![Linus Torvalds](/assets/img/avatar_default.png)
As discussed on LKML http://marc.info/?i=54611D86.4040306%40de.ibm.com ACCESS_ONCE might fail with specific compilers for non-scalar accesses. Here is a set of patches to tackle that problem. The first patch introduce READ_ONCE and ASSIGN_ONCE. If the data structure is larger than the machine word size memcpy is used and a warning is emitted. The next patches fix up several in-tree users of ACCESS_ONCE on non-scalar types. This merge does not yet contain a patch that forces ACCESS_ONCE to work only on scalar types. This is targetted for the next merge window as Linux next already contains new offenders regarding ACCESS_ONCE vs. non-scalar types. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.14 (GNU/Linux) iQIcBAABAgAGBQJUkrVGAAoJEBF7vIC1phx8stkP/2LmN5y6LOseoEW06xa5MX4m cbIKsZNtsGHl7EDcTzzuWs6Sq5/Cj7V3yzeBF7QGbUKOqvFWU3jvpUBCCfjMg37C 77/Vf0ZPrxTXXxeJ4Ykdy2CGvuMtuYY9TWkrRNKmLU0xex7lGblEzCt9z6+mZviw 26/DN8ctjkHRvIUAi+7RfQBBc3oSMYAC1mzxYKBAsAFLV+LyFmsGU/4iofZMAsdt XFyVXlrLn0Bjx/MeceGkOlMDiVx4FnfccfFaD4hhuTLBJXWitkUK/MRa4JBiXWzH agY8942A8/j9wkI2DFp/pqZYqA/sTXLndyOWlhE//ZSti0n0BSJaOx3S27rTLkAc 5VmZEVyIrS3hyOpyyAi0sSoPkDnjeCHmQg9Rqn34/poKLd7JDrW2UkERNCf/T3eh GI2rbhAlZz3v5mIShn8RrxzslWYmOObpMr3HYNUdRk8YUfTf6d6aZ3txHp2nP4mD VBAEzsvP9rcVT2caVhU2dnBzeaZAj3zeDxBtjcb3X2osY9tI7qgLc9Fa/fWKgILk 2evkLcctsae2mlLNGHyaK3Dm/ZmYJv+57MyaQQEZNfZZgeB1y4k0DkxH4w1CFmCi s8XlH5voEHgnyjSQXXgc/PNVlkPAKr78ZyTiAfiKmh8rpe41/W4hGcgao7L9Lgiu SI0uSwKibuZt4dHGxQuG =IQ5o -----END PGP SIGNATURE----- Merge tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux Pull ACCESS_ONCE cleanup preparation from Christian Borntraeger: "kernel: Provide READ_ONCE and ASSIGN_ONCE As discussed on LKML http://marc.info/?i=54611D86.4040306%40de.ibm.com ACCESS_ONCE might fail with specific compilers for non-scalar accesses. Here is a set of patches to tackle that problem. The first patch introduce READ_ONCE and ASSIGN_ONCE. If the data structure is larger than the machine word size memcpy is used and a warning is emitted. The next patches fix up several in-tree users of ACCESS_ONCE on non-scalar types. This does not yet contain a patch that forces ACCESS_ONCE to work only on scalar types. This is targetted for the next merge window as Linux next already contains new offenders regarding ACCESS_ONCE vs. non-scalar types" * tag 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux: s390/kvm: REPLACE barrier fixup with READ_ONCE arm/spinlock: Replace ACCESS_ONCE with READ_ONCE arm64/spinlock: Replace ACCESS_ONCE READ_ONCE mips/gup: Replace ACCESS_ONCE with READ_ONCE x86/gup: Replace ACCESS_ONCE with READ_ONCE x86/spinlock: Replace ACCESS_ONCE with READ_ONCE mm: replace ACCESS_ONCE with READ_ONCE or barriers kernel: Provide READ_ONCE and ASSIGN_ONCE
1098 lines
31 KiB
C
1098 lines
31 KiB
C
#include <linux/kernel.h>
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#include <linux/errno.h>
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#include <linux/err.h>
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#include <linux/spinlock.h>
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#include <linux/mm.h>
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#include <linux/pagemap.h>
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#include <linux/rmap.h>
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#include <linux/swap.h>
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#include <linux/swapops.h>
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#include <linux/sched.h>
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#include <linux/rwsem.h>
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#include <linux/hugetlb.h>
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#include <asm/pgtable.h>
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#include "internal.h"
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static struct page *no_page_table(struct vm_area_struct *vma,
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unsigned int flags)
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{
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/*
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* When core dumping an enormous anonymous area that nobody
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* has touched so far, we don't want to allocate unnecessary pages or
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* page tables. Return error instead of NULL to skip handle_mm_fault,
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* then get_dump_page() will return NULL to leave a hole in the dump.
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* But we can only make this optimization where a hole would surely
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* be zero-filled if handle_mm_fault() actually did handle it.
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*/
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if ((flags & FOLL_DUMP) && (!vma->vm_ops || !vma->vm_ops->fault))
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return ERR_PTR(-EFAULT);
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return NULL;
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}
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static struct page *follow_page_pte(struct vm_area_struct *vma,
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unsigned long address, pmd_t *pmd, unsigned int flags)
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{
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struct mm_struct *mm = vma->vm_mm;
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struct page *page;
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spinlock_t *ptl;
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pte_t *ptep, pte;
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retry:
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if (unlikely(pmd_bad(*pmd)))
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return no_page_table(vma, flags);
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ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
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pte = *ptep;
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if (!pte_present(pte)) {
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swp_entry_t entry;
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/*
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* KSM's break_ksm() relies upon recognizing a ksm page
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* even while it is being migrated, so for that case we
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* need migration_entry_wait().
