2 * This file contains the routines for handling the MMU on those
3 * PowerPC implementations where the MMU is not using the hash
4 * table, such as 8xx, 4xx, BookE's etc...
6 * Copyright 2008 Ben Herrenschmidt <benh@kernel.crashing.org>
9 * Derived from previous arch/powerpc/mm/mmu_context.c
10 * and arch/powerpc/include/asm/mmu_context.h
12 * This program is free software; you can redistribute it and/or
13 * modify it under the terms of the GNU General Public License
14 * as published by the Free Software Foundation; either version
15 * 2 of the License, or (at your option) any later version.
19 * - The global context lock will not scale very well
20 * - The maps should be dynamically allocated to allow for processors
21 * that support more PID bits at runtime
22 * - Implement flush_tlb_mm() by making the context stale and picking
24 * - More aggressively clear stale map bits and maybe find some way to
25 * also clear mm->cpu_vm_mask bits when processes are migrated
29 #define DEBUG_STEAL_ONLY
30 #undef DEBUG_MAP_CONSISTENCY
31 /*#define DEBUG_CLAMP_LAST_CONTEXT 15 */
33 #include <linux/kernel.h>
35 #include <linux/init.h>
36 #include <linux/spinlock.h>
37 #include <linux/bootmem.h>
38 #include <linux/notifier.h>
39 #include <linux/cpu.h>
41 #include <asm/mmu_context.h>
42 #include <asm/tlbflush.h>
44 static unsigned int first_context
, last_context
;
45 static unsigned int next_context
, nr_free_contexts
;
46 static unsigned long *context_map
;
47 static unsigned long *stale_map
[NR_CPUS
];
48 static struct mm_struct
**context_mm
;
49 static spinlock_t context_lock
= SPIN_LOCK_UNLOCKED
;
51 #define CTX_MAP_SIZE \
52 (sizeof(unsigned long) * (last_context / BITS_PER_LONG + 1))
55 /* Steal a context from a task that has one at the moment.
57 * This is used when we are running out of available PID numbers
60 * This isn't an LRU system, it just frees up each context in
61 * turn (sort-of pseudo-random replacement :). This would be the
62 * place to implement an LRU scheme if anyone was motivated to do it.
65 * For context stealing, we use a slightly different approach for
66 * SMP and UP. Basically, the UP one is simpler and doesn't use
67 * the stale map as we can just flush the local CPU
71 static unsigned int steal_context_smp(unsigned int id
)
74 unsigned int cpu
, max
;
77 max
= last_context
- first_context
;
79 /* Attempt to free next_context first and then loop until we manage */
81 /* Pick up the victim mm */
84 /* We have a candidate victim, check if it's active, on SMP
85 * we cannot steal active contexts
87 if (mm
->context
.active
) {
89 if (id
> last_context
)
93 pr_debug("[%d] steal context %d from mm @%p\n",
94 smp_processor_id(), id
, mm
);
96 /* Mark this mm has having no context anymore */
97 mm
->context
.id
= MMU_NO_CONTEXT
;
99 /* Mark it stale on all CPUs that used this mm */
100 for_each_cpu(cpu
, mm_cpumask(mm
))
101 __set_bit(id
, stale_map
[cpu
]);
105 /* This will happen if you have more CPUs than available contexts,
106 * all we can do here is wait a bit and try again
108 spin_unlock(&context_lock
);
110 spin_lock(&context_lock
);
113 #endif /* CONFIG_SMP */
115 /* Note that this will also be called on SMP if all other CPUs are
116 * offlined, which means that it may be called for cpu != 0. For
117 * this to work, we somewhat assume that CPUs that are onlined
118 * come up with a fully clean TLB (or are cleaned when offlined)
