arch/cris/mm/tlb.c

   1 /*
   2  *  linux/arch/cris/mm/tlb.c
   3  *
   4  *  Copyright (C) 2000, 2001  Axis Communications AB
   5  *
   6  *  Authors:   Bjorn Wesen (bjornw@axis.com)
   7  *
   8  */
   9
  10 #include <linux/init.h>
  11 #include <linux/kernel.h>
  12 #include <asm/tlb.h>
  13
  14 #define D(x)
  15
  16 /* The TLB can host up to 64 different mm contexts at the same time.
  17  * The running context is R_MMU_CONTEXT, and each TLB entry contains a
  18  * page_id that has to match to give a hit. In page_id_map, we keep track
  19  * of which mm we have assigned to which page_id, so that we know when
  20  * to invalidate TLB entries.
  21  *
  22  * The last page_id is never running - it is used as an invalid page_id
  23  * so we can make TLB entries that will never match.
  24  *
  25  * Notice that we need to make the flushes atomic, otherwise an interrupt
  26  * handler that uses vmalloced memory might cause a TLB load in the middle
  27  * of a flush causing.
  28  */
  29
  30 struct mm_struct *page_id_map[NUM_PAGEID];
  31 static int map_replace_ptr = 1;  /* which page_id_map entry to replace next */
  32
  33 /* the following functions are similar to those used in the PPC port */
  34
  35 static inline void
  36 alloc_context(struct mm_struct *mm)
  37 {
  38         struct mm_struct *old_mm;
  39
  40         D(printk("tlb: alloc context %d (%p)\n", map_replace_ptr, mm));
  41
  42         /* did we replace an mm ? */
  43
  44         old_mm = page_id_map[map_replace_ptr];
  45
  46         if(old_mm) {
  47                 /* throw out any TLB entries belonging to the mm we replace
  48                  * in the map
  49                  */
  50                 flush_tlb_mm(old_mm);
  51
  52                 old_mm->context.page_id = NO_CONTEXT;
  53         }
  54
  55         /* insert it into the page_id_map */
  56
  57         mm->context.page_id = map_replace_ptr;
  58         page_id_map[map_replace_ptr] = mm;
  59
  60         map_replace_ptr++;
  61
  62         if(map_replace_ptr == INVALID_PAGEID)
  63                 map_replace_ptr = 0;         /* wrap around */
  64 }
  65
  66 /*
  67  * if needed, get a new MMU context for the mm. otherwise nothing is done.
  68  */
  69
  70 void
  71 get_mmu_context(struct mm_struct *mm)
  72 {
  73         if(mm->context.page_id == NO_CONTEXT)
  74                 alloc_context(mm);
  75 }
  76
  77 /* called by __exit_mm to destroy the used MMU context if any before
  78  * destroying the mm itself. this is only called when the last user of the mm
  79  * drops it.
  80  *
  81  * the only thing we really need to do here is mark the used PID slot
  82  * as empty.
  83  */
  84
  85 void
  86 destroy_context(struct mm_struct *mm)
  87 {
  88         if(mm->context.page_id != NO_CONTEXT) {
  89                 D(printk("destroy_context %d (%p)\n", mm->context.page_id, mm));
  90                 flush_tlb_mm(mm);  /* TODO this might be redundant ? */
  91                 page_id_map[mm->context.page_id] = NULL;
  92         }
  93 }
  94
  95 /* called once during VM initialization, from init.c */
  96
  97 void __init
  98 tlb_init(void)
  99 {
 100         int i;
 101
 102         /* clear the page_id map */
 103
 104         for (i = 1; i < ARRAY_SIZE(page_id_map); i++)
 105                 page_id_map[i] = NULL;
 106
 107         /* invalidate the entire TLB */
 108
 109         flush_tlb_all();
 110
 111         /* the init_mm has context 0 from the boot */
 112
 113         page_id_map[0] = &init_mm;
 114 }