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*/
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if (likely(!(flags & FOLL_MIGRATION)))
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goto no_page;
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if (pte_none(pte) || pte_file(pte))
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goto no_page;
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entry = pte_to_swp_entry(pte);
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if (!is_migration_entry(entry))
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goto no_page;
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pte_unmap_unlock(ptep, ptl);
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migration_entry_wait(mm, pmd, address);
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goto retry;
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}
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if ((flags & FOLL_NUMA) && pte_numa(pte))
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goto no_page;
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if ((flags & FOLL_WRITE) && !pte_write(pte)) {
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pte_unmap_unlock(ptep, ptl);
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return NULL;
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}
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page = vm_normal_page(vma, address, pte);
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if (unlikely(!page)) {
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if ((flags & FOLL_DUMP) ||
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!is_zero_pfn(pte_pfn(pte)))
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goto bad_page;
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page = pte_page(pte);
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}
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if (flags & FOLL_GET)
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get_page_foll(page);
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if (flags & FOLL_TOUCH) {
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if ((flags & FOLL_WRITE) &&
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!pte_dirty(pte) && !PageDirty(page))
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set_page_dirty(page);
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/*
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* pte_mkyoung() would be more correct here, but atomic care
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* is needed to avoid losing the dirty bit: it is easier to use
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* mark_page_accessed().
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*/
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mark_page_accessed(page);
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}
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if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
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/*
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* The preliminary mapping check is mainly to avoid the
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* pointless overhead of lock_page on the ZERO_PAGE
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* which might bounce very badly if there is contention.
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*
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* If the page is already locked, we don't need to
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* handle it now - vmscan will handle it later if and
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* when it attempts to reclaim the page.
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*/
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if (page->mapping && trylock_page(page)) {
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lru_add_drain(); /* push cached pages to LRU */
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/*
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* Because we lock page here, and migration is
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* blocked by the pte's page reference, and we
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* know the page is still mapped, we don't even
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* need to check for file-cache page truncation.
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*/
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mlock_vma_page(page);
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unlock_page(page);
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}
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}
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pte_unmap_unlock(ptep, ptl);
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return page;
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bad_page:
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pte_unmap_unlock(ptep, ptl);
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return ERR_PTR(-EFAULT);
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no_page:
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pte_unmap_unlock(ptep, ptl);
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if (!pte_none(pte))
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return NULL;
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return no_page_table(vma, flags);
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}
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/**
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* follow_page_mask - look up a page descriptor from a user-virtual address
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* @vma: vm_area_struct mapping @address
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* @address: virtual address to look up
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* @flags: flags modifying lookup behaviour
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* @page_mask: on output, *page_mask is set according to the size of the page
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*
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* @flags can have FOLL_ flags set, defined in <linux/mm.h>
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*
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* Returns the mapped (struct page *), %NULL if no mapping exists, or
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* an error pointer if there is a mapping to something not represented
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* by a page descriptor (see also vm_normal_page()).
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*/
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struct page *follow_page_mask(struct vm_area_struct *vma,
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unsigned long address, unsigned int flags,
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unsigned int *page_mask)
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{
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pgd_t *pgd;
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pud_t *pud;
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pmd_t *pmd;
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spinlock_t *ptl;
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struct page *page;
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struct mm_struct *mm = vma->vm_mm;
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*page_mask = 0;
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page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
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if (!IS_ERR(page)) {
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BUG_ON(flags & FOLL_GET);
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return page;
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}
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pgd = pgd_offset(mm, address);
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if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
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return no_page_table(vma, flags);
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pud = pud_offset(pgd, address);
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if (pud_none(*pud))
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return no_page_table(vma, flags);
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if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
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if (flags & FOLL_GET)
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return NULL;
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page = follow_huge_pud(mm, address, pud, flags & FOLL_WRITE);
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return page;
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}
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if (unlikely(pud_bad(*pud)))
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return no_page_table(vma, flags);
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pmd = pmd_offset(pud, address);
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if (pmd_none(*pmd))
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return no_page_table(vma, flags);
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if (pmd_huge(*pmd) && vma->vm_flags & VM_HUGETLB) {
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page = follow_huge_pmd(mm, address, pmd, flags & FOLL_WRITE);
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if (flags & FOLL_GET) {
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/*
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* Refcount on tail pages are not well-defined and
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* shouldn't be taken. The caller should handle a NULL
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* return when trying to follow tail pages.
