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Diffstat (limited to '')
| -rw-r--r-- | arch/powerpc/mm/mmu_context_nohash.c | 397 |
1 files changed, 397 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 000000000000..52a0cfc38b64 --- /dev/null +++ b/arch/powerpc/mm/mmu_context_nohash.c @@ -0,0 +1,397 @@ +/* + * 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. + * + * TODO: + * + * - The global context lock will not scale very well + * - The maps should be dynamically allocated to allow for processors + * that support more PID bits at runtime + * - Implement flush_tlb_mm() by making the context stale and picking + * a new one + * - More aggressively clear stale map bits and maybe find some way to + * also clear mm->cpu_vm_mask bits when processes are migrated + */ + +#undef DEBUG +#define DEBUG_STEAL_ONLY +#undef DEBUG_MAP_CONSISTENCY +/*#define DEBUG_CLAMP_LAST_CONTEXT 15 */ + +#include <linux/kernel.h> +#include <linux/mm.h> +#include <linux/init.h> +#include <linux/spinlock.h> +#include <linux/bootmem.h> +#include <linux/notifier.h> +#include <linux/cpu.h> + +#include <asm/mmu_context.h> +#include <asm/tlbflush.h> + +static unsigned int first_context, last_context; +static unsigned int next_context, nr_free_contexts; +static unsigned long *context_map; +static unsigned long *stale_map[NR_CPUS]; +static struct mm_struct **context_mm; +static spinlock_t context_lock = SPIN_LOCK_UNLOCKED; + +#define CTX_MAP_SIZE \ + (sizeof(unsigned long) * (last_context / BITS_PER_LONG + 1)) + + +/* Steal a context from a task that has one at the moment. + * + * This is used when we are running out of available PID numbers + * on the processors. + * + * 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 + * + * For context stealing, we use a slightly different approach for + * SMP and UP. Basically, the UP one is simpler and doesn't use + * the stale map as we can just flush the local CPU + * -- benh + */ +#ifdef CONFIG_SMP +static unsigned int steal_context_smp(unsigned int id) +{ + struct mm_struct *mm; + unsigned int cpu, max; + + again: + max = last_context - first_context; + + /* Attempt to free next_context first and then loop until we manage */ + while (max--) { + /* Pick up the victim mm */ + mm = context_mm[id]; + + /* We have a candidate victim, check if it's active, on SMP + * we cannot steal active contexts + */ + if (mm->context.active) { + id++; + if (id > last_context) + id = first_context; + continue; + } + pr_debug("[%d] steal context %d from mm @%p\n", + smp_processor_id(), id, mm); + + /* Mark this mm has having no context anymore */ + mm->context.id = MMU_NO_CONTEXT; + + /* Mark it stale on all CPUs that used this mm */ + for_each_cpu_mask_nr(cpu, mm->cpu_vm_mask) + __set_bit(id, stale_map[cpu]); + return id; + } + + /* This will happen if you have more CPUs than available contexts, + * all we can do here is wait a bit and try again + */ + spin_unlock(&context_lock); + cpu_relax(); + spin_lock(&context_lock); + goto again; +} +#endif /* CONFIG_SMP */ + +/* Note that this will also be called on SMP if all other CPUs are + * offlined, which means that it may be called for cpu != 0. For + * this to work, we somewhat assume that CPUs that are onlined + * come up with a fully clean TLB (or are cleaned when offlined) + */ +static unsigned int steal_context_up(unsigned int id) +{ + struct mm_struct *mm; + int cpu = smp_processor_id(); + + /* Pick up the victim mm */ + mm = context_mm[id]; + + pr_debug("[%d] steal context %d from mm @%p\n", cpu, id, mm); + + /* Mark this mm has having no context anymore */ + mm->context.id = MMU_NO_CONTEXT; + + /* Flush the TLB for that context */ + local_flush_tlb_mm(mm); + + /* XXX This clear should ultimately be part of local_flush_tlb_mm */ + __clear_bit(id, stale_map[cpu]); + + return id; +} + +#ifdef DEBUG_MAP_CONSISTENCY +static void context_check_map(void) +{ + unsigned int id, nrf, nact; + + nrf = nact = 0; + for (id = first_context; id <= last_context; id++) { + int used = test_bit(id, context_map); + if (!used) + nrf++; + if (used != (context_mm[id] != NULL)) + pr_err("MMU: Context %d is %s and MM is %p !\n", + id, used ? "used" : "free", context_mm[id]); + if (context_mm[id] != NULL) + nact += context_mm[id]->context.active; + } + if (nrf != nr_free_contexts) { + pr_err("MMU: Free context count out of sync ! (%d vs %d)\n", + nr_free_contexts, nrf); + nr_free_contexts = nrf; + } + if (nact > num_online_cpus()) + pr_err("MMU: More active contexts than CPUs ! (%d vs %d)\n", + nact, num_online_cpus()); + if (first_context > 0 && !test_bit(0, context_map)) + pr_err("MMU: Context 0 has been freed !!!\n"); +} +#else +static void context_check_map(void) { } +#endif + +void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next) +{ + unsigned int id, cpu = smp_processor_id(); + unsigned long *map; + + /* No lockless fast path .. yet */ + spin_lock(&context_lock); + +#ifndef DEBUG_STEAL_ONLY + pr_debug("[%d] activating context for mm @%p, active=%d, id=%d\n", + cpu, next, next->context.active, next->context.id); +#endif + +#ifdef CONFIG_SMP + /* Mark us active and the previous one not anymore */ + next->context.active++; + if (prev) { +#ifndef DEBUG_STEAL_ONLY + pr_debug(" old context %p active was: %d\n", + prev, prev->context.active); +#endif + WARN_ON(prev->context.active < 1); + prev->context.active--; + } +#endif /* CONFIG_SMP */ + + /* If we already have a valid assigned context, skip all that */ + id = next->context.id; + if (likely(id != MMU_NO_CONTEXT)) + goto ctxt_ok; + + /* We really don't have a context, let's try to acquire one */ + id = next_context; + if (id > last_context) + id = first_context; + map = context_map; + + /* No more free contexts, let's try to steal one */ + if (nr_free_contexts == 0) { +#ifdef CONFIG_SMP + if (num_online_cpus() > 1) { + id = steal_context_smp(id); + goto stolen; + } +#endif /* CONFIG_SMP */ + id = steal_context_up(id); + goto stolen; + } + nr_free_contexts--; + + /* We know there's at least one free context, try to find it */ + while (__test_and_set_bit(id, map)) { + id = find_next_zero_bit(map, last_context+1, id); + if (id > last_context) + id = first_context; + } + stolen: + next_context = id + 1; + context_mm[id] = next; + next->context.id = id; + +#ifndef DEBUG_STEAL_ONLY + pr_debug("[%d] picked up new id %d, nrf is now %d\n", + cpu, id, nr_free_contexts); +#endif + + context_check_map(); + ctxt_ok: + + /* If that context got marked stale on this CPU, then flush the + * local TLB for it and unmark it before we use it + */ + if (test_bit(id, stale_map[cpu])) { + pr_debug("[%d] flushing stale context %d for mm @%p !\n", + cpu, id, next); + local_flush_tlb_mm(next); + + /* XXX This clear should ultimately be part of local_flush_tlb_mm */ + __clear_bit(id, stale_map[cpu]); + } + + /* Flick the MMU and release lock */ + set_context(id, next->pgd); + spin_unlock(&context_lock); +} + +/* + * Set up the context for a new address space. + */ +int init_new_context(struct task_struct *t, struct mm_struct *mm) +{ + mm->context.id = MMU_NO_CONTEXT; + mm->context.active = 0; + + return 0; +} + +/* + * We're finished using the context for an address space. + */ +void destroy_context(struct mm_struct *mm) +{ + unsigned int id; + + if (mm->context.id == MMU_NO_CONTEXT) + return; + + WARN_ON(mm->context.active != 0); + + spin_lock(&context_lock); + id = mm->context.id; + if (id != MMU_NO_CONTEXT) { + __clear_bit(id, context_map); + mm->context.id = MMU_NO_CONTEXT; +#ifdef DEBUG_MAP_CONSISTENCY + mm->context.active = 0; + context_mm[id] = NULL; +#endif + nr_free_contexts++; + } + spin_unlock(&context_lock); +} + +#ifdef CONFIG_SMP + +static int __cpuinit mmu_context_cpu_notify(struct notifier_block *self, + unsigned long action, void *hcpu) +{ + unsigned int cpu = (unsigned int)(long)hcpu; + + /* We don't touch CPU 0 map, it's allocated at aboot and kept + * around forever + */ + if (cpu == 0) + return NOTIFY_OK; + + switch (action) { + case CPU_ONLINE: + case CPU_ONLINE_FROZEN: + pr_debug("MMU: Allocating stale context map for CPU %d\n", cpu); + stale_map[cpu] = kzalloc(CTX_MAP_SIZE, GFP_KERNEL); + break; +#ifdef CONFIG_HOTPLUG_CPU + case CPU_DEAD: + case CPU_DEAD_FROZEN: + pr_debug("MMU: Freeing stale context map for CPU %d\n", cpu); + kfree(stale_map[cpu]); + stale_map[cpu] = NULL; + break; +#endif + } + return NOTIFY_OK; +} + +static struct notifier_block __cpuinitdata mmu_context_cpu_nb = { + .notifier_call = mmu_context_cpu_notify, +}; + +#endif /* CONFIG_SMP */ + +/* + * Initialize the context management stuff. + */ +void __init mmu_context_init(void) +{ + /* Mark init_mm as being active on all possible CPUs since + * we'll get called with prev == init_mm the first time + * we schedule on a given CPU + */ + init_mm.context.active = NR_CPUS; + + /* + * 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 + */ + if (mmu_has_feature(MMU_FTR_TYPE_8xx)) { + first_context = 0; + last_context = 15; + } else { + first_context = 1; + last_context = 255; + } + +#ifdef DEBUG_CLAMP_LAST_CONTEXT + last_context = DEBUG_CLAMP_LAST_CONTEXT; +#endif + /* + * Allocate the maps used by context management + */ + context_map = alloc_bootmem(CTX_MAP_SIZE); + context_mm = alloc_bootmem(sizeof(void *) * (last_context + 1)); + stale_map[0] = alloc_bootmem(CTX_MAP_SIZE); + +#ifdef CONFIG_SMP + register_cpu_notifier(&mmu_context_cpu_nb); +#endif + + printk(KERN_INFO + "MMU: Allocated %d bytes of context maps for %d contexts\n", + 2 * CTX_MAP_SIZE + (sizeof(void *) * (last_context + 1)), + last_context - first_context + 1); + + /* + * 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_context = first_context; + nr_free_contexts = last_context - first_context + 1; +} + |