Benjamin Herrenschmidt | 5e69661 | 2008-12-18 19:13:24 +0000 | [diff] [blame^] | 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 | |
| 60 | static unsigned long next_mmu_context; |
| 61 | static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1]; |
| 62 | |
| 63 | |
| 64 | /* |
| 65 | * Set up the context for a new address space. |
| 66 | */ |
| 67 | int init_new_context(struct task_struct *t, struct mm_struct *mm) |
| 68 | { |
| 69 | unsigned long ctx = next_mmu_context; |
| 70 | |
| 71 | while (test_and_set_bit(ctx, context_map)) { |
| 72 | ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx); |
| 73 | if (ctx > LAST_CONTEXT) |
| 74 | ctx = 0; |
| 75 | } |
| 76 | next_mmu_context = (ctx + 1) & LAST_CONTEXT; |
| 77 | mm->context.id = ctx; |
| 78 | |
| 79 | return 0; |
| 80 | } |
| 81 | |
| 82 | /* |
| 83 | * We're finished using the context for an address space. |
| 84 | */ |
| 85 | void destroy_context(struct mm_struct *mm) |
| 86 | { |
| 87 | preempt_disable(); |
| 88 | if (mm->context.id != NO_CONTEXT) { |
| 89 | clear_bit(mm->context.id, context_map); |
| 90 | mm->context.id = NO_CONTEXT; |
| 91 | } |
| 92 | preempt_enable(); |
| 93 | } |
| 94 | |
| 95 | /* |
| 96 | * Initialize the context management stuff. |
| 97 | */ |
| 98 | void __init mmu_context_init(void) |
| 99 | { |
| 100 | /* Reserve context 0 for kernel use */ |
| 101 | context_map[0] = (1 << FIRST_CONTEXT) - 1; |
| 102 | next_mmu_context = FIRST_CONTEXT; |
| 103 | } |