diff options
Diffstat (limited to 'arch/powerpc/mm/mmu_context_nohash.c')
-rw-r--r-- | arch/powerpc/mm/mmu_context_nohash.c | 162 |
1 files changed, 162 insertions, 0 deletions
diff --git a/arch/powerpc/mm/mmu_context_nohash.c b/arch/powerpc/mm/mmu_context_nohash.c new file mode 100644 index 00000000000..00e02150abe --- /dev/null +++ b/arch/powerpc/mm/mmu_context_nohash.c @@ -0,0 +1,162 @@ +/* + * This file contains the routines for handling the MMU on those + * PowerPC implementations where the MMU is not using the hash + * table, such as 8xx, 4xx, BookE's etc... + * + * Copyright 2008 Ben Herrenschmidt <benh@kernel.crashing.org> + * IBM Corp. + * + * Derived from previous arch/powerpc/mm/mmu_context.c + * and arch/powerpc/include/asm/mmu_context.h + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; either version + * 2 of the License, or (at your option) any later version. + * + */ + +#include <linux/mm.h> +#include <linux/init.h> + +#include <asm/mmu_context.h> +#include <asm/tlbflush.h> + +/* + * The MPC8xx has only 16 contexts. We rotate through them on each + * task switch. A better way would be to keep track of tasks that + * own contexts, and implement an LRU usage. That way very active + * tasks don't always have to pay the TLB reload overhead. The + * kernel pages are mapped shared, so the kernel can run on behalf + * of any task that makes a kernel entry. Shared does not mean they + * are not protected, just that the ASID comparison is not performed. + * -- Dan + * + * The IBM4xx has 256 contexts, so we can just rotate through these + * as a way of "switching" contexts. If the TID of the TLB is zero, + * the PID/TID comparison is disabled, so we can use a TID of zero + * to represent all kernel pages as shared among all contexts. + * -- Dan + */ + +#ifdef CONFIG_8xx +#define NO_CONTEXT 16 +#define LAST_CONTEXT 15 +#define FIRST_CONTEXT 0 + +#elif defined(CONFIG_4xx) +#define NO_CONTEXT 256 +#define LAST_CONTEXT 255 +#define FIRST_CONTEXT 1 + +#elif defined(CONFIG_E200) || defined(CONFIG_E500) +#define NO_CONTEXT 256 +#define LAST_CONTEXT 255 +#define FIRST_CONTEXT 1 + +#else +#error Unsupported processor type +#endif + +static unsigned long next_mmu_context; +static unsigned long context_map[LAST_CONTEXT / BITS_PER_LONG + 1]; +static atomic_t nr_free_contexts; +static struct mm_struct *context_mm[LAST_CONTEXT+1]; +static void steal_context(void); + +/* Steal a context from a task that has one at the moment. + * This is only used on 8xx and 4xx and we presently assume that + * they don't do SMP. If they do then this will have to check + * whether the MM we steal is in use. + * We also assume that this is only used on systems that don't + * use an MMU hash table - this is true for 8xx and 4xx. + * This isn't an LRU system, it just frees up each context in + * turn (sort-of pseudo-random replacement :). This would be the + * place to implement an LRU scheme if anyone was motivated to do it. + * -- paulus + */ +static void steal_context(void) +{ + struct mm_struct *mm; + + /* free up context `next_mmu_context' */ + /* if we shouldn't free context 0, don't... */ + if (next_mmu_context < FIRST_CONTEXT) + next_mmu_context = FIRST_CONTEXT; + mm = context_mm[next_mmu_context]; + flush_tlb_mm(mm); + destroy_context(mm); +} + + +/* + * Get a new mmu context for the address space described by `mm'. + */ +static inline void get_mmu_context(struct mm_struct *mm) +{ + unsigned long ctx; + + if (mm->context.id != NO_CONTEXT) + return; + + while (atomic_dec_if_positive(&nr_free_contexts) < 0) + steal_context(); + + 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; + mm->context.id = ctx; + context_mm[ctx] = mm; +} + +void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next) +{ + get_mmu_context(next); + + set_context(next->context.id, next->pgd); +} + +/* + * Set up the context for a new address space. + */ +int init_new_context(struct task_struct *t, struct mm_struct *mm) +{ + mm->context.id = NO_CONTEXT; + return 0; +} + +/* + * 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) { + clear_bit(mm->context.id, context_map); + mm->context.id = NO_CONTEXT; + atomic_inc(&nr_free_contexts); + } + preempt_enable(); +} + + +/* + * Initialize the context management stuff. + */ +void __init mmu_context_init(void) +{ + /* + * Some processors have too few contexts to reserve one for + * init_mm, and require using context 0 for a normal task. + * Other processors reserve the use of context zero for the kernel. + * This code assumes FIRST_CONTEXT < 32. + */ + context_map[0] = (1 << FIRST_CONTEXT) - 1; + next_mmu_context = FIRST_CONTEXT; + atomic_set(&nr_free_contexts, LAST_CONTEXT - FIRST_CONTEXT + 1); +} + |