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