arch/s390/mm/pgalloc.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  Page table allocation functions
   4  *
   5  *    Copyright IBM Corp. 2016
   6  *    Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>
   7  */
   8
   9 #include <linux/sysctl.h>
  10 #include <linux/slab.h>
  11 #include <linux/mm.h>
  12 #include <asm/mmu_context.h>
  13 #include <asm/pgalloc.h>
  14 #include <asm/gmap.h>
  15 #include <asm/tlb.h>
  16 #include <asm/tlbflush.h>
  17
  18 #ifdef CONFIG_PGSTE
  19
  20 static int page_table_allocate_pgste_min = 0;
  21 static int page_table_allocate_pgste_max = 1;
  22 int page_table_allocate_pgste = 0;
  23 EXPORT_SYMBOL(page_table_allocate_pgste);
  24
  25 static struct ctl_table page_table_sysctl[] = {
  26         {
  27                 .procname       = "allocate_pgste",
  28                 .data           = &page_table_allocate_pgste,
  29                 .maxlen         = sizeof(int),
  30                 .mode           = S_IRUGO | S_IWUSR,
  31                 .proc_handler   = proc_dointvec,
  32                 .extra1         = &page_table_allocate_pgste_min,
  33                 .extra2         = &page_table_allocate_pgste_max,
  34         },
  35         { }
  36 };
  37
  38 static struct ctl_table page_table_sysctl_dir[] = {
  39         {
  40                 .procname       = "vm",
  41                 .maxlen         = 0,
  42                 .mode           = 0555,
  43                 .child          = page_table_sysctl,
  44         },
  45         { }
  46 };
  47
  48 static int __init page_table_register_sysctl(void)
  49 {
  50         return register_sysctl_table(page_table_sysctl_dir) ? 0 : -ENOMEM;
  51 }
  52 __initcall(page_table_register_sysctl);
  53
  54 #endif /* CONFIG_PGSTE */
  55
  56 unsigned long *crst_table_alloc(struct mm_struct *mm)
  57 {
  58         struct page *page = alloc_pages(GFP_KERNEL, 2);
  59
  60         if (!page)
  61                 return NULL;
  62         arch_set_page_dat(page, 2);
  63         return (unsigned long *) page_to_phys(page);
  64 }
  65
  66 void crst_table_free(struct mm_struct *mm, unsigned long *table)
  67 {
  68         free_pages((unsigned long) table, 2);
  69 }
  70
  71 static void __crst_table_upgrade(void *arg)
  72 {
  73         struct mm_struct *mm = arg;
  74
  75         if (current->active_mm == mm)
  76                 set_user_asce(mm);
  77         __tlb_flush_local();
  78 }
  79
  80 int crst_table_upgrade(struct mm_struct *mm, unsigned long end)
  81 {
  82         unsigned long *table, *pgd;
  83         int rc, notify;
  84
  85         /* upgrade should only happen from 3 to 4, 3 to 5, or 4 to 5 levels */
  86         VM_BUG_ON(mm->context.asce_limit < _REGION2_SIZE);
  87         rc = 0;
  88         notify = 0;
  89         while (mm->context.asce_limit < end) {
  90                 table = crst_table_alloc(mm);
  91                 if (!table) {
  92                         rc = -ENOMEM;
  93                         break;
  94                 }
  95                 spin_lock_bh(&mm->page_table_lock);
  96                 pgd = (unsigned long *) mm->pgd;
  97                 if (mm->context.asce_limit == _REGION2_SIZE) {
  98                         crst_table_init(table, _REGION2_ENTRY_EMPTY);
  99                         p4d_populate(mm, (p4d_t *) table, (pud_t *) pgd);
 100                         mm->pgd = (pgd_t *) table;
 101                         mm->context.asce_limit = _REGION1_SIZE;
 102                         mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
 103                                 _ASCE_USER_BITS | _ASCE_TYPE_REGION2;
 104                 } else {
 105                         crst_table_init(table, _REGION1_ENTRY_EMPTY);
 106                         pgd_populate(mm, (pgd_t *) table, (p4d_t *) pgd);
 107                         mm->pgd = (pgd_t *) table;
 108                         mm->context.asce_limit = -PAGE_SIZE;
 109                         mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
 110                                 _ASCE_USER_BITS | _ASCE_TYPE_REGION1;
 111                 }
 112                 notify = 1;
