Root/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/module.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
97static void flush_all_zero_pkmaps(void)
98{
99    int i;
100    int need_flush = 0;
101
102    flush_cache_kmaps();
103
104    for (i = 0; i < LAST_PKMAP; i++) {
105        struct page *page;
106
107        /*
108         * zero means we don't have anything to do,
109         * >1 means that it is still in use. Only
110         * a count of 1 means that it is free but
111         * needs to be unmapped
112         */
113        if (pkmap_count[i] != 1)
114            continue;
115        pkmap_count[i] = 0;
116
117        /* sanity check */
118        BUG_ON(pte_none(pkmap_page_table[i]));
119
120        /*
121         * Don't need an atomic fetch-and-clear op here;
122         * no-one has the page mapped, and cannot get at
123         * its virtual address (and hence PTE) without first
124         * getting the kmap_lock (which is held here).
125         * So no dangers, even with speculative execution.
126         */
127        page = pte_page(pkmap_page_table[i]);
128        pte_clear(&init_mm, (unsigned long)page_address(page),
129              &pkmap_page_table[i]);
130
131        set_page_address(page, NULL);
132        need_flush = 1;
133    }
134    if (need_flush)
135        flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
136}
137
138/**
139 * kmap_flush_unused - flush all unused kmap mappings in order to remove stray mappings
140 */
141void kmap_flush_unused(void)
142{
143    lock_kmap();
144    flush_all_zero_pkmaps();
145    unlock_kmap();
146}
147
148static inline unsigned long map_new_virtual(struct page *page)
149{
150    unsigned long vaddr;
151    int count;
152
153start:
154    count = LAST_PKMAP;
155    /* Find an empty entry */
156    for (;;) {
157        last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
158        if (!last_pkmap_nr) {
159            flush_all_zero_pkmaps();
160            count = LAST_PKMAP;
161        }
162        if (!pkmap_count[last_pkmap_nr])
163            break; /* Found a usable entry */
164        if (--count)
165            continue;
166
167        /*
168         * Sleep for somebody else to unmap their entries
169         */
170        {
171            DECLARE_WAITQUEUE(wait, current);
172
173            __set_current_state(TASK_UNINTERRUPTIBLE);
174            add_wait_queue(&pkmap_map_wait, &wait);
175            unlock_kmap();
176            schedule();
177            remove_wait_queue(&pkmap_map_wait, &wait);
178            lock_kmap();
179
180            /* Somebody else might have mapped it while we slept */
181            if (page_address(page))
182                return (unsigned long)page_address(page);
183
184            /* Re-start */
185            goto start;
186        }
187    }
188    vaddr = PKMAP_ADDR(last_pkmap_nr);
189    set_pte_at(&init_mm, vaddr,
190           &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));
191
192    pkmap_count[last_pkmap_nr] = 1;
193    set_page_address(page, (void *)vaddr);
194
195    return vaddr;
196}
197
198/**
199 * kmap_high - map a highmem page into memory
200 * @page: &struct page to map
201 *
202 * Returns the page's virtual memory address.
203 *
204 * We cannot call this from interrupts, as it may block.
205 */
206void *kmap_high(struct page *page)
207{
208    unsigned long vaddr;
209
210    /*
211     * For highmem pages, we can't trust "virtual" until
212     * after we have the lock.
213     */
214    lock_kmap();
215    vaddr = (unsigned long)page_address(page);
216    if (!vaddr)
217        vaddr = map_new_virtual(page);
218    pkmap_count[PKMAP_NR(vaddr)]++;
219    BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 2);
220    unlock_kmap();
221    return (void*) vaddr;
222}
223
224EXPORT_SYMBOL(kmap_high);
225
226#ifdef ARCH_NEEDS_KMAP_HIGH_GET
227/**
228 * kmap_high_get - pin a highmem page into memory
229 * @page: &struct page to pin
230 *
231 * Returns the page's current virtual memory address, or NULL if no mapping
232 * exists. If and only if a non null address is returned then a
233 * matching call to kunmap_high() is necessary.
234 *
235 * This can be called from any context.
236 */
237void *kmap_high_get(struct page *page)
238{
239    unsigned long vaddr, flags;
240
241    lock_kmap_any(flags);
242    vaddr = (unsigned long)page_address(page);
243    if (vaddr) {
244        BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 1);
245        pkmap_count[PKMAP_NR(vaddr)]++;
246    }
247    unlock_kmap_any(flags);
248    return (void*) vaddr;
249}
250#endif
251
252/**
253 * kunmap_high - map a highmem page into memory
254 * @page: &struct page to unmap
255 *
256 * If ARCH_NEEDS_KMAP_HIGH_GET is not defined then this may be called
257 * only from user context.
