicable to this mm.
  30  */
  31 static inline bool vmacache_valid_mm(struct mm_struct *mm)
  32 {
  33         return current->mm == mm && !(current->flags & PF_KTHREAD);
  34 }
  35
  36 void vmacache_update(unsigned long addr, struct vm_area_struct *newvma)
  37 {
  38         if (vmacache_valid_mm(newvma->vm_mm))
  39                 current->vmacache.vmas[VMACACHE_HASH(addr)] = newvma;
  40 }
  41
  42 static bool vmacache_valid(struct mm_struct *mm)
  43 {
  44         struct task_struct *curr;
  45
  46         if (!vmacache_valid_mm(mm))
  47                 return false;
  48
  49         curr = current;
  50         if (mm->vmacache_seqnum != curr->vmacache.seqnum) {
  51                 /*
  52                  * First attempt will always be invalid, initialize
  53                  * the new cache for this task here.
  54                  */
  55                 curr->vmacache.seqnum = mm->vmacache_seqnum;
  56                 vmacache_flush(curr);
  57                 return false;
  58         }
  59         return true;
  60 }
  61
  62 struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
  63 {
  64         int idx = VMACACHE_HASH(addr);
  65         int i;
  66
  67         count_vm_vmacache_event(VMACACHE_FIND_CALLS);
  68
  69         if (!vmacache_valid(mm))
  70                 return NULL;
  71
  72         for (i = 0; i < VMACACHE_SIZE; i++) {
  73                 struct vm_area_struct *vma = current->vmacache.vmas[idx];
  74
  75                 if (vma) {
  76 #ifdef CONFIG_DEBUG_VM_VMACACHE
  77                         if (WARN_ON_ONCE(vma->vm_mm != mm))
  78                                 break;
  79 #endif
  80                         if (vma->vm_start <= addr && vma->vm_end > addr) {
  81                                 count_vm_vmacache_event(VMACACHE_FIND_HITS);
  82                                 return vma;
  83                         }
  84                 }
  85                 if (++idx == VMACACHE_SIZE)
  86                         idx = 0;
  87         }
  88
  89         return NULL;
  90 }
  91
  92 #ifndef CONFIG_MMU
  93 struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
  94                                            unsigned long start,
  95                                            unsigned long end)
  96 {
  97         int idx = VMACACHE_HASH(start);
  98         int i;
  99
 100         count_vm_vmacache_event(VMACACHE_FIND_CALLS);
 101
 102         if (!vmacache_valid(mm))
 103                 return NULL;
 104
 105         for (i = 0; i < VMACACHE_SIZE; i++) {
 106                 struct vm_area_struct *vma = current->vmacache.vmas[idx];
 107
 108                 if (vma && vma->vm_start == start && vma->vm_end == end) {
 109                         count_vm_vmacache_event(VMACACHE_FIND_HITS);
 110                         return vma;
 111                 }
 112                 if (++idx == VMACACHE_SIZE)
 113                         idx = 0;
 114         }
 115
 116         return NULL;
 117 }
 118 #endif