Root/arch/mips/mm/gup.c

Source at commit 694c7fbe86b8a9c91392e505afcb9fcfc91deccc created 12 years 8 months ago.
By Maarten ter Huurne, MIPS: JZ4740: Add cpufreq support
1/*
2 * Lockless get_user_pages_fast for MIPS
3 *
4 * Copyright (C) 2008 Nick Piggin
5 * Copyright (C) 2008 Novell Inc.
6 * Copyright (C) 2011 Ralf Baechle
7 */
8#include <linux/sched.h>
9#include <linux/mm.h>
10#include <linux/vmstat.h>
11#include <linux/highmem.h>
12#include <linux/swap.h>
13#include <linux/hugetlb.h>
14
15#include <asm/cpu-features.h>
16#include <asm/pgtable.h>
17
18static inline pte_t gup_get_pte(pte_t *ptep)
19{
20#if defined(CONFIG_64BIT_PHYS_ADDR) && defined(CONFIG_CPU_MIPS32)
21    pte_t pte;
22
23retry:
24    pte.pte_low = ptep->pte_low;
25    smp_rmb();
26    pte.pte_high = ptep->pte_high;
27    smp_rmb();
28    if (unlikely(pte.pte_low != ptep->pte_low))
29        goto retry;
30
31    return pte;
32#else
33    return ACCESS_ONCE(*ptep);
34#endif
35}
36
37static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
38            int write, struct page **pages, int *nr)
39{
40    pte_t *ptep = pte_offset_map(&pmd, addr);
41    do {
42        pte_t pte = gup_get_pte(ptep);
43        struct page *page;
44
45        if (!pte_present(pte) ||
46            pte_special(pte) || (write && !pte_write(pte))) {
47            pte_unmap(ptep);
48            return 0;
49        }
50        VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
51        page = pte_page(pte);
52        get_page(page);
53        SetPageReferenced(page);
54        pages[*nr] = page;
55        (*nr)++;
56
57    } while (ptep++, addr += PAGE_SIZE, addr != end);
58
59    pte_unmap(ptep - 1);
60    return 1;
61}
62
63static inline void get_head_page_multiple(struct page *page, int nr)
64{
65    VM_BUG_ON(page != compound_head(page));
66    VM_BUG_ON(page_count(page) == 0);
67    atomic_add(nr, &page->_count);
68    SetPageReferenced(page);
69}
70
71static int gup_huge_pmd(pmd_t pmd, unsigned long addr, unsigned long end,
72            int write, struct page **pages, int *nr)
73{
74    pte_t pte = *(pte_t *)&pmd;
75    struct page *head, *page;
76    int refs;
77
78    if (write && !pte_write(pte))
79        return 0;
80    /* hugepages are never "special" */
81    VM_BUG_ON(pte_special(pte));
82    VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
83
84    refs = 0;
85    head = pte_page(pte);
86    page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
87    do {
88        VM_BUG_ON(compound_head(page) != head);
89        pages[*nr] = page;
90        if (PageTail(page))
91            get_huge_page_tail(page);
92        (*nr)++;
93        page++;
94        refs++;
95    } while (addr += PAGE_SIZE, addr != end);
96
97    get_head_page_multiple(head, refs);
98    return 1;
99}
100
101static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
102            int write, struct page **pages, int *nr)
103{
104    unsigned long next;
105    pmd_t *pmdp;
106
107    pmdp = pmd_offset(&pud, addr);
108    do {
109        pmd_t pmd = *pmdp;
110
111        next = pmd_addr_end(addr, end);
112        /*
113         * The pmd_trans_splitting() check below explains why
114         * pmdp_splitting_flush has to flush the tlb, to stop
115         * this gup-fast code from running while we set the
116         * splitting bit in the pmd. Returning zero will take
117         * the slow path that will call wait_split_huge_page()
118         * if the pmd is still in splitting state. gup-fast
119         * can't because it has irq disabled and
120         * wait_split_huge_page() would never return as the
121         * tlb flush IPI wouldn't run.