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*/
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if (PageHead(page))
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get_page(page);
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else
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page = NULL;
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}
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return page;
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}
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if ((flags & FOLL_NUMA) && pmd_numa(*pmd))
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return no_page_table(vma, flags);
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if (pmd_trans_huge(*pmd)) {
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if (flags & FOLL_SPLIT) {
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split_huge_page_pmd(vma, address, pmd);
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return follow_page_pte(vma, address, pmd, flags);
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}
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ptl = pmd_lock(mm, pmd);
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if (likely(pmd_trans_huge(*pmd))) {
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if (unlikely(pmd_trans_splitting(*pmd))) {
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spin_unlock(ptl);
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wait_split_huge_page(vma->anon_vma, pmd);
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} else {
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page = follow_trans_huge_pmd(vma, address,
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pmd, flags);
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spin_unlock(ptl);
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*page_mask = HPAGE_PMD_NR - 1;
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return page;
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}
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} else
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spin_unlock(ptl);
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}
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return follow_page_pte(vma, address, pmd, flags);
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}
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static int get_gate_page(struct mm_struct *mm, unsigned long address,
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unsigned int gup_flags, struct vm_area_struct **vma,
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struct page **page)
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{
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pgd_t *pgd;
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pud_t *pud;
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pmd_t *pmd;
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pte_t *pte;
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int ret = -EFAULT;
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/* user gate pages are read-only */
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if (gup_flags & FOLL_WRITE)
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return -EFAULT;
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if (address > TASK_SIZE)
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pgd = pgd_offset_k(address);
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else
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pgd = pgd_offset_gate(mm, address);
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BUG_ON(pgd_none(*pgd));
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pud = pud_offset(pgd, address);
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BUG_ON(pud_none(*pud));
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pmd = pmd_offset(pud, address);
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if (pmd_none(*pmd))
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return -EFAULT;
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VM_BUG_ON(pmd_trans_huge(*pmd));
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pte = pte_offset_map(pmd, address);
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if (pte_none(*pte))
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goto unmap;
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*vma = get_gate_vma(mm);
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if (!page)
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goto out;
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*page = vm_normal_page(*vma, address, *pte);
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if (!*page) {
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if ((gup_flags & FOLL_DUMP) || !is_zero_pfn(pte_pfn(*pte)))
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goto unmap;
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*page = pte_page(*pte);
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}
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get_page(*page);
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out:
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ret = 0;
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unmap:
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pte_unmap(pte);
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return ret;
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}
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/*
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* mmap_sem must be held on entry. If @nonblocking != NULL and
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* *@flags does not include FOLL_NOWAIT, the mmap_sem may be released.
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* If it is, *@nonblocking will be set to 0 and -EBUSY returned.
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*/
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static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
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unsigned long address, unsigned int *flags, int *nonblocking)
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{
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struct mm_struct *mm = vma->vm_mm;
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unsigned int fault_flags = 0;
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int ret;
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/* For mlock, just skip the stack guard page. */
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if ((*flags & FOLL_MLOCK) &&
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(stack_guard_page_start(vma, address) ||
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stack_guard_page_end(vma, address + PAGE_SIZE)))
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return -ENOENT;
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if (*flags & FOLL_WRITE)
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fault_flags |= FAULT_FLAG_WRITE;
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if (nonblocking)
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fault_flags |= FAULT_FLAG_ALLOW_RETRY;
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if (*flags & FOLL_NOWAIT)
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fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
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if (*flags & FOLL_TRIED) {
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VM_WARN_ON_ONCE(fault_flags & FAULT_FLAG_ALLOW_RETRY);
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fault_flags |= FAULT_FLAG_TRIED;
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}
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ret = handle_mm_fault(mm, vma, address, fault_flags);
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if (ret & VM_FAULT_ERROR) {
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if (ret & VM_FAULT_OOM)
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return -ENOMEM;
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if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
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return *flags & FOLL_HWPOISON ? -EHWPOISON : -EFAULT;
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if (ret & VM_FAULT_SIGBUS)
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return -EFAULT;
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BUG();
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}
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if (tsk) {
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if (ret & VM_FAULT_MAJOR)
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tsk->maj_flt++;
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else
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tsk->min_flt++;
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}
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if (ret & VM_FAULT_RETRY) {
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if (nonblocking)
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*nonblocking = 0;
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return -EBUSY;
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}
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/*
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* The VM_FAULT_WRITE bit tells us that do_wp_page has broken COW when
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* necessary, even if maybe_mkwrite decided not to set pte_write. We
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* can thus safely do subsequent page lookups as if they were reads.
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* But only do so when looping for pte_write is futile: in some cases
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* userspace may also be wanting to write to the gotten user page,
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* which a read fault here might prevent (a readonly page might get
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* reCOWed by userspace write).
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*/
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if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE))
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*flags &= ~FOLL_WRITE;
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return 0;
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}
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static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
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{
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vm_flags_t vm_flags = vma->vm_flags;
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if (vm_flags & (VM_IO | VM_PFNMAP))
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return -EFAULT;
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if (gup_flags & FOLL_WRITE) {
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if (!(vm_flags & VM_WRITE)) {
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if (!(gup_flags & FOLL_FORCE))
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return -EFAULT;
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/*
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* We used to let the write,force case do COW in a
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* VM_MAYWRITE VM_SHARED !VM_WRITE vma, so ptrace could
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* set a breakpoint in a read-only mapping of an
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* executable, without corrupting the file (yet only
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* when that file had been opened for writing!).
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* Anon pages in shared mappings are surprising: now
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* just reject it.
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*/
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if (!is_cow_mapping(vm_flags)) {
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WARN_ON_ONCE(vm_flags & VM_MAYWRITE);
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return -EFAULT;
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}
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}
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} else if (!(vm_flags & VM_READ)) {
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if (!(gup_flags & FOLL_FORCE))
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return -EFAULT;
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/*
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* Is there actually any vma we can reach here which does not
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* have VM_MAYREAD set?
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*/
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if (!(vm_flags & VM_MAYREAD))
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return -EFAULT;
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}
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return 0;
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}
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/**
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* __get_user_pages() - pin user pages in memory
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* @tsk: task_struct of target task
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* @mm: mm_struct of target mm
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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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* @gup_flags: flags modifying pin behaviour
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* @pages: array that receives pointers to the pages pinned.
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* Should be at least nr_pages long. Or NULL, if caller
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* only intends to ensure the pages are faulted in.
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* @vmas: array of pointers to vmas corresponding to each page.
