1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * This file contains the routines for handling the MMU on those
4 * PowerPC implementations where the MMU is not using the hash
5 * table, such as 8xx, 4xx, BookE's etc...
6 *
7 * Copyright 2008 Ben Herrenschmidt <benh@kernel.crashing.org>
8 * IBM Corp.
9 *
10 * Derived from previous arch/powerpc/mm/mmu_context.c
11 * and arch/powerpc/include/asm/mmu_context.h
12 *
13 * TODO:
14 *
15 * - The global context lock will not scale very well
16 * - The maps should be dynamically allocated to allow for processors
17 * that support more PID bits at runtime
18 * - Implement flush_tlb_mm() by making the context stale and picking
19 * a new one
20 * - More aggressively clear stale map bits and maybe find some way to
21 * also clear mm->cpu_vm_mask bits when processes are migrated
22 */
23
24 //#define DEBUG_MAP_CONSISTENCY
25 //#define DEBUG_CLAMP_LAST_CONTEXT 31
26 //#define DEBUG_HARDER
27
28 /* We don't use DEBUG because it tends to be compiled in always nowadays
29 * and this would generate way too much output
30 */
31 #ifdef DEBUG_HARDER
32 #define pr_hard(args...) printk(KERN_DEBUG args)
33 #define pr_hardcont(args...) printk(KERN_CONT args)
34 #else
35 #define pr_hard(args...) do { } while(0)
36 #define pr_hardcont(args...) do { } while(0)
37 #endif
38
39 #include <linux/kernel.h>
40 #include <linux/mm.h>
41 #include <linux/init.h>
42 #include <linux/spinlock.h>
43 #include <linux/memblock.h>
44 #include <linux/notifier.h>
45 #include <linux/cpu.h>
46 #include <linux/slab.h>
47
48 #include <asm/mmu_context.h>
49 #include <asm/tlbflush.h>
50
51 #include <mm/mmu_decl.h>
52
53 /*
54 * The MPC8xx has only 16 contexts. We rotate through them on each task switch.
55 * A better way would be to keep track of tasks that own contexts, and implement
56 * an LRU usage. That way very active tasks don't always have to pay the TLB
57 * reload overhead. The kernel pages are mapped shared, so the kernel can run on
58 * behalf of any task that makes a kernel entry. Shared does not mean they are
59 * not protected, just that the ASID comparison is not performed. -- Dan
60 *
61 * The IBM4xx has 256 contexts, so we can just rotate through these as a way of
62 * "switching" contexts. If the TID of the TLB is zero, the PID/TID comparison
63 * is disabled, so we can use a TID of zero to represent all kernel pages as
64 * shared among all contexts. -- Dan
65 *
66 * The IBM 47x core supports 16-bit PIDs, thus 65535 contexts. We should
67 * normally never have to steal though the facility is present if needed.
68 * -- BenH
69 */
70 #define FIRST_CONTEXT 1
71 #ifdef DEBUG_CLAMP_LAST_CONTEXT
72 #define LAST_CONTEXT DEBUG_CLAMP_LAST_CONTEXT
73 #elif defined(CONFIG_PPC_8xx)
74 #define LAST_CONTEXT 16
75 #elif defined(CONFIG_PPC_47x)
76 #define LAST_CONTEXT 65535
77 #else
78 #define LAST_CONTEXT 255
79 #endif
80
81 static unsigned int next_context, nr_free_contexts;
82 static unsigned long *context_map;
83 #ifdef CONFIG_SMP
84 static unsigned long *stale_map[NR_CPUS];
85 #endif
86 static struct mm_struct **context_mm;
87 static DEFINE_RAW_SPINLOCK(context_lock);
88
89 #define CTX_MAP_SIZE \
90 (sizeof(unsigned long) * (LAST_CONTEXT / BITS_PER_LONG + 1))
91
92
93 /* Steal a context from a task that has one at the moment.
94 *
95 * This is used when we are running out of available PID numbers
96 * on the processors.
97 *
98 * This isn't an LRU system, it just frees up each context in
99 * turn (sort-of pseudo-random replacement :). This would be the
100 * place to implement an LRU scheme if anyone was motivated to do it.