 113                 spin_unlock_bh(&mm->page_table_lock);
 114         }
 115         if (notify)
 116                 on_each_cpu(__crst_table_upgrade, mm, 0);
 117         return rc;
 118 }
 119
 120 void crst_table_downgrade(struct mm_struct *mm)
 121 {
 122         pgd_t *pgd;
 123
 124         /* downgrade should only happen from 3 to 2 levels (compat only) */
 125         VM_BUG_ON(mm->context.asce_limit != _REGION2_SIZE);
 126
 127         if (current->active_mm == mm) {
 128                 clear_user_asce();
 129                 __tlb_flush_mm(mm);
 130         }
 131
 132         pgd = mm->pgd;
 133         mm->pgd = (pgd_t *) (pgd_val(*pgd) & _REGION_ENTRY_ORIGIN);
 134         mm->context.asce_limit = _REGION3_SIZE;
 135         mm->context.asce = __pa(mm->pgd) | _ASCE_TABLE_LENGTH |
 136                            _ASCE_USER_BITS | _ASCE_TYPE_SEGMENT;
 137         crst_table_free(mm, (unsigned long *) pgd);
 138
 139         if (current->active_mm == mm)
 140                 set_user_asce(mm);
 141 }
 142
 143 static inline unsigned int atomic_xor_bits(atomic_t *v, unsigned int bits)
 144 {
 145         unsigned int old, new;
 146
 147         do {
 148                 old = atomic_read(v);
 149                 new = old ^ bits;
 150         } while (atomic_cmpxchg(v, old, new) != old);
 151         return new;
 152 }
 153
 154 #ifdef CONFIG_PGSTE
 155
 156 struct page *page_table_alloc_pgste(struct mm_struct *mm)
 157 {
 158         struct page *page;
 159         u64 *table;
 160
 161         page = alloc_page(GFP_KERNEL);
 162         if (page) {
 163                 table = (u64 *)page_to_phys(page);
 164                 memset64(table, _PAGE_INVALID, PTRS_PER_PTE);
 165                 memset64(table + PTRS_PER_PTE, 0, PTRS_PER_PTE);
 166         }
 167         return page;
 168 }
 169
 170 void page_table_free_pgste(struct page *page)
 171 {
 172         __free_page(page);
 173 }
 174
 175 #endif /* CONFIG_PGSTE */
 176
 177 /*
 178  * page table entry allocation/free routines.
 179  */
 180 unsigned long *page_table_alloc(struct mm_struct *mm)
 181 {
 182         unsigned long *table;
 183         struct page *page;
 184         unsigned int mask, bit;
 185
 186         /* Try to get a fragment of a 4K page as a 2K page table */
 187         if (!mm_alloc_pgste(mm)) {
 188                 table = NULL;
 189                 spin_lock_bh(&mm->context.lock);
 190                 if (!list_empty(&mm->context.pgtable_list)) {
 191                         page = list_first_entry(&mm->context.pgtable_list,
 192                                                 struct page, lru);
 193                         mask = atomic_read(&page->_refcount) >> 24;
 194                         mask = (mask | (mask >> 4)) & 3;
 195                         if (mask != 3) {
 196                                 table = (unsigned long *) page_to_phys(page);
 197                                 bit = mask & 1;         /* =1 -> second 2K */
 198                                 if (bit)
 199                                         table += PTRS_PER_PTE;
 200                                 atomic_xor_bits(&page->_refcount,
 201                                                         1U << (bit + 24));
 202                                 list_del(&page->lru);
 203                         }
 204                 }
 205                 spin_unlock_bh(&mm->context.lock);
 206                 if (table)
 207                         return table;
 208         }
 209         /* Allocate a fresh page */
 210         page = alloc_page(GFP_KERNEL);
 211         if (!page)
 212                 return NULL;
 213         if (!pgtable_page_ctor(page)) {
 214                 __free_page(page);
 215                 return NULL;
 216         }
 217         arch_set_page_dat(page, 0);
 218         /* Initialize page table */
 219         table = (unsigned long *) page_to_phys(page);
 220         if (mm_alloc_pgste(mm)) {
 221                 /* Return 4K page table with PGSTEs */
 222                 atomic_xor_bits(&page->_refcount, 3 << 24);
 223                 memset64((u64 *)table, _PAGE_INVALID, PTRS_PER_PTE);