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* Or NULL if the caller does not require them.
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* @nonblocking: whether waiting for disk IO or mmap_sem contention
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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. Each page returned must be released
|
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* with a put_page() call when it is finished with. vmas will only
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* remain valid while mmap_sem is held.
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*
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* Must be called with mmap_sem held. It may be released. See below.
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*
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* __get_user_pages walks a process's page tables and takes a reference to
|
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* each struct page that each user address corresponds to at a given
|
|
* instant. That is, it takes the page that would be accessed if a user
|
|
* thread accesses the given user virtual address at that instant.
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*
|
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* This does not guarantee that the page exists in the user mappings when
|
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* __get_user_pages returns, and there may even be a completely different
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* page there in some cases (eg. if mmapped pagecache has been invalidated
|
|
* and subsequently re faulted). However it does guarantee that the page
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* won't be freed completely. And mostly callers simply care that the page
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* contains data that was valid *at some point in time*. Typically, an IO
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* or similar operation cannot guarantee anything stronger anyway because
|
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* locks can't be held over the syscall boundary.
|
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*
|
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* If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If
|
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* the page is written to, set_page_dirty (or set_page_dirty_lock, as
|
|
* appropriate) must be called after the page is finished with, and
|
|
* before put_page is called.
|
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*
|
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* If @nonblocking != NULL, __get_user_pages will not wait for disk IO
|
|
* or mmap_sem contention, and if waiting is needed to pin all pages,
|
|
* *@nonblocking will be set to 0. Further, if @gup_flags does not
|
|
* include FOLL_NOWAIT, the mmap_sem will be released via up_read() in
|
|
* this case.
|
|
*
|
|
* A caller using such a combination of @nonblocking and @gup_flags
|
|
* must therefore hold the mmap_sem for reading only, and recognize
|
|
* when it's been released. Otherwise, it must be held for either
|
|
* reading or writing and will not be released.
|
|
*
|
|
* In most cases, get_user_pages or get_user_pages_fast should be used
|
|
* instead of __get_user_pages. __get_user_pages should be used only if
|
|
* you need some special @gup_flags.
|
|
*/
|
|
long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
|
|
unsigned long start, unsigned long nr_pages,
|
|
unsigned int gup_flags, struct page **pages,
|
|
struct vm_area_struct **vmas, int *nonblocking)
|
|
{
|
|
long i = 0;
|
|
unsigned int page_mask;
|
|
struct vm_area_struct *vma = NULL;
|
|
|
|
if (!nr_pages)
|
|
return 0;
|
|
|
|
VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));
|
|
|
|
/*
|
|
* If FOLL_FORCE is set then do not force a full fault as the hinting
|
|
* fault information is unrelated to the reference behaviour of a task
|
|
* using the address space
|
|
*/
|
|
if (!(gup_flags & FOLL_FORCE))
|
|
gup_flags |= FOLL_NUMA;
|
|
|
|
do {
|
|
struct page *page;
|
|
unsigned int foll_flags = gup_flags;
|
|
unsigned int page_increm;
|
|
|
|
/* first iteration or cross vma bound */
|
|
if (!vma || start >= vma->vm_end) {
|
|
vma = find_extend_vma(mm, start);
|
|
if (!vma && in_gate_area(mm, start)) {
|
|
int ret;
|
|
ret = get_gate_page(mm, start & PAGE_MASK,
|
|
gup_flags, &vma,
|
|
pages ? &pages[i] : NULL);
|
|
if (ret)
|
|
return i ? : ret;
|
|
page_mask = 0;
|
|
goto next_page;
|
|
}
|
|
|
|
if (!vma || check_vma_flags(vma, gup_flags))
|
|
return i ? : -EFAULT;
|
|
if (is_vm_hugetlb_page(vma)) {
|
|
i = follow_hugetlb_page(mm, vma, pages, vmas,
|
|
&start, &nr_pages, i,
|
|
gup_flags);
|
|
continue;
|
|
}
|
|
}
|
|
retry:
|
|
/*
|
|
* If we have a pending SIGKILL, don't keep faulting pages and
|
|
* potentially allocating memory.
|
|
*/
|
|
if (unlikely(fatal_signal_pending(current)))
|
|
return i ? i : -ERESTARTSYS;
|
|
cond_resched();
|
|
page = follow_page_mask(vma, start, foll_flags, &page_mask);
|
|
if (!page) {
|
|
int ret;
|
|
ret = faultin_page(tsk, vma, start, &foll_flags,
|
|
nonblocking);
|
|
switch (ret) {
|
|
case 0:
|
|
goto retry;
|
|
case -EFAULT:
|
|
case -ENOMEM:
|
|
case -EHWPOISON:
|
|
return i ? i : ret;
|
|
case -EBUSY:
|
|
return i;
|
|
case -ENOENT:
|
|
goto next_page;
|
|
}
|
|
BUG();
|
|
}
|
|
if (IS_ERR(page))
|
|
return i ? i : PTR_ERR(page);
|
|
if (pages) {
|
|
pages[i] = page;
|
|
flush_anon_page(vma, page, start);
|
|
flush_dcache_page(page);
|
|
page_mask = 0;
|
|
}
|
|
next_page:
|
|
if (vmas) {
|
|
vmas[i] = vma;
|
|
page_mask = 0;
|
|
}
|
|
page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
|
|
if (page_increm > nr_pages)
|
|
page_increm = nr_pages;
|
|
i += page_increm;
|
|
start += page_increm * PAGE_SIZE;
|
|
nr_pages -= page_increm;
|
|
} while (nr_pages);
|
|
return i;
|
|
}
|
|
EXPORT_SYMBOL(__get_user_pages);
|
|
|
|
/*
|
|
* fixup_user_fault() - manually resolve a user page fault
|
|
* @tsk: the task_struct to use for page fault accounting, or
|
|
* NULL if faults are not to be recorded.
