arch/powerpc/mm/mmu_context_32.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 POWER3 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  *
  15  *  Derived from "arch/i386/mm/init.c"
  16  *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  17  *
  18  *  This program is free software; you can redistribute it and/or
  19  *  modify it under the terms of the GNU General Public License
  20  *  as published by the Free Software Foundation; either version
  21  *  2 of the License, or (at your option) any later version.
  22  *
  23  */
  24
  25 #include <linux/mm.h>
  26 #include <linux/init.h>
  27
  28 #include <asm/mmu_context.h>
  29 #include <asm/tlbflush.h>
  30
  31 unsigned long next_mmu_context;
  32 unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
  33 #ifdef FEW_CONTEXTS
  34 atomic_t nr_free_contexts;
  35 struct mm_struct *context_mm[LAST_CONTEXT+1];
  36 void steal_context(void);
  37 #endif /* FEW_CONTEXTS */
  38
  39 /*
  40  * Initialize the context management stuff.
  41  */
  42 void __init
  43 mmu_context_init(void)
  44 {
  45         /*
  46          * Some processors have too few contexts to reserve one for
  47          * init_mm, and require using context 0 for a normal task.
  48          * Other processors reserve the use of context zero for the kernel.
  49          * This code assumes FIRST_CONTEXT < 32.
  50          */
  51         context_map[0] = (1 << FIRST_CONTEXT) - 1;
  52         next_mmu_context = FIRST_CONTEXT;
  53 #ifdef FEW_CONTEXTS
  54         atomic_set(&nr_free_contexts, LAST_CONTEXT - FIRST_CONTEXT + 1);
  55 #endif /* FEW_CONTEXTS */
  56 }
  57
  58 #ifdef FEW_CONTEXTS
  59 /*
  60  * Steal a context from a task that has one at the moment.
  61  * This is only used on 8xx and 4xx and we presently assume that
  62  * they don't do SMP.  If they do then this will have to check
  63  * whether the MM we steal is in use.
  64  * We also assume that this is only used on systems that don't
  65  * use an MMU hash table - this is true for 8xx and 4xx.
  66  * This isn't an LRU system, it just frees up each context in
  67  * turn (sort-of pseudo-random replacement :).  This would be the
  68  * place to implement an LRU scheme if anyone was motivated to do it.
  69  *  -- paulus
  70  */
  71 void
  72 steal_context(void)
  73 {
  74         struct mm_struct *mm;
  75
  76         /* free up context `next_mmu_context' */
  77         /* if we shouldn't free context 0, don't... */
  78         if (next_mmu_context < FIRST_CONTEXT)
  79                 next_mmu_context = FIRST_CONTEXT;
  80         mm = context_mm[next_mmu_context];
  81         flush_tlb_mm(mm);
  82         destroy_context(mm);
  83 }
  84 #endif /* FEW_CONTEXTS */