 224                 memset64((u64 *)table + PTRS_PER_PTE, 0, PTRS_PER_PTE);
 225         } else {
 226                 /* Return the first 2K fragment of the page */
 227                 atomic_xor_bits(&page->_refcount, 1 << 24);
 228                 memset64((u64 *)table, _PAGE_INVALID, 2 * PTRS_PER_PTE);
 229                 spin_lock_bh(&mm->context.lock);
 230                 list_add(&page->lru, &mm->context.pgtable_list);
 231                 spin_unlock_bh(&mm->context.lock);
 232         }
 233         return table;
 234 }
 235
 236 void page_table_free(struct mm_struct *mm, unsigned long *table)
 237 {
 238         struct page *page;
 239         unsigned int bit, mask;
 240
 241         page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
 242         if (!mm_alloc_pgste(mm)) {
 243                 /* Free 2K page table fragment of a 4K page */
 244                 bit = (__pa(table) & ~PAGE_MASK)/(PTRS_PER_PTE*sizeof(pte_t));
 245                 spin_lock_bh(&mm->context.lock);
 246                 mask = atomic_xor_bits(&page->_refcount, 1U << (bit + 24));
 247                 mask >>= 24;
 248                 if (mask & 3)
 249                         list_add(&page->lru, &mm->context.pgtable_list);
 250                 else
 251                         list_del(&page->lru);
 252                 spin_unlock_bh(&mm->context.lock);
 253                 if (mask != 0)
 254                         return;
 255         }
 256
 257         pgtable_page_dtor(page);
 258         __free_page(page);
 259 }
 260
 261 void page_table_free_rcu(struct mmu_gather *tlb, unsigned long *table,
 262                          unsigned long vmaddr)
 263 {
 264         struct mm_struct *mm;
 265         struct page *page;
 266         unsigned int bit, mask;
 267
 268         mm = tlb->mm;
 269         page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
 270         if (mm_alloc_pgste(mm)) {
 271                 gmap_unlink(mm, table, vmaddr);
 272                 table = (unsigned long *) (__pa(table) | 3);
 273                 tlb_remove_table(tlb, table);
 274                 return;
 275         }
 276         bit = (__pa(table) & ~PAGE_MASK) / (PTRS_PER_PTE*sizeof(pte_t));
 277         spin_lock_bh(&mm->context.lock);
 278         mask = atomic_xor_bits(&page->_refcount, 0x11U << (bit + 24));
 279         mask >>= 24;
 280         if (mask & 3)
 281                 list_add_tail(&page->lru, &mm->context.pgtable_list);
 282         else
 283                 list_del(&page->lru);
 284         spin_unlock_bh(&mm->context.lock);
 285         table = (unsigned long *) (__pa(table) | (1U << bit));
 286         tlb_remove_table(tlb, table);
 287 }
 288
 289 static void __tlb_remove_table(void *_table)
 290 {
 291         unsigned int mask = (unsigned long) _table & 3;
 292         void *table = (void *)((unsigned long) _table ^ mask);
 293         struct page *page = pfn_to_page(__pa(table) >> PAGE_SHIFT);
 294
 295         switch (mask) {
 296         case 0:         /* pmd, pud, or p4d */
 297                 free_pages((unsigned long) table, 2);
 298                 break;
 299         case 1:         /* lower 2K of a 4K page table */
 300         case 2:         /* higher 2K of a 4K page table */
 301                 mask = atomic_xor_bits(&page->_refcount, mask << (4 + 24));
 302                 mask >>= 24;
 303                 if (mask != 0)
 304                         break;
 305                 /* fallthrough */
 306         case 3:         /* 4K page table with pgstes */
 307                 pgtable_page_dtor(page);
 308                 __free_page(page);
 309                 break;
 310         }
 311 }
 312
 313 static void tlb_remove_table_smp_sync(void *arg)
 314 {
 315         /* Simply deliver the interrupt */
 316 }
 317
 318 static void tlb_remove_table_one(void *table)
 319 {
 320         /*
 321          * This isn't an RCU grace period and hence the page-tables cannot be
 322          * assumed to be actually RCU-freed.
 323          *
 324          * It is however sufficient for software page-table walkers that rely
 325          * on IRQ disabling. See the comment near struct mmu_table_batch.
