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