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 */
 30void *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
 48static unsigned long next_mmu_context;
 49static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
 50
 51unsigned 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}
 64EXPORT_SYMBOL_GPL(__init_new_context);
 65
 66/*
 67 * Set up the context for a new address space.
 68 */
 69int 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 */
 85void __destroy_context(unsigned long ctx)
 86{
 87	clear_bit(ctx, context_map);
 88}
 89EXPORT_SYMBOL_GPL(__destroy_context);
 90
 91/*
 92 * We're finished using the context for an address space.
 93 */
 94void 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 */
107void __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
114void 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}
134EXPORT_SYMBOL(switch_mmu_context);