linux/mm/highmem.c
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   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)
  34DEFINE_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
  47unsigned long totalhigh_pages __read_mostly;
  48EXPORT_SYMBOL(totalhigh_pages);
  49
  50
  51EXPORT_PER_CPU_SYMBOL(__kmap_atomic_idx);
  52
  53unsigned 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
  70static int pkmap_count[LAST_PKMAP];
  71static unsigned int last_pkmap_nr;
  72static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);
  73
  74pte_t * pkmap_page_table;
  75
  76static 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
  97struct 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 = (addr - PKMAP_ADDR(0)) >> PAGE_SHIFT;
 103                return pte_page(pkmap_page_table[i]);
 104        }
 105
 106        return virt_to_page(addr);
 107}
 108EXPORT_SYMBOL(kmap_to_page);
 109
 110static void flush_all_zero_pkmaps(void)
 111{
 112        int i;
 113        int need_flush = 0;
 114
 115        flush_cache_kmaps();
 116
 117        for (i = 0; i < LAST_PKMAP; i++) {
 118                struct page *page;
 119
 120                /*
 121                 * zero means we don't have anything to do,
 122                 * >1 means that it is still in use. Only
 123                 * a count of 1 means that it is free but
 124                 * needs to be unmapped
 125                 */
 126                if (pkmap_count[i] != 1)
 127                        continue;
 128                pkmap_count[i] = 0;
 129
 130                /* sanity check */
 131                BUG_ON(pte_none(pkmap_page_table[i]));
 132
 133                /*
 134                 * Don't need an atomic fetch-and-clear op here;
 135                 * no-one has the page mapped, and cannot get at
 136                 * its virtual address (and hence PTE) without first
 137                 * getting the kmap_lock (which is held here).
 138                 * So no dangers, even with speculative execution.
 139                 */
 140                page = pte_page(pkmap_page_table[i]);
 141                pte_clear(&init_mm, (unsigned long)page_address(page),
 142                          &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 */
 154void kmap_flush_unused(void)
 155{
 156        lock_kmap();
 157        flush_all_zero_pkmaps();
 158        unlock_kmap();
 159}
 160
 161static inline unsigned long map_new_virtual(struct page *page)
 162{
 163        unsigned long vaddr;
 164        int count;
 165
 166start:
 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 */
 219void *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
 237EXPORT_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 */
 250void *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 */
 272void 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
 312EXPORT_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 */
 322struct page_address_map {
 323        struct page *page;
 324        void *virtual;
 325        struct list_head list;
 326};
 327
 328/*
 329 * page_address_map freelist, allocated from page_address_maps.
 330 */
 331static struct list_head page_address_pool;      /* freelist */
 332static spinlock_t pool_lock;                    /* protects page_address_pool */
 333
 334/*
 335 * Hash table bucket
 336 */
 337static struct page_address_slot {
 338        struct list_head lh;                    /* List of page_address_maps */
 339        spinlock_t lock;                        /* Protect this bucket's list */
 340} ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];
 341
 342static struct page_address_slot *page_slot(const struct page *page)
 343{
 344        return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
 345}
 346
 347/**
 348 * page_address - get the mapped virtual address of a page
 349 * @page: &struct page to get the virtual address of
 350 *
 351 * Returns the page's virtual address.
 352 */
 353void *page_address(const struct page *page)
 354{
 355        unsigned long flags;
 356        void *ret;
 357        struct page_address_slot *pas;
 358
 359        if (!PageHighMem(page))
 360                return lowmem_page_address(page);
 361
 362        pas = page_slot(page);
 363        ret = NULL;
 364        spin_lock_irqsave(&pas->lock, flags);
 365        if (!list_empty(&pas->lh)) {
 366                struct page_address_map *pam;
 367
 368                list_for_each_entry(pam, &pas->lh, list) {
 369                        if (pam->page == page) {
 370                                ret = pam->virtual;
 371                                goto done;
 372                        }
 373                }
 374        }
 375done:
 376        spin_unlock_irqrestore(&pas->lock, flags);
 377        return ret;
 378}
 379
 380EXPORT_SYMBOL(page_address);
 381
 382/**
 383 * set_page_address - set a page's virtual address
 384 * @page: &struct page to set
 385 * @virtual: virtual address to use
 386 */
 387void set_page_address(struct page *page, void *virtual)
 388{
 389        unsigned long flags;
 390        struct page_address_slot *pas;
 391        struct page_address_map *pam;
 392
 393        BUG_ON(!PageHighMem(page));
 394
 395        pas = page_slot(page);
 396        if (virtual) {          /* Add */
 397                BUG_ON(list_empty(&page_address_pool));
 398
 399                spin_lock_irqsave(&pool_lock, flags);
 400                pam = list_entry(page_address_pool.next,
 401                                struct page_address_map, list);
 402                list_del(&pam->list);
 403                spin_unlock_irqrestore(&pool_lock, flags);
 404
 405                pam->page = page;
 406                pam->virtual = virtual;
 407
 408                spin_lock_irqsave(&pas->lock, flags);
 409                list_add_tail(&pam->list, &pas->lh);
 410                spin_unlock_irqrestore(&pas->lock, flags);
 411        } else {                /* Remove */
 412                spin_lock_irqsave(&pas->lock, flags);
 413                list_for_each_entry(pam, &pas->lh, list) {
 414                        if (pam->page == page) {
 415                                list_del(&pam->list);
 416                                spin_unlock_irqrestore(&pas->lock, flags);
 417                                spin_lock_irqsave(&pool_lock, flags);
 418                                list_add_tail(&pam->list, &page_address_pool);
 419                                spin_unlock_irqrestore(&pool_lock, flags);
 420                                goto done;
 421                        }
 422                }
 423                spin_unlock_irqrestore(&pas->lock, flags);
 424        }
 425done:
 426        return;
 427}
 428
 429static struct page_address_map page_address_maps[LAST_PKMAP];
 430
 431void __init page_address_init(void)
 432{
 433        int i;
 434
 435        INIT_LIST_HEAD(&page_address_pool);
 436        for (i = 0; i < ARRAY_SIZE(page_address_maps); i++)
 437                list_add(&page_address_maps[i].list, &page_address_pool);
 438        for (i = 0; i < ARRAY_SIZE(page_address_htable); i++) {
 439                INIT_LIST_HEAD(&page_address_htable[i].lh);
 440                spin_lock_init(&page_address_htable[i].lock);
 441        }
 442        spin_lock_init(&pool_lock);
 443}
 444
 445#endif  /* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */
 446
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