arch/powerpc/mm/mmu_context_nohash.c - kernel/common - Git at Google

 /*
  * 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 <[email protected]>
  *                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
  */

 //#define DEBUG_MAP_CONSISTENCY
 //#define DEBUG_CLAMP_LAST_CONTEXT   31
 //#define DEBUG_HARDER

 /* We don't use DEBUG because it tends to be compiled in always nowadays
  * and this would generate way too much output
  */
 #ifdef DEBUG_HARDER
 #define pr_hard(args...)	printk(KERN_DEBUG args)
 #define pr_hardcont(args...)	printk(KERN_CONT args)
 #else
 #define pr_hard(args...)	do { } while(0)
 #define pr_hardcont(args...)	do { } while(0)
 #endif

 #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 <linux/slab.h>

 #include <asm/mmu_context.h>
 #include <asm/tlbflush.h>

 #include "mmu_decl.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_RAW_SPINLOCK(context_lock);
 static bool no_selective_tlbil;

 #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, i;

 	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_hardcont(" | steal %d from 0x%p", 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 threaded
 		 * implementations, we set it on all threads on each core
 		 * represented in the mask. A future implementation will use
 		 * a core map instead but this will do for now.
 		 */
 		for_each_cpu(cpu, mm_cpumask(mm)) {
 			for (i = cpu_first_thread_sibling(cpu);
 			     i <= cpu_last_thread_sibling(cpu); i++) {
 				if (stale_map[i])
 					__set_bit(id, stale_map[i]);
 			}
 			cpu = i - 1;
 		}
 		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
 	 */
 	raw_spin_unlock(&context_lock);
 	cpu_relax();
 	raw_spin_lock(&context_lock);

 	/* This will cause the caller to try again */
 	return MMU_NO_CONTEXT;
 }
 #endif  /* CONFIG_SMP */

 static unsigned int steal_all_contexts(void)
 {
 	struct mm_struct *mm;
 	int cpu = smp_processor_id();
 	unsigned int id;

 	for (id = first_context; id <= last_context; id++) {
 		/* Pick up the victim mm */
 		mm = context_mm[id];

 		pr_hardcont(" | steal %d from 0x%p", id, mm);

 		/* Mark this mm as having no context anymore */
 		mm->context.id = MMU_NO_CONTEXT;
 		if (id != first_context) {
 			context_mm[id] = NULL;
 			__clear_bit(id, context_map);
 #ifdef DEBUG_MAP_CONSISTENCY
 			mm->context.active = 0;
 #endif
 		}
 		__clear_bit(id, stale_map[cpu]);
 	}

 	/* Flush the TLB for all contexts (not to be used on SMP) */
 	_tlbil_all();

 	nr_free_contexts = last_context - first_context;

 	return first_context;
 }

 /* 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_hardcont(" | steal %d from 0x%p", 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,
 			struct task_struct *tsk)
 {
 	unsigned int i, id, cpu = smp_processor_id();
 	unsigned long *map;

 	/* No lockless fast path .. yet */
 	raw_spin_lock(&context_lock);

 	pr_hard("[%d] activating context for mm @%p, active=%d, id=%d",
 		cpu, next, next->context.active, next->context.id);

 #ifdef CONFIG_SMP
 	/* Mark us active and the previous one not anymore */
 	next->context.active++;
 	if (prev) {
 		pr_hardcont(" (old=0x%p a=%d)", prev, prev->context.active);
 		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)) {
 #ifdef DEBUG_MAP_CONSISTENCY
 		if (context_mm[id] != next)
 			pr_err("MMU: mm 0x%p has id %d but context_mm[%d] says 0x%p\n",
 			       next, id, id, context_mm[id]);
 #endif
 		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 */
 		if (no_selective_tlbil)
 			id = steal_all_contexts();
 		else
 			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;
 	pr_hardcont(" | new id=%d,nrf=%d", id, nr_free_contexts);

 	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_hardcont(" | stale flush %d [%d..%d]",
 			    id, cpu_first_thread_sibling(cpu),
 			    cpu_last_thread_sibling(cpu));

 		local_flush_tlb_mm(next);

 		/* XXX This clear should ultimately be part of local_flush_tlb_mm */
 		for (i = cpu_first_thread_sibling(cpu);
 		     i <= cpu_last_thread_sibling(cpu); i++) {
 			if (stale_map[i])
 				__clear_bit(id, stale_map[i]);
 		}
 	}

 	/* Flick the MMU and release lock */
 	pr_hardcont(" -> %d\n", id);
 	set_context(id, next->pgd);
 	raw_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)
 {
 	pr_hard("initing context for mm @%p\n", mm);

 	mm->context.id = MMU_NO_CONTEXT;
 	mm->context.active = 0;

 #ifdef CONFIG_PPC_MM_SLICES
 	slice_set_user_psize(mm, mmu_virtual_psize);
 #endif

 	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);

 	raw_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++;
 	}
 	raw_spin_unlock_irqrestore(&context_lock, flags);
 }