258 */
259void kunmap_high(struct page *page)
260{
261    unsigned long vaddr;
262    unsigned long nr;
263    unsigned long flags;
264    int need_wakeup;
265
266    lock_kmap_any(flags);
267    vaddr = (unsigned long)page_address(page);
268    BUG_ON(!vaddr);
269    nr = PKMAP_NR(vaddr);
270
271    /*
272     * A count must never go down to zero
273     * without a TLB flush!
274     */
275    need_wakeup = 0;
276    switch (--pkmap_count[nr]) {
277    case 0:
278        BUG();
279    case 1:
280        /*
281         * Avoid an unnecessary wake_up() function call.
282         * The common case is pkmap_count[] == 1, but
283         * no waiters.
284         * The tasks queued in the wait-queue are guarded
285         * by both the lock in the wait-queue-head and by
286         * the kmap_lock. As the kmap_lock is held here,
287         * no need for the wait-queue-head's lock. Simply
288         * test if the queue is empty.
289         */
290        need_wakeup = waitqueue_active(&pkmap_map_wait);
291    }
292    unlock_kmap_any(flags);
293
294    /* do wake-up, if needed, race-free outside of the spin lock */
295    if (need_wakeup)
296        wake_up(&pkmap_map_wait);
297}
298
299EXPORT_SYMBOL(kunmap_high);
300#endif
301
302#if defined(HASHED_PAGE_VIRTUAL)
303
304#define PA_HASH_ORDER 7
305
306/*
307 * Describes one page->virtual association
308 */
309struct page_address_map {
310    struct page *page;
311    void *virtual;
312    struct list_head list;
313};
314
315/*
316 * page_address_map freelist, allocated from page_address_maps.
317 */
318static struct list_head page_address_pool; /* freelist */
319static spinlock_t pool_lock; /* protects page_address_pool */
320
321/*
322 * Hash table bucket
323 */
324static struct page_address_slot {
325    struct list_head lh; /* List of page_address_maps */
326    spinlock_t lock; /* Protect this bucket's list */
327} ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];
328
329static struct page_address_slot *page_slot(struct page *page)
330{
331    return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
332}
333
334/**
335 * page_address - get the mapped virtual address of a page
336 * @page: &struct page to get the virtual address of
337 *
338 * Returns the page's virtual address.
339 */
340void *page_address(struct page *page)
341{
342    unsigned long flags;
343    void *ret;
344    struct page_address_slot *pas;
345
346    if (!PageHighMem(page))
347        return lowmem_page_address(page);
348
349    pas = page_slot(page);
350    ret = NULL;
351    spin_lock_irqsave(&pas->lock, flags);
352    if (!list_empty(&pas->lh)) {
353        struct page_address_map *pam;
354
355        list_for_each_entry(pam, &pas->lh, list) {
356            if (pam->page == page) {
357                ret = pam->virtual;
358                goto done;
359            }
360        }
361    }
362done:
363    spin_unlock_irqrestore(&pas->lock, flags);
364    return ret;
365}
366
367EXPORT_SYMBOL(page_address);
368
369/**
370 * set_page_address - set a page's virtual address
371 * @page: &struct page to set
372 * @virtual: virtual address to use
373 */
374void set_page_address(struct page *page, void *virtual)
375{
376    unsigned long flags;
377    struct page_address_slot *pas;
378    struct page_address_map *pam;
379
380    BUG_ON(!PageHighMem(page));
381
382    pas = page_slot(page);
383    if (virtual) { /* Add */
384        BUG_ON(list_empty(&page_address_pool));
385
386        spin_lock_irqsave(&pool_lock, flags);
387        pam = list_entry(page_address_pool.next,
388                struct page_address_map, list);
389        list_del(&pam->list);
390        spin_unlock_irqrestore(&pool_lock, flags);
391
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                spin_lock_irqsave(&pool_lock, flags);
405                list_add_tail(&pam->list, &page_address_pool);
406                spin_unlock_irqrestore(&pool_lock, flags);
407                goto done;
408            }
409        }
410        spin_unlock_irqrestore(&pas->lock, flags);
411    }
412done:
413    return;
414}
415
416static struct page_address_map page_address_maps[LAST_PKMAP];
417
418void __init page_address_init(void)
419{
420    int i;
421
422    INIT_LIST_HEAD(&page_address_pool);
423    for (i = 0; i < ARRAY_SIZE(page_address_maps); i++)
424        list_add(&page_address_maps[i].list, &page_address_pool);
425    for (i = 0; i < ARRAY_SIZE(page_address_htable); i++) {
426        INIT_LIST_HEAD(&page_address_htable[i].lh);
427        spin_lock_init(&page_address_htable[i].lock);
428    }
429    spin_lock_init(&pool_lock);
430}
431
432#endif /* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */
433

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