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 <linux/mm_types.h>
  13
  14 #include <asm/tlb.h>
  15
  16 #define D(x)
  17
  18 /* The TLB can host up to 64 different mm contexts at the same time.
  19  * The running context is R_MMU_CONTEXT, and each TLB entry contains a
  20  * page_id that has to match to give a hit. In page_id_map, we keep track
  21  * of which mm we have assigned to which page_id, so that we know when
  22  * to invalidate TLB entries.
  23  *
  24  * The last page_id is never running - it is used as an invalid page_id
  25  * so we can make TLB entries that will never match.
  26  *
  27  * Notice that we need to make the flushes atomic, otherwise an interrupt
  28  * handler that uses vmalloced memory might cause a TLB load in the middle
  29  * of a flush causing.
  30  */
  31
  32 struct mm_struct *page_id_map[NUM_PAGEID];
  33 static int map_replace_ptr = 1;  /* which page_id_map entry to replace next */
  34
  35 /* the following functions are similar to those used in the PPC port */
  36
  37 static inline void
  38 alloc_context(struct mm_struct *mm)
  39 {
  40         struct mm_struct *old_mm;
  41
  42         D(printk("tlb: alloc context %d (%p)\n", map_replace_ptr, mm));
  43
  44         /* did we replace an mm ? */
  45
  46         old_mm = page_id_map[map_replace_ptr];
  47
  48         if(old_mm) {
  49                 /* throw out any TLB entries belonging to the mm we replace
  50                  * in the map
  51                  */
  52                 flush_tlb_mm(old_mm);
  53
  54                 old_mm->context.page_id = NO_CONTEXT;
  55         }
  56
  57         /* insert it into the page_id_map */
  58
  59         mm->context.page_id = map_replace_ptr;
  60         page_id_map[map_replace_ptr] = mm;
  61
  62         map_replace_ptr++;
  63
  64         if(map_replace_ptr == INVALID_PAGEID)
  65                 map_replace_ptr = 0;         /* wrap around */
  66 }
  67
  68 /*
  69  * if needed, get a new MMU context for the mm. otherwise nothing is done.
  70  */
  71
  72 void
  73 get_mmu_context(struct mm_struct *mm)
  74 {
  75         if(mm->context.page_id == NO_CONTEXT)
  76                 alloc_context(mm);
  77 }
  78
  79 /* called by __exit_mm to destroy the used MMU context if any before
  80  * destroying the mm itself. this is only called when the last user of the mm
  81  * drops it.
  82  *
  83  * the only thing we really need to do here is mark the used PID slot
  84  * as empty.
  85  */
  86
  87 void
  88 destroy_context(struct mm_struct *mm)
  89 {
  90         if(mm->context.page_id != NO_CONTEXT) {
  91                 D(printk("destroy_context %d (%p)\n", mm->context.page_id, mm));
  92                 flush_tlb_mm(mm);  /* TODO this might be redundant ? */
  93                 page_id_map[mm->context.page_id] = NULL;
  94         }
  95 }
  96
  97 /* called once during VM initialization, from init.c */
  98
  99 void __init
 100 tlb_init(void)
 101 {
 102         int i;
 103
 104         /* clear the page_id map */
 105
 106         for (i = 1; i < ARRAY_SIZE(page_id_map); i++)
 107                 page_id_map[i] = NULL;
 108
 109         /* invalidate the entire TLB */
 110
 111         flush_tlb_all();
 112
 113         /* the init_mm has context 0 from the boot */
 114
 115         page_id_map[0] = &init_mm;
 116 }