|
|
* @mm: mm_struct of target mm
|
|
* @address: user address
|
|
* @fault_flags:flags to pass down to handle_mm_fault()
|
|
*
|
|
* This is meant to be called in the specific scenario where for locking reasons
|
|
* we try to access user memory in atomic context (within a pagefault_disable()
|
|
* section), this returns -EFAULT, and we want to resolve the user fault before
|
|
* trying again.
|
|
*
|
|
* Typically this is meant to be used by the futex code.
|
|
*
|
|
* The main difference with get_user_pages() is that this function will
|
|
* unconditionally call handle_mm_fault() which will in turn perform all the
|
|
* necessary SW fixup of the dirty and young bits in the PTE, while
|
|
* handle_mm_fault() only guarantees to update these in the struct page.
|
|
*
|
|
* This is important for some architectures where those bits also gate the
|
|
* access permission to the page because they are maintained in software. On
|
|
* such architectures, gup() will not be enough to make a subsequent access
|
|
* succeed.
|
|
*
|
|
* This has the same semantics wrt the @mm->mmap_sem as does filemap_fault().
|
|
*/
|
|
int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
|
|
unsigned long address, unsigned int fault_flags)
|
|
{
|
|
struct vm_area_struct *vma;
|
|
vm_flags_t vm_flags;
|
|
int ret;
|
|
|
|
vma = find_extend_vma(mm, address);
|
|
if (!vma || address < vma->vm_start)
|
|
return -EFAULT;
|
|
|
|
vm_flags = (fault_flags & FAULT_FLAG_WRITE) ? VM_WRITE : VM_READ;
|
|
if (!(vm_flags & vma->vm_flags))
|
|
return -EFAULT;
|
|
|
|
ret = handle_mm_fault(mm, vma, address, fault_flags);
|
|
if (ret & VM_FAULT_ERROR) {
|
|
if (ret & VM_FAULT_OOM)
|
|
return -ENOMEM;
|
|
if (ret & (VM_FAULT_HWPOISON | VM_FAULT_HWPOISON_LARGE))
|
|
return -EHWPOISON;
|
|
if (ret & VM_FAULT_SIGBUS)
|
|
return -EFAULT;
|
|
BUG();
|
|
}
|
|
if (tsk) {
|
|
if (ret & VM_FAULT_MAJOR)
|
|
tsk->maj_flt++;
|
|
else
|
|
tsk->min_flt++;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* get_user_pages() - pin user pages in memory
|
|
* @tsk: the task_struct to use for page fault accounting, or
|
|
* NULL if faults are not to be recorded.
|
|
* @mm: mm_struct of target mm
|
|
* @start: starting user address
|
|
* @nr_pages: number of pages from start to pin
|
|
* @write: whether pages will be written to by the caller
|
|
* @force: whether to force access even when user mapping is currently
|
|
* protected (but never forces write access to shared mapping).
|
|
* @pages: array that receives pointers to the pages pinned.
|
|
* Should be at least nr_pages long. Or NULL, if caller
|
|
* only intends to ensure the pages are faulted in.
|
|
* @vmas: array of pointers to vmas corresponding to each page.
|
|
* Or NULL if the caller does not require them.
|
|
*
|
|
* Returns number of pages pinned. This may be fewer than the number
|
|
* requested. If nr_pages is 0 or negative, returns 0. If no pages
|
|
* were pinned, returns -errno. Each page returned must be released
|
|
* with a put_page() call when it is finished with. vmas will only
|
|
* remain valid while mmap_sem is held.
|
|
*
|
|
* Must be called with mmap_sem held for read or write.
|
|
*
|
|
* get_user_pages walks a process's page tables and takes a reference to
|
|
* each struct page that each user address corresponds to at a given
|
|
* instant. That is, it takes the page that would be accessed if a user
|
|
* thread accesses the given user virtual address at that instant.
|
|
*
|
|
* This does not guarantee that the page exists in the user mappings when
|
|
* get_user_pages returns, and there may even be a completely different
|
|
* page there in some cases (eg. if mmapped pagecache has been invalidated
|
|
* and subsequently re faulted). However it does guarantee that the page
|
|
* won't be freed completely. And mostly callers simply care that the page
|
|
* contains data that was valid *at some point in time*. Typically, an IO
|
|
* or similar operation cannot guarantee anything stronger anyway because
|
|
* locks can't be held over the syscall boundary.
|
|
*
|
|
* If write=0, the page must not be written to. If the page is written to,
|
|
* set_page_dirty (or set_page_dirty_lock, as appropriate) must be called
|
|
* after the page is finished with, and before put_page is called.
|
|
*
|
|
* get_user_pages is typically used for fewer-copy IO operations, to get a
|
|
* handle on the memory by some means other than accesses via the user virtual
|
|
* addresses. The pages may be submitted for DMA to devices or accessed via
|
|
* their kernel linear mapping (via the kmap APIs). Care should be taken to
|
|
* use the correct cache flushing APIs.
|
|
*
|
|
* See also get_user_pages_fast, for performance critical applications.
