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