xref: /openbmc/linux/mm/highmem.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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/blktrace_api.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 
42 unsigned long totalhigh_pages __read_mostly;
43 
44 unsigned int nr_free_highpages (void)
45 {
46 	pg_data_t *pgdat;
47 	unsigned int pages = 0;
48 
49 	for_each_online_pgdat(pgdat)
50 		pages += zone_page_state(&pgdat->node_zones[ZONE_HIGHMEM],
51 			NR_FREE_PAGES);
52 
53 	return pages;
54 }
55 
56 static int pkmap_count[LAST_PKMAP];
57 static unsigned int last_pkmap_nr;
58 static  __cacheline_aligned_in_smp DEFINE_SPINLOCK(kmap_lock);
59 
60 pte_t * pkmap_page_table;
61 
62 static DECLARE_WAIT_QUEUE_HEAD(pkmap_map_wait);
63 
64 static void flush_all_zero_pkmaps(void)
65 {
66 	int i;
67 
68 	flush_cache_kmaps();
69 
70 	for (i = 0; i < LAST_PKMAP; i++) {
71 		struct page *page;
72 
73 		/*
74 		 * zero means we don't have anything to do,
75 		 * >1 means that it is still in use. Only
76 		 * a count of 1 means that it is free but
77 		 * needs to be unmapped
78 		 */
79 		if (pkmap_count[i] != 1)
80 			continue;
81 		pkmap_count[i] = 0;
82 
83 		/* sanity check */
84 		BUG_ON(pte_none(pkmap_page_table[i]));
85 
86 		/*
87 		 * Don't need an atomic fetch-and-clear op here;
88 		 * no-one has the page mapped, and cannot get at
89 		 * its virtual address (and hence PTE) without first
90 		 * getting the kmap_lock (which is held here).
91 		 * So no dangers, even with speculative execution.
92 		 */
93 		page = pte_page(pkmap_page_table[i]);
94 		pte_clear(&init_mm, (unsigned long)page_address(page),
95 			  &pkmap_page_table[i]);
96 
97 		set_page_address(page, NULL);
98 	}
99 	flush_tlb_kernel_range(PKMAP_ADDR(0), PKMAP_ADDR(LAST_PKMAP));
100 }
101 
102 /* Flush all unused kmap mappings in order to remove stray
103    mappings. */
104 void kmap_flush_unused(void)
105 {
106 	spin_lock(&kmap_lock);
107 	flush_all_zero_pkmaps();
108 	spin_unlock(&kmap_lock);
109 }
110 
111 static inline unsigned long map_new_virtual(struct page *page)
112 {
113 	unsigned long vaddr;
114 	int count;
115 
116 start:
117 	count = LAST_PKMAP;
118 	/* Find an empty entry */
119 	for (;;) {
120 		last_pkmap_nr = (last_pkmap_nr + 1) & LAST_PKMAP_MASK;
121 		if (!last_pkmap_nr) {
122 			flush_all_zero_pkmaps();
123 			count = LAST_PKMAP;
124 		}
125 		if (!pkmap_count[last_pkmap_nr])
126 			break;	/* Found a usable entry */
127 		if (--count)
128 			continue;
129 
130 		/*
131 		 * Sleep for somebody else to unmap their entries
132 		 */
133 		{
134 			DECLARE_WAITQUEUE(wait, current);
135 
136 			__set_current_state(TASK_UNINTERRUPTIBLE);
137 			add_wait_queue(&pkmap_map_wait, &wait);
138 			spin_unlock(&kmap_lock);
139 			schedule();
140 			remove_wait_queue(&pkmap_map_wait, &wait);
141 			spin_lock(&kmap_lock);
142 
143 			/* Somebody else might have mapped it while we slept */
144 			if (page_address(page))
145 				return (unsigned long)page_address(page);
146 
147 			/* Re-start */
148 			goto start;
149 		}
150 	}
151 	vaddr = PKMAP_ADDR(last_pkmap_nr);
152 	set_pte_at(&init_mm, vaddr,
153 		   &(pkmap_page_table[last_pkmap_nr]), mk_pte(page, kmap_prot));
154 
155 	pkmap_count[last_pkmap_nr] = 1;
156 	set_page_address(page, (void *)vaddr);
157 
158 	return vaddr;
159 }
160 
161 void fastcall *kmap_high(struct page *page)
162 {
163 	unsigned long vaddr;
164 
165 	/*
166 	 * For highmem pages, we can't trust "virtual" until
167 	 * after we have the lock.
168 	 *
169 	 * We cannot call this from interrupts, as it may block
170 	 */
171 	spin_lock(&kmap_lock);
172 	vaddr = (unsigned long)page_address(page);
173 	if (!vaddr)
174 		vaddr = map_new_virtual(page);
175 	pkmap_count[PKMAP_NR(vaddr)]++;
176 	BUG_ON(pkmap_count[PKMAP_NR(vaddr)] < 2);
177 	spin_unlock(&kmap_lock);
178 	return (void*) vaddr;
179 }
180 
181 EXPORT_SYMBOL(kmap_high);
182 
183 void fastcall kunmap_high(struct page *page)
184 {
185 	unsigned long vaddr;
186 	unsigned long nr;
187 	int need_wakeup;
188 
189 	spin_lock(&kmap_lock);
190 	vaddr = (unsigned long)page_address(page);
191 	BUG_ON(!vaddr);
192 	nr = PKMAP_NR(vaddr);
193 
194 	/*
195 	 * A count must never go down to zero
196 	 * without a TLB flush!
197 	 */
198 	need_wakeup = 0;
199 	switch (--pkmap_count[nr]) {
200 	case 0:
201 		BUG();
202 	case 1:
203 		/*
204 		 * Avoid an unnecessary wake_up() function call.
205 		 * The common case is pkmap_count[] == 1, but
206 		 * no waiters.
207 		 * The tasks queued in the wait-queue are guarded
208 		 * by both the lock in the wait-queue-head and by
209 		 * the kmap_lock.  As the kmap_lock is held here,
210 		 * no need for the wait-queue-head's lock.  Simply
211 		 * test if the queue is empty.
212 		 */
213 		need_wakeup = waitqueue_active(&pkmap_map_wait);
214 	}
215 	spin_unlock(&kmap_lock);
216 
217 	/* do wake-up, if needed, race-free outside of the spin lock */
218 	if (need_wakeup)
219 		wake_up(&pkmap_map_wait);
220 }
221 
222 EXPORT_SYMBOL(kunmap_high);
223 #endif
224 
225 #if defined(HASHED_PAGE_VIRTUAL)
226 
227 #define PA_HASH_ORDER	7
228 
229 /*
230  * Describes one page->virtual association
231  */
232 struct page_address_map {
233 	struct page *page;
234 	void *virtual;
235 	struct list_head list;
236 };
237 
238 /*
239  * page_address_map freelist, allocated from page_address_maps.
240  */
241 static struct list_head page_address_pool;	/* freelist */
242 static spinlock_t pool_lock;			/* protects page_address_pool */
243 
244 /*
245  * Hash table bucket
246  */
247 static struct page_address_slot {
248 	struct list_head lh;			/* List of page_address_maps */
249 	spinlock_t lock;			/* Protect this bucket's list */
250 } ____cacheline_aligned_in_smp page_address_htable[1<<PA_HASH_ORDER];
251 
252 static struct page_address_slot *page_slot(struct page *page)
253 {
254 	return &page_address_htable[hash_ptr(page, PA_HASH_ORDER)];
255 }
256 
257 void *page_address(struct page *page)
258 {
259 	unsigned long flags;
260 	void *ret;
261 	struct page_address_slot *pas;
262 
263 	if (!PageHighMem(page))
264 		return lowmem_page_address(page);
265 
266 	pas = page_slot(page);
267 	ret = NULL;
268 	spin_lock_irqsave(&pas->lock, flags);
269 	if (!list_empty(&pas->lh)) {
270 		struct page_address_map *pam;
271 
272 		list_for_each_entry(pam, &pas->lh, list) {
273 			if (pam->page == page) {
274 				ret = pam->virtual;
275 				goto done;
276 			}
277 		}
278 	}
279 done:
280 	spin_unlock_irqrestore(&pas->lock, flags);
281 	return ret;
282 }
283 
284 EXPORT_SYMBOL(page_address);
285 
286 void set_page_address(struct page *page, void *virtual)
287 {
288 	unsigned long flags;
289 	struct page_address_slot *pas;
290 	struct page_address_map *pam;
291 
292 	BUG_ON(!PageHighMem(page));
293 
294 	pas = page_slot(page);
295 	if (virtual) {		/* Add */
296 		BUG_ON(list_empty(&page_address_pool));
297 
298 		spin_lock_irqsave(&pool_lock, flags);
299 		pam = list_entry(page_address_pool.next,
300 				struct page_address_map, list);
301 		list_del(&pam->list);
302 		spin_unlock_irqrestore(&pool_lock, flags);
303 
304 		pam->page = page;
305 		pam->virtual = virtual;
306 
307 		spin_lock_irqsave(&pas->lock, flags);
308 		list_add_tail(&pam->list, &pas->lh);
309 		spin_unlock_irqrestore(&pas->lock, flags);
310 	} else {		/* Remove */
311 		spin_lock_irqsave(&pas->lock, flags);
312 		list_for_each_entry(pam, &pas->lh, list) {
313 			if (pam->page == page) {
314 				list_del(&pam->list);
315 				spin_unlock_irqrestore(&pas->lock, flags);
316 				spin_lock_irqsave(&pool_lock, flags);
317 				list_add_tail(&pam->list, &page_address_pool);
318 				spin_unlock_irqrestore(&pool_lock, flags);
319 				goto done;
320 			}
321 		}
322 		spin_unlock_irqrestore(&pas->lock, flags);
323 	}
324 done:
325 	return;
326 }
327 
328 static struct page_address_map page_address_maps[LAST_PKMAP];
329 
330 void __init page_address_init(void)
331 {
332 	int i;
333 
334 	INIT_LIST_HEAD(&page_address_pool);
335 	for (i = 0; i < ARRAY_SIZE(page_address_maps); i++)
336 		list_add(&page_address_maps[i].list, &page_address_pool);
337 	for (i = 0; i < ARRAY_SIZE(page_address_htable); i++) {
338 		INIT_LIST_HEAD(&page_address_htable[i].lh);
339 		spin_lock_init(&page_address_htable[i].lock);
340 	}
341 	spin_lock_init(&pool_lock);
342 }
343 
344 #endif	/* defined(CONFIG_HIGHMEM) && !defined(WANT_PAGE_VIRTUAL) */
345