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70428da94c
Calling 'mfsr' to get the content of segment registers is heavy, in addition it requires clearing of the 'reserved' bits. In order to avoid this operation, save it in mm context and in thread struct. The saved sr0 is the one used by kernel, this means that on locking entry it can be used as is. For unlocking, the only thing to do is to clear SR_NX. This improves null_syscall selftest by 12 cycles, ie 4%. Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/b02baf2ed8f09bad910dfaeeb7353b2ae6830525.1634627931.git.christophe.leroy@csgroup.eu
135 lines
3.5 KiB
C
135 lines
3.5 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* This file contains the routines for handling the MMU on those
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* PowerPC implementations where the MMU substantially follows the
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* architecture specification. This includes the 6xx, 7xx, 7xxx,
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* and 8260 implementations but excludes the 8xx and 4xx.
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* -- paulus
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*
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* Derived from arch/ppc/mm/init.c:
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* Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
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*
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* Modifications by Paul Mackerras (PowerMac) (paulus@cs.anu.edu.au)
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* and Cort Dougan (PReP) (cort@cs.nmt.edu)
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* Copyright (C) 1996 Paul Mackerras
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*
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* Derived from "arch/i386/mm/init.c"
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* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
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*/
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#include <linux/mm.h>
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#include <linux/init.h>
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#include <linux/export.h>
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#include <asm/mmu_context.h>
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/*
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* Room for two PTE pointers, usually the kernel and current user pointers
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* to their respective root page table.
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*/
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void *abatron_pteptrs[2];
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/*
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* On 32-bit PowerPC 6xx/7xx/7xxx CPUs, we use a set of 16 VSIDs
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* (virtual segment identifiers) for each context. Although the
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* hardware supports 24-bit VSIDs, and thus >1 million contexts,
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* we only use 32,768 of them. That is ample, since there can be
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* at most around 30,000 tasks in the system anyway, and it means
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* that we can use a bitmap to indicate which contexts are in use.
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* Using a bitmap means that we entirely avoid all of the problems
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* that we used to have when the context number overflowed,
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* particularly on SMP systems.
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* -- paulus.
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*/
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#define NO_CONTEXT ((unsigned long) -1)
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#define LAST_CONTEXT 32767
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#define FIRST_CONTEXT 1
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static unsigned long next_mmu_context;
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static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1];
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unsigned long __init_new_context(void)
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{
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unsigned long ctx = next_mmu_context;
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while (test_and_set_bit(ctx, context_map)) {
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ctx = find_next_zero_bit(context_map, LAST_CONTEXT+1, ctx);
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if (ctx > LAST_CONTEXT)
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ctx = 0;
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}
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next_mmu_context = (ctx + 1) & LAST_CONTEXT;
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return ctx;
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}
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EXPORT_SYMBOL_GPL(__init_new_context);
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/*
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* Set up the context for a new address space.
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*/
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int init_new_context(struct task_struct *t, struct mm_struct *mm)
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{
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mm->context.id = __init_new_context();
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mm->context.sr0 = CTX_TO_VSID(mm->context.id, 0);
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if (!kuep_is_disabled())
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mm->context.sr0 |= SR_NX;
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if (!kuap_is_disabled())
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mm->context.sr0 |= SR_KS;
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return 0;
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}
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/*
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* Free a context ID. Make sure to call this with preempt disabled!
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*/
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void __destroy_context(unsigned long ctx)
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{
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clear_bit(ctx, context_map);
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}
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EXPORT_SYMBOL_GPL(__destroy_context);
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/*
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* We're finished using the context for an address space.
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*/
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void destroy_context(struct mm_struct *mm)
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{
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preempt_disable();
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if (mm->context.id != NO_CONTEXT) {
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__destroy_context(mm->context.id);
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mm->context.id = NO_CONTEXT;
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}
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preempt_enable();
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}
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/*
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* Initialize the context management stuff.
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*/
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void __init mmu_context_init(void)
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{
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/* Reserve context 0 for kernel use */
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context_map[0] = (1 << FIRST_CONTEXT) - 1;
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next_mmu_context = FIRST_CONTEXT;
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}
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void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next, struct task_struct *tsk)
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{
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long id = next->context.id;
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if (id < 0)
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panic("mm_struct %p has no context ID", next);
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isync();
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update_user_segments(next->context.sr0);
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if (IS_ENABLED(CONFIG_BDI_SWITCH))
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abatron_pteptrs[1] = next->pgd;
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if (!mmu_has_feature(MMU_FTR_HPTE_TABLE))
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mtspr(SPRN_SDR1, rol32(__pa(next->pgd), 4) & 0xffff01ff);
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mb(); /* sync */
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isync();
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}
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EXPORT_SYMBOL(switch_mmu_context);
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