mmu_context.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 *  MMU context allocation for 64-bit kernels.
  4 *
  5 *  Copyright (C) 2004 Anton Blanchard, IBM Corp. <anton@samba.org>
  6 */
  7
  8#include <linux/sched.h>
  9#include <linux/kernel.h>
 10#include <linux/errno.h>
 11#include <linux/string.h>
 12#include <linux/types.h>
 13#include <linux/mm.h>
 14#include <linux/pkeys.h>
 15#include <linux/spinlock.h>
 16#include <linux/idr.h>
 17#include <linux/export.h>
 18#include <linux/gfp.h>
 19#include <linux/slab.h>
 20#include <linux/cpu.h>
 21
 22#include <asm/mmu_context.h>
 23#include <asm/pgalloc.h>
 24
 25#include "internal.h"
 26
 27static DEFINE_IDA(mmu_context_ida);
 28
 29static int alloc_context_id(int min_id, int max_id)
 30{
 31	return ida_alloc_range(&mmu_context_ida, min_id, max_id, GFP_KERNEL);
 32}
 33
 34#ifdef CONFIG_PPC_64S_HASH_MMU
 35void __init hash__reserve_context_id(int id)
 36{
 37	int result = ida_alloc_range(&mmu_context_ida, id, id, GFP_KERNEL);
 38
 39	WARN(result != id, "mmu: Failed to reserve context id %d (rc %d)\n", id, result);
 40}
 41
 42int hash__alloc_context_id(void)
 43{
 44	unsigned long max;
 45
 46	if (mmu_has_feature(MMU_FTR_68_BIT_VA))
 47		max = MAX_USER_CONTEXT;
 48	else
 49		max = MAX_USER_CONTEXT_65BIT_VA;
 50
 51	return alloc_context_id(MIN_USER_CONTEXT, max);
 52}
 53EXPORT_SYMBOL_GPL(hash__alloc_context_id);
 54#endif
 55
 56#ifdef CONFIG_PPC_64S_HASH_MMU
 57static int realloc_context_ids(mm_context_t *ctx)
 58{
 59	int i, id;
 60
 61	/*
 62	 * id 0 (aka. ctx->id) is special, we always allocate a new one, even if
 63	 * there wasn't one allocated previously (which happens in the exec
 64	 * case where ctx is newly allocated).
 65	 *
 66	 * We have to be a bit careful here. We must keep the existing ids in
 67	 * the array, so that we can test if they're non-zero to decide if we
 68	 * need to allocate a new one. However in case of error we must free the
 69	 * ids we've allocated but *not* any of the existing ones (or risk a
 70	 * UAF). That's why we decrement i at the start of the error handling
 71	 * loop, to skip the id that we just tested but couldn't reallocate.
 72	 */
 73	for (i = 0; i < ARRAY_SIZE(ctx->extended_id); i++) {
 74		if (i == 0 || ctx->extended_id[i]) {
 75			id = hash__alloc_context_id();
 76			if (id < 0)
 77				goto error;
 78
 79			ctx->extended_id[i] = id;
 80		}
 81	}
 82
 83	/* The caller expects us to return id */
 84	return ctx->id;
 85
 86error:
 87	for (i--; i >= 0; i--) {
 88		if (ctx->extended_id[i])
 89			ida_free(&mmu_context_ida, ctx->extended_id[i]);
 90	}
 91
 92	return id;
 93}
 94
 95static int hash__init_new_context(struct mm_struct *mm)
 96{
 97	int index;
 98
 99	mm->context.hash_context = kmalloc(sizeof(struct hash_mm_context),
100					   GFP_KERNEL);
101	if (!mm->context.hash_context)
102		return -ENOMEM;
103
104	/*
105	 * The old code would re-promote on fork, we don't do that when using
106	 * slices as it could cause problem promoting slices that have been
107	 * forced down to 4K.
108	 *
109	 * For book3s we have MMU_NO_CONTEXT set to be ~0. Hence check
110	 * explicitly against context.id == 0. This ensures that we properly
111	 * initialize context slice details for newly allocated mm's (which will
112	 * have id == 0) and don't alter context slice inherited via fork (which
113	 * will have id != 0).
