LXR linux/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
  30struct mm_struct *page_id_map[NUM_PAGEID];
  31static 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
  35static inline void
  36alloc_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
  70void
  71get_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
  85void
  86destroy_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
  97void __init
  98tlb_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}
 115