/arch/sh/mm/gup.c

  1/*
  2 * Lockless get_user_pages_fast for SuperH
  3 *
  4 * Copyright (C) 2009 - 2010  Paul Mundt
  5 *
  6 * Cloned from the x86 and PowerPC versions, by:
  7 *
  8 *	Copyright (C) 2008 Nick Piggin
  9 *	Copyright (C) 2008 Novell Inc.
 10 */
 11#include <linux/sched.h>
 12#include <linux/mm.h>
 13#include <linux/vmstat.h>
 14#include <linux/highmem.h>
 15#include <asm/pgtable.h>
 16
 17static inline pte_t gup_get_pte(pte_t *ptep)
 18{
 19#ifndef CONFIG_X2TLB
 20	return ACCESS_ONCE(*ptep);
 21#else
 22	/*
 23	 * With get_user_pages_fast, we walk down the pagetables without
 24	 * taking any locks.  For this we would like to load the pointers
 25	 * atomically, but that is not possible with 64-bit PTEs.  What
 26	 * we do have is the guarantee that a pte will only either go
 27	 * from not present to present, or present to not present or both
 28	 * -- it will not switch to a completely different present page
 29	 * without a TLB flush in between; something that we are blocking
 30	 * by holding interrupts off.
 31	 *
 32	 * Setting ptes from not present to present goes:
 33	 * ptep->pte_high = h;
 34	 * smp_wmb();
 35	 * ptep->pte_low = l;
 36	 *
 37	 * And present to not present goes:
 38	 * ptep->pte_low = 0;
 39	 * smp_wmb();
 40	 * ptep->pte_high = 0;
 41	 *
 42	 * We must ensure here that the load of pte_low sees l iff pte_high
 43	 * sees h. We load pte_high *after* loading pte_low, which ensures we
 44	 * don't see an older value of pte_high.  *Then* we recheck pte_low,
 45	 * which ensures that we haven't picked up a changed pte high. We might
 46	 * have got rubbish values from pte_low and pte_high, but we are
 47	 * guaranteed that pte_low will not have the present bit set *unless*
 48	 * it is 'l'. And get_user_pages_fast only operates on present ptes, so
 49	 * we're safe.
 50	 *
 51	 * gup_get_pte should not be used or copied outside gup.c without being
 52	 * very careful -- it does not atomically load the pte or anything that
 53	 * is likely to be useful for you.
 54	 */
 55	pte_t pte;
 56
 57retry:
 58	pte.pte_low = ptep->pte_low;
 59	smp_rmb();
 60	pte.pte_high = ptep->pte_high;
 61	smp_rmb();
 62	if (unlikely(pte.pte_low != ptep->pte_low))
 63		goto retry;
 64
 65	return pte;
 66#endif
 67}
 68
 69/*
 70 * The performance critical leaf functions are made noinline otherwise gcc
 71 * inlines everything into a single function which results in too much
 72 * register pressure.
 73 */
 74static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
 75		unsigned long end, int write, struct page **pages, int *nr)
 76{
 77	u64 mask, result;
 78	pte_t *ptep;
 79
 80#ifdef CONFIG_X2TLB
 81	result = _PAGE_PRESENT | _PAGE_EXT(_PAGE_EXT_KERN_READ | _PAGE_EXT_USER_READ);
 82	if (write)
 83		result |= _PAGE_EXT(_PAGE_EXT_KERN_WRITE | _PAGE_EXT_USER_WRITE);
 84#elif defined(CONFIG_SUPERH64)
 85	result = _PAGE_PRESENT | _PAGE_USER | _PAGE_READ;
 86	if (write)
 87		result |= _PAGE_WRITE;
 88#else
 89	result = _PAGE_PRESENT | _PAGE_USER;
 90	if (write)
 91		result |= _PAGE_RW;
 92#endif
 93
 94	mask = result | _PAGE_SPECIAL;
 95
 96	ptep = pte_offset_map(&pmd, addr);
 97	do {
 98		pte_t pte = gup_get_pte(ptep);
 99		struct page *page;
100
101		if ((pte_val(pte) & mask) != result) {
102			pte_unmap(ptep);
103			return 0;
104		}
105		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
106		page = pte_page(pte);
107		get_page(page);
108		pages[*nr] = page;
109		(*nr)++;
110
111	} while (ptep++, addr += PAGE_SIZE, addr != end);
112	pte_unmap(ptep - 1);
113
114	return 1;
115}
116
117static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
118		int write, struct page **pages, int *nr)
119{
120	unsigned long next;
121	pmd_t *pmdp;
122
123	pmdp = pmd_offset(&pud, addr);
124	do {
125		pmd_t pmd = *pmdp;
126
127		next = pmd_addr_end(addr, end);
128		if (pmd_none(pmd))
129			return 0;
130		if (!gup_pte_range(pmd, addr, next, write, pages, nr))
131			return 0;
132	} while (pmdp++, addr = next, addr != end);
133
134	return 1;
135}
136
137static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
138			int write, struct page **pages, int *nr)
139{
140	unsigned long next;
141	pud_t *pudp;
142
143	pudp = pud_offset(&pgd, addr);
144	do {
145		pud_t pud = *pudp;
146
147		next = pud_addr_end(addr, end);
148		if (pud_none(pud))
149			return 0;
150		if (!gup_pmd_range(pud, addr, next, write, pages, nr))
151			return 0;
152	} while (pudp++, addr = next, addr != end);
153
154	return 1;
155}
156
157/*
158 * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
159 * back to the regular GUP.
