arch/powerpc/mm/book3s32/mmu_context.c

   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  * Room for two PTE pointers, usually the kernel and current user pointers
  28  * to their respective root page table.
  29  */
  30 void *abatron_pteptrs[2];
  31
  32 /*
  33  * On 32-bit PowerPC 6xx/7xx/7xxx CPUs, we use a set of 16 VSIDs
  34  * (virtual segment identifiers) for each context.  Although the
  35  * hardware supports 24-bit VSIDs, and thus >1 million contexts,
  36  * we only use 32,768 of them.  That is ample, since there can be
  37  * at most around 30,000 tasks in the system anyway, and it means
  38  * that we can use a bitmap to indicate which contexts are in use.
  39  * Using a bitmap means that we entirely avoid all of the problems
  40  * that we used to have when the context number overflowed,
  41  * particularly on SMP systems.
  42  *  -- paulus.
  43  */
  44 #define NO_CONTEXT              ((unsigned long) -1)
  45 #define LAST_CONTEXT            32767
  46 #define FIRST_CONTEXT           1
  47
  48 static unsigned long next_mmu_context;
  49 static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
  50
  51 unsigned long __init_new_context(void)
  52 {
  53         unsigned long ctx = next_mmu_context;
  54
  55         while (test_and_set_bit(ctx, context_map)) {
  56                 ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx);
  57                 if (ctx > LAST_CONTEXT)
  58                         ctx = 0;
  59         }
  60         next_mmu_context = (ctx + 1) & LAST_CONTEXT;
  61
  62         return ctx;
  63 }
  64 EXPORT_SYMBOL_GPL(__init_new_context);
  65
  66 /*
  67  * Set up the context for a new address space.
  68  */
  69 int init_new_context(struct task_struct *t, struct mm_struct *mm)
  70 {
  71         mm->context.id = __init_new_context();
  72         mm->context.sr0 = CTX_TO_VSID(mm->context.id, 0);
  73
  74         if (IS_ENABLED(CONFIG_PPC_KUEP))
  75                 mm->context.sr0 |= SR_NX;
  76         if (!kuap_is_disabled())
  77                 mm->context.sr0 |= SR_KS;
  78
  79         return 0;
  80 }
  81
  82 /*
  83  * Free a context ID. Make sure to call this with preempt disabled!
  84  */
  85 void __destroy_context(unsigned long ctx)
  86 {
  87         clear_bit(ctx, context_map);
  88 }
  89 EXPORT_SYMBOL_GPL(__destroy_context);
  90
  91 /*
  92  * We're finished using the context for an address space.
  93  */
  94 void destroy_context(struct mm_struct *mm)
  95 {
  96         preempt_disable();
  97         if (mm->context.id != NO_CONTEXT) {
  98                 __destroy_context(mm->context.id);
  99                 mm->context.id = NO_CONTEXT;
 100         }
 101         preempt_enable();
 102 }
 103
 104 /*
 105  * Initialize the context management stuff.
 106  */
 107 void __init mmu_context_init(void)
 108 {
 109         /* Reserve context 0 for kernel use */
 110         context_map[0] = (1 << FIRST_CONTEXT) - 1;
 111         next_mmu_context = FIRST_CONTEXT;
 112 }
 113
 114 void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next, struct task_struct *tsk)
 115 {
 116         long id = next->context.id;
 117
 118         if (id < 0)
 119                 panic("mm_struct %p has no context ID", next);
 120
 121         isync();
 122
 123         update_user_segments(next->context.sr0);
 124
 125         if (IS_ENABLED(CONFIG_BDI_SWITCH))
 126                 abatron_pteptrs[1] = next->pgd;
 127
 128         if (!mmu_has_feature(MMU_FTR_HPTE_TABLE))
 129                 mtspr(SPRN_SDR1, rol32(__pa(next->pgd), 4) & 0xffff01ff);
 130
 131         mb();   /* sync */
 132         isync();
 133 }
 134 EXPORT_SYMBOL(switch_mmu_context);