root/mm/highmem.c

DEFINITIONS

1. get_pkmap_color
2. get_next_pkmap_nr
3. no_more_pkmaps
4. get_pkmap_entries_count
5. get_pkmap_wait_queue_head
6. nr_free_highpages
7. kmap_to_page
8. flush_all_zero_pkmaps
9. kmap_flush_unused
10. map_new_virtual
11. kmap_high
12. kmap_high_get
13. kunmap_high
14. page_slot
15. page_address
16. set_page_address
17. page_address_init

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * High memory handling common code and variables.
   4  *
   5  * (C) 1999 Andrea Arcangeli, SuSE GmbH, andrea@suse.de
   6  *          Gerhard Wichert, Siemens AG, Gerhard.Wichert@pdb.siemens.de
   7  *
   8  *
   9  * Redesigned the x86 32-bit VM architecture to deal with
  10  * 64-bit physical space. With current x86 CPUs this
  11  * means up to 64 Gigabytes physical RAM.
  12  *
  13  * Rewrote high memory support to move the page cache into
  14  * high memory. Implemented permanent (schedulable) kmaps
  15  * based on Linus' idea.
  16  *
  17  * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
  18  */
  19 
  20 #include <linux/mm.h>
  21 #include <linux/export.h>
  22 #include <linux/swap.h>
  23 #include <linux/bio.h>
  24 #include <linux/pagemap.h>
  25 #include <linux/mempool.h>
  26 #include <linux/blkdev.h>
  27 #include <linux/init.h>
  28 #include <linux/hash.h>
  29 #include <linux/highmem.h>
  30 #include <linux/kgdb.h>
  31 #include <asm/tlbflush.h>
  32 
  33 
  34 #if defined(CONFIG_HIGHMEM) || defined(CONFIG_X86_32)
  35 DEFINE_PER_CPU(int, __kmap_atomic_idx);
  36 #endif
  37 
  38 /*
  39  * Virtual_count is not a pure "count".
  40  *  0 means that it is not mapped, and has not been mapped
  41  *    since a TLB flush - it is usable.
  42  *  1 means that there are no users, but it has been mapped
  43  *    since the last TLB flush - so we can't use it.
  44  *  n means that there are (n-1) current users of it.
  45  */
  46 #ifdef CONFIG_HIGHMEM
  47 
  48 /*
  49  * Architecture with aliasing data cache may define the following family of
  50  * helper functions in its asm/highmem.h to control cache color of virtual
  51  * addresses where physical memory pages are mapped by kmap.
  52  */
  53 #ifndef get_pkmap_color
  54 
  55 /*
  56  * Determine color of virtual address where the page should be mapped.
  57  */
  58 static inline unsigned int get_pkmap_color(struct page *page)
  59 {
  60         return 0;
  61 }
  62 #define get_pkmap_color get_pkmap_color
  63 
  64 /*
  65  * Get next index for mapping inside PKMAP region for page with given color.
  66  */
  67 static inline unsigned int get_next_pkmap_nr(unsigned int color)
  68 {
  69         static unsigned int last_pkmap_nr;
  70 
  71         last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
  72         return last_pkmap_nr;
  73 }
  74 
  75 /*
  76  * Determine if page index inside PKMAP region (pkmap_nr) of given color
  77  * has wrapped around PKMAP region end. When this happens an attempt to
  78  * flush all unused PKMAP slots is made.
  79  */
  80 static inline int no_more_pkmaps(unsigned int pkmap_nr, unsigned int color)
  81 {
  82         return pkmap_nr == 0;
  83 }
  84 
  85 /*
  86  * Get the number of PKMAP entries of the given color. If no free slot is
  87  * found after checking that many entries, kmap will sleep waiting for
  88  * someone to call kunmap and free PKMAP slot.
  89  */
  90 static inline int get_pkmap_entries_count(unsigned int color)
  91 {
  92         return LAST_PKMAP;
  93 }
  94 
  95 /*
  96  * Get head of a wait queue for PKMAP entries of the given color.
  97  * Wait queues for different mapping colors should be independent to avoid
  98  * unnecessary wakeups caused by freeing of slots of other colors.