|
|
*/
|
|
long get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
|
|
unsigned long start, unsigned long nr_pages, int write,
|
|
int force, struct page **pages, struct vm_area_struct **vmas)
|
|
{
|
|
int flags = FOLL_TOUCH;
|
|
|
|
if (pages)
|
|
flags |= FOLL_GET;
|
|
if (write)
|
|
flags |= FOLL_WRITE;
|
|
if (force)
|
|
flags |= FOLL_FORCE;
|
|
|
|
return __get_user_pages(tsk, mm, start, nr_pages, flags, pages, vmas,
|
|
NULL);
|
|
}
|
|
EXPORT_SYMBOL(get_user_pages);
|
|
|
|
/**
|
|
* get_dump_page() - pin user page in memory while writing it to core dump
|
|
* @addr: user address
|
|
*
|
|
* Returns struct page pointer of user page pinned for dump,
|
|
* to be freed afterwards by page_cache_release() or put_page().
|
|
*
|
|
* Returns NULL on any kind of failure - a hole must then be inserted into
|
|
* the corefile, to preserve alignment with its headers; and also returns
|
|
* NULL wherever the ZERO_PAGE, or an anonymous pte_none, has been found -
|
|
* allowing a hole to be left in the corefile to save diskspace.
|
|
*
|
|
* Called without mmap_sem, but after all other threads have been killed.
|
|
*/
|
|
#ifdef CONFIG_ELF_CORE
|
|
struct page *get_dump_page(unsigned long addr)
|
|
{
|
|
struct vm_area_struct *vma;
|
|
struct page *page;
|
|
|
|
if (__get_user_pages(current, current->mm, addr, 1,
|
|
FOLL_FORCE | FOLL_DUMP | FOLL_GET, &page, &vma,
|
|
NULL) < 1)
|
|
return NULL;
|
|
flush_cache_page(vma, addr, page_to_pfn(page));
|
|
return page;
|
|
}
|
|
#endif /* CONFIG_ELF_CORE */
|
|
|
|
/*
|
|
* Generic RCU Fast GUP
|
|
*
|
|
* get_user_pages_fast attempts to pin user pages by walking the page
|
|
* tables directly and avoids taking locks. Thus the walker needs to be
|
|
* protected from page table pages being freed from under it, and should
|
|
* block any THP splits.
|
|
*
|
|
* One way to achieve this is to have the walker disable interrupts, and
|
|
* rely on IPIs from the TLB flushing code blocking before the page table
|
|
* pages are freed. This is unsuitable for architectures that do not need
|
|
* to broadcast an IPI when invalidating TLBs.
|
|
*
|
|
* Another way to achieve this is to batch up page table containing pages
|
|
* belonging to more than one mm_user, then rcu_sched a callback to free those
|
|
* pages. Disabling interrupts will allow the fast_gup walker to both block
|
|
* the rcu_sched callback, and an IPI that we broadcast for splitting THPs
|
|
* (which is a relatively rare event). The code below adopts this strategy.
|
|
*
|
|
* Before activating this code, please be aware that the following assumptions
|
|
* are currently made:
|
|
*
|
|
* *) HAVE_RCU_TABLE_FREE is enabled, and tlb_remove_table is used to free
|
|
* pages containing page tables.
|
|
*
|
|
* *) THP splits will broadcast an IPI, this can be achieved by overriding
|
|
* pmdp_splitting_flush.
|
|
*
|
|
* *) ptes can be read atomically by the architecture.
|
|
*
|
|
* *) access_ok is sufficient to validate userspace address ranges.
|
|
*
|
|
* The last two assumptions can be relaxed by the addition of helper functions.
|
|
*
|
|
* This code is based heavily on the PowerPC implementation by Nick Piggin.
|
|
*/
|
|
#ifdef CONFIG_HAVE_GENERIC_RCU_GUP
|
|
|
|
#ifdef __HAVE_ARCH_PTE_SPECIAL
|
|
static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
|
|
int write, struct page **pages, int *nr)
|
|
{
|
|
pte_t *ptep, *ptem;
|
|
int ret = 0;
|
|
|
|
ptem = ptep = pte_offset_map(&pmd, addr);
|
|
do {
|
|
/*
|
|
* In the line below we are assuming that the pte can be read
|
|
* atomically. If this is not the case for your architecture,
|
|
* please wrap this in a helper function!
|
|
*
|
|
* for an example see gup_get_pte in arch/x86/mm/gup.c
|
|
*/
|
|
pte_t pte = ACCESS_ONCE(*ptep);
|
|
struct page *page;
|
|
|
|
/*
|
|
* Similar to the PMD case below, NUMA hinting must take slow
|
|
* path
|
|
*/
|
|
if (!pte_present(pte) || pte_special(pte) ||
|
|
pte_numa(pte) || (write && !pte_write(pte)))
|
|
goto pte_unmap;
|
|
|
|
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
|
|
page = pte_page(pte);
|
|
|
|
if (!page_cache_get_speculative(page))
|
|
goto pte_unmap;
|
|
|
|
if (unlikely(pte_val(pte) != pte_val(*ptep))) {
|
|
put_page(page);
|
|
goto pte_unmap;
|
|
}
|
|
|
|
pages[*nr] = page;
|
|
(*nr)++;
|
|
|
|
} while (ptep++, addr += PAGE_SIZE, addr != end);
|
|
|
|
ret = 1;
|
|
|
|
pte_unmap:
|
|
pte_unmap(ptem);
|
|
return ret;
|
|
}
|
|
#else
|
|
|
|
/*
|
|
* If we can't determine whether or not a pte is special, then fail immediately
|
|
* for ptes. Note, we can still pin HugeTLB and THP as these are guaranteed not
|
|
* to be special.
