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  * Flush vma caches for threads that share a given mm.
  24  *
  25  * The operation is safe because the caller holds the mmap_sem
  26  * exclusively and other threads accessing the vma cache will
  27  * have mmap_sem held at least for read, so no extra locking
  28  * is required to maintain the vma cache.
  29  */
  30 void vmacache_flush_all(struct mm_struct *mm)
  31 {
  32         struct task_struct *g, *p;
  33
  34         count_vm_vmacache_event(VMACACHE_FULL_FLUSHES);
  35
  36         /*
  37          * Single threaded tasks need not iterate the entire
  38          * list of process. We can avoid the flushing as well
  39          * since the mm's seqnum was increased and don't have
  40          * to worry about other threads' seqnum. Current's
  41          * flush will occur upon the next lookup.
  42          */
  43         if (atomic_read(&mm->mm_users) == 1)
  44                 return;
  45
  46         rcu_read_lock();
  47         for_each_process_thread(g, p) {
  48                 /*
  49                  * Only flush the vmacache pointers as the
  50                  * mm seqnum is already set and curr's will
  51                  * be set upon invalidation when the next
  52                  * lookup is done.
  53                  */
  54                 if (mm == p->mm)
  55                         vmacache_flush(p);
  56         }
  57         rcu_read_unlock();
  58 }
  59
  60 /*
  61  * This task may be accessing a foreign mm via (for example)
  62  * get_user_pages()->find_vma().  The vmacache is task-local and this
  63  * task's vmacache pertains to a different mm (ie, its own).  There is
  64  * nothing we can do here.
  65  *
  66  * Also handle the case where a kernel thread has adopted this mm via use_mm().
  67  * That kernel thread's vmacache is not applicable to this mm.
  68  */
  69 static inline bool vmacache_valid_mm(struct mm_struct *mm)
  70 {
  71         return current->mm == mm && !(current->flags & PF_KTHREAD);
  72 }
  73
  74 void vmacache_update(unsigned long addr, struct vm_area_struct *newvma)
  75 {
  76         if (vmacache_valid_mm(newvma->vm_mm))
  77                 current->vmacache.vmas[VMACACHE_HASH(addr)] = newvma;
  78 }
  79
  80 static bool vmacache_valid(struct mm_struct *mm)
  81 {
  82         struct task_struct *curr;
  83
  84         if (!vmacache_valid_mm(mm))
  85                 return false;
  86
  87         curr = current;
  88         if (mm->vmacache_seqnum != curr->vmacache.seqnum) {
  89                 /*
  90                  * First attempt will always be invalid, initialize
  91                  * the new cache for this task here.
  92                  */
  93                 curr->vmacache.seqnum = mm->vmacache_seqnum;
  94                 vmacache_flush(curr);
  95                 return false;
  96         }
  97         return true;
  98 }
  99
 100 struct vm_area_struct *vmacache_find(struct mm_struct *mm, unsigned long addr)
 101 {
 102         int idx = VMACACHE_HASH(addr);
 103         int i;
 104
 105         count_vm_vmacache_event(VMACACHE_FIND_CALLS);
 106
 107         if (!vmacache_valid(mm))
 108                 return NULL;
 109
 110         for (i = 0; i < VMACACHE_SIZE; i++) {
 111                 struct vm_area_struct *vma = current->vmacache.vmas[idx];
 112
 113                 if (vma) {
 114 #ifdef CONFIG_DEBUG_VM_VMACACHE
 115                         if (WARN_ON_ONCE(vma->vm_mm != mm))
 116                                 break;
 117 #endif
 118                         if (vma->vm_start <= addr && vma->vm_end > addr) {
 119                                 count_vm_vmacache_event(VMACACHE_FIND_HITS);
 120                                 return vma;
 121                         }
 122                 }
 123                 if (++idx == VMACACHE_SIZE)
 124                         idx = 0;
 125         }
 126
 127         return NULL;
 128 }
 129
 130 #ifndef CONFIG_MMU
 131 struct vm_area_struct *vmacache_find_exact(struct mm_struct *mm,
 132                                            unsigned long start,
 133                                            unsigned long end)
 134 {
 135         int idx = VMACACHE_HASH(start);
 136         int i;
 137
 138         count_vm_vmacache_event(VMACACHE_FIND_CALLS);
 139
 140         if (!vmacache_valid(mm))
 141                 return NULL;
 142
 143         for (i = 0; i < VMACACHE_SIZE; i++) {
 144                 struct vm_area_struct *vma = current->vmacache.vmas[idx];
 145
 146                 if (vma && vma->vm_start == start && vma->vm_end == end) {
 147                         count_vm_vmacache_event(VMACACHE_FIND_HITS);
 148                         return vma;
 149                 }
 150                 if (++idx == VMACACHE_SIZE)
 151                         idx = 0;
 152         }
 153
 154         return NULL;
 155 }
 156 #endif