122         */
123        if (pmd_none(pmd) || pmd_trans_splitting(pmd))
124            return 0;
125        if (unlikely(pmd_huge(pmd))) {
126            if (!gup_huge_pmd(pmd, addr, next, write, pages,nr))
127                return 0;
128        } else {
129            if (!gup_pte_range(pmd, addr, next, write, pages,nr))
130                return 0;
131        }
132    } while (pmdp++, addr = next, addr != end);
133
134    return 1;
135}
136
137static int gup_huge_pud(pud_t pud, unsigned long addr, unsigned long end,
138            int write, struct page **pages, int *nr)
139{
140    pte_t pte = *(pte_t *)&pud;
141    struct page *head, *page;
142    int refs;
143
144    if (write && !pte_write(pte))
145        return 0;
146    /* hugepages are never "special" */
147    VM_BUG_ON(pte_special(pte));
148    VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
149
150    refs = 0;
151    head = pte_page(pte);
152    page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
153    do {
154        VM_BUG_ON(compound_head(page) != head);
155        pages[*nr] = page;
156        if (PageTail(page))
157            get_huge_page_tail(page);
158        (*nr)++;
159        page++;
160        refs++;
161    } while (addr += PAGE_SIZE, addr != end);
162
163    get_head_page_multiple(head, refs);
164    return 1;
165}
166
167static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
168            int write, struct page **pages, int *nr)
169{
170    unsigned long next;
171    pud_t *pudp;
172
173    pudp = pud_offset(&pgd, addr);
174    do {
175        pud_t pud = *pudp;
176
177        next = pud_addr_end(addr, end);
178        if (pud_none(pud))
179            return 0;
180        if (unlikely(pud_huge(pud))) {
181            if (!gup_huge_pud(pud, addr, next, write, pages,nr))
182                return 0;
183        } else {
184            if (!gup_pmd_range(pud, addr, next, write, pages,nr))
185                return 0;
186        }
187    } while (pudp++, addr = next, addr != end);
188
189    return 1;
190}
191
192/*
193 * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
194 * back to the regular GUP.
195 */
196int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
197              struct page **pages)
198{
199    struct mm_struct *mm = current->mm;
200    unsigned long addr, len, end;
201    unsigned long next;
202    unsigned long flags;
203    pgd_t *pgdp;
204    int nr = 0;
205
206    start &= PAGE_MASK;
207    addr = start;
208    len = (unsigned long) nr_pages << PAGE_SHIFT;
209    end = start + len;
210    if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
211                    (void __user *)start, len)))
212        return 0;
213
214    /*
215     * XXX: batch / limit 'nr', to avoid large irq off latency
216     * needs some instrumenting to determine the common sizes used by
217     * important workloads (eg. DB2), and whether limiting the batch
218     * size will decrease performance.
219     *
220     * It seems like we're in the clear for the moment. Direct-IO is
221     * the main guy that batches up lots of get_user_pages, and even
222     * they are limited to 64-at-a-time which is not so many.
223     */
224    /*
225     * This doesn't prevent pagetable teardown, but does prevent
226     * the pagetables and pages from being freed.
227     *
228     * So long as we atomically load page table pointers versus teardown,
229     * we can follow the address down to the page and take a ref on it.
230     */
231    local_irq_save(flags);
232    pgdp = pgd_offset(mm, addr);
233    do {
234        pgd_t pgd = *pgdp;
235
236        next = pgd_addr_end(addr, end);
237        if (pgd_none(pgd))
238            break;
239        if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
240            break;
241    } while (pgdp++, addr = next, addr != end);
242    local_irq_restore(flags);
243
244    return nr;
245}
246
247/**
248 * get_user_pages_fast() - pin user pages in memory
249 * @start: starting user address
250 * @nr_pages: number of pages from start to pin
251 * @write: whether pages will be written to
252 * @pages: array that receives pointers to the pages pinned.
253 * Should be at least nr_pages long.
254 *
255 * Attempt to pin user pages in memory without taking mm->mmap_sem.
256 * If not successful, it will fall back to taking the lock and
257 * calling get_user_pages().
258 *
259 * Returns number of pages pinned. This may be fewer than the number
260 * requested. If nr_pages is 0 or negative, returns 0. If no pages
261 * were pinned, returns -errno.
262 */
263int get_user_pages_fast(unsigned long start, int nr_pages, int write,
264            struct page **pages)
265{
266    struct mm_struct *mm = current->mm;
267    unsigned long addr, len, end;
268    unsigned long next;
269    pgd_t *pgdp;
270    int ret, nr = 0;
271
272    start &= PAGE_MASK;
273    addr = start;
274    len = (unsigned long) nr_pages << PAGE_SHIFT;
275
276    end = start + len;
277    if (end < start || cpu_has_dc_aliases)
278        goto slow_irqon;
279
280    /* XXX: batch / limit 'nr' */
281    local_irq_disable();
282    pgdp = pgd_offset(mm, addr);
283    do {
284        pgd_t pgd = *pgdp;
285
286        next = pgd_addr_end(addr, end);
287        if (pgd_none(pgd))
288            goto slow;
289        if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
290            goto slow;
291    } while (pgdp++, addr = next, addr != end);
292    local_irq_enable();
293
294    VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
295    return nr;
296slow:
297    local_irq_enable();
298
299slow_irqon:
300    /* Try to get the remaining pages with get_user_pages */
301    start += nr << PAGE_SHIFT;
302    pages += nr;
303
304    down_read(&mm->mmap_sem);
305    ret = get_user_pages(current, mm, start,
306                (end - start) >> PAGE_SHIFT,
307                write, 0, pages, NULL);
308    up_read(&mm->mmap_sem);
309
310    /* Have to be a bit careful with return values */
311    if (nr > 0) {
312        if (ret < 0)
313            ret = nr;
314        else
315            ret += nr;
316    }
317    return ret;
318}
319

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