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