101 * -- paulus
102 *
103 * For context stealing, we use a slightly different approach for
104 * SMP and UP. Basically, the UP one is simpler and doesn't use
105 * the stale map as we can just flush the local CPU
106 * -- benh
107 */
108 #ifdef CONFIG_SMP
steal_context_smp(unsigned int id)109 static unsigned int steal_context_smp(unsigned int id)
110 {
111 struct mm_struct *mm;
112 unsigned int cpu, max, i;
113
114 max = LAST_CONTEXT - FIRST_CONTEXT;
115
116 /* Attempt to free next_context first and then loop until we manage */
117 while (max--) {
118 /* Pick up the victim mm */
119 mm = context_mm[id];
120
121 /* We have a candidate victim, check if it's active, on SMP
122 * we cannot steal active contexts
123 */
124 if (mm->context.active) {
125 id++;
126 if (id > LAST_CONTEXT)
127 id = FIRST_CONTEXT;
128 continue;
129 }
130 pr_hardcont(" | steal %d from 0x%p", id, mm);
131
132 /* Mark this mm has having no context anymore */
133 mm->context.id = MMU_NO_CONTEXT;
134
135 /* Mark it stale on all CPUs that used this mm. For threaded
136 * implementations, we set it on all threads on each core
137 * represented in the mask. A future implementation will use
138 * a core map instead but this will do for now.
139 */
140 for_each_cpu(cpu, mm_cpumask(mm)) {
141 for (i = cpu_first_thread_sibling(cpu);
142 i <= cpu_last_thread_sibling(cpu); i++) {
143 if (stale_map[i])
144 __set_bit(id, stale_map[i]);
145 }
146 cpu = i - 1;
147 }
148 return id;
149 }
150
151 /* This will happen if you have more CPUs than available contexts,
152 * all we can do here is wait a bit and try again
153 */
154 raw_spin_unlock(&context_lock);
155 cpu_relax();
156 raw_spin_lock(&context_lock);
157
158 /* This will cause the caller to try again */
159 return MMU_NO_CONTEXT;
160 }
161 #endif /* CONFIG_SMP */
162
steal_all_contexts(void)163 static unsigned int steal_all_contexts(void)
164 {
165 struct mm_struct *mm;
166 #ifdef CONFIG_SMP
167 int cpu = smp_processor_id();
168 #endif
169 unsigned int id;
170
171 for (id = FIRST_CONTEXT; id <= LAST_CONTEXT; id++) {
172 /* Pick up the victim mm */
173 mm = context_mm[id];
174
175 pr_hardcont(" | steal %d from 0x%p", id, mm);
176
177 /* Mark this mm as having no context anymore */
178 mm->context.id = MMU_NO_CONTEXT;
179 if (id != FIRST_CONTEXT) {
180 context_mm[id] = NULL;
181 __clear_bit(id, context_map);
182 #ifdef DEBUG_MAP_CONSISTENCY
183 mm->context.active = 0;
184 #endif
185 }
186 #ifdef CONFIG_SMP
187 __clear_bit(id, stale_map[cpu]);
188 #endif
189 }
190
191 /* Flush the TLB for all contexts (not to be used on SMP) */
192 _tlbil_all();
193
194 nr_free_contexts = LAST_CONTEXT - FIRST_CONTEXT;
195
196 return FIRST_CONTEXT;
197 }
198
199 /* Note that this will also be called on SMP if all other CPUs are
200 * offlined, which means that it may be called for cpu != 0. For
201 * this to work, we somewhat assume that CPUs that are onlined
202 * come up with a fully clean TLB (or are cleaned when offlined)
203 */
steal_context_up(unsigned int id)204 static unsigned int steal_context_up(unsigned int id)
205 {
206 struct mm_struct *mm;
207 #ifdef CONFIG_SMP
208 int cpu = smp_processor_id();
209 #endif
210
211 /* Pick up the victim mm */
212 mm = context_mm[id];
213
214 pr_hardcont(" | steal %d from 0x%p", id, mm);
215
216 /* Flush the TLB for that context */
217 local_flush_tlb_mm(mm);
218
219 /* Mark this mm has having no context anymore */
220 mm->context.id = MMU_NO_CONTEXT;
221
222 /* XXX This clear should ultimately be part of local_flush_tlb_mm */
223 #ifdef CONFIG_SMP
224 __clear_bit(id, stale_map[cpu]);
225 #endif
226
227 return id;
228 }
229
230 #ifdef DEBUG_MAP_CONSISTENCY
context_check_map(void)231 static void context_check_map(void)
232 {
233 unsigned int id, nrf, nact;
234
235 nrf = nact = 0;
236 for (id = FIRST_CONTEXT; id <= LAST_CONTEXT; id++) {
237 int used = test_bit(id, context_map);
238 if (!used)
239 nrf++;
240 if (used != (context_mm[id] != NULL))
241 pr_err("MMU: Context %d is %s and MM is %p !\n",
242 id, used ? "used" : "free", context_mm[id]);
243 if (context_mm[id] != NULL)
