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/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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