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