244 nact += context_mm[id]->context.active;
245 }
246 if (nrf != nr_free_contexts) {
247 pr_err("MMU: Free context count out of sync ! (%d vs %d)\n",
248 nr_free_contexts, nrf);
249 nr_free_contexts = nrf;
250 }
251 if (nact > num_online_cpus())
252 pr_err("MMU: More active contexts than CPUs ! (%d vs %d)\n",
253 nact, num_online_cpus());
254 if (FIRST_CONTEXT > 0 && !test_bit(0, context_map))
255 pr_err("MMU: Context 0 has been freed !!!\n");
256 }
257 #else
context_check_map(void)258 static void context_check_map(void) { }
259 #endif
260
switch_mmu_context(struct mm_struct * prev,struct mm_struct * next,struct task_struct * tsk)261 void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next,
262 struct task_struct *tsk)
263 {
264 unsigned int id;
265 #ifdef CONFIG_SMP
266 unsigned int i, cpu = smp_processor_id();
267 #endif
268 unsigned long *map;
269
270 /* No lockless fast path .. yet */
271 raw_spin_lock(&context_lock);
272
273 pr_hard("[%d] activating context for mm @%p, active=%d, id=%d",
274 cpu, next, next->context.active, next->context.id);
275
276 #ifdef CONFIG_SMP
277 /* Mark us active and the previous one not anymore */
278 next->context.active++;
279 if (prev) {
280 pr_hardcont(" (old=0x%p a=%d)", prev, prev->context.active);
281 WARN_ON(prev->context.active < 1);
282 prev->context.active--;
283 }
284
285 again:
286 #endif /* CONFIG_SMP */
287
288 /* If we already have a valid assigned context, skip all that */
289 id = next->context.id;
290 if (likely(id != MMU_NO_CONTEXT)) {
291 #ifdef DEBUG_MAP_CONSISTENCY
292 if (context_mm[id] != next)
293 pr_err("MMU: mm 0x%p has id %d but context_mm[%d] says 0x%p\n",
294 next, id, id, context_mm[id]);
295 #endif
296 goto ctxt_ok;
297 }
298
299 /* We really don't have a context, let's try to acquire one */
300 id = next_context;
301 if (id > LAST_CONTEXT)
302 id = FIRST_CONTEXT;
303 map = context_map;
304
305 /* No more free contexts, let's try to steal one */
306 if (nr_free_contexts == 0) {
307 #ifdef CONFIG_SMP
308 if (num_online_cpus() > 1) {
309 id = steal_context_smp(id);
310 if (id == MMU_NO_CONTEXT)
311 goto again;
312 goto stolen;
313 }
314 #endif /* CONFIG_SMP */
315 if (IS_ENABLED(CONFIG_PPC_8xx))
316 id = steal_all_contexts();
317 else
318 id = steal_context_up(id);
319 goto stolen;
320 }
321 nr_free_contexts--;
322
323 /* We know there's at least one free context, try to find it */
324 while (__test_and_set_bit(id, map)) {
325 id = find_next_zero_bit(map, LAST_CONTEXT+1, id);
326 if (id > LAST_CONTEXT)
327 id = FIRST_CONTEXT;
328 }
329 stolen:
330 next_context = id + 1;
331 context_mm[id] = next;
332 next->context.id = id;
333 pr_hardcont(" | new id=%d,nrf=%d", id, nr_free_contexts);
334
335 context_check_map();
336 ctxt_ok:
337
338 /* If that context got marked stale on this CPU, then flush the
339 * local TLB for it and unmark it before we use it
340 */
341 #ifdef CONFIG_SMP
342 if (test_bit(id, stale_map[cpu])) {
343 pr_hardcont(" | stale flush %d [%d..%d]",
344 id, cpu_first_thread_sibling(cpu),
345 cpu_last_thread_sibling(cpu));
346
347 local_flush_tlb_mm(next);
348
349 /* XXX This clear should ultimately be part of local_flush_tlb_mm */
350 for (i = cpu_first_thread_sibling(cpu);
351 i <= cpu_last_thread_sibling(cpu); i++) {
352 if (stale_map[i])
353 __clear_bit(id, stale_map[i]);
354 }
355 }
356 #endif
357
358 /* Flick the MMU and release lock */
359 pr_hardcont(" -> %d\n", id);
360 set_context(id, next->pgd);
361 raw_spin_unlock(&context_lock);
362 }
363
364 /*
365 * Set up the context for a new address space.
366 */
init_new_context(struct task_struct * t,struct mm_struct * mm)367 int init_new_context(struct task_struct *t, struct mm_struct *mm)
368 {
369 pr_hard("initing context for mm @%p\n", mm);
370
371 /*
372 * We have MMU_NO_CONTEXT set to be ~0. Hence check
373 * explicitly against context.id == 0. This ensures that we properly
374 * initialize context slice details for newly allocated mm's (which will
375 * have id == 0) and don't alter context slice inherited via fork (which
376 * will have id != 0).