  99  */
 100 static inline wait_queue_head_t *get_pkmap_wait_queue_head(unsigned int color)
 101 {
 102         static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
 103 
 104         return &pkmap_map_wait;
 105 }
 106 #endif
 107 
 108 atomic_long_t _totalhigh_pages __read_mostly;
 109 EXPORT_SYMBOL(_totalhigh_pages);
 110 
 111 EXPORT_PER_CPU_SYMBOL(__kmap_atomic_idx);
 112 
 113 unsigned int nr_free_highpages (void)
 114 {
 115         struct zone *zone;
 116         unsigned int pages = 0;
 117 
 118         for_each_populated_zone(zone) {
 119                 if (is_highmem(zone))
 120                         pages += zone_page_state(zone, NR_FREE_PAGES);
 121         }
 122 
 123         return pages;
 124 }
 125 
 126 static int pkmap_count[LAST_PKMAP];
 127 static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);
 128 
 129 pte_t * pkmap_page_table;
 130 
 131 /*
 132  * Most architectures have no use for kmap_high_get(), so let's abstract
 133  * the disabling of IRQ out of the locking in that case to save on a
 134  * potential useless overhead.
 135  */
 136 #ifdef ARCH_NEEDS_KMAP_HIGH_GET
 137 #define lock_kmap()             spin_lock_irq(&kmap_lock)
 138 #define unlock_kmap()           spin_unlock_irq(&kmap_lock)
 139 #define lock_kmap_any(flags)    spin_lock_irqsave(&kmap_lock, flags)
 140 #define unlock_kmap_any(flags)  spin_unlock_irqrestore(&kmap_lock, flags)
 141 #else
 142 #define lock_kmap()             spin_lock(&kmap_lock)
 143 #define unlock_kmap()           spin_unlock(&kmap_lock)
 144 #define lock_kmap_any(flags)    \
 145                 do { spin_lock(&kmap_lock); (void)(flags); } while (0)
 146 #define unlock_kmap_any(flags)  \
 147                 do { spin_unlock(&kmap_lock); (void)(flags); } while (0)
 148 #endif
 149 
 150 struct page *kmap_to_page(void *vaddr)
 151 {
 152         unsigned long addr = (unsigned long)vaddr;
 153 
 154         if (addr >= PKMAP_ADDR(0) && addr < PKMAP_ADDR(LAST_PKMAP)) {
 155                 int i = PKMAP_NR(addr);
 156                 return pte_page(pkmap_page_table[i]);
 157         }
 158 
 159         return virt_to_page(addr);
 160 }
 161 EXPORT_SYMBOL(kmap_to_page);
 162 
 163 static void flush_all_zero_pkmaps(void)
 164 {
 165         int i;
 166         int need_flush = 0;
 167 
 168         flush_cache_kmaps();
 169 
 170         for (i = 0; i < LAST_PKMAP; i++) {
 171                 struct page *page;
 172 
 173                 /*
 174                  * zero means we don't have anything to do,
 175                  * >1 means that it is still in use. Only
 176                  * a count of 1 means that it is free but
 177                  * needs to be unmapped
 178                  */
 179                 if (pkmap_count[i] != 1)
 180                         continue;
 181                 pkmap_count[i] = 0;
 182 
 183                 /* sanity check */
 184                 BUG_ON(pte_none(pkmap_page_table[i]));
 185 
 186                 /*
 187                  * Don't need an atomic fetch-and-clear op here;
 188                  * no-one has the page mapped, and cannot get at
 189                  * its virtual address (and hence PTE) without first
 190                  * getting the kmap_lock (which is held here).
 191                  * So no dangers, even with speculative execution.