 326          */
 327         smp_call_function(tlb_remove_table_smp_sync, NULL, 1);
 328         __tlb_remove_table(table);
 329 }
 330
 331 static void tlb_remove_table_rcu(struct rcu_head *head)
 332 {
 333         struct mmu_table_batch *batch;
 334         int i;
 335
 336         batch = container_of(head, struct mmu_table_batch, rcu);
 337
 338         for (i = 0; i < batch->nr; i++)
 339                 __tlb_remove_table(batch->tables[i]);
 340
 341         free_page((unsigned long)batch);
 342 }
 343
 344 void tlb_table_flush(struct mmu_gather *tlb)
 345 {
 346         struct mmu_table_batch **batch = &tlb->batch;
 347
 348         if (*batch) {
 349                 call_rcu_sched(&(*batch)->rcu, tlb_remove_table_rcu);
 350                 *batch = NULL;
 351         }
 352 }
 353
 354 void tlb_remove_table(struct mmu_gather *tlb, void *table)
 355 {
 356         struct mmu_table_batch **batch = &tlb->batch;
 357
 358         tlb->mm->context.flush_mm = 1;
 359         if (*batch == NULL) {
 360                 *batch = (struct mmu_table_batch *)
 361                         __get_free_page(GFP_NOWAIT | __GFP_NOWARN);
 362                 if (*batch == NULL) {
 363                         __tlb_flush_mm_lazy(tlb->mm);
 364                         tlb_remove_table_one(table);
 365                         return;
 366                 }
 367                 (*batch)->nr = 0;
 368         }
 369         (*batch)->tables[(*batch)->nr++] = table;
 370         if ((*batch)->nr == MAX_TABLE_BATCH)
 371                 tlb_flush_mmu(tlb);
 372 }
 373
 374 /*
 375  * Base infrastructure required to generate basic asces, region, segment,
 376  * and page tables that do not make use of enhanced features like EDAT1.
 377  */
 378
 379 static struct kmem_cache *base_pgt_cache;
 380
 381 static unsigned long base_pgt_alloc(void)
 382 {
 383         u64 *table;
 384
 385         table = kmem_cache_alloc(base_pgt_cache, GFP_KERNEL);
 386         if (table)
 387                 memset64(table, _PAGE_INVALID, PTRS_PER_PTE);
 388         return (unsigned long) table;
 389 }
 390
 391 static void base_pgt_free(unsigned long table)
 392 {
 393         kmem_cache_free(base_pgt_cache, (void *) table);
 394 }
 395
 396 static unsigned long base_crst_alloc(unsigned long val)
 397 {
 398         unsigned long table;
 399
 400         table =  __get_free_pages(GFP_KERNEL, CRST_ALLOC_ORDER);
 401         if (table)
 402                 crst_table_init((unsigned long *)table, val);
 403         return table;
 404 }
 405
 406 static void base_crst_free(unsigned long table)
 407 {
 408         free_pages(table, CRST_ALLOC_ORDER);
 409 }
 410
 411 #define BASE_ADDR_END_FUNC(NAME, SIZE)                                  \
 412 static inline unsigned long base_##NAME##_addr_end(unsigned long addr,  \
 413                                                    unsigned long end)   \
 414 {                                                                       \
 415         unsigned long next = (addr + (SIZE)) & ~((SIZE) - 1);           \
 416                                                                         \
 417         return (next - 1) < (end - 1) ? next : end;                     \
 418 }
 419
 420 BASE_ADDR_END_FUNC(page,    _PAGE_SIZE)
 421 BASE_ADDR_END_FUNC(segment, _SEGMENT_SIZE)
 422 BASE_ADDR_END_FUNC(region3, _REGION3_SIZE)
 423 BASE_ADDR_END_FUNC(region2, _REGION2_SIZE)
 424 BASE_ADDR_END_FUNC(region1, _REGION1_SIZE)
 425
 426 static inline unsigned long base_lra(unsigned long address)
 427 {
 428         unsigned long real;
 429
 430         asm volatile(
 431                 "       lra     %0,0(%1)\n"
 432                 : "=d" (real) : "a" (address) : "cc");
 433         return real;
 434 }
 435
 436 static int base_page_walk(unsigned long origin, unsigned long addr,
 437                           unsigned long end, int alloc)
 438 {
 439         unsigned long *pte, next;
 440
 441         if (!alloc)
 442                 return 0;
 443         pte = (unsigned long *) origin;
 444         pte += (addr & _PAGE_INDEX) >> _PAGE_SHIFT;
 445         do {
 446                 next = base_page_addr_end(addr, end);
 447                 *pte = base_lra(addr);
 448         } while (pte++, addr = next, addr < end);
 449         return 0;
 450 }
 451
 452 static int base_segment_walk(unsigned long origin, unsigned long addr,
 453                              unsigned long end, int alloc)
 454 {
 455         unsigned long *ste, next, table;
 456         int rc;
 457
 458         ste = (unsigned long *) origin;
 459         ste += (addr & _SEGMENT_INDEX) >> _SEGMENT_SHIFT;
 460         do {
