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 * Virtual_count is not a pure "count".
34 * 0 means that it is not mapped, and has not been mapped
35 * since a TLB flush - it is usable.
36 * 1 means that there are no users, but it has been mapped
37 * since the last TLB flush - so we can't use it.
38 * n means that there are (n-1) current users of it.
39 */
40#ifdef CONFIG_HIGHMEM
41
42unsigned long totalhigh_pages __read_mostly;
43EXPORT_SYMBOL(totalhigh_pages);
44
45unsigned int nr_free_highpages (void)
46{
47    pg_data_t *pgdat;
48    unsigned int pages = 0;
49
50    for_each_online_pgdat(pgdat) {
51        pages += zone_page_state(&pgdat->node_zones[ZONE_HIGHMEM],
52            NR_FREE_PAGES);
53        if (zone_movable_is_highmem())
54            pages += zone_page_state(
55                    &pgdat->node_zones[ZONE_MOVABLE],
56                    NR_FREE_PAGES);
57    }
58
59    return pages;
60}
61
62static int pkmap_count[LAST_PKMAP];
63static unsigned int last_pkmap_nr;
64static __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);
65
66pte_t * pkmap_page_table;
67
68static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
69
70/*
71 * Most architectures have no use for kmap_high_get(), so let's abstract
72 * the disabling of IRQ out of the locking in that case to save on a
73 * potential useless overhead.
74 */
75#ifdef ARCH_NEEDS_KMAP_HIGH_GET
76#define lock_kmap() spin_lock_irq(&kmap_lock)
77#define unlock_kmap() spin_unlock_irq(&kmap_lock)
78#define lock_kmap_any(flags) spin_lock_irqsave(&kmap_lock, flags)
79#define unlock_kmap_any(flags) spin_unlock_irqrestore(&kmap_lock, flags)
80#else
81#define lock_kmap() spin_lock(&kmap_lock)
82#define unlock_kmap() spin_unlock(&kmap_lock)
83#define lock_kmap_any(flags) \
84        do { spin_lock(&kmap_lock); (void)(flags); } while (0)
85#define unlock_kmap_any(flags) \
86        do { spin_unlock(&kmap_lock); (void)(flags); } while (0)
87#endif
88
89static void flush_all_zero_pkmaps(void)
90{
91    int i;
92    int need_flush = 0;
93
94    flush_cache_kmaps();
95
96    for (i = 0; i < LAST_PKMAP; i++) {
97        struct page *page;
98
99        /*
100         * zero means we don't have anything to do,
101         * >1 means that it is still in use. Only
102         * a count of 1 means that it is free but
103         * needs to be unmapped
104         */
105        if (pkmap_count[i] != 1)
106            continue;
107        pkmap_count[i] = 0;
108
109        /* sanity check */
110        BUG_ON(pte_none(pkmap_page_table[i]));
111
112        /*
113         * Don't need an atomic fetch-and-clear op here;
114         * no-one has the page mapped, and cannot get at
115         * its virtual address (and hence PTE) without first
116         * getting the kmap_lock (which is held here).
117         * So no dangers, even with speculative execution.
118         */
119        page = pte_page(pkmap_page_table[i]);
120        pte_clear(&init_mm, (unsigned long)page_address(page),
121              &pkmap_page_table[i]);
122
123        set_page_address(page, NULL);
124        need_flush = 1;
125    }
126    if (need_flush)
127        flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
128}
129
130/**
131 * kmap_flush_unused - flush all unused kmap mappings in order to remove stray mappings
132 */
133void kmap_flush_unused(void)
134{
135    lock_kmap();
136    flush_all_zero_pkmaps();
137    unlock_kmap();
138}
139
140static inline unsigned long map_new_virtual(struct page *page)
141{
142    unsigned long vaddr;
143    int count;
144
145start:
146    count = LAST_PKMAP;
147    /* Find an empty entry */
148    for (;;) {
149        last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
150        if (!last_pkmap_nr) {
151            flush_all_zero_pkmaps();
152            count = LAST_PKMAP;
153        }
154        if (!pkmap_count[last_pkmap_nr])
155            break; /* Found a usable entry */
156        if (--count)
157            continue;
158
159        /*
160         * Sleep for somebody else to unmap their entries
161         */
162        {
163            DECLARE_WAITQUEUE(wait, current);
164
165            __set_current_state(TASK_UNINTERRUPTIBLE);
166            add_wait_queue(&pkmap_map_wait, &wait);
167            unlock_kmap();
168            schedule();
169            remove_wait_queue(&pkmap_map_wait, &wait);
170            lock_kmap();
171
172            /* Somebody else might have mapped it while we slept */
173            if (page_address(page))
174                return (unsigned long)page_address(page);
175
176            /* Re-start */
177            goto start;
178        }
179    }
180    vaddr = PKMAP_ADDR(last_pkmap_nr);
181    set_pte_at(&init_mm, vaddr,
182           &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));
183
184    pkmap_count[last_pkmap_nr] = 1;
185    set_page_address(page, (void *)vaddr);
186
187    return vaddr;
188}
189
190/**
191 * kmap_high - map a highmem page into memory
192 * @page: &struct page to map
193 *
194 * Returns the page's virtual memory address.