|
|
*
|
|
* For a futex to be placed on a THP tail page, get_futex_key requires a
|
|
* __get_user_pages_fast implementation that can pin pages. Thus it's still
|
|
* useful to have gup_huge_pmd even if we can't operate on ptes.
|
|
*/
|
|
static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
|
|
int write, struct page **pages, int *nr)
|
|
{
|
|
return 0;
|
|
}
|
|
#endif /* __HAVE_ARCH_PTE_SPECIAL */
|
|
|
|
static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
|
|
unsigned long end, int write, struct page **pages, int *nr)
|
|
{
|
|
struct page *head, *page, *tail;
|
|
int refs;
|
|
|
|
if (write && !pmd_write(orig))
|
|
return 0;
|
|
|
|
refs = 0;
|
|
head = pmd_page(orig);
|
|
page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
|
|
tail = page;
|
|
do {
|
|
VM_BUG_ON_PAGE(compound_head(page) != head, page);
|
|
pages[*nr] = page;
|
|
(*nr)++;
|
|
page++;
|
|
refs++;
|
|
} while (addr += PAGE_SIZE, addr != end);
|
|
|
|
if (!page_cache_add_speculative(head, refs)) {
|
|
*nr -= refs;
|
|
return 0;
|
|
}
|
|
|
|
if (unlikely(pmd_val(orig) != pmd_val(*pmdp))) {
|
|
*nr -= refs;
|
|
while (refs--)
|
|
put_page(head);
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Any tail pages need their mapcount reference taken before we
|
|
* return. (This allows the THP code to bump their ref count when
|
|
* they are split into base pages).
|
|
*/
|
|
while (refs--) {
|
|
if (PageTail(tail))
|
|
get_huge_page_tail(tail);
|
|
tail++;
|
|
}
|
|
|
|
return 1;
|
|
}
|
|
|
|
static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
|
|
unsigned long end, int write, struct page **pages, int *nr)
|
|
{
|
|
struct page *head, *page, *tail;
|
|
int refs;
|
|
|
|
if (write && !pud_write(orig))
|
|
return 0;
|
|
|
|
refs = 0;
|
|
head = pud_page(orig);
|
|
page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
|
|
tail = page;
|
|
do {
|
|
VM_BUG_ON_PAGE(compound_head(page) != head, page);
|
|
pages[*nr] = page;
|
|
(*nr)++;
|
|
page++;
|
|
refs++;
|
|
} while (addr += PAGE_SIZE, addr != end);
|
|
|
|
if (!page_cache_add_speculative(head, refs)) {
|
|
*nr -= refs;
|
|
return 0;
|
|
}
|
|
|
|
if (unlikely(pud_val(orig) != pud_val(*pudp))) {
|
|
*nr -= refs;
|
|
while (refs--)
|
|
put_page(head);
|
|
return 0;
|
|
}
|
|
|
|
while (refs--) {
|
|
if (PageTail(tail))
|
|
get_huge_page_tail(tail);
|
|
tail++;
|
|
}
|
|
|
|
return 1;
|
|
}
|
|
|
|
static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
|
|
unsigned long end, int write,
|
|
struct page **pages, int *nr)
|
|
{
|
|
int refs;
|
|
struct page *head, *page, *tail;
|
|
|
|
if (write && !pgd_write(orig))
|
|
return 0;
|
|
|
|
refs = 0;
|
|
head = pgd_page(orig);
|
|
page = head + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
|
|
tail = page;
|
|
do {
|
|
VM_BUG_ON_PAGE(compound_head(page) != head, page);
|
|
pages[*nr] = page;
|
|
(*nr)++;
|
|
page++;
|
|
refs++;
|
|
} while (addr += PAGE_SIZE, addr != end);
|
|
|
|
if (!page_cache_add_speculative(head, refs)) {
|
|
*nr -= refs;
|
|
return 0;
|
|
}
|
|
|
|
if (unlikely(pgd_val(orig) != pgd_val(*pgdp))) {
|
|
*nr -= refs;
|
|
while (refs--)
|
|
put_page(head);
|
|
return 0;
|
|
}
|
|
|
|
while (refs--) {
|
|
if (PageTail(tail))
|
|
get_huge_page_tail(tail);
|
|
tail++;
|
|
}
|
|
|
|
return 1;
|
|
}
|
|
|
|
static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
|
|
int write, struct page **pages, int *nr)
|
|
{
|
|
unsigned long next;
|
|
pmd_t *pmdp;
|
|
|
|
pmdp = pmd_offset(&pud, addr);
|
|
do {
|
|
pmd_t pmd = ACCESS_ONCE(*pmdp);
|
|
|
|
next = pmd_addr_end(addr, end);
|
|
if (pmd_none(pmd) || pmd_trans_splitting(pmd))
|
|
return 0;
|
|
|
|
if (unlikely(pmd_trans_huge(pmd) || pmd_huge(pmd))) {
|
|
/*
|
|
* NUMA hinting faults need to be handled in the GUP
|
|
* slowpath for accounting purposes and so that they
|
|
* can be serialised against THP migration.
