mmu_context.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * 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,
 * and 8260 implementations but excludes the 8xx and 4xx.
 *  -- paulus
 *
 *  Derived from arch/ppc/mm/init.c:
 *    Copyright (C) 1995-1996 Gary Thomas ([email protected])
 *
 *  Modifications by Paul Mackerras (PowerMac) ([email protected])
 *  and Cort Dougan (PReP) ([email protected])
 *    Copyright (C) 1996 Paul Mackerras
 *
 *  Derived from "arch/i386/mm/init.c"
 *    Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 */

#include <linux/mm.h>
#include <linux/init.h>
#include <linux/export.h>

#include <asm/mmu_context.h>

/*
 * Room for two PTE pointers, usually the kernel and current user pointers
 * to their respective root page table.
 */
void *abatron_pteptrs[2];

/*
 * 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

static unsigned long next_mmu_context;
static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];

unsigned long __init_new_context(void)
{
	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;

	return ctx;
}
EXPORT_SYMBOL_GPL(__init_new_context);

/*
 * Set up the context for a new address space.
 */
int init_new_context(struct task_struct *t, struct mm_struct *mm)
{
	mm->context.id = __init_new_context();
	mm->context.sr0 = CTX_TO_VSID(mm->context.id, 0);

	if (IS_ENABLED(CONFIG_PPC_KUEP))
		mm->context.sr0 |= SR_NX;
	if (!kuap_is_disabled())
		mm->context.sr0 |= SR_KS;

	return 0;
}

/*
 * Free a context ID. Make sure to call this with preempt disabled!
 */
void __destroy_context(unsigned long ctx)
{
	clear_bit(ctx, context_map);
}
EXPORT_SYMBOL_GPL(__destroy_context);

/*
 * 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) {
		__destroy_context(mm->context.id);
		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;
}

void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next, struct task_struct *tsk)
{
	long id = next->context.id;

	if (id < 0)
		panic("mm_struct %p has no context ID", next);

	isync();

	update_user_segments(next->context.sr0);

	if (IS_ENABLED(CONFIG_BDI_SWITCH))
		abatron_pteptrs[1] = next->pgd;

	if (!mmu_has_feature(MMU_FTR_HPTE_TABLE))
		mtspr(SPRN_SDR1, rol32(__pa(next->pgd), 4) & 0xffff01ff);

	mb();	/* sync */
	isync();
}
EXPORT_SYMBOL(switch_mmu_context);