120 static unsigned int steal_context_up(unsigned int id
)
122 struct mm_struct
*mm
;
123 int cpu
= smp_processor_id();
125 /* Pick up the victim mm */
128 pr_debug("[%d] steal context %d from mm @%p\n", cpu
, id
, mm
);
130 /* Flush the TLB for that context */
131 local_flush_tlb_mm(mm
);
133 /* Mark this mm has having no context anymore */
134 mm
->context
.id
= MMU_NO_CONTEXT
;
136 /* XXX This clear should ultimately be part of local_flush_tlb_mm */
137 __clear_bit(id
, stale_map
[cpu
]);
142 #ifdef DEBUG_MAP_CONSISTENCY
143 static void context_check_map(void)
145 unsigned int id
, nrf
, nact
;
148 for (id
= first_context
; id
<= last_context
; id
++) {
149 int used
= test_bit(id
, context_map
);
152 if (used
!= (context_mm
[id
] != NULL
))
153 pr_err("MMU: Context %d is %s and MM is %p !\n",
154 id
, used
? "used" : "free", context_mm
[id
]);
155 if (context_mm
[id
] != NULL
)
156 nact
+= context_mm
[id
]->context
.active
;
158 if (nrf
!= nr_free_contexts
) {
159 pr_err("MMU: Free context count out of sync ! (%d vs %d)\n",
160 nr_free_contexts
, nrf
);
161 nr_free_contexts
= nrf
;
163 if (nact
> num_online_cpus())
164 pr_err("MMU: More active contexts than CPUs ! (%d vs %d)\n",
165 nact
, num_online_cpus());
166 if (first_context
> 0 && !test_bit(0, context_map
))
167 pr_err("MMU: Context 0 has been freed !!!\n");
170 static void context_check_map(void) { }
173 void switch_mmu_context(struct mm_struct
*prev
, struct mm_struct
*next
)
175 unsigned int id
, cpu
= smp_processor_id();
178 /* No lockless fast path .. yet */
179 spin_lock(&context_lock
);
181 #ifndef DEBUG_STEAL_ONLY
182 pr_debug("[%d] activating context for mm @%p, active=%d, id=%d\n",
183 cpu
, next
, next
->context
.active
, next
->context
.id
);
187 /* Mark us active and the previous one not anymore */
188 next
->context
.active
++;
190 #ifndef DEBUG_STEAL_ONLY
191 pr_debug(" old context %p active was: %d\n",
192 prev
, prev
->context
.active
);
194 WARN_ON(prev
->context
.active
< 1);
195 prev
->context
.active
--;
197 #endif /* CONFIG_SMP */
199 /* If we already have a valid assigned context, skip all that */
200 id
= next
->context
.id
;
201 if (likely(id
!= MMU_NO_CONTEXT
))
204 /* We really don't have a context, let's try to acquire one */
206 if (id
> last_context
)
210 /* No more free contexts, let's try to steal one */
211 if (nr_free_contexts
== 0) {
213 if (num_online_cpus() > 1) {
214 id
= steal_context_smp(id
);
217 #endif /* CONFIG_SMP */
218 id
= steal_context_up(id
);
223 /* We know there's at least one free context, try to find it */
224 while (__test_and_set_bit(id
, map
)) {
225 id
= find_next_zero_bit(map
, last_context
+1, id
);
226 if (id
> last_context
)
230 next_context
= id
+ 1;
231 context_mm
[id
] = next
;
232 next
->context
.id
= id
;
234 #ifndef DEBUG_STEAL_ONLY
235 pr_debug("[%d] picked up new id %d, nrf is now %d\n",
236 cpu
, id
, nr_free_contexts
);
242 /* If that context got marked stale on this CPU, then flush the
243 * local TLB for it and unmark it before we use it
245 if (test_bit(id
, stale_map
[cpu
])) {
246 pr_debug("[%d] flushing stale context %d for mm @%p !\n",
248 local_flush_tlb_mm(next
);
250 /* XXX This clear should ultimately be part of local_flush_tlb_mm */
251 __clear_bit(id
, stale_map
[cpu
]);
254 /* Flick the MMU and release lock */
255 set_context(id
, next
->pgd
);
256 spin_unlock(&context_lock
);
260 * Set up the context for a new address space.