|
|
*/
|
|
if (pmd_numa(pmd))
|
|
return 0;
|
|
|
|
if (!gup_huge_pmd(pmd, pmdp, addr, next, write,
|
|
pages, nr))
|
|
return 0;
|
|
|
|
} else if (unlikely(is_hugepd(__hugepd(pmd_val(pmd))))) {
|
|
/*
|
|
* architecture have different format for hugetlbfs
|
|
* pmd format and THP pmd format
|
|
*/
|
|
if (!gup_huge_pd(__hugepd(pmd_val(pmd)), addr,
|
|
PMD_SHIFT, next, write, pages, nr))
|
|
return 0;
|
|
} else if (!gup_pte_range(pmd, addr, next, write, pages, nr))
|
|
return 0;
|
|
} while (pmdp++, addr = next, addr != end);
|
|
|
|
return 1;
|
|
}
|
|
|
|
static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long end,
|
|
int write, struct page **pages, int *nr)
|
|
{
|
|
unsigned long next;
|
|
pud_t *pudp;
|
|
|
|
pudp = pud_offset(&pgd, addr);
|
|
do {
|
|
pud_t pud = READ_ONCE(*pudp);
|
|
|
|
next = pud_addr_end(addr, end);
|
|
if (pud_none(pud))
|
|
return 0;
|
|
if (unlikely(pud_huge(pud))) {
|
|
if (!gup_huge_pud(pud, pudp, addr, next, write,
|
|
pages, nr))
|
|
return 0;
|
|
} else if (unlikely(is_hugepd(__hugepd(pud_val(pud))))) {
|
|
if (!gup_huge_pd(__hugepd(pud_val(pud)), addr,
|
|
PUD_SHIFT, next, write, pages, nr))
|
|
return 0;
|
|
} else if (!gup_pmd_range(pud, addr, next, write, pages, nr))
|
|
return 0;
|
|
} while (pudp++, addr = next, addr != end);
|
|
|
|
return 1;
|
|
}
|
|
|
|
/*
|
|
* Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to
|
|
* the regular GUP. It will only return non-negative values.
|
|
*/
|
|
int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
|
|
struct page **pages)
|
|
{
|
|
struct mm_struct *mm = current->mm;
|
|
unsigned long addr, len, end;
|
|
unsigned long next, flags;
|
|
pgd_t *pgdp;
|
|
int nr = 0;
|
|
|
|
start &= PAGE_MASK;
|
|
addr = start;
|
|
len = (unsigned long) nr_pages << PAGE_SHIFT;
|
|
end = start + len;
|
|
|
|
if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
|
|
start, len)))
|
|
return 0;
|
|
|
|
/*
|
|
* Disable interrupts. We use the nested form as we can already have
|
|
* interrupts disabled by get_futex_key.
|
|
*
|
|
* With interrupts disabled, we block page table pages from being
|
|
* freed from under us. See mmu_gather_tlb in asm-generic/tlb.h
|
|
* for more details.
|
|
*
|
|
* We do not adopt an rcu_read_lock(.) here as we also want to
|
|
* block IPIs that come from THPs splitting.
|
|
*/
|
|
|
|
local_irq_save(flags);
|
|
pgdp = pgd_offset(mm, addr);
|
|
do {
|
|
pgd_t pgd = ACCESS_ONCE(*pgdp);
|
|
|
|
next = pgd_addr_end(addr, end);
|
|
if (pgd_none(pgd))
|
|
break;
|
|
if (unlikely(pgd_huge(pgd))) {
|
|
if (!gup_huge_pgd(pgd, pgdp, addr, next, write,
|
|
pages, &nr))
|
|
break;
|
|
} else if (unlikely(is_hugepd(__hugepd(pgd_val(pgd))))) {
|
|
if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr,
|
|
PGDIR_SHIFT, next, write, pages, &nr))
|
|
break;
|
|
} else if (!gup_pud_range(pgd, addr, next, write, pages, &nr))
|
|
break;
|
|
} while (pgdp++, addr = next, addr != end);
|
|
local_irq_restore(flags);
|
|
|
|
return nr;
|
|
}
|
|
|
|
/**
|
|
* get_user_pages_fast() - pin user pages in memory
|
|
* @start: starting user address
|
|
* @nr_pages: number of pages from start to pin
|
|
* @write: whether pages will be written to
|
|
* @pages: array that receives pointers to the pages pinned.
|
|
* Should be at least nr_pages long.
|
|
*
|
|
* Attempt to pin user pages in memory without taking mm->mmap_sem.
|
|
* If not successful, it will fall back to taking the lock and
|
|
* calling get_user_pages().
|
|
*
|
|
* Returns number of pages pinned. This may be fewer than the number
|
|
* requested. If nr_pages is 0 or negative, returns 0. If no pages
|
|
* were pinned, returns -errno.
|
|
*/
|
|
int get_user_pages_fast(unsigned long start, int nr_pages, int write,
|
|
struct page **pages)
|
|
{
|
|
struct mm_struct *mm = current->mm;
|
|
int nr, ret;
|
|
|
|
start &= PAGE_MASK;
|
|
nr = __get_user_pages_fast(start, nr_pages, write, pages);
|
|
ret = nr;
|
|
|
|
if (nr < nr_pages) {
|
|
/* Try to get the remaining pages with get_user_pages */
|
|
start += nr << PAGE_SHIFT;
|
|
pages += nr;
|
|
|
|
down_read(&mm->mmap_sem);
|
|
ret = get_user_pages(current, mm, start,
|
|
nr_pages - nr, write, 0, pages, NULL);
|
|
up_read(&mm->mmap_sem);
|
|
|
|
/* Have to be a bit careful with return values */
|
|
if (nr > 0) {
|
|
if (ret < 0)
|
|
ret = nr;
|
|
else
|
|
ret += nr;
|
|
}
|
|
}
|
|
|
|
return ret;
|
|
}
|
|
|
|
#endif /* CONFIG_HAVE_GENERIC_RCU_GUP */
|