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