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