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![Linus Torvalds](/assets/img/avatar_default.png)
This series tightens the rules for ACCESS_ONCE to only work on scalar types. It also contains the necessary fixups as indicated by build bots of linux-next. Now everything is in place to prevent new non-scalar users of ACCESS_ONCE and we can continue to convert code to READ_ONCE/WRITE_ONCE. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.14 (GNU/Linux) iQIcBAABAgAGBQJU2H5MAAoJEBF7vIC1phx8Jm4QALPqKOMDSUBCrqJFWJeujtv2 ILxJKsnjrAlt3dxnlVI3q6e5wi896hSce75PcvZ/vs/K3GdgMxOjrakBJGTJ2Qjg 5njW9aGJDDr/SYFX33MLWfqy222TLtpxgSz379UgXjEzB0ymMWbJJ3FnGjVqQJdp RXDutpncRySc/rGHh9UPREIRR5GvimONsWE2zxgXjUzB8vIr2fCGvHTXfIb6RKbQ yaFoihzn0m+eisc5Gy4tQ1qhhnaYyWEGrINjHTjMFTQOWTlH80BZAyQeLdbyj2K5 qloBPS/VhBTr/5TxV5onM+nVhu0LiblVNrdMHVeb7jyST4LeFOCaWK98lB3axSB5 v/2D1YKNb3g1U1x3In/oNGQvs36zGiO1uEdMF1l8ZFXgCvHmATSFSTWBtqUhb5Ew JA3YyqMTG6dpRTMSnmu3/frr4wDqnxlB/ktQC1pf3tDp87mr1ZYEy/dQld+tltjh 9Z5GSdrw0nf91wNI3DJf+26ZDdz5B+EpDnPnOKG8anI1lc/mQneI21/K/xUteFXw UZ1XGPLV2vbv9/a13u44SdjenHvQs1egsGeebMxVPoj6WmDLVmcIqinyS6NawYzn IlDGy/b3bSnXWMBP0ZVBX94KWLxqDDc4a/ayxsmxsP1tPZ+jDXjVDa7E3zskcHxG Uj5ULCPyU087t8Sl76mv =Dj70 -----END PGP SIGNATURE----- Merge tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux Pull ACCESS_ONCE() rule tightening from Christian Borntraeger: "Tighten rules for ACCESS_ONCE This series tightens the rules for ACCESS_ONCE to only work on scalar types. It also contains the necessary fixups as indicated by build bots of linux-next. Now everything is in place to prevent new non-scalar users of ACCESS_ONCE and we can continue to convert code to READ_ONCE/WRITE_ONCE" * tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux: kernel: Fix sparse warning for ACCESS_ONCE next: sh: Fix compile error kernel: tighten rules for ACCESS ONCE mm/gup: Replace ACCESS_ONCE with READ_ONCE x86/spinlock: Leftover conversion ACCESS_ONCE->READ_ONCE x86/xen/p2m: Replace ACCESS_ONCE with READ_ONCE ppc/hugetlbfs: Replace ACCESS_ONCE with READ_ONCE ppc/kvm: Replace ACCESS_ONCE with READ_ONCE
273 lines
6.6 KiB
C
273 lines
6.6 KiB
C
/*
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* Lockless get_user_pages_fast for SuperH
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*
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* Copyright (C) 2009 - 2010 Paul Mundt
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*
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* Cloned from the x86 and PowerPC versions, by:
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*
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* Copyright (C) 2008 Nick Piggin
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* Copyright (C) 2008 Novell Inc.
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*/
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#include <linux/sched.h>
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#include <linux/mm.h>
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#include <linux/vmstat.h>
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#include <linux/highmem.h>
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#include <asm/pgtable.h>
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static inline pte_t gup_get_pte(pte_t *ptep)
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{
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#ifndef CONFIG_X2TLB
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return READ_ONCE(*ptep);
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#else
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/*
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* With get_user_pages_fast, we walk down the pagetables without
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* taking any locks. For this we would like to load the pointers
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* atomically, but that is not possible with 64-bit PTEs. What
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* we do have is the guarantee that a pte will only either go
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* from not present to present, or present to not present or both
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* -- it will not switch to a completely different present page
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* without a TLB flush in between; something that we are blocking
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* by holding interrupts off.
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*
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* Setting ptes from not present to present goes:
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* ptep->pte_high = h;
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* smp_wmb();
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* ptep->pte_low = l;
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*
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* And present to not present goes:
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* ptep->pte_low = 0;
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* smp_wmb();
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* ptep->pte_high = 0;
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*
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* We must ensure here that the load of pte_low sees l iff pte_high
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* sees h. We load pte_high *after* loading pte_low, which ensures we
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* don't see an older value of pte_high. *Then* we recheck pte_low,
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* which ensures that we haven't picked up a changed pte high. We might
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* have got rubbish values from pte_low and pte_high, but we are
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* guaranteed that pte_low will not have the present bit set *unless*
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* it is 'l'. And get_user_pages_fast only operates on present ptes, so
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* we're safe.
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*
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* gup_get_pte should not be used or copied outside gup.c without being
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* very careful -- it does not atomically load the pte or anything that
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* is likely to be useful for you.
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*/
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pte_t pte;
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retry:
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pte.pte_low = ptep->pte_low;
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smp_rmb();
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pte.pte_high = ptep->pte_high;
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smp_rmb();
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if (unlikely(pte.pte_low != ptep->pte_low))
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goto retry;
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return pte;
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#endif
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}
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/*
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* The performance critical leaf functions are made noinline otherwise gcc
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* inlines everything into a single function which results in too much
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* register pressure.
