1 /*
2  * This file contains the routines for handling the MMU.
3  *
4  *    Copyright (C) 2007 Xilinx, Inc.  All rights reserved.
5  *
6  *  Derived from arch/ppc/mm/4xx_mmu.c:
7  *  -- paulus
8  *
9  *  Derived from arch/ppc/mm/init.c:
10  *    Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
11  *
12  *  Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
13  *  and Cort Dougan (PReP) (cort@cs.nmt.edu)
14  *    Copyright (C) 1996 Paul Mackerras
15  *  Amiga/APUS changes by Jesper Skov (jskov@cygnus.co.uk).
16  *
17  *  Derived from "arch/i386/mm/init.c"
18  *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
19  *
20  *  This program is free software; you can redistribute it and/or
21  *  modify it under the terms of the GNU General Public License
22  *  as published by the Free Software Foundation; either version
23  *  2 of the License, or (at your option) any later version.
24  *
25  */
26 
27 #include <linux/mm.h>
28 #include <linux/init.h>
29 
30 #include <asm/tlbflush.h>
31 #include <asm/mmu_context.h>
32 
33 mm_context_t next_mmu_context;
34 unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
35 atomic_t nr_free_contexts;
36 struct mm_struct *context_mm[LAST_CONTEXT+1];
37 
38 /*
39  * Initialize the context management stuff.
40  */
mmu_context_init(void)41 void __init mmu_context_init(void)
42 {
43 	/*
44 	 * The use of context zero is reserved for the kernel.
45 	 * This code assumes FIRST_CONTEXT < 32.
46 	 */
47 	context_map[0] = (1 << FIRST_CONTEXT) - 1;
48 	next_mmu_context = FIRST_CONTEXT;
49 	atomic_set(&nr_free_contexts, LAST_CONTEXT - FIRST_CONTEXT + 1);
50 }
51 
52 /*
53  * Steal a context from a task that has one at the moment.
54  *
55  * This isn't an LRU system, it just frees up each context in
56  * turn (sort-of pseudo-random replacement :).  This would be the
57  * place to implement an LRU scheme if anyone were motivated to do it.
58  */
steal_context(void)59 void steal_context(void)
60 {
61 	struct mm_struct *mm;
62 
63 	/* free up context `next_mmu_context' */
64 	/* if we shouldn't free context 0, don't... */
65 	if (next_mmu_context < FIRST_CONTEXT)
66 		next_mmu_context = FIRST_CONTEXT;
67 	mm = context_mm[next_mmu_context];
68 	flush_tlb_mm(mm);
69 	destroy_context(mm);
70 }
71