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![Hugh Dickins](/assets/img/avatar_default.png)
Add a block of comments on pte_offset_map_lock(), pte_offset_map() and pte_offset_map_nolock() to mm/pgtable-generic.c, to help explain them. Link: https://lkml.kernel.org/r/b791c3b0-25c6-a263-d785-d564344eb644@google.com Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Alexander Gordeev <agordeev@linux.ibm.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Christian Borntraeger <borntraeger@linux.ibm.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Christoph Hellwig <hch@infradead.org> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Cc: David Hildenbrand <david@redhat.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Huang, Ying <ying.huang@intel.com> Cc: Ira Weiny <ira.weiny@intel.com> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Lorenzo Stoakes <lstoakes@gmail.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Miaohe Lin <linmiaohe@huawei.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Minchan Kim <minchan@kernel.org> Cc: Naoya Horiguchi <naoya.horiguchi@nec.com> Cc: Pavel Tatashin <pasha.tatashin@soleen.com> Cc: Peter Xu <peterx@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Qi Zheng <zhengqi.arch@bytedance.com> Cc: Ralph Campbell <rcampbell@nvidia.com> Cc: Russell King <linux@armlinux.org.uk> Cc: SeongJae Park <sj@kernel.org> Cc: Song Liu <song@kernel.org> Cc: Steven Price <steven.price@arm.com> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Will Deacon <will@kernel.org> Cc: Yang Shi <shy828301@gmail.com> Cc: Yu Zhao <yuzhao@google.com> Cc: Zack Rusin <zackr@vmware.com> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
380 lines
11 KiB
C
380 lines
11 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* mm/pgtable-generic.c
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*
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* Generic pgtable methods declared in linux/pgtable.h
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*
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* Copyright (C) 2010 Linus Torvalds
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*/
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#include <linux/pagemap.h>
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#include <linux/hugetlb.h>
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#include <linux/pgtable.h>
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#include <linux/swap.h>
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#include <linux/swapops.h>
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#include <linux/mm_inline.h>
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#include <asm/pgalloc.h>
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#include <asm/tlb.h>
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/*
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* If a p?d_bad entry is found while walking page tables, report
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* the error, before resetting entry to p?d_none. Usually (but
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* very seldom) called out from the p?d_none_or_clear_bad macros.
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*/
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void pgd_clear_bad(pgd_t *pgd)
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{
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pgd_ERROR(*pgd);
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pgd_clear(pgd);
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}
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#ifndef __PAGETABLE_P4D_FOLDED
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void p4d_clear_bad(p4d_t *p4d)
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{
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p4d_ERROR(*p4d);
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p4d_clear(p4d);
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}
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#endif
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#ifndef __PAGETABLE_PUD_FOLDED
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void pud_clear_bad(pud_t *pud)
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{
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pud_ERROR(*pud);
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pud_clear(pud);
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}
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#endif
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/*
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* Note that the pmd variant below can't be stub'ed out just as for p4d/pud
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* above. pmd folding is special and typically pmd_* macros refer to upper
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* level even when folded
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*/
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void pmd_clear_bad(pmd_t *pmd)
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{
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pmd_ERROR(*pmd);
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pmd_clear(pmd);
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}
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#ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
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/*
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* Only sets the access flags (dirty, accessed), as well as write
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* permission. Furthermore, we know it always gets set to a "more
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* permissive" setting, which allows most architectures to optimize
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* this. We return whether the PTE actually changed, which in turn
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* instructs the caller to do things like update__mmu_cache. This
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* used to be done in the caller, but sparc needs minor faults to
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* force that call on sun4c so we changed this macro slightly
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*/
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int ptep_set_access_flags(struct vm_area_struct *vma,
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unsigned long address, pte_t *ptep,
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pte_t entry, int dirty)
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{
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int changed = !pte_same(ptep_get(ptep), entry);
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if (changed) {
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set_pte_at(vma->vm_mm, address, ptep, entry);
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flush_tlb_fix_spurious_fault(vma, address, ptep);
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}
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return changed;
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}
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#endif
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#ifndef __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH
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int ptep_clear_flush_young(struct vm_area_struct *vma,
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unsigned long address, pte_t *ptep)
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{
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int young;
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young = ptep_test_and_clear_young(vma, address, ptep);
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if (young)
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flush_tlb_page(vma, address);
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return young;
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}
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#endif
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#ifndef __HAVE_ARCH_PTEP_CLEAR_FLUSH
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pte_t ptep_clear