114	 *
115	 * We should not be calling init_new_context() on init_mm. Hence a
116	 * check against 0 is OK.
117	 */
118	if (mm->context.id == 0) {
119		memset(mm->context.hash_context, 0, sizeof(struct hash_mm_context));
120		slice_init_new_context_exec(mm);
121	} else {
122		/* This is fork. Copy hash_context details from current->mm */
123		memcpy(mm->context.hash_context, current->mm->context.hash_context, sizeof(struct hash_mm_context));
124#ifdef CONFIG_PPC_SUBPAGE_PROT
125		/* inherit subpage prot details if we have one. */
126		if (current->mm->context.hash_context->spt) {
127			mm->context.hash_context->spt = kmalloc(sizeof(struct subpage_prot_table),
128								GFP_KERNEL);
129			if (!mm->context.hash_context->spt) {
130				kfree(mm->context.hash_context);
131				return -ENOMEM;
132			}
133		}
134#endif
135	}
136
137	index = realloc_context_ids(&mm->context);
138	if (index < 0) {
139#ifdef CONFIG_PPC_SUBPAGE_PROT
140		kfree(mm->context.hash_context->spt);
141#endif
142		kfree(mm->context.hash_context);
143		return index;
144	}
145
146	pkey_mm_init(mm);
147	return index;
148}
149
150void hash__setup_new_exec(void)
151{
152	slice_setup_new_exec();
153}
154#else
155static inline int hash__init_new_context(struct mm_struct *mm)
156{
157	BUILD_BUG();
158	return 0;
159}
160#endif
161
162static int radix__init_new_context(struct mm_struct *mm)
163{
164	unsigned long rts_field;
165	int index, max_id;
166
167	max_id = (1 << mmu_pid_bits) - 1;
168	index = alloc_context_id(mmu_base_pid, max_id);
169	if (index < 0)
170		return index;
171
172	/*
173	 * set the process table entry,
174	 */
175	rts_field = radix__get_tree_size();
176	process_tb[index].prtb0 = cpu_to_be64(rts_field | __pa(mm->pgd) | RADIX_PGD_INDEX_SIZE);
177
178	/*
179	 * Order the above store with subsequent update of the PID
180	 * register (at which point HW can start loading/caching
181	 * the entry) and the corresponding load by the MMU from
182	 * the L2 cache.
183	 */
184	asm volatile("ptesync;isync" : : : "memory");
185
186#ifdef CONFIG_PPC_64S_HASH_MMU
187	mm->context.hash_context = NULL;
188#endif
189
190	return index;
191}
192
193int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
194{
195	int index;
196
197	if (radix_enabled())
198		index = radix__init_new_context(mm);
199	else
200		index = hash__init_new_context(mm);
201
202	if (index < 0)
203		return index;
204
205	mm->context.id = index;
206
207	mm->context.pte_frag = NULL;
208	mm->context.pmd_frag = NULL;
209#ifdef CONFIG_SPAPR_TCE_IOMMU
210	mm_iommu_init(mm);
211#endif
212	atomic_set(&mm->context.active_cpus, 0);
213	atomic_set(&mm->context.copros, 0);
214
215	return 0;
216}
217
218void __destroy_context(int context_id)
219{
220	ida_free(&mmu_context_ida, context_id);
221}
222EXPORT_SYMBOL_GPL(__destroy_context);
223
224static void destroy_contexts(mm_context_t *ctx)
225{
226	if (radix_enabled()) {
227		ida_free(&mmu_context_ida, ctx->id);
228	} else {
229#ifdef CONFIG_PPC_64S_HASH_MMU
230		int index, context_id;
231
232		for (index = 0; index < ARRAY_SIZE(ctx->extended_id); index++) {
233			context_id = ctx->extended_id[index];
234			if (context_id)
235				ida_free(&mmu_context_ida, context_id);
236		}
237		kfree(ctx->hash_context);
238#else
239		BUILD_BUG(); // radix_enabled() should be constant true
240#endif
