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113 lines
3.1 KiB
113 lines
3.1 KiB
// SPDX-License-Identifier: GPL-2.0-or-later |
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/* |
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* This file contains the routines for handling the MMU on those |
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* PowerPC implementations where the MMU substantially follows the |
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* architecture specification. This includes the 6xx, 7xx, 7xxx, |
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* and 8260 implementations but excludes the 8xx and 4xx. |
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* -- paulus |
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* |
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* Derived from arch/ppc/mm/init.c: |
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* Copyright (C) 1995-1996 Gary Thomas ([email protected]) |
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* |
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* Modifications by Paul Mackerras (PowerMac) ([email protected]) |
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* and Cort Dougan (PReP) ([email protected]) |
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* Copyright (C) 1996 Paul Mackerras |
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* |
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* Derived from "arch/i386/mm/init.c" |
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* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds |
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*/ |
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#include <linux/mm.h> |
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#include <linux/init.h> |
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#include <linux/export.h> |
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#include <asm/mmu_context.h> |
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/* |
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* On 32-bit PowerPC 6xx/7xx/7xxx CPUs, we use a set of 16 VSIDs |
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* (virtual segment identifiers) for each context. Although the |
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* hardware supports 24-bit VSIDs, and thus >1 million contexts, |
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* we only use 32,768 of them. That is ample, since there can be |
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* at most around 30,000 tasks in the system anyway, and it means |
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* that we can use a bitmap to indicate which contexts are in use. |
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* Using a bitmap means that we entirely avoid all of the problems |
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* that we used to have when the context number overflowed, |
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* particularly on SMP systems. |
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* -- paulus. |
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*/ |
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#define NO_CONTEXT ((unsigned long) -1) |
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#define LAST_CONTEXT 32767 |
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#define FIRST_CONTEXT 1 |
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/* |
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* This function defines the mapping from contexts to VSIDs (virtual |
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* segment IDs). We use a skew on both the context and the high 4 bits |
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* of the 32-bit virtual address (the "effective segment ID") in order |
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* to spread out the entries in the MMU hash table. Note, if this |
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* function is changed then arch/ppc/mm/hashtable.S will have to be |
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* changed to correspond. |
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* |
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* |
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* CTX_TO_VSID(ctx, va) (((ctx) * (897 * 16) + ((va) >> 28) * 0x111) \ |
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* & 0xffffff) |
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*/ |
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static unsigned long next_mmu_context; |
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static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1]; |
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unsigned long __init_new_context(void) |
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{ |
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unsigned long ctx = next_mmu_context; |
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while (test_and_set_bit(ctx, context_map)) { |
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ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx); |
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if (ctx > LAST_CONTEXT) |
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ctx = 0; |
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} |
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next_mmu_context = (ctx + 1) & LAST_CONTEXT; |
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return ctx; |
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} |
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EXPORT_SYMBOL_GPL(__init_new_context); |
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/* |
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* Set up the context for a new address space. |
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*/ |
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int init_new_context(struct task_struct *t, struct mm_struct *mm) |
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{ |
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mm->context.id = __init_new_context(); |
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return 0; |
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} |
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/* |
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* Free a context ID. Make sure to call this with preempt disabled! |
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*/ |
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void __destroy_context(unsigned long ctx) |
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{ |
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clear_bit(ctx, context_map); |
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} |
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EXPORT_SYMBOL_GPL(__destroy_context); |
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/* |
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* We're finished using the context for an address space. |
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*/ |
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void destroy_context(struct mm_struct *mm) |
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{ |
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preempt_disable(); |
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if (mm->context.id != NO_CONTEXT) { |
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__destroy_context(mm->context.id); |
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mm->context.id = NO_CONTEXT; |
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} |
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preempt_enable(); |
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} |
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/* |
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* Initialize the context management stuff. |
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*/ |
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void __init mmu_context_init(void) |
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{ |
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/* Reserve context 0 for kernel use */ |
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context_map[0] = (1 << FIRST_CONTEXT) - 1; |
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next_mmu_context = FIRST_CONTEXT; |
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}
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