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*/
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static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
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unsigned long end, int write, struct page **pages, int *nr)
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{
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u64 mask, result;
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pte_t *ptep;
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#ifdef CONFIG_X2TLB
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result = _PAGE_PRESENT | _PAGE_EXT(_PAGE_EXT_KERN_READ | _PAGE_EXT_USER_READ);
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if (write)
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result |= _PAGE_EXT(_PAGE_EXT_KERN_WRITE | _PAGE_EXT_USER_WRITE);
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#elif defined(CONFIG_SUPERH64)
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result = _PAGE_PRESENT | _PAGE_USER | _PAGE_READ;
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if (write)
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result |= _PAGE_WRITE;
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#else
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result = _PAGE_PRESENT | _PAGE_USER;
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if (write)
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result |= _PAGE_RW;
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#endif
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mask = result | _PAGE_SPECIAL;
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ptep = pte_offset_map(&pmd, addr);
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do {
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pte_t pte = gup_get_pte(ptep);
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struct page *page;
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if ((pte_val(pte) & mask) != result) {
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pte_unmap(ptep);
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return 0;
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}
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VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
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page = pte_page(pte);
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get_page(page);
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__flush_anon_page(page, addr);
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flush_dcache_page(page);
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pages[*nr] = page;
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(*nr)++;
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} while (ptep++, addr += PAGE_SIZE, addr != end);
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pte_unmap(ptep - 1);
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return 1;
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}
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static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
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int write, struct page **pages, int *nr)
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{
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unsigned long next;
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pmd_t *pmdp;
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pmdp = pmd_offset(&pud, addr);
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do {
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pmd_t pmd = *pmdp;
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next = pmd_addr_end(addr, end);
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if (pmd_none(pmd))
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return 0;
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if (!gup_pte_range(pmd, addr, next, write, pages, nr))
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return 0;
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} while (pmdp++, addr = next, addr != end);
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return 1;
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}
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static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
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int write, struct page **pages, int *nr)
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{
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unsigned long next;
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pud_t *pudp;
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pudp = pud_offset(&pgd, addr);
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do {
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pud_t pud = *pudp;
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next = pud_addr_end(addr, end);
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if (pud_none(pud))
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return 0;
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if (!gup_pmd_range(pud, addr, next, write, pages, nr))
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return 0;
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} while (pudp++, addr = next, addr != end);
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return 1;
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}
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/*
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* Like get_user_pages_fast() except its IRQ-safe in that it won't fall
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* back to the regular GUP.
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*/
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int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
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struct page **pages)
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{
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struct mm_struct *mm = current->mm;
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unsigned long addr, len, end;
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unsigned long next;
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unsigned long flags;
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pgd_t *pgdp;
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int nr = 0;
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start &= PAGE_MASK;
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addr = start;
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len = (unsigned long) nr_pages << PAGE_SHIFT;
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end = start + len;
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if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
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(void __user *)start, len)))
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return 0;
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/*
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* This doesn't prevent pagetable teardown, but does prevent
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* the pagetables and pages from being freed.
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*/
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local_irq_save(flags);
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pgdp = pgd_offset(mm, addr);
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do {
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pgd_t pgd = *pgdp;
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next = pgd_addr_end(addr, end);
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if (pgd_none(pgd))
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break;
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if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
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break;
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} while (pgdp++, addr = next, addr != end);
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local_irq_restore(flags);
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return nr;
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}
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/**
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* get_user_pages_fast() - pin user pages in memory
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* @start: starting user address
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* @nr_pages: number of pages from start to pin
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* @write: whether pages will be written to
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* @pages: array that receives pointers to the pages pinned.
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* Should be at least nr_pages long.
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*
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* Attempt to pin user pages in memory without taking mm->mmap_sem.
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* If not successful, it will fall back to taking the lock and
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* calling get_user_pages().
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*
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* Returns number of pages pinned. This may be fewer than the number
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* requested. If nr_pages is 0 or negative, returns 0. If no pages
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* were pinned, returns -errno.
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*/
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int get_user_pages_fast(unsigned long start, int nr_pages, int write,
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struct page **pages)
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{
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struct mm_struct *mm = current->mm;
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unsigned long addr, len, end;
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unsigned long next;
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pgd_t *pgdp;
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int nr = 0;
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start &= PAGE_MASK;
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addr = start;
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len = (unsigned long) nr_pages << PAGE_SHIFT;
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end = start + len;
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if (end < start)
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goto slow_irqon;
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local_irq_disable();
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pgdp = pgd_offset(mm, addr);
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do {
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pgd_t pgd = *pgdp;
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next = pgd_addr_end(addr, end);
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if (pgd_none(pgd))
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goto slow;
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if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
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goto slow;
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} while (pgdp++, addr = next, addr != end);
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local_irq_enable();
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VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
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return nr;
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{
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int ret;
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slow:
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local_irq_enable();
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slow_irqon:
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/* Try to get the remaining pages with get_user_pages */
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start += nr << PAGE_SHIFT;
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pages += nr;
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ret = get_user_pages_unlocked(current, mm, start,
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(end - start) >> PAGE_SHIFT, write, 0, pages);
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/* Have to be a bit careful with return values */
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if (nr > 0) {
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if (ret < 0)
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ret = nr;
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else
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ret += nr;
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}
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return ret;
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}
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}
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