 461                 next = base_segment_addr_end(addr, end);
 462                 if (*ste & _SEGMENT_ENTRY_INVALID) {
 463                         if (!alloc)
 464                                 continue;
 465                         table = base_pgt_alloc();
 466                         if (!table)
 467                                 return -ENOMEM;
 468                         *ste = table | _SEGMENT_ENTRY;
 469                 }
 470                 table = *ste & _SEGMENT_ENTRY_ORIGIN;
 471                 rc = base_page_walk(table, addr, next, alloc);
 472                 if (rc)
 473                         return rc;
 474                 if (!alloc)
 475                         base_pgt_free(table);
 476                 cond_resched();
 477         } while (ste++, addr = next, addr < end);
 478         return 0;
 479 }
 480
 481 static int base_region3_walk(unsigned long origin, unsigned long addr,
 482                              unsigned long end, int alloc)
 483 {
 484         unsigned long *rtte, next, table;
 485         int rc;
 486
 487         rtte = (unsigned long *) origin;
 488         rtte += (addr & _REGION3_INDEX) >> _REGION3_SHIFT;
 489         do {
 490                 next = base_region3_addr_end(addr, end);
 491                 if (*rtte & _REGION_ENTRY_INVALID) {
 492                         if (!alloc)
 493                                 continue;
 494                         table = base_crst_alloc(_SEGMENT_ENTRY_EMPTY);
 495                         if (!table)
 496                                 return -ENOMEM;
 497                         *rtte = table | _REGION3_ENTRY;
 498                 }
 499                 table = *rtte & _REGION_ENTRY_ORIGIN;
 500                 rc = base_segment_walk(table, addr, next, alloc);
 501                 if (rc)
 502                         return rc;
 503                 if (!alloc)
 504                         base_crst_free(table);
 505         } while (rtte++, addr = next, addr < end);
 506         return 0;
 507 }
 508
 509 static int base_region2_walk(unsigned long origin, unsigned long addr,
 510                              unsigned long end, int alloc)
 511 {
 512         unsigned long *rste, next, table;
 513         int rc;
 514
 515         rste = (unsigned long *) origin;
 516         rste += (addr & _REGION2_INDEX) >> _REGION2_SHIFT;
 517         do {
 518                 next = base_region2_addr_end(addr, end);
 519                 if (*rste & _REGION_ENTRY_INVALID) {
 520                         if (!alloc)
 521                                 continue;
 522                         table = base_crst_alloc(_REGION3_ENTRY_EMPTY);
 523                         if (!table)
 524                                 return -ENOMEM;
 525                         *rste = table | _REGION2_ENTRY;
 526                 }
 527                 table = *rste & _REGION_ENTRY_ORIGIN;
 528                 rc = base_region3_walk(table, addr, next, alloc);
 529                 if (rc)
 530                         return rc;
 531                 if (!alloc)
 532                         base_crst_free(table);
 533         } while (rste++, addr = next, addr < end);
 534         return 0;
 535 }
 536
 537 static int base_region1_walk(unsigned long origin, unsigned long addr,
 538                              unsigned long end, int alloc)
 539 {
 540         unsigned long *rfte, next, table;
 541         int rc;
 542
 543         rfte = (unsigned long *) origin;
 544         rfte += (addr & _REGION1_INDEX) >> _REGION1_SHIFT;
 545         do {
 546                 next = base_region1_addr_end(addr, end);
 547                 if (*rfte & _REGION_ENTRY_INVALID) {
 548                         if (!alloc)
 549                                 continue;
 550                         table = base_crst_alloc(_REGION2_ENTRY_EMPTY);
 551                         if (!table)
 552                                 return -ENOMEM;
 553                         *rfte = table | _REGION1_ENTRY;
 554                 }
 555                 table = *rfte & _REGION_ENTRY_ORIGIN;
 556                 rc = base_region2_walk(table, addr, next, alloc);
 557                 if (rc)
 558                         return rc;
 559                 if (!alloc)
 560                         base_crst_free(table);
 561         } while (rfte++, addr = next, addr < end);
 562         return 0;
 563 }
 564
 565 /**
 566  * base_asce_free - free asce and tables returned from base_asce_alloc()
 567  * @asce: asce to be freed
 568  *
 569  * Frees all region, segment, and page tables that were allocated with a
 570  * corresponding base_asce_alloc() call.
 571  */
 572 void base_asce_free(unsigned long asce)
 573 {
 574         unsigned long table = asce & _ASCE_ORIGIN;
 575
 576         if (!asce)
 577                 return;
 578         switch (asce & _ASCE_TYPE_MASK) {
 579         case _ASCE_TYPE_SEGMENT:
 580                 base_segment_walk(table, 0, _REGION3_SIZE, 0);
 581                 break;
 582         case _ASCE_TYPE_REGION3:
 583                 base_region3_walk(table, 0, _REGION2_SIZE, 0);
 584                 break;
 585         case _ASCE_TYPE_REGION2:
 586                 base_region2_walk(table, 0, _REGION1_SIZE, 0);
 587                 break;
 588         case _ASCE_TYPE_REGION1:
 589                 base_region1_walk(table, 0, -_PAGE_SIZE, 0);
 590                 break;
 591         }
 592         base_crst_free(table);
 593 }
 594
 595 static int base_pgt_cache_init(void)
 596 {
 597         static DEFINE_MUTEX(base_pgt_cache_mutex);
 598         unsigned long sz = _PAGE_TABLE_SIZE;
 599
 600         if (base_pgt_cache)
 601                 return 0;
 602         mutex_lock(&base_pgt_cache_mutex);
 603         if (!base_pgt_cache)
 604                 base_pgt_cache = kmem_cache_create("base_pgt", sz, sz, 0, NULL);
 605         mutex_unlock(&base_pgt_cache_mutex);
 606         return base_pgt_cache ? 0 : -ENOMEM;
 607 }
 608
 609 /**
 610  * base_asce_alloc - create kernel mapping without enhanced DAT features
 611  * @addr: virtual start address of kernel mapping
 612  * @num_pages: number of consecutive pages
 613  *
 614  * Generate an asce, including all required region, segment and page tables,
 615  * that can be used to access the virtual kernel mapping. The difference is
 616  * that the returned asce does not make use of any enhanced DAT features like
 617  * e.g. large pages. This is required for some I/O functions that pass an
 618  * asce, like e.g. some service call requests.
 619  *
 620  * Note: the returned asce may NEVER be attached to any cpu. It may only be
 621  *       used for I/O requests. tlb entries that might result because the
 622  *       asce was attached to a cpu won't be cleared.
 623  */
 624 unsigned long base_asce_alloc(unsigned long addr, unsigned long num_pages)
 625 {
 626         unsigned long asce, table, end;
 627         int rc;
 628
 629         if (base_pgt_cache_init())
 630                 return 0;
 631         end = addr + num_pages * PAGE_SIZE;
 632         if (end <= _REGION3_SIZE) {
 633                 table = base_crst_alloc(_SEGMENT_ENTRY_EMPTY);
 634                 if (!table)
 635                         return 0;
 636                 rc = base_segment_walk(table, addr, end, 1);
 637                 asce = table | _ASCE_TYPE_SEGMENT | _ASCE_TABLE_LENGTH;
 638         } else if (end <= _REGION2_SIZE) {
 639                 table = base_crst_alloc(_REGION3_ENTRY_EMPTY);
 640                 if (!table)
 641                         return 0;
 642                 rc = base_region3_walk(table, addr, end, 1);
 643                 asce = table | _ASCE_TYPE_REGION3 | _ASCE_TABLE_LENGTH;
 644         } else if (end <= _REGION1_SIZE) {
 645                 table = base_crst_alloc(_REGION2_ENTRY_EMPTY);
 646                 if (!table)
 647                         return 0;
 648                 rc = base_region2_walk(table, addr, end, 1);
 649                 asce = table | _ASCE_TYPE_REGION2 | _ASCE_TABLE_LENGTH;
 650         } else {
 651                 table = base_crst_alloc(_REGION1_ENTRY_EMPTY);
 652                 if (!table)
 653                         return 0;
 654                 rc = base_region1_walk(table, addr, end, 1);
 655                 asce = table | _ASCE_TYPE_REGION1 | _ASCE_TABLE_LENGTH;
 656         }
 657         if (rc) {
 658                 base_asce_free(asce);
 659                 asce = 0;
 660         }
 661         return asce;
 662 }