LXR linux/arch/powerpc/mm/book3s32/mmu

   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*
   3 * This file contains the routines for handling the MMU on those
   4 * PowerPC implementations where the MMU substantially follows the
   5 * architecture specification.  This includes the 6xx, 7xx, 7xxx,
   6 * and 8260 implementations but excludes the 8xx and 4xx.
   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 *
  16 *  Derived from "arch/i386/mm/init.c"
  17 *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  18 */
  19
  20#include <linux/mm.h>
  21#include <linux/init.h>
  22#include <linux/export.h>
  23
  24#include <asm/mmu_context.h>
  25
  26/*
  27 * On 32-bit PowerPC 6xx/7xx/7xxx CPUs, we use a set of 16 VSIDs
  28 * (virtual segment identifiers) for each context.  Although the
  29 * hardware supports 24-bit VSIDs, and thus >1 million contexts,
  30 * we only use 32,768 of them.  That is ample, since there can be
  31 * at most around 30,000 tasks in the system anyway, and it means
  32 * that we can use a bitmap to indicate which contexts are in use.
  33 * Using a bitmap means that we entirely avoid all of the problems
  34 * that we used to have when the context number overflowed,
  35 * particularly on SMP systems.
  36 *  -- paulus.
  37 */
  38#define NO_CONTEXT              ((unsigned long) -1)
  39#define LAST_CONTEXT            32767
  40#define FIRST_CONTEXT           1
  41
  42/*
  43 * This function defines the mapping from contexts to VSIDs (virtual
  44 * segment IDs).  We use a skew on both the context and the high 4 bits
  45 * of the 32-bit virtual address (the "effective segment ID") in order
  46 * to spread out the entries in the MMU hash table.  Note, if this
  47 * function is changed then arch/ppc/mm/hashtable.S will have to be
  48 * changed to correspond.
  49 *
  50 *
  51 * CTX_TO_VSID(ctx, va) (((ctx) * (897 * 16) + ((va) >> 28) * 0x111) \
  52 *                               & 0xffffff)
  53 */
  54
  55static unsigned long next_mmu_context;
  56static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
  57
  58unsigned long __init_new_context(void)
  59{
  60        unsigned long ctx = next_mmu_context;
  61
  62        while (test_and_set_bit(ctx, context_map)) {
  63                ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx);
  64                if (ctx > LAST_CONTEXT)
  65                        ctx = 0;
  66        }
  67        next_mmu_context = (ctx + 1) & LAST_CONTEXT;
  68
  69        return ctx;
  70}
  71EXPORT_SYMBOL_GPL(__init_new_context);
  72
  73/*
  74 * Set up the context for a new address space.
  75 */
  76int init_new_context(struct task_struct *t, struct mm_struct *mm)
  77{
  78        mm->context.id = __init_new_context();
  79
  80        return 0;
  81}
  82
  83/*
  84 * Free a context ID. Make sure to call this with preempt disabled!
  85 */
  86void __destroy_context(unsigned long ctx)
  87{
  88        clear_bit(ctx, context_map);
  89}
  90EXPORT_SYMBOL_GPL(__destroy_context);
  91
  92/*
  93 * We're finished using the context for an address space.
  94 */
  95void destroy_context(struct mm_struct *mm)
  96{
  97        preempt_disable();
  98        if (mm->context.id != NO_CONTEXT) {
  99                __destroy_context(mm->context.id);
 100                mm->context.id = NO_CONTEXT;
 101        }
 102        preempt_enable();
 103}
 104
 105/*
 106 * Initialize the context management stuff.
 107 */
 108void __init mmu_context_init(void)
 109{
 110        /* Reserve context 0 for kernel use */
 111        context_map[0] = (1 << FIRST_CONTEXT) - 1;
 112        next_mmu_context = FIRST_CONTEXT;
 113}
 114