arch/ppc/mm/mmu_context.c

   1 /*
   2  * This file contains the routines for handling the MMU on those
   3  * PowerPC implementations where the MMU substantially follows the
   4  * architecture specification.  This includes the 6xx, 7xx, 7xxx,
   5  * 8260, and 83xx implementations but excludes the 8xx and 4xx.
   6  *  -- paulus
   7  *
   8  *  Derived from arch/ppc/mm/init.c:
   9  *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
  10  *
  11  *  Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
  12  *  and Cort Dougan (PReP) (cort@cs.nmt.edu)
  13  *    Copyright (C) 1996 Paul Mackerras
  14  *  Amiga/APUS changes by Jesper Skov (jskov@cygnus.co.uk).
  15  *
  16  *  Derived from "arch/i386/mm/init.c"
  17  *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  18  *
  19  *  This program is free software; you can redistribute it and/or
  20  *  modify it under the terms of the GNU General Public License
  21  *  as published by the Free Software Foundation; either version
  22  *  2 of the License, or (at your option) any later version.
  23  *
  24  */
  25
  26 #include <linux/mm.h>
  27 #include <linux/init.h>
  28
  29 #include <asm/mmu_context.h>
  30 #include <asm/tlbflush.h>
  31
  32 unsigned long next_mmu_context;
  33 unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
  34 #ifdef FEW_CONTEXTS
  35 atomic_t nr_free_contexts;
  36 struct mm_struct *context_mm[LAST_CONTEXT+1];
  37 void steal_context(void);
  38 #endif /* FEW_CONTEXTS */
  39
  40 /*
  41  * Initialize the context management stuff.
  42  */
  43 void __init
  44 mmu_context_init(void)
  45 {
  46         /*
  47          * Some processors have too few contexts to reserve one for
  48          * init_mm, and require using context 0 for a normal task.
  49          * Other processors reserve the use of context zero for the kernel.
  50          * This code assumes FIRST_CONTEXT < 32.
  51          */
  52         context_map[0] = (1 << FIRST_CONTEXT) - 1;
  53         next_mmu_context = FIRST_CONTEXT;
  54 #ifdef FEW_CONTEXTS
  55         atomic_set(&nr_free_contexts, LAST_CONTEXT - FIRST_CONTEXT + 1);
  56 #endif /* FEW_CONTEXTS */
  57 }
  58
  59 #ifdef FEW_CONTEXTS
  60 /*
  61  * Steal a context from a task that has one at the moment.
  62  * This is only used on 8xx and 4xx and we presently assume that
  63  * they don't do SMP.  If they do then this will have to check
  64  * whether the MM we steal is in use.
  65  * We also assume that this is only used on systems that don't
  66  * use an MMU hash table - this is true for 8xx and 4xx.
  67  * This isn't an LRU system, it just frees up each context in
  68  * turn (sort-of pseudo-random replacement :).  This would be the
  69  * place to implement an LRU scheme if anyone was motivated to do it.
  70  *  -- paulus
  71  */
  72 void
  73 steal_context(void)
  74 {
  75         struct mm_struct *mm;
  76
  77         /* free up context `next_mmu_context' */
  78         /* if we shouldn't free context 0, don't... */
  79         if (next_mmu_context < FIRST_CONTEXT)
  80                 next_mmu_context = FIRST_CONTEXT;
  81         mm = context_mm[next_mmu_context];
  82         flush_tlb_mm(mm);
  83         destroy_context(mm);
  84 }
  85 #endif /* FEW_CONTEXTS */