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/* 32 * On 32-bit PowerPC 6xx/7xx/7xxx CPUs, we use a set of 16 VSIDs 33 * (virtual segment identifiers) for each context. Although the 34 * hardware supports 24-bit VSIDs, and thus >1 million contexts, 35 * we only use 32,768 of them. That is ample, since there can be 36 * at most around 30,000 tasks in the system anyway, and it means 37 * that we can use a bitmap to indicate which contexts are in use. 38 * Using a bitmap means that we entirely avoid all of the problems 39 * that we used to have when the context number overflowed, 40 * particularly on SMP systems. 41 * -- paulus. 42 */ 43#define NO_CONTEXT ((unsigned long) -1) 44#define LAST_CONTEXT 32767 45#define FIRST_CONTEXT 1 46 47/* 48 * This function defines the mapping from contexts to VSIDs (virtual 49 * segment IDs). We use a skew on both the context and the high 4 bits 50 * of the 32-bit virtual address (the "effective segment ID") in order 51 * to spread out the entries in the MMU hash table. Note, if this 52 * function is changed then arch/ppc/mm/hashtable.S will have to be 53 * changed to correspond. 54 * 55 * 56 * CTX_TO_VSID(ctx, va) (((ctx) * (897 * 16) + ((va) >> 28) * 0x111) \ 57 * & 0xffffff) 58 */ 59 60static unsigned long next_mmu_context; 61static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1]; 62 63unsigned long __init_new_context(void) 64{ 65 unsigned long ctx = next_mmu_context; 66 67 while (test_and_set_bit(ctx, context_map)) { 68 ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx); 69 if (ctx > LAST_CONTEXT) 70 ctx = 0; 71 } 72 next_mmu_context = (ctx + 1) & LAST_CONTEXT; 73 74 return ctx; 75} 76EXPORT_SYMBOL_GPL(__init_new_context); 77 78/* 79 * Set up the context for a new address space. 80 */ 81int init_new_context(struct task_struct *t, struct mm_struct *mm) 82{ 83 mm->context.id = __init_new_context(); 84 85 return 0; 86} 87 88/* 89 * Free a context ID. Make sure to call this with preempt disabled! 90 */ 91void __destroy_context(unsigned long ctx) 92{ 93 clear_bit(ctx, context_map); 94} 95EXPORT_SYMBOL_GPL(__destroy_context); 96 97/* 98 * We're finished using the context for an address space. 99 */ 100void destroy_context(struct mm_struct *mm) 101{ 102 preempt_disable(); 103 if (mm->context.id != NO_CONTEXT) { 104 __destroy_context(mm->context.id); 105 mm->context.id = NO_CONTEXT; 106 } 107 preempt_enable(); 108} 109 110/* 111 * Initialize the context management stuff. 112 */ 113void __init mmu_context_init(void) 114{ 115 /* Reserve context 0 for kernel use */ 116 context_map[0] = (1 << FIRST_CONTEXT) - 1; 117 next_mmu_context = FIRST_CONTEXT; 118} 119