241	}
242}
243
244static void pmd_frag_destroy(void *pmd_frag)
245{
246	int count;
247	struct ptdesc *ptdesc;
248
249	ptdesc = virt_to_ptdesc(pmd_frag);
250	/* drop all the pending references */
251	count = ((unsigned long)pmd_frag & ~PAGE_MASK) >> PMD_FRAG_SIZE_SHIFT;
252	/* We allow PTE_FRAG_NR fragments from a PTE page */
253	if (atomic_sub_and_test(PMD_FRAG_NR - count, &ptdesc->pt_frag_refcount)) {
254		pagetable_dtor(ptdesc);
255		pagetable_free(ptdesc);
256	}
257}
258
259static void destroy_pagetable_cache(struct mm_struct *mm)
260{
261	void *frag;
262
263	frag = mm->context.pte_frag;
264	if (frag)
265		pte_frag_destroy(frag);
266
267	frag = mm->context.pmd_frag;
268	if (frag)
269		pmd_frag_destroy(frag);
270	return;
271}
272
273void destroy_context(struct mm_struct *mm)
274{
275#ifdef CONFIG_SPAPR_TCE_IOMMU
276	WARN_ON_ONCE(!list_empty(&mm->context.iommu_group_mem_list));
277#endif
278	/*
279	 * For tasks which were successfully initialized we end up calling
280	 * arch_exit_mmap() which clears the process table entry. And
281	 * arch_exit_mmap() is called before the required fullmm TLB flush
282	 * which does a RIC=2 flush. Hence for an initialized task, we do clear
283	 * any cached process table entries.
284	 *
285	 * The condition below handles the error case during task init. We have
286	 * set the process table entry early and if we fail a task
287	 * initialization, we need to ensure the process table entry is zeroed.
288	 * We need not worry about process table entry caches because the task
289	 * never ran with the PID value.
290	 */
291	if (radix_enabled())
292		process_tb[mm->context.id].prtb0 = 0;
293	else
294		subpage_prot_free(mm);
295	destroy_contexts(&mm->context);
296	mm->context.id = MMU_NO_CONTEXT;
297}
298
299void arch_exit_mmap(struct mm_struct *mm)
300{
301	destroy_pagetable_cache(mm);
302
303	if (radix_enabled()) {
304		/*
305		 * Radix doesn't have a valid bit in the process table
306		 * entries. However we know that at least P9 implementation
307		 * will avoid caching an entry with an invalid RTS field,
308		 * and 0 is invalid. So this will do.
309		 *
310		 * This runs before the "fullmm" tlb flush in exit_mmap,
311		 * which does a RIC=2 tlbie to clear the process table
312		 * entry. See the "fullmm" comments in tlb-radix.c.
313		 *
314		 * No barrier required here after the store because
315		 * this process will do the invalidate, which starts with
316		 * ptesync.
317		 */
318		process_tb[mm->context.id].prtb0 = 0;
319	}
320}
321
322#ifdef CONFIG_PPC_RADIX_MMU
323void radix__switch_mmu_context(struct mm_struct *prev, struct mm_struct *next)
324{
325	mtspr(SPRN_PID, next->context.id);
326	isync();
327}
328#endif
329
330/**
331 * cleanup_cpu_mmu_context - Clean up MMU details for this CPU (newly offlined)
332 *
333 * This clears the CPU from mm_cpumask for all processes, and then flushes the
334 * local TLB to ensure TLB coherency in case the CPU is onlined again.
335 *
336 * KVM guest translations are not necessarily flushed here. If KVM started
337 * using mm_cpumask or the Linux APIs which do, this would have to be resolved.
338 */
339#ifdef CONFIG_HOTPLUG_CPU
340void cleanup_cpu_mmu_context(void)
341{
342	int cpu = smp_processor_id();
343
344	clear_tasks_mm_cpumask(cpu);
345	tlbiel_all();
346}
347#endif