281 lines
6.4 KiB
C
281 lines
6.4 KiB
C
/*
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* Lockless get_user_pages_fast for powerpc
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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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#undef DEBUG
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#include <linux/sched.h>
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#include <linux/mm.h>
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#include <linux/hugetlb.h>
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#include <linux/vmstat.h>
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#include <linux/pagemap.h>
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#include <linux/rwsem.h>
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#include <asm/pgtable.h>
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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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unsigned long mask, result;
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pte_t *ptep;
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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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mask = result | _PAGE_SPECIAL;
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ptep = pte_offset_kernel(&pmd, addr);
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do {
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pte_t pte = *ptep;
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struct page *page;
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if ((pte_val(pte) & mask) != result)
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return 0;
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VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
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page = pte_page(pte);
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if (!page_cache_get_speculative(page))
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return 0;
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if (unlikely(pte != *ptep)) {
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put_page(page);
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return 0;
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}
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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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return 1;
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}
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#ifdef CONFIG_HUGETLB_PAGE
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static noinline int gup_huge_pte(pte_t *ptep, struct hstate *hstate,
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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 mask;
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unsigned long pte_end;
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struct page *head, *page;
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pte_t pte;
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int refs;
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pte_end = (*addr + huge_page_size(hstate)) & huge_page_mask(hstate);
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if (pte_end < end)
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end = pte_end;
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pte = *ptep;
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mask = _PAGE_PRESENT|_PAGE_USER;
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if (write)
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mask |= _PAGE_RW;
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if ((pte_val(pte) & mask) != mask)
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return 0;
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/* hugepages are never "special" */
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VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
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refs = 0;
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head = pte_page(pte);
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page = head + ((*addr & ~huge_page_mask(hstate)) >> PAGE_SHIFT);
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do {
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VM_BUG_ON(compound_head(page) != head);
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pages[*nr] = page;
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(*nr)++;
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page++;
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refs++;
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} while (*addr += PAGE_SIZE, *addr != end);
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if (!page_cache_add_speculative(head, refs)) {
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*nr -= refs;
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return 0;
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}
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if (unlikely(pte != *ptep)) {
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/* Could be optimized better */
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while (*nr) {
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put_page(page);
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(*nr)--;
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}
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}
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return 1;
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}
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#endif /* CONFIG_HUGETLB_PAGE */
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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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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 psize, nr = 0;
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unsigned int shift;
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pr_debug("%s(%lx,%x,%s)\n", __func__, start, nr_pages, write ? "write" : "read");
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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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start, len)))
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goto slow_irqon;
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pr_debug(" aligned: %lx .. %lx\n", start, end);
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#ifdef CONFIG_HUGETLB_PAGE
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/* We bail out on slice boundary crossing when hugetlb is
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* enabled in order to not have to deal with two different
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* page table formats
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*/
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if (addr < SLICE_LOW_TOP) {
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if (end > SLICE_LOW_TOP)
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goto slow_irqon;
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if (unlikely(GET_LOW_SLICE_INDEX(addr) !=
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GET_LOW_SLICE_INDEX(end - 1)))
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goto slow_irqon;
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} else {
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if (unlikely(GET_HIGH_SLICE_INDEX(addr) !=
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GET_HIGH_SLICE_INDEX(end - 1)))
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goto slow_irqon;
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}
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#endif /* CONFIG_HUGETLB_PAGE */
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/*
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* XXX: batch / limit 'nr', to avoid large irq off latency
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* needs some instrumenting to determine the common sizes used by
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* important workloads (eg. DB2), and whether limiting the batch size
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* will decrease performance.
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*
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* It seems like we're in the clear for the moment. Direct-IO is
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* the main guy that batches up lots of get_user_pages, and even
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* they are limited to 64-at-a-time which is not so many.
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*/
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/*
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* This doesn't prevent pagetable teardown, but does prevent
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* the pagetables from being freed on powerpc.
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*
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* So long as we atomically load page table pointers versus teardown,
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* we can follow the address down to the the page and take a ref on it.
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*/
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local_irq_disable();
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psize = get_slice_psize(mm, addr);
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shift = mmu_psize_defs[psize].shift;
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#ifdef CONFIG_HUGETLB_PAGE
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if (unlikely(mmu_huge_psizes[psize])) {
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pte_t *ptep;
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unsigned long a = addr;
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unsigned long sz = ((1UL) << shift);
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struct hstate *hstate = size_to_hstate(sz);
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BUG_ON(!hstate);
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/*
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* XXX: could be optimized to avoid hstate
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* lookup entirely (just use shift)
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*/
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do {
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VM_BUG_ON(shift != mmu_psize_defs[get_slice_psize(mm, a)].shift);
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ptep = huge_pte_offset(mm, a);
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pr_debug(" %016lx: huge ptep %p\n", a, ptep);
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if (!ptep || !gup_huge_pte(ptep, hstate, &a, end, write, pages,
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&nr))
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goto slow;
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} while (a != end);
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} else
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#endif /* CONFIG_HUGETLB_PAGE */
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{
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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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VM_BUG_ON(shift != mmu_psize_defs[get_slice_psize(mm, addr)].shift);
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pr_debug(" %016lx: normal pgd %p\n", addr, (void *)pgd);
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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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}
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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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pr_debug(" slow path ! nr = %d\n", nr);
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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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down_read(&mm->mmap_sem);
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ret = get_user_pages(current, mm, start,
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(end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
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up_read(&mm->mmap_sem);
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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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