262 int init_new_context(struct task_struct
*t
, struct mm_struct
*mm
)
264 mm
->context
.id
= MMU_NO_CONTEXT
;
265 mm
->context
.active
= 0;
271 * We're finished using the context for an address space.
273 void destroy_context(struct mm_struct
*mm
)
277 if (mm
->context
.id
== MMU_NO_CONTEXT
)
280 WARN_ON(mm
->context
.active
!= 0);
282 spin_lock(&context_lock
);
284 if (id
!= MMU_NO_CONTEXT
) {
285 __clear_bit(id
, context_map
);
286 mm
->context
.id
= MMU_NO_CONTEXT
;
287 #ifdef DEBUG_MAP_CONSISTENCY
288 mm
->context
.active
= 0;
289 context_mm
[id
] = NULL
;
293 spin_unlock(&context_lock
);
298 static int __cpuinit
mmu_context_cpu_notify(struct notifier_block
*self
,
299 unsigned long action
, void *hcpu
)
301 unsigned int cpu
= (unsigned int)(long)hcpu
;
303 /* We don't touch CPU 0 map, it's allocated at aboot and kept
311 case CPU_ONLINE_FROZEN
:
312 pr_debug("MMU: Allocating stale context map for CPU %d\n", cpu
);
313 stale_map
[cpu
] = kzalloc(CTX_MAP_SIZE
, GFP_KERNEL
);
315 #ifdef CONFIG_HOTPLUG_CPU
317 case CPU_DEAD_FROZEN
:
318 pr_debug("MMU: Freeing stale context map for CPU %d\n", cpu
);
319 kfree(stale_map
[cpu
]);
320 stale_map
[cpu
] = NULL
;
327 static struct notifier_block __cpuinitdata mmu_context_cpu_nb
= {
328 .notifier_call
= mmu_context_cpu_notify
,
331 #endif /* CONFIG_SMP */
334 * Initialize the context management stuff.
336 void __init
mmu_context_init(void)
338 /* Mark init_mm as being active on all possible CPUs since
339 * we'll get called with prev == init_mm the first time
340 * we schedule on a given CPU
342 init_mm
.context
.active
= NR_CPUS
;
345 * The MPC8xx has only 16 contexts. We rotate through them on each
346 * task switch. A better way would be to keep track of tasks that
347 * own contexts, and implement an LRU usage. That way very active
348 * tasks don't always have to pay the TLB reload overhead. The
349 * kernel pages are mapped shared, so the kernel can run on behalf
350 * of any task that makes a kernel entry. Shared does not mean they
351 * are not protected, just that the ASID comparison is not performed.
354 * The IBM4xx has 256 contexts, so we can just rotate through these
355 * as a way of "switching" contexts. If the TID of the TLB is zero,
356 * the PID/TID comparison is disabled, so we can use a TID of zero
357 * to represent all kernel pages as shared among all contexts.
360 if (mmu_has_feature(MMU_FTR_TYPE_8xx
)) {
368 #ifdef DEBUG_CLAMP_LAST_CONTEXT
369 last_context
= DEBUG_CLAMP_LAST_CONTEXT
;
372 * Allocate the maps used by context management
374 context_map
= alloc_bootmem(CTX_MAP_SIZE
);
375 context_mm
= alloc_bootmem(sizeof(void *) * (last_context
+ 1));
376 stale_map
[0] = alloc_bootmem(CTX_MAP_SIZE
);
379 register_cpu_notifier(&mmu_context_cpu_nb
);
383 "MMU: Allocated %zu bytes of context maps for %d contexts\n",
384 2 * CTX_MAP_SIZE
+ (sizeof(void *) * (last_context
+ 1)),
385 last_context
- first_context
+ 1);
388 * Some processors have too few contexts to reserve one for
389 * init_mm, and require using context 0 for a normal task.
390 * Other processors reserve the use of context zero for the kernel.
391 * This code assumes first_context < 32.
393 context_map
[0] = (1 << first_context
) - 1;
394 next_context
= first_context
;
395 nr_free_contexts
= last_context
- first_context
+ 1;