 192                  */
 193                 page = pte_page(pkmap_page_table[i]);
 194                 pte_clear(&init_mm, PKMAP_ADDR(i), &pkmap_page_table[i]);
 195 
 196                 set_page_address(page, NULL);
 197                 need_flush = 1;
 198         }
 199         if (need_flush)
 200                 flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
 201 }
 202 
 203 /**
 204  * kmap_flush_unused - flush all unused kmap mappings in order to remove stray mappings
 205  */
 206 void kmap_flush_unused(void)
 207 {
 208         lock_kmap();
 209         flush_all_zero_pkmaps();
 210         unlock_kmap();
 211 }
 212 
 213 static inline unsigned long map_new_virtual(struct page *page)
 214 {
 215         unsigned long vaddr;
 216         int count;
 217         unsigned int last_pkmap_nr;
 218         unsigned int color = get_pkmap_color(page);
 219 
 220 start:
 221         count = get_pkmap_entries_count(color);
 222         /* Find an empty entry */
 223         for (;;) {
 224                 last_pkmap_nr = get_next_pkmap_nr(color);
 225                 if (no_more_pkmaps(last_pkmap_nr, color)) {
 226                         flush_all_zero_pkmaps();
 227                         count = get_pkmap_entries_count(color);
 228                 }
 229                 if (!pkmap_count[last_pkmap_nr])
 230                         break;  /* Found a usable entry */
 231                 if (--count)
 232                         continue;
 233 
 234                 /*
 235                  * Sleep for somebody else to unmap their entries
 236                  */
 237                 {
 238                         DECLARE_WAITQUEUE(wait, current);
 239                         wait_queue_head_t *pkmap_map_wait =
 240                                 get_pkmap_wait_queue_head(color);
 241 
 242                         __set_current_state(TASK_UNINTERRUPTIBLE);
 243                         add_wait_queue(pkmap_map_wait, &wait);
 244                         unlock_kmap();
 245                         schedule();
 246                         remove_wait_queue(pkmap_map_wait, &wait);
 247                         lock_kmap();
 248 
 249                         /* Somebody else might have mapped it while we slept */
 250                         if (page_address(page))
 251                                 return (unsigned long)page_address(page);
 252 
 253                         /* Re-start */
 254                         goto start;
 255                 }
 256         }
 257         vaddr = PKMAP_ADDR(last_pkmap_nr);
 258         set_pte_at(&init_mm, vaddr,
 259                    &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));
 260 
 261         pkmap_count[last_pkmap_nr] = 1;
 262         set_page_address(page, (void *)vaddr);
 263 
 264         return vaddr;
 265 }
 266 
 267 /**
 268  * kmap_high - map a highmem page into memory
 269  * @page: &struct page to map
 270  *
 271  * Returns the page's virtual memory address.
 272  *
 273  * We cannot call this from interrupts, as it may block.
 274  */
 275 void *kmap_high(struct page *page)
 276 {
 277         unsigned long vaddr;
 278 
 279         /*
 280          * For highmem pages, we can't trust "virtual" until
 281          * after we have the lock.
 282          */
 283         lock_kmap();
 284         vaddr = (unsigned long)page_address(page);
 285         if (!vaddr)
 286                 vaddr = map_new_virtual(page);
 287         pkmap_count[PKMAP_NR(vaddr)]++;
 288         BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 2);
 289         unlock_kmap();
 290         return (void*) vaddr;
 291 }
 292 
 293 EXPORT_SYMBOL(kmap_high);
 294 
 295 #ifdef ARCH_NEEDS_KMAP_HIGH_GET
 296 /**
 297  * kmap_high_get - pin a highmem page into memory
 298  * @page: &struct page to pin
 299  *
 300  * Returns the page's current virtual memory address, or NULL if no mapping
 301  * exists.  If and only if a non null address is returned then a
 302  * matching call to kunmap_high() is necessary.
 303  *
 304  * This can be called from any context.
 305  */
 306 void *kmap_high_get(struct page *page)
 307 {
 308         unsigned long vaddr, flags;
 309 
 310         lock_kmap_any(flags);
 311         vaddr = (unsigned long)page_address(page);
 312         if (vaddr) {
 313                 BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 1);
 314                 pkmap_count[PKMAP_NR(vaddr)]++;
 315         }
 316         unlock_kmap_any(flags);
 317         return (void*) vaddr;
 318 }
 319 #endif
 320 
 321 /**
 322  * kunmap_high - unmap a highmem page into memory
 323  * @page: &struct page to unmap
 324  *
 325  * If ARCH_NEEDS_KMAP_HIGH_GET is not defined then this may be called
 326  * only from user context.
 327  */
 328 void kunmap_high(struct page *page)
 329 {
 330         unsigned long vaddr;
 331         unsigned long nr;
 332         unsigned long flags;
 333         int need_wakeup;
 334         unsigned int color = get_pkmap_color(page);
 335         wait_queue_head_t *pkmap_map_wait;
 336 
 337         lock_kmap_any(flags);
 338         vaddr = (unsigned long)page_address(page);
 339         BUG_ON(!vaddr);
 340         nr = PKMAP_NR(vaddr);
 341 
 342         /*
 343          * A count must never go down to zero
 344          * without a TLB flush!
 345          */
 346         need_wakeup = 0;
 347         switch (--pkmap_count[nr]) {
 348         case 0:
 349                 BUG();
 350         case 1:
 351                 /*
 352                  * Avoid an unnecessary wake_up() function call.
