root/arch/powerpc/mm/book3s64/mmu_context.c

DEFINITIONS

1. alloc_context_id
2. hash__reserve_context_id
3. hash__alloc_context_id
4. realloc_context_ids
5. hash__init_new_context
6. hash__setup_new_exec
7. radix__init_new_context
8. init_new_context
9. __destroy_context
10. destroy_contexts
11. pmd_frag_destroy
12. destroy_pagetable_cache
13. destroy_context
14. arch_exit_mmap
15. radix__switch_mmu_context

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