 #ifdef CONFIG_SMP
 static int mmu_ctx_cpu_prepare(unsigned int cpu)
 {
 	/* We don't touch CPU 0 map, it's allocated at aboot and kept
 	 * around forever
 	 */
 	if (cpu == boot_cpuid)
 		return 0;

 	pr_devel("MMU: Allocating stale context map for CPU %d\n", cpu);
 	stale_map[cpu] = kzalloc(CTX_MAP_SIZE, GFP_KERNEL);
 	return 0;
 }

 static int mmu_ctx_cpu_dead(unsigned int cpu)
 {
 #ifdef CONFIG_HOTPLUG_CPU
 	if (cpu == boot_cpuid)
 		return 0;

 	pr_devel("MMU: Freeing stale context map for CPU %d\n", cpu);
 	kfree(stale_map[cpu]);
 	stale_map[cpu] = NULL;

 	/* We also clear the cpu_vm_mask bits of CPUs going away */
 	clear_tasks_mm_cpumask(cpu);
 #endif
 	return 0;
 }

 #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
 	 *
 	 * The IBM 47x core supports 16-bit PIDs, thus 65535 contexts. We
 	 * should normally never have to steal though the facility is
 	 * present if needed.
 	 *      -- BenH
 	 */
 	if (mmu_has_feature(MMU_FTR_TYPE_8xx)) {
 		first_context = 0;
 		last_context = 15;
 		no_selective_tlbil = true;
 	} else if (mmu_has_feature(MMU_FTR_TYPE_47x)) {
 		first_context = 1;
 		last_context = 65535;
 		no_selective_tlbil = false;
 	} else {
 		first_context = 1;
 		last_context = 255;
 		no_selective_tlbil = false;
 	}

 #ifdef DEBUG_CLAMP_LAST_CONTEXT
 	last_context = DEBUG_CLAMP_LAST_CONTEXT;
 #endif
 	/*
 	 * Allocate the maps used by context management
 	 */
 	context_map = memblock_virt_alloc(CTX_MAP_SIZE, 0);
 	context_mm = memblock_virt_alloc(sizeof(void *) * (last_context + 1), 0);
 #ifndef CONFIG_SMP
 	stale_map[0] = memblock_virt_alloc(CTX_MAP_SIZE, 0);
 #else
 	stale_map[boot_cpuid] = memblock_virt_alloc(CTX_MAP_SIZE, 0);

 	cpuhp_setup_state_nocalls(CPUHP_POWERPC_MMU_CTX_PREPARE,
 				  "powerpc/mmu/ctx:prepare",
 				  mmu_ctx_cpu_prepare, mmu_ctx_cpu_dead);
 #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;
 }
	/*
	* 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 <[email protected]>
	* 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
	*/

	//#define DEBUG_MAP_CONSISTENCY
	//#define DEBUG_CLAMP_LAST_CONTEXT 31
	//#define DEBUG_HARDER

	/* We don't use DEBUG because it tends to be compiled in always nowadays
	* and this would generate way too much output
	*/
	#ifdef DEBUG_HARDER
	#define pr_hard(args...) printk(KERN_DEBUG args)
	#define pr_hardcont(args...) printk(KERN_CONT args)
	#else
	#define pr_hard(args...) do { } while(0)
	#define pr_hardcont(args...) do { } while(0)
	#endif

	#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 <linux/slab.h>

	#include <asm/mmu_context.h>
	#include <asm/tlbflush.h>

	#include "mmu_decl.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_RAW_SPINLOCK(context_lock);
	static bool no_selective_tlbil;

	#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, i;

	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_hardcont(" \| steal %d from 0x%p", 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 threaded
	* implementations, we set it on all threads on each core
	* represented in the mask. A future implementation will use
	* a core map instead but this will do for now.
	*/
	for_each_cpu(cpu, mm_cpumask(mm)) {
	for (i = cpu_first_thread_sibling(cpu);
	i <= cpu_last_thread_sibling(cpu); i++) {
	if (stale_map[i])
	__set_bit(id, stale_map[i]);
	}
	cpu = i - 1;
	}
	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
	*/
	raw_spin_unlock(&context_lock);
	cpu_relax();
	raw_spin_lock(&context_lock);

	/* This will cause the caller to try again */
	return MMU_NO_CONTEXT;
	}
	#endif /* CONFIG_SMP */

	static unsigned int steal_all_contexts(void)
	{
	struct mm_struct *mm;
	int cpu = smp_processor_id();
	unsigned int id;

	for (id = first_context; id <= last_context; id++) {
	/* Pick up the victim mm */
	mm = context_mm[id];

	pr_hardcont(" \| steal %d from 0x%p", id, mm);

	/* Mark this mm as having no context anymore */
	mm->context.id = MMU_NO_CONTEXT;
	if (id != first_context) {
	context_mm[id] = NULL;
	__clear_bit(id, context_map);
	#ifdef DEBUG_MAP_CONSISTENCY
	mm->context.active = 0;
	#endif
	}
	__clear_bit(id, stale_map[cpu]);
	}

