1 // SPDX-License-Identifier: GPL-2.0
3 * Lockless get_user_pages_fast for SuperH
5 * Copyright (C) 2009 - 2010 Paul Mundt
7 * Cloned from the x86 and PowerPC versions, by:
9 * Copyright (C) 2008 Nick Piggin
10 * Copyright (C) 2008 Novell Inc.
12 #include <linux/sched.h>
14 #include <linux/vmstat.h>
15 #include <linux/highmem.h>
16 #include <asm/pgtable.h>
18 static inline pte_t gup_get_pte(pte_t *ptep)
21 return READ_ONCE(*ptep);
24 * With get_user_pages_fast, we walk down the pagetables without
25 * taking any locks. For this we would like to load the pointers
26 * atomically, but that is not possible with 64-bit PTEs. What
27 * we do have is the guarantee that a pte will only either go
28 * from not present to present, or present to not present or both
29 * -- it will not switch to a completely different present page
30 * without a TLB flush in between; something that we are blocking
31 * by holding interrupts off.
33 * Setting ptes from not present to present goes:
38 * And present to not present goes:
43 * We must ensure here that the load of pte_low sees l iff pte_high
44 * sees h. We load pte_high *after* loading pte_low, which ensures we
45 * don't see an older value of pte_high. *Then* we recheck pte_low,
46 * which ensures that we haven't picked up a changed pte high. We might
47 * have got rubbish values from pte_low and pte_high, but we are
48 * guaranteed that pte_low will not have the present bit set *unless*
49 * it is 'l'. And get_user_pages_fast only operates on present ptes, so
52 * gup_get_pte should not be used or copied outside gup.c without being
53 * very careful -- it does not atomically load the pte or anything that
54 * is likely to be useful for you.
59 pte.pte_low = ptep->pte_low;
61 pte.pte_high = ptep->pte_high;
63 if (unlikely(pte.pte_low != ptep->pte_low))
71 * The performance critical leaf functions are made noinline otherwise gcc
72 * inlines everything into a single function which results in too much
75 static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
76 unsigned long end, int write, struct page **pages, int *nr)
82 result = _PAGE_PRESENT | _PAGE_EXT(_PAGE_EXT_KERN_READ | _PAGE_EXT_USER_READ);
84 result |= _PAGE_EXT(_PAGE_EXT_KERN_WRITE | _PAGE_EXT_USER_WRITE);
85 #elif defined(CONFIG_SUPERH64)
86 result = _PAGE_PRESENT | _PAGE_USER | _PAGE_READ;
88 result |= _PAGE_WRITE;
90 result = _PAGE_PRESENT | _PAGE_USER;
95 mask = result | _PAGE_SPECIAL;
97 ptep = pte_offset_map(&pmd, addr);
99 pte_t pte = gup_get_pte(ptep);
102 if ((pte_val(pte) & mask) != result) {
106 VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
107 page = pte_page(pte);
109 __flush_anon_page(page, addr);
110 flush_dcache_page(page);
114 } while (ptep++, addr += PAGE_SIZE, addr != end);
120 static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
121 int write, struct page **pages, int *nr)
126 pmdp = pmd_offset(&pud, addr);
130 next = pmd_addr_end(addr, end);
133 if (!gup_pte_range(pmd, addr, next, write, pages, nr))
135 } while (pmdp++, addr = next, addr != end);
140 static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
141 int write, struct page **pages, int *nr)
146 pudp = pud_offset(&pgd, addr);
150 next = pud_addr_end(addr, end);
153 if (!gup_pmd_range(pud, addr, next, write, pages, nr))
155 } while (pudp++, addr = next, addr != end);
161 * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
162 * back to the regular GUP.
163 * Note a difference with get_user_pages_fast: this always returns the
164 * number of pages pinned, 0 if no pages were pinned.
166 int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
169 struct mm_struct *mm = current->mm;
170 unsigned long addr, len, end;
178 len = (unsigned long) nr_pages << PAGE_SHIFT;
180 if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
181 (void __user *)start, len)))
185 * This doesn't prevent pagetable teardown, but does prevent
186 * the pagetables and pages from being freed.
188 local_irq_save(flags);
189 pgdp = pgd_offset(mm, addr);
193 next = pgd_addr_end(addr, end);
196 if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
198 } while (pgdp++, addr = next, addr != end);
199 local_irq_restore(flags);
205 * get_user_pages_fast() - pin user pages in memory
206 * @start: starting user address
207 * @nr_pages: number of pages from start to pin
208 * @write: whether pages will be written to
209 * @pages: array that receives pointers to the pages pinned.
210 * Should be at least nr_pages long.
212 * Attempt to pin user pages in memory without taking mm->mmap_sem.
213 * If not successful, it will fall back to taking the lock and
214 * calling get_user_pages().
216 * Returns number of pages pinned. This may be fewer than the number
217 * requested. If nr_pages is 0 or negative, returns 0. If no pages
218 * were pinned, returns -errno.
220 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
223 struct mm_struct *mm = current->mm;
224 unsigned long addr, len, end;
231 len = (unsigned long) nr_pages << PAGE_SHIFT;
238 pgdp = pgd_offset(mm, addr);
242 next = pgd_addr_end(addr, end);
245 if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
247 } while (pgdp++, addr = next, addr != end);
250 VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
259 /* Try to get the remaining pages with get_user_pages */
260 start += nr << PAGE_SHIFT;
263 ret = get_user_pages_unlocked(start,
264 (end - start) >> PAGE_SHIFT, pages,
265 write ? FOLL_WRITE : 0);
267 /* Have to be a bit careful with return values */