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
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 - unmap 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(const 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(const 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