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/*
* This file contains the routines for handling the MMU on those
* PowerPC implementations where the MMU substantially follows the
* architecture specification. This includes the 6xx, 7xx, 7xxx,
* 8260, and POWER3 implementations but excludes the 8xx and 4xx.
* -- paulus
*
* Derived from arch/ppc/mm/init.c:
* Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
*
* Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
* and Cort Dougan (PReP) (cort@cs.nmt.edu)
* Copyright (C) 1996 Paul Mackerras
*
* Derived from "arch/i386/mm/init.c"
* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*
*/
#include <linux/mm.h>
#include <linux/init.h>
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
/*
* On 32-bit PowerPC 6xx/7xx/7xxx CPUs, we use a set of 16 VSIDs
* (virtual segment identifiers) for each context. Although the
* hardware supports 24-bit VSIDs, and thus >1 million contexts,
* we only use 32,768 of them. That is ample, since there can be
* at most around 30,000 tasks in the system anyway, and it means
* that we can use a bitmap to indicate which contexts are in use.
* Using a bitmap means that we entirely avoid all of the problems
* that we used to have when the context number overflowed,
* particularly on SMP systems.
* -- paulus.
*/
#define NO_CONTEXT ((unsigned long) -1)
#define LAST_CONTEXT 32767
#define FIRST_CONTEXT 1
/*
* This function defines the mapping from contexts to VSIDs (virtual
* segment IDs). We use a skew on both the context and the high 4 bits
* of the 32-bit virtual address (the "effective segment ID") in order
* to spread out the entries in the MMU hash table. Note, if this
* function is changed then arch/ppc/mm/hashtable.S will have to be
* changed to correspond.
*
*
* CTX_TO_VSID(ctx, va) (((ctx) * (897 * 16) + ((va) >> 28) * 0x111) \
* & 0xffffff)
*/
static unsigned long next_mmu_context;
static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
/*
* Set up the context for a new address space.
*/
int init_new_context(struct task_struct *t, struct mm_struct *mm)
{
unsigned long ctx = next_mmu_context;
while (test_and_set_bit(ctx, context_map)) {
ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx);
if (ctx > LAST_CONTEXT)
ctx = 0;
}
next_mmu_context = (ctx + 1) & LAST_CONTEXT;
mm->context.id = ctx;
return 0;
}
/*
* We're finished using the context for an address space.
*/
void destroy_context(struct mm_struct *mm)
{
preempt_disable();
if (mm->context.id != NO_CONTEXT) {
clear_bit(mm->context.id, context_map);
mm->context.id = NO_CONTEXT;
}
preempt_enable();
}
/*
* Initialize the context management stuff.
*/
void __init mmu_context_init(void)
{
/* Reserve context 0 for kernel use */
context_map[0] = (1 << FIRST_CONTEXT) - 1;
next_mmu_context = FIRST_CONTEXT;
}
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