195 *
196 * We cannot call this from interrupts, as it may block.
197 */
198void *kmap_high(struct page *page)
199{
200    unsigned long vaddr;
201
202    /*
203     * For highmem pages, we can't trust "virtual" until
204     * after we have the lock.
205     */
206    lock_kmap();
207    vaddr = (unsigned long)page_address(page);
208    if (!vaddr)
209        vaddr = map_new_virtual(page);
210    pkmap_count[PKMAP_NR(vaddr)]++;
211    BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 2);
212    unlock_kmap();
213    return (void*) vaddr;
214}
215
216EXPORT_SYMBOL(kmap_high);
217
218#ifdef ARCH_NEEDS_KMAP_HIGH_GET
219/**
220 * kmap_high_get - pin a highmem page into memory
221 * @page: &struct page to pin
222 *
223 * Returns the page's current virtual memory address, or NULL if no mapping
224 * exists. If and only if a non null address is returned then a
225 * matching call to kunmap_high() is necessary.
226 *
227 * This can be called from any context.
228 */
229void *kmap_high_get(struct page *page)
230{
231    unsigned long vaddr, flags;
232
233    lock_kmap_any(flags);
234    vaddr = (unsigned long)page_address(page);
235    if (vaddr) {
236        BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 1);
237        pkmap_count[PKMAP_NR(vaddr)]++;
238    }
239    unlock_kmap_any(flags);
240    return (void*) vaddr;
241}
242#endif
243
244/**
245 * kunmap_high - map a highmem page into memory
246 * @page: &struct page to unmap
247 *
248 * If ARCH_NEEDS_KMAP_HIGH_GET is not defined then this may be called
249 * only from user context.
250 */
251void kunmap_high(struct page *page)
252{
253    unsigned long vaddr;
254    unsigned long nr;
255    unsigned long flags;
256    int need_wakeup;
257
258    lock_kmap_any(flags);
259    vaddr = (unsigned long)page_address(page);
260    BUG_ON(!vaddr);
261    nr = PKMAP_NR(vaddr);
262
263    /*
264     * A count must never go down to zero
265     * without a TLB flush!
266     */
267    need_wakeup = 0;
268    switch (--pkmap_count[nr]) {
269    case 0:
270        BUG();
271    case 1:
272        /*
273         * Avoid an unnecessary wake_up() function call.
274         * The common case is pkmap_count[] == 1, but
275         * no waiters.
276         * The tasks queued in the wait-queue are guarded
277         * by both the lock in the wait-queue-head and by
278         * the kmap_lock. As the kmap_lock is held here,
279         * no need for the wait-queue-head's lock. Simply
280         * test if the queue is empty.
281         */
282        need_wakeup = waitqueue_active(&pkmap_map_wait);
283    }
284    unlock_kmap_any(flags);
285
286    /* do wake-up, if needed, race-free outside of the spin lock */
287    if (need_wakeup)
288        wake_up(&pkmap_map_wait);
289}
290
291EXPORT_SYMBOL(kunmap_high);
292#endif
293
294#if defined(HASHED_PAGE_VIRTUAL)
295
296#define PA_HASH_ORDER 7
297
298/*
299 * Describes one page->virtual association
300 */
301struct page_address_map {
302    struct page *page;
303    void *virtual;
304    struct list_head list;
305};
306
307/*
308 * page_address_map freelist, allocated from page_address_maps.
309 */
310static struct list_head page_address_pool; /* freelist */
311static spinlock_t pool_lock; /* protects page_address_pool */
312
313/*
314 * Hash table bucket
315 */
316static struct page_address_slot {
317    struct list_head lh; /* List of page_address_maps */
318    spinlock_t lock; /* Protect this bucket's list */
319} ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];
320
321static struct page_address_slot *page_slot(struct page *page)
322{
323    return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
324}
325
326/**
327 * page_address - get the mapped virtual address of a page
328 * @page: &struct page to get the virtual address of
329 *
330 * Returns the page's virtual address.