377 */
378 if (mm->context.id == 0)
379 slice_init_new_context_exec(mm);
380 mm->context.id = MMU_NO_CONTEXT;
381 mm->context.active = 0;
382 pte_frag_set(&mm->context, NULL);
383 return 0;
384 }
385
386 /*
387 * We're finished using the context for an address space.
388 */
destroy_context(struct mm_struct * mm)389 void destroy_context(struct mm_struct *mm)
390 {
391 unsigned long flags;
392 unsigned int id;
393
394 if (mm->context.id == MMU_NO_CONTEXT)
395 return;
396
397 WARN_ON(mm->context.active != 0);
398
399 raw_spin_lock_irqsave(&context_lock, flags);
400 id = mm->context.id;
401 if (id != MMU_NO_CONTEXT) {
402 __clear_bit(id, context_map);
403 mm->context.id = MMU_NO_CONTEXT;
404 #ifdef DEBUG_MAP_CONSISTENCY
405 mm->context.active = 0;
406 #endif
407 context_mm[id] = NULL;
408 nr_free_contexts++;
409 }
410 raw_spin_unlock_irqrestore(&context_lock, flags);
411 }
412
413 #ifdef CONFIG_SMP
mmu_ctx_cpu_prepare(unsigned int cpu)414 static int mmu_ctx_cpu_prepare(unsigned int cpu)
415 {
416 /* We don't touch CPU 0 map, it's allocated at aboot and kept
417 * around forever
418 */
419 if (cpu == boot_cpuid)
420 return 0;
421
422 pr_devel("MMU: Allocating stale context map for CPU %d\n", cpu);
423 stale_map[cpu] = kzalloc(CTX_MAP_SIZE, GFP_KERNEL);
424 return 0;
425 }
426
mmu_ctx_cpu_dead(unsigned int cpu)427 static int mmu_ctx_cpu_dead(unsigned int cpu)
428 {
429 #ifdef CONFIG_HOTPLUG_CPU
430 if (cpu == boot_cpuid)
431 return 0;
432
433 pr_devel("MMU: Freeing stale context map for CPU %d\n", cpu);
434 kfree(stale_map[cpu]);
435 stale_map[cpu] = NULL;
436
437 /* We also clear the cpu_vm_mask bits of CPUs going away */
438 clear_tasks_mm_cpumask(cpu);
439 #endif
440 return 0;
441 }
442
443 #endif /* CONFIG_SMP */
444
445 /*
446 * Initialize the context management stuff.
447 */
mmu_context_init(void)448 void __init mmu_context_init(void)
449 {
450 /* Mark init_mm as being active on all possible CPUs since
451 * we'll get called with prev == init_mm the first time
452 * we schedule on a given CPU
453 */
454 init_mm.context.active = NR_CPUS;
455
456 /*
457 * Allocate the maps used by context management
458 */
459 context_map = memblock_alloc(CTX_MAP_SIZE, SMP_CACHE_BYTES);
460 if (!context_map)
461 panic("%s: Failed to allocate %zu bytes\n", __func__,
462 CTX_MAP_SIZE);
463 context_mm = memblock_alloc(sizeof(void *) * (LAST_CONTEXT + 1),
464 SMP_CACHE_BYTES);
465 if (!context_mm)
466 panic("%s: Failed to allocate %zu bytes\n", __func__,
467 sizeof(void *) * (LAST_CONTEXT + 1));
468 #ifdef CONFIG_SMP
469 stale_map[boot_cpuid] = memblock_alloc(CTX_MAP_SIZE, SMP_CACHE_BYTES);
470 if (!stale_map[boot_cpuid])
471 panic("%s: Failed to allocate %zu bytes\n", __func__,
472 CTX_MAP_SIZE);
473
474 cpuhp_setup_state_nocalls(CPUHP_POWERPC_MMU_CTX_PREPARE,
475 "powerpc/mmu/ctx:prepare",
476 mmu_ctx_cpu_prepare, mmu_ctx_cpu_dead);
477 #endif
478
479 printk(KERN_INFO
480 "MMU: Allocated %zu bytes of context maps for %d contexts\n",
481 2 * CTX_MAP_SIZE + (sizeof(void *) * (LAST_CONTEXT + 1)),
482 LAST_CONTEXT - FIRST_CONTEXT + 1);
483
484 /*
485 * Some processors have too few contexts to reserve one for
486 * init_mm, and require using context 0 for a normal task.
487 * Other processors reserve the use of context zero for the kernel.
488 * This code assumes FIRST_CONTEXT < 32.
489 */
490 context_map[0] = (1 << FIRST_CONTEXT) - 1;
491 next_context = FIRST_CONTEXT;
492 nr_free_contexts = LAST_CONTEXT - FIRST_CONTEXT + 1;
493 }
494
