mm/vmacache.c

   1 /*
   2  * Copyright (C) 2014 Davidlohr Bueso.
   3  */
   4 #include <linux/sched/signal.h>
   5 #include <linux/sched/task.h>
   6 #include <linux/mm.h>
   7 #include <linux/vmacache.h>
   8
   9 /*
  10  * Flush vma caches for threads that share a given mm.
  11  *
  12  * The operation is safe because the caller holds the mmap_sem
  13  * exclusively and other threads accessing the vma cache will
  14  * have mmap_sem held at least for read, so no extra locking
  15  * is required to maintain the vma cache.
  16  */
  17 void vmacache_flush_all(struct mm_struct *mm)
  18 {
  19         struct task_struct *g, *p;
  20
  21         count_vm_vmacache_event(VMACACHE_FULL_FLUSHES);
  22
  23         /*
  24          * Single threaded tasks need not iterate the entire
  25          * list of process. We can avoid the flushing as well
  26          * since the mm's seqnum was increased and don't have
  27          * to worry about other threads' seqnum. Current's
  28          * flush will occur upon the next lookup.
  29          */
  30         if (atomic_read(&mm->mm_users) == 1)
  31                 return;
  32
  33         rcu_read_lock();
  34         for_each_process_thread(g, p) {
  35                 /*
  36                  * Only flush the vmacache pointers as the
  37                  * mm seqnum is already set and curr's will
  38                  * be set upon invalidation when the next
  39                  * lookup is done.
  40                  */
  41                 if (mm == p->mm)
  42                         vmacache_flush(p);
  43         }
  44         rcu_read_unlock();
  45 }
  46
  47 /*
  48  * This task may be accessing a foreign mm via (for example)
  49  * get_user_pages()->find_vma().  The vmacache is task-local and this
  50  * task's vmacache pertains to a different mm (ie, its own).  There is
  51  * nothing we can do here.
  52  *
  53  * Also handle the case where a kernel thread has adopted this mm via use_mm().
  54  * That kernel thread's vmacache is not applicable to this mm.
  55  */
  56 static inline bool vmacache_valid_mm(struct mm_struct *mm)
  57 {
  58         return current->mm == mm && !(current->flags & PF_KTHREAD);
  59 }
  60
  61 void vmacache_update(unsigned long addr, struct vm_area_struct *newvma)
  62 {
  63         if (vmacache_valid_mm(newvma->vm_mm))
  64                 current->vmacache.vmas[VMACACHE_HASH(addr)] = newvma;
  65 }
  66
  67 static bool vmacache_valid(struct mm_struct *mm)
  68 {
  69         struct task_struct *curr;
  70
  71         if (!vmacache_valid_mm(mm))
  72                 return false;
  73
  74         curr = current;
  75         if (mm->vmacache_seqnum != curr->vmacache.seqnum) {
  76                 /*
  77                  * First attempt will always be invalid, initialize
  78                  * the new cache for this task here.
  79                  */
  80                 curr->vmacache.seqnum = mm->vmacache_seqnum;
  81                 vmacache_flush(curr);
  82                 return false;
  83         }
  84         return true;
  85 }
  86
  87 struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
  88 {
  89         int i;
  90
  91         count_vm_vmacache_event(VMACACHE_FIND_CALLS);
  92
  93         if (!vmacache_valid(mm))
  94                 return NULL;
  95
  96         for (i = 0; i < VMACACHE_SIZE; i++) {
  97                 struct vm_area_struct *vma = current->vmacache.vmas[i];
  98
  99                 if (!vma)
 100                         continue;
 101                 if (WARN_ON_ONCE(vma->vm_mm != mm))
 102                         break;
 103                 if (vma->vm_start <= addr && vma->vm_end > addr) {
 104                         count_vm_vmacache_event(VMACACHE_FIND_HITS);
 105                         return vma;
 106                 }
 107         }
 108
 109         return NULL;
 110 }
 111
 112 #ifndef CONFIG_MMU
 113 struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
 114                                            unsigned long start,
 115                                            unsigned long end)
 116 {
 117         int i;
 118
 119         count_vm_vmacache_event(VMACACHE_FIND_CALLS);
 120
 121         if (!vmacache_valid(mm))
 122                 return NULL;
 123
 124         for (i = 0; i < VMACACHE_SIZE; i++) {
 125                 struct vm_area_struct *vma = current->vmacache.vmas[i];
 126
 127                 if (vma && vma->vm_start == start && vma->vm_end == end) {
 128                         count_vm_vmacache_event(VMACACHE_FIND_HITS);
 129                         return vma;
 130                 }
 131         }
 132
 133         return NULL;
 134 }
 135 #endif