331 */
332void *page_address(struct page *page)
333{
334    unsigned long flags;
335    void *ret;
336    struct page_address_slot *pas;
337
338    if (!PageHighMem(page))
339        return lowmem_page_address(page);
340
341    pas = page_slot(page);
342    ret = NULL;
343    spin_lock_irqsave(&pas->lock, flags);
344    if (!list_empty(&pas->lh)) {
345        struct page_address_map *pam;
346
347        list_for_each_entry(pam, &pas->lh, list) {
348            if (pam->page == page) {
349                ret = pam->virtual;
350                goto done;
351            }
352        }
353    }
354done:
355    spin_unlock_irqrestore(&pas->lock, flags);
356    return ret;
357}
358
359EXPORT_SYMBOL(page_address);
360
361/**
362 * set_page_address - set a page's virtual address
363 * @page: &struct page to set
364 * @virtual: virtual address to use
365 */
366void set_page_address(struct page *page, void *virtual)
367{
368    unsigned long flags;
369    struct page_address_slot *pas;
370    struct page_address_map *pam;
371
372    BUG_ON(!PageHighMem(page));
373
374    pas = page_slot(page);
375    if (virtual) { /* Add */
376        BUG_ON(list_empty(&page_address_pool));
377
378        spin_lock_irqsave(&pool_lock, flags);
379        pam = list_entry(page_address_pool.next,
380                struct page_address_map, list);
381        list_del(&pam->list);
382        spin_unlock_irqrestore(&pool_lock, flags);
383
384        pam->page = page;
385        pam->virtual = virtual;
386
387        spin_lock_irqsave(&pas->lock, flags);
388        list_add_tail(&pam->list, &pas->lh);
389        spin_unlock_irqrestore(&pas->lock, flags);
390    } else { /* Remove */
391        spin_lock_irqsave(&pas->lock, flags);
392        list_for_each_entry(pam, &pas->lh, list) {
393            if (pam->page == page) {
394                list_del(&pam->list);
395                spin_unlock_irqrestore(&pas->lock, flags);
396                spin_lock_irqsave(&pool_lock, flags);
397                list_add_tail(&pam->list, &page_address_pool);
398                spin_unlock_irqrestore(&pool_lock, flags);
399                goto done;
400            }
401        }
402        spin_unlock_irqrestore(&pas->lock, flags);
403    }
404done:
405    return;
406}
407
408static struct page_address_map page_address_maps[LAST_PKMAP];
409
410void __init page_address_init(void)
411{
412    int i;
413
414    INIT_LIST_HEAD(&page_address_pool);
415    for (i = 0; i < ARRAY_SIZE(page_address_maps); i++)
416        list_add(&page_address_maps[i].list, &page_address_pool);
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    spin_lock_init(&pool_lock);
422}
423
424#endif /* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */
425
426#ifdef CONFIG_DEBUG_HIGHMEM
427
428void debug_kmap_atomic(enum km_type type)
429{
430    static int warn_count = 10;
431
432    if (unlikely(warn_count < 0))
433        return;
434
435    if (unlikely(in_interrupt())) {
436        if (in_nmi()) {
437            if (type != KM_NMI && type != KM_NMI_PTE) {
438                WARN_ON(1);
439                warn_count--;
440            }
441        } else if (in_irq()) {
442            if (type != KM_IRQ0 && type != KM_IRQ1 &&
443                type != KM_BIO_SRC_IRQ && type != KM_BIO_DST_IRQ &&
444                type != KM_BOUNCE_READ && type != KM_IRQ_PTE) {
445                WARN_ON(1);
446                warn_count--;
447            }
448        } else if (!irqs_disabled()) { /* softirq */
449            if (type != KM_IRQ0 && type != KM_IRQ1 &&
450                type != KM_SOFTIRQ0 && type != KM_SOFTIRQ1 &&
451                type != KM_SKB_SUNRPC_DATA &&
452                type != KM_SKB_DATA_SOFTIRQ &&
453                type != KM_BOUNCE_READ) {
454                WARN_ON(1);
455                warn_count--;
456            }
457        }
458    }
459
460    if (type == KM_IRQ0 || type == KM_IRQ1 || type == KM_BOUNCE_READ ||
461            type == KM_BIO_SRC_IRQ || type == KM_BIO_DST_IRQ ||
462            type == KM_IRQ_PTE || type == KM_NMI ||
463            type == KM_NMI_PTE ) {
464        if (!irqs_disabled()) {
465            WARN_ON(1);
466            warn_count--;
467        }
468    } else if (type == KM_SOFTIRQ0 || type == KM_SOFTIRQ1) {
469        if (irq_count() == 0 && !irqs_disabled()) {
470            WARN_ON(1);
471            warn_count--;
472        }
473    }
474#ifdef CONFIG_KGDB_KDB
475    if (unlikely(type == KM_KDB && atomic_read(&kgdb_active) == -1)) {
476        WARN_ON(1);
477        warn_count--;
478    }
479#endif /* CONFIG_KGDB_KDB */
480}
481
482#endif
483

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