![Heiko Carstens](/assets/img/avatar_default.png)
If [__]get_user_pages_fast() gets called with nr_pages == 0, the current code would walk the page tables and pin as many pages until the first invalid pte (or the kernel crashed while writing struct page pointers to the pages array). So let's handle at least the nr_pages == 0 case correctly and exit early. Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
247 lines
6.2 KiB
C
247 lines
6.2 KiB
C
/*
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* Lockless get_user_pages_fast for s390
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*
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* Copyright IBM Corp. 2010
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* Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>
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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/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 inline int gup_pte_range(pmd_t *pmdp, 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;
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pte_t *ptep, pte;
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struct page *page;
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mask = (write ? _PAGE_PROTECT : 0) | _PAGE_INVALID | _PAGE_SPECIAL;
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ptep = ((pte_t *) pmd_deref(pmd)) + pte_index(addr);
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do {
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pte = *ptep;
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barrier();
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if ((pte_val(pte) & mask) != 0)
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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_val(pte) != pte_val(*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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static inline int gup_huge_pmd(pmd_t *pmdp, 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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struct page *head, *page, *tail;
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int refs;
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result = write ? 0 : _SEGMENT_ENTRY_PROTECT;
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mask = result | _SEGMENT_ENTRY_INVALID;
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if ((pmd_val(pmd) & mask) != result)
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return 0;
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VM_BUG_ON(!pfn_valid(pmd_val(pmd) >> PAGE_SHIFT));
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refs = 0;
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head = pmd_page(pmd);
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page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
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tail = page;
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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(pmd_val(pmd) != pmd_val(*pmdp))) {
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*nr -= refs;
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while (refs--)
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put_page(head);
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return 0;
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}
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/*
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* Any tail page need their mapcount reference taken before we
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* return.
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*/
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while (refs--) {
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if (PageTail(tail))
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get_huge_page_tail(tail);
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tail++;
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}
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return 1;
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}
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static inline int gup_pmd_range(pud_t *pudp, pud_t pud, 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 next;
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pmd_t *pmdp, pmd;
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pmdp = (pmd_t *) pudp;
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#ifdef CONFIG_64BIT
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if ((pud_val(pud) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3)
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pmdp = (pmd_t *) pud_deref(pud);
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pmdp += pmd_index(addr);
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#endif
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do {
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pmd = *pmdp;
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barrier();
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next = pmd_addr_end(addr, end);
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/*
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* The pmd_trans_splitting() check below explains why
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* pmdp_splitting_flush() has to serialize with
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* smp_call_function() against our disabled IRQs, to stop
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* this gup-fast code from running while we set the
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* splitting bit in the pmd. Returning zero will take
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* the slow path that will call wait_split_huge_page()
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* if the pmd is still in splitting state.
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*/
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if (pmd_none(pmd) || pmd_trans_splitting(pmd))
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return 0;
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if (unlikely(pmd_large(pmd))) {
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if (!gup_huge_pmd(pmdp, pmd, addr, next,
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write, pages, nr))
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return 0;
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} else if (!gup_pte_range(pmdp, pmd, addr, next,
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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 inline int gup_pud_range(pgd_t *pgdp, pgd_t pgd, 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 next;
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pud_t *pudp, pud;
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pudp = (pud_t *) pgdp;
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#ifdef CONFIG_64BIT
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if ((pgd_val(pgd) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R2)
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pudp = (pud_t *) pgd_deref(pgd);
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pudp += pud_index(addr);
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#endif
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do {
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pud = *pudp;
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barrier();
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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(pudp, 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, flags;
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pgd_t *pgdp, pgd;
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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) || (end > TASK_SIZE))
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return 0;
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/*
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* local_irq_save() doesn't prevent pagetable teardown, but does
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* prevent the pagetables from being freed on s390.
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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_save(flags);
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pgdp = pgd_offset(mm, addr);
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do {
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pgd = *pgdp;
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barrier();
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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(pgdp, 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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int nr, ret;
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start &= PAGE_MASK;
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nr = __get_user_pages_fast(start, nr_pages, write, pages);
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if (nr == nr_pages)
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return 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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nr_pages - nr, 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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ret = (ret < 0) ? nr : ret + nr;
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return ret;
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}
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