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