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