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/config.h>
  27 #include <linux/mm.h>
  28 #include <linux/init.h>
  29
  30 #include <asm/mmu_context.h>
  31 #include <asm/tlbflush.h>
  32
  33 mm_context_t next_mmu_context;
  34 unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
  35 #ifdef FEW_CONTEXTS
  36 atomic_t nr_free_contexts;
  37 struct mm_struct *context_mm[LAST_CONTEXT+1];
  38 void steal_context(void);
  39 #endif /* FEW_CONTEXTS */
  40
  41 /*
  42  * Initialize the context management stuff.
  43  */
  44 void __init
  45 mmu_context_init(void)
  46 {
  47         /*
  48          * Some processors have too few contexts to reserve one for
  49          * init_mm, and require using context 0 for a normal task.
  50          * Other processors reserve the use of context zero for the kernel.
  51          * This code assumes FIRST_CONTEXT < 32.
  52          */
  53         context_map[0] = (1 << FIRST_CONTEXT) - 1;
  54         next_mmu_context = FIRST_CONTEXT;
  55 #ifdef FEW_CONTEXTS
  56         atomic_set(&nr_free_contexts, LAST_CONTEXT - FIRST_CONTEXT + 1);
  57 #endif /* FEW_CONTEXTS */
  58 }
  59
  60 #ifdef FEW_CONTEXTS
  61 /*
  62  * Steal a context from a task that has one at the moment.
  63  * This is only used on 8xx and 4xx and we presently assume that
  64  * they don't do SMP.  If they do then this will have to check
  65  * whether the MM we steal is in use.
  66  * We also assume that this is only used on systems that don't
  67  * use an MMU hash table - this is true for 8xx and 4xx.
  68  * This isn't an LRU system, it just frees up each context in
  69  * turn (sort-of pseudo-random replacement :).  This would be the
  70  * place to implement an LRU scheme if anyone was motivated to do it.
  71  *  -- paulus
  72  */
  73 void
  74 steal_context(void)
  75 {
  76         struct mm_struct *mm;
  77
  78         /* free up context `next_mmu_context' */
  79         /* if we shouldn't free context 0, don't... */
  80         if (next_mmu_context < FIRST_CONTEXT)
  81                 next_mmu_context = FIRST_CONTEXT;
  82         mm = context_mm[next_mmu_context];
  83         flush_tlb_mm(mm);
  84         destroy_context(mm);
  85 }
  86 #endif /* FEW_CONTEXTS */