 353                  * The common case is pkmap_count[] == 1, but
 354                  * no waiters.
 355                  * The tasks queued in the wait-queue are guarded
 356                  * by both the lock in the wait-queue-head and by
 357                  * the kmap_lock.  As the kmap_lock is held here,
 358                  * no need for the wait-queue-head's lock.  Simply
 359                  * test if the queue is empty.
 360                  */
 361                 pkmap_map_wait = get_pkmap_wait_queue_head(color);
 362                 need_wakeup = waitqueue_active(pkmap_map_wait);
 363         }
 364         unlock_kmap_any(flags);
 365 
 366         /* do wake-up, if needed, race-free outside of the spin lock */
 367         if (need_wakeup)
 368                 wake_up(pkmap_map_wait);
 369 }
 370 
 371 EXPORT_SYMBOL(kunmap_high);
 372 #endif
 373 
 374 #if defined(HASHED_PAGE_VIRTUAL)
 375 
 376 #define PA_HASH_ORDER   7
 377 
 378 /*
 379  * Describes one page->virtual association
 380  */
 381 struct page_address_map {
 382         struct page *page;
 383         void *virtual;
 384         struct list_head list;
 385 };
 386 
 387 static struct page_address_map page_address_maps[LAST_PKMAP];
 388 
 389 /*
 390  * Hash table bucket
 391  */
 392 static struct page_address_slot {
 393         struct list_head lh;                    /* List of page_address_maps */
 394         spinlock_t lock;                        /* Protect this bucket's list */
 395 } ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];
 396 
 397 static struct page_address_slot *page_slot(const struct page *page)
 398 {
 399         return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
 400 }
 401 
 402 /**
 403  * page_address - get the mapped virtual address of a page
 404  * @page: &struct page to get the virtual address of
 405  *
 406  * Returns the page's virtual address.
 407  */
 408 void *page_address(const struct page *page)
 409 {
 410         unsigned long flags;
 411         void *ret;
 412         struct page_address_slot *pas;
 413 
 414         if (!PageHighMem(page))
 415                 return lowmem_page_address(page);
 416 
 417         pas = page_slot(page);
 418         ret = NULL;
 419         spin_lock_irqsave(&pas->lock, flags);
 420         if (!list_empty(&pas->lh)) {
 421                 struct page_address_map *pam;
 422 
 423                 list_for_each_entry(pam, &pas->lh, list) {
 424                         if (pam->page == page) {
 425                                 ret = pam->virtual;
 426                                 goto done;
 427                         }
 428                 }
 429         }
 430 done:
 431         spin_unlock_irqrestore(&pas->lock, flags);
 432         return ret;
 433 }
 434 
 435 EXPORT_SYMBOL(page_address);
 436 
 437 /**
 438  * set_page_address - set a page's virtual address
 439  * @page: &struct page to set
 440  * @virtual: virtual address to use
 441  */
 442 void set_page_address(struct page *page, void *virtual)
 443 {
 444         unsigned long flags;
 445         struct page_address_slot *pas;
 446         struct page_address_map *pam;
 447 
 448         BUG_ON(!PageHighMem(page));
 449 
 450         pas = page_slot(page);
 451         if (virtual) {          /* Add */
 452                 pam = &page_address_maps[PKMAP_NR((unsigned long)virtual)];
 453                 pam->page = page;
 454                 pam->virtual = virtual;
 455 
 456                 spin_lock_irqsave(&pas->lock, flags);
 457                 list_add_tail(&pam->list, &pas->lh);
 458                 spin_unlock_irqrestore(&pas->lock, flags);
 459         } else {                /* Remove */
 460                 spin_lock_irqsave(&pas->lock, flags);
 461                 list_for_each_entry(pam, &pas->lh, list) {
 462                         if (pam->page == page) {
 463                                 list_del(&pam->list);
 464                                 spin_unlock_irqrestore(&pas->lock, flags);
 465                                 goto done;
 466                         }
 467                 }
 468                 spin_unlock_irqrestore(&pas->lock, flags);
 469         }
 470 done:
 471         return;
 472 }
 473 
 474 void __init page_address_init(void)
 475 {
 476         int i;
 477 
 478         for (i = 0; i < ARRAY_SIZE(page_address_htable); i++) {
 479                 INIT_LIST_HEAD(&page_address_htable[i].lh);
 480                 spin_lock_init(&page_address_htable[i].lock);
 481         }
 482 }
 483 
 484 #endif  /* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */