mm/highmem.c

   1 /*
   2  * High memory handling common code and variables.
   3  *
   4  * (C) 1999 Andrea Arcangeli, SuSE GmbH, andrea@suse.de
   5  *          Gerhard Wichert, Siemens AG, Gerhard.Wichert@pdb.siemens.de
   6  *
   7  *
   8  * Redesigned the x86 32-bit VM architecture to deal with
   9  * 64-bit physical space. With current x86 CPUs this
  10  * means up to 64 Gigabytes physical RAM.
  11  *
  12  * Rewrote high memory support to move the page cache into
  13  * high memory. Implemented permanent (schedulable) kmaps
  14  * based on Linus' idea.
  15  *
  16  * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
  17  */
  18
  19 #include <linux/mm.h>
  20 #include <linux/export.h>
  21 #include <linux/swap.h>
  22 #include <linux/bio.h>
  23 #include <linux/pagemap.h>
  24 #include <linux/mempool.h>
  25 #include <linux/blkdev.h>
  26 #include <linux/init.h>
  27 #include <linux/hash.h>
  28 #include <linux/highmem.h>
  29 #include <linux/kgdb.h>
  30 #include <asm/tlbflush.h>
  31
  32
  33 #if defined(CONFIG_HIGHMEM) || defined(CONFIG_X86_32)
  34 DEFINE_PER_CPU(int, __kmap_atomic_idx);
  35 #endif
  36
  37 /*
  38  * Virtual_count is not a pure "count".
  39  *  0 means that it is not mapped, and has not been mapped
  40  *    since a TLB flush - it is usable.
  41  *  1 means that there are no users, but it has been mapped
  42  *    since the last TLB flush - so we can't use it.
  43  *  n means that there are (n-1) current users of it.
  44  */
  45 #ifdef CONFIG_HIGHMEM
  46
  47 unsigned long totalhigh_pages __read_mostly;
  48 EXPORT_SYMBOL(totalhigh_pages);
  49
  50
  51 EXPORT_PER_CPU_SYMBOL(__kmap_atomic_idx);
  52
  53 unsigned int nr_free_highpages (void)
  54 {
  55         pg_data_t *pgdat;
  56         unsigned int pages = 0;
  57
  58         for_each_online_pgdat(pgdat) {
  59                 pages += zone_page_state(&pgdat->node_zones[ZONE_HIGHMEM],
  60                         NR_FREE_PAGES);
  61                 if (zone_movable_is_highmem())
  62                         pages += zone_page_state(
  63                                         &pgdat->node_zones[ZONE_MOVABLE],
  64                                         NR_FREE_PAGES);
  65         }
  66
  67         return pages;
  68 }
  69
  70 static int pkmap_count[LAST_PKMAP];
  71 static unsigned int last_pkmap_nr;
  72 static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);
  73
  74 pte_t * pkmap_page_table;
  75
  76 static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
  77
  78 /*
  79  * Most architectures have no use for kmap_high_get(), so let's abstract
  80  * the disabling of IRQ out of the locking in that case to save on a
  81  * potential useless overhead.
  82  */
  83 #ifdef ARCH_NEEDS_KMAP_HIGH_GET
  84 #define lock_kmap()             spin_lock_irq(&kmap_lock)
  85 #define unlock_kmap()           spin_unlock_irq(&kmap_lock)
  86 #define lock_kmap_any(flags)    spin_lock_irqsave(&kmap_lock, flags)
  87 #define unlock_kmap_any(flags)  spin_unlock_irqrestore(&kmap_lock, flags)
  88 #else
  89 #define lock_kmap()             spin_lock(&kmap_lock)
  90 #define unlock_kmap()           spin_unlock(&kmap_lock)
  91 #define lock_kmap_any(flags)    \
  92                 do { spin_lock(&kmap_lock); (void)(flags); } while (0)
  93 #define unlock_kmap_any(flags)  \
  94                 do { spin_unlock(&kmap_lock); (void)(flags); } while (0)
  95 #endif
  96
  97 static void flush_all_zero_pkmaps(void)
  98 {
  99         int i;
 100         int need_flush = 0;
 101
 102         flush_cache_kmaps();
 103
 104         for (i = 0; i < LAST_PKMAP; i++) {
 105                 struct page *page;
 106
 107                 /*
 108                  * zero means we don't have anything to do,
 109                  * >1 means that it is still in use. Only
 110                  * a count of 1 means that it is free but
 111                  * needs to be unmapped
 112                  */
 113                 if (pkmap_count[i] != 1)
 114                         continue;
 115                 pkmap_count[i] = 0;
 116
 117                 /* sanity check */
 118                 BUG_ON(pte_none(pkmap_page_table[i]));
 119
 120                 /*
 121                  * Don't need an atomic fetch-and-clear op here;
 122                  * no-one has the page mapped, and cannot get at
 123                  * its virtual address (and hence PTE) without first
 124                  * getting the kmap_lock (which is held here).
 125                  * So no dangers, even with speculative execution.
 126                  */
 127                 page = pte_page(pkmap_page_table[i]);
 128                 pte_clear(&init_mm, (unsigned long)page_address(page),
 129                           &pkmap_page_table[i]);
 130
 131                 set_page_address(page, NULL);
 132                 need_flush = 1;
 133         }
 134         if (need_flush)
 135                 flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
 136 }
 137
 138 /**
 139  * kmap_flush_unused - flush all unused kmap mappings in order to remove stray mappings
 140  */
 141 void kmap_flush_unused(void)
 142 {
 143         lock_kmap();
 144         flush_all_zero_pkmaps();
 145         unlock_kmap();
 146 }
 147
 148 static inline unsigned long map_new_virtual(struct page *page)
 149 {
 150         unsigned long vaddr;
 151         int count;
 152
 153 start:
 154         count = LAST_PKMAP;
 155         /* Find an empty entry */
 156         for (;;) {
 157                 last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
 158                 if (!last_pkmap_nr) {
 159                         flush_all_zero_pkmaps();
 160                         count = LAST_PKMAP;
 161                 }
 162                 if (!pkmap_count[last_pkmap_nr])
 163                         break;  /* Found a usable entry */
 164                 if (--count)
 165                         continue;
 166
 167                 /*
 168                  * Sleep for somebody else to unmap their entries
 169                  */
 170                 {
 171                         DECLARE_WAITQUEUE(wait, current);
 172
 173                         __set_current_state(TASK_UNINTERRUPTIBLE);
 174                         add_wait_queue(&pkmap_map_wait, &wait);
 175                         unlock_kmap();
 176                         schedule();
 177                         remove_wait_queue(&pkmap_map_wait, &wait);
 178                         lock_kmap();
 179
 180                         /* Somebody else might have mapped it while we slept */
 181                         if (page_address(page))
 182                                 return (unsigned long)page_address(page);
 183
 184                         /* Re-start */
 185                         goto start;
 186                 }
 187         }
 188         vaddr = PKMAP_ADDR(last_pkmap_nr);
 189         set_pte_at(&init_mm, vaddr,
 190                    &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));
 191
 192         pkmap_count[last_pkmap_nr] = 1;
 193         set_page_address(page, (void *)vaddr);
 194
 195         return vaddr;
 196 }
 197
 198 /**
 199  * kmap_high - map a highmem page into memory
 200  * @page: &struct page to map
 201  *
 202  * Returns the page's virtual memory address.
 203  *
 204  * We cannot call this from interrupts, as it may block.
 205  */
 206 void *kmap_high(struct page *page)
 207 {
 208         unsigned long vaddr;
 209
 210         /*
 211          * For highmem pages, we can't trust "virtual" until
 212          * after we have the lock.
 213          */
 214         lock_kmap();
 215         vaddr = (unsigned long)page_address(page);
 216         if (!vaddr)
 217                 vaddr = map_new_virtual(page);
 218         pkmap_count[PKMAP_NR(vaddr)]++;
 219         BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 2);
 220         unlock_kmap();
 221         return (void*) vaddr;
 222 }
 223
 224 EXPORT_SYMBOL(kmap_high);
 225
 226 #ifdef ARCH_NEEDS_KMAP_HIGH_GET
 227 /**
 228  * kmap_high_get - pin a highmem page into memory
 229  * @page: &struct page to pin
 230  *
 231  * Returns the page's current virtual memory address, or NULL if no mapping
 232  * exists.  If and only if a non null address is returned then a
 233  * matching call to kunmap_high() is necessary.
 234  *
 235  * This can be called from any context.
 236  */
 237 void *kmap_high_get(struct page *page)
 238 {
 239         unsigned long vaddr, flags;
 240
 241         lock_kmap_any(flags);
 242         vaddr = (unsigned long)page_address(page);
 243         if (vaddr) {
 244                 BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 1);
 245                 pkmap_count[PKMAP_NR(vaddr)]++;
 246         }
 247         unlock_kmap_any(flags);
 248         return (void*) vaddr;
 249 }
 250 #endif
 251
 252 /**
 253  * kunmap_high - unmap a highmem page into memory
 254  * @page: &struct page to unmap
 255  *
 256  * If ARCH_NEEDS_KMAP_HIGH_GET is not defined then this may be called
 257  * only from user context.
 258  */
 259 void kunmap_high(struct page *page)
 260 {
 261         unsigned long vaddr;
 262         unsigned long nr;
 263         unsigned long flags;
 264         int need_wakeup;
 265
 266         lock_kmap_any(flags);
 267         vaddr = (unsigned long)page_address(page);
 268         BUG_ON(!vaddr);
 269         nr = PKMAP_NR(vaddr);
 270
 271         /*
 272          * A count must never go down to zero
 273          * without a TLB flush!
 274          */
 275         need_wakeup = 0;
 276         switch (--pkmap_count[nr]) {
 277         case 0:
 278                 BUG();
 279         case 1:
 280                 /*
 281                  * Avoid an unnecessary wake_up() function call.
 282                  * The common case is pkmap_count[] == 1, but
 283                  * no waiters.
 284                  * The tasks queued in the wait-queue are guarded
 285                  * by both the lock in the wait-queue-head and by
 286                  * the kmap_lock.  As the kmap_lock is held here,
 287                  * no need for the wait-queue-head's lock.  Simply
 288                  * test if the queue is empty.
 289                  */
 290                 need_wakeup = waitqueue_active(&pkmap_map_wait);
 291         }
 292         unlock_kmap_any(flags);
 293
 294         /* do wake-up, if needed, race-free outside of the spin lock */
 295         if (need_wakeup)
 296                 wake_up(&pkmap_map_wait);
 297 }
 298
 299 EXPORT_SYMBOL(kunmap_high);
 300 #endif
 301
 302 #if defined(HASHED_PAGE_VIRTUAL)
 303
 304 #define PA_HASH_ORDER   7
 305
 306 /*
 307  * Describes one page->virtual association
 308  */
 309 struct page_address_map {
 310         struct page *page;
 311         void *virtual;
 312         struct list_head list;
 313 };
 314
 315 /*
 316  * page_address_map freelist, allocated from page_address_maps.
 317  */
 318 static struct list_head page_address_pool;      /* freelist */
 319 static spinlock_t pool_lock;                    /* protects page_address_pool */
 320
 321 /*
 322  * Hash table bucket
 323  */
 324 static struct page_address_slot {
 325         struct list_head lh;                    /* List of page_address_maps */
 326         spinlock_t lock;                        /* Protect this bucket's list */
 327 } ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];
 328
 329 static struct page_address_slot *page_slot(const struct page *page)
 330 {
 331         return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
 332 }
 333
 334 /**
 335  * page_address - get the mapped virtual address of a page
 336  * @page: &struct page to get the virtual address of
 337  *
 338  * Returns the page's virtual address.
 339  */
 340 void *page_address(const struct page *page)
 341 {
 342         unsigned long flags;
 343         void *ret;
 344         struct page_address_slot *pas;
 345
 346         if (!PageHighMem(page))
 347                 return lowmem_page_address(page);
 348
 349         pas = page_slot(page);
 350         ret = NULL;
 351         spin_lock_irqsave(&pas->lock, flags);
 352         if (!list_empty(&pas->lh)) {
 353                 struct page_address_map *pam;
 354
 355                 list_for_each_entry(pam, &pas->lh, list) {
 356                         if (pam->page == page) {
 357                                 ret = pam->virtual;
 358                                 goto done;
 359                         }
 360                 }
 361         }
 362 done:
 363         spin_unlock_irqrestore(&pas->lock, flags);
 364         return ret;
 365 }
 366
 367 EXPORT_SYMBOL(page_address);
 368
 369 /**
 370  * set_page_address - set a page's virtual address
 371  * @page: &struct page to set
 372  * @virtual: virtual address to use
 373  */
 374 void set_page_address(struct page *page, void *virtual)
 375 {
 376         unsigned long flags;
 377         struct page_address_slot *pas;
 378         struct page_address_map *pam;
 379
 380         BUG_ON(!PageHighMem(page));
 381
 382         pas = page_slot(page);
 383         if (virtual) {          /* Add */
 384                 BUG_ON(list_empty(&page_address_pool));
 385
 386                 spin_lock_irqsave(&pool_lock, flags);
 387                 pam = list_entry(page_address_pool.next,
 388                                 struct page_address_map, list);
 389                 list_del(&pam->list);
 390                 spin_unlock_irqrestore(&pool_lock, flags);
 391
 392                 pam->page = page;
 393                 pam->virtual = virtual;
 394
 395                 spin_lock_irqsave(&pas->lock, flags);
 396                 list_add_tail(&pam->list, &pas->lh);
 397                 spin_unlock_irqrestore(&pas->lock, flags);
 398         } else {                /* Remove */
 399                 spin_lock_irqsave(&pas->lock, flags);
 400                 list_for_each_entry(pam, &pas->lh, list) {
 401                         if (pam->page == page) {
 402                                 list_del(&pam->list);
 403                                 spin_unlock_irqrestore(&pas->lock, flags);
 404                                 spin_lock_irqsave(&pool_lock, flags);
 405                                 list_add_tail(&pam->list, &page_address_pool);
 406                                 spin_unlock_irqrestore(&pool_lock, flags);
 407                                 goto done;
 408                         }
 409                 }
 410                 spin_unlock_irqrestore(&pas->lock, flags);
 411         }
 412 done:
 413         return;
 414 }
 415
 416 static struct page_address_map page_address_maps[LAST_PKMAP];
 417
 418 void __init page_address_init(void)
 419 {
 420         int i;
 421
 422         INIT_LIST_HEAD(&page_address_pool);
 423         for (i = 0; i < ARRAY_SIZE(page_address_maps); i++)
 424                 list_add(&page_address_maps[i].list, &page_address_pool);
 425         for (i = 0; i < ARRAY_SIZE(page_address_htable); i++) {
 426                 INIT_LIST_HEAD(&page_address_htable[i].lh);
 427                 spin_lock_init(&page_address_htable[i].lock);
 428         }
 429         spin_lock_init(&pool_lock);
 430 }
 431
 432 #endif  /* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */