| /* |
| * 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 DEFINE_SPINLOCK(context_lock); |
| |
| #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; |
| |
| 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_devel("[%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(cpu, mm_cpumask(mm)) |
| __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); |
| |
| /* This will cause the caller to try again */ |
| return MMU_NO_CONTEXT; |
| } |
| #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_devel("[%d] steal context %d from mm @%p\n", cpu, id, mm); |
| |
| /* Flush the TLB for that context */ |
| local_flush_tlb_mm(mm); |
| |
| /* Mark this mm has having no context anymore */ |
| mm->context.id = MMU_NO_CONTEXT; |
| |
| /* 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_devel("[%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_devel(" old context %p active was: %d\n", |
| prev, prev->context.active); |
| #endif |
| WARN_ON(prev->context.active < 1); |
| prev->context.active--; |
| } |
| |
| again: |
| #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); |
| if (id == MMU_NO_CONTEXT) |
| goto again; |
| 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_devel("[%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_devel("[%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 long flags; |
| unsigned int id; |
| |
| if (mm->context.id == MMU_NO_CONTEXT) |
| return; |
| |
| WARN_ON(mm->context.active != 0); |
| |
| spin_lock_irqsave(&context_lock, flags); |
| 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; |
| #endif |
| context_mm[id] = NULL; |
| nr_free_contexts++; |
| } |
| spin_unlock_irqrestore(&context_lock, flags); |
| } |
| |
| #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_devel("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_devel("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 %zu 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; |
| } |
| |