	/* Flush the TLB for all contexts (not to be used on SMP) */
	_tlbil_all();

	nr_free_contexts = last_context - first_context;

	return first_context;
	}

	/* 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_hardcont(" \| steal %d from 0x%p", 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,
	struct task_struct *tsk)
	{
	unsigned int i, id, cpu = smp_processor_id();
	unsigned long *map;

	/* No lockless fast path .. yet */
	raw_spin_lock(&context_lock);

	pr_hard("[%d] activating context for mm @%p, active=%d, id=%d",
	cpu, next, next->context.active, next->context.id);

	#ifdef CONFIG_SMP
	/* Mark us active and the previous one not anymore */
	next->context.active++;
	if (prev) {
	pr_hardcont(" (old=0x%p a=%d)", prev, prev->context.active);
	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)) {
	#ifdef DEBUG_MAP_CONSISTENCY
	if (context_mm[id] != next)
	pr_err("MMU: mm 0x%p has id %d but context_mm[%d] says 0x%p\n",
	next, id, id, context_mm[id]);
	#endif
	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 */
	if (no_selective_tlbil)
	id = steal_all_contexts();
	else
	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;
	pr_hardcont(" \| new id=%d,nrf=%d", id, nr_free_contexts);

	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_hardcont(" \| stale flush %d [%d..%d]",
	id, cpu_first_thread_sibling(cpu),
	cpu_last_thread_sibling(cpu));

	local_flush_tlb_mm(next);

	/* XXX This clear should ultimately be part of local_flush_tlb_mm */
	for (i = cpu_first_thread_sibling(cpu);
	i <= cpu_last_thread_sibling(cpu); i++) {
	if (stale_map[i])
	__clear_bit(id, stale_map[i]);
	}
	}

	/* Flick the MMU and release lock */
	pr_hardcont(" -> %d\n", id);
	set_context(id, next->pgd);
	raw_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)
	{
	pr_hard("initing context for mm @%p\n", mm);

	mm->context.id = MMU_NO_CONTEXT;
	mm->context.active = 0;

	#ifdef CONFIG_PPC_MM_SLICES
	slice_set_user_psize(mm, mmu_virtual_psize);
	#endif

	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);

	raw_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++;
	}
	raw_spin_unlock_irqrestore(&context_lock, flags);
	}

	#ifdef CONFIG_SMP
	static int mmu_ctx_cpu_prepare(unsigned int cpu)
	{
	/* We don't touch CPU 0 map, it's allocated at aboot and kept
	* around forever
	*/
	if (cpu == boot_cpuid)
	return 0;

	pr_devel("MMU: Allocating stale context map for CPU %d\n", cpu);
	stale_map[cpu] = kzalloc(CTX_MAP_SIZE, GFP_KERNEL);
	return 0;
	}

	static int mmu_ctx_cpu_dead(unsigned int cpu)
	{
	#ifdef CONFIG_HOTPLUG_CPU
	if (cpu == boot_cpuid)
	return 0;

	pr_devel("MMU: Freeing stale context map for CPU %d\n", cpu);
	kfree(stale_map[cpu]);
	stale_map[cpu] = NULL;

	/* We also clear the cpu_vm_mask bits of CPUs going away */
	clear_tasks_mm_cpumask(cpu);
	#endif
	return 0;
	}

	#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
	*
	* The IBM 47x core supports 16-bit PIDs, thus 65535 contexts. We
	* should normally never have to steal though the facility is
	* present if needed.
	* -- BenH
	*/
	if (mmu_has_feature(MMU_FTR_TYPE_8xx)) {
	first_context = 0;
	last_context = 15;
	no_selective_tlbil = true;
	} else if (mmu_has_feature(MMU_FTR_TYPE_47x)) {
	first_context = 1;
	last_context = 65535;
	no_selective_tlbil = false;
	} else {
	first_context = 1;
	last_context = 255;
	no_selective_tlbil = false;
	}

	#ifdef DEBUG_CLAMP_LAST_CONTEXT
	last_context = DEBUG_CLAMP_LAST_CONTEXT;
	#endif
	/*
	* Allocate the maps used by context management
	*/
	context_map = memblock_virt_alloc(CTX_MAP_SIZE, 0);
	context_mm = memblock_virt_alloc(sizeof(void ) (last_context + 1), 0);
	#ifndef CONFIG_SMP
	stale_map[0] = memblock_virt_alloc(CTX_MAP_SIZE, 0);
	#else
	stale_map[boot_cpuid] = memblock_virt_alloc(CTX_MAP_SIZE, 0);

	cpuhp_setup_state_nocalls(CPUHP_POWERPC_MMU_CTX_PREPARE,
	"powerpc/mmu/ctx:prepare",
	mmu_ctx_cpu_prepare, mmu_ctx_cpu_dead);
	#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;
	}