160 */
161int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
162			  struct page **pages)
163{
164	struct mm_struct *mm = current->mm;
165	unsigned long addr, len, end;
166	unsigned long next;
167	unsigned long flags;
168	pgd_t *pgdp;
169	int nr = 0;
170
171	start &= PAGE_MASK;
172	addr = start;
173	len = (unsigned long) nr_pages << PAGE_SHIFT;
174	end = start + len;
175	if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
176					(void __user *)start, len)))
177		return 0;
178
179	/*
180	 * This doesn't prevent pagetable teardown, but does prevent
181	 * the pagetables and pages from being freed.
182	 */
183	local_irq_save(flags);
184	pgdp = pgd_offset(mm, addr);
185	do {
186		pgd_t pgd = *pgdp;
187
188		next = pgd_addr_end(addr, end);
189		if (pgd_none(pgd))
190			break;
191		if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
192			break;
193	} while (pgdp++, addr = next, addr != end);
194	local_irq_restore(flags);
195
196	return nr;
197}
198
199/**
200 * get_user_pages_fast() - pin user pages in memory
201 * @start:	starting user address
202 * @nr_pages:	number of pages from start to pin
203 * @write:	whether pages will be written to
204 * @pages:	array that receives pointers to the pages pinned.
205 *		Should be at least nr_pages long.
206 *
207 * Attempt to pin user pages in memory without taking mm->mmap_sem.
208 * If not successful, it will fall back to taking the lock and
209 * calling get_user_pages().
210 *
211 * Returns number of pages pinned. This may be fewer than the number
212 * requested. If nr_pages is 0 or negative, returns 0. If no pages
213 * were pinned, returns -errno.
214 */
215int get_user_pages_fast(unsigned long start, int nr_pages, int write,
216			struct page **pages)
217{
218	struct mm_struct *mm = current->mm;
219	unsigned long addr, len, end;
220	unsigned long next;
221	pgd_t *pgdp;
222	int nr = 0;
223
224	start &= PAGE_MASK;
225	addr = start;
226	len = (unsigned long) nr_pages << PAGE_SHIFT;
227
228	end = start + len;
229	if (end < start)
230		goto slow_irqon;
231
232	local_irq_disable();
233	pgdp = pgd_offset(mm, addr);
234	do {
235		pgd_t pgd = *pgdp;
236
237		next = pgd_addr_end(addr, end);
238		if (pgd_none(pgd))
239			goto slow;
240		if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
241			goto slow;
242	} while (pgdp++, addr = next, addr != end);
243	local_irq_enable();
244
245	VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
246	return nr;
247
248	{
249		int ret;
250
251slow:
252		local_irq_enable();
253slow_irqon:
254		/* Try to get the remaining pages with get_user_pages */
255		start += nr << PAGE_SHIFT;
256		pages += nr;
257
258		down_read(&mm->mmap_sem);
259		ret = get_user_pages(current, mm, start,
260			(end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
261		up_read(&mm->mmap_sem);
262
263		/* Have to be a bit careful with return values */
264		if (nr > 0) {
265			if (ret < 0)
266				ret = nr;
267			else
268				ret += nr;
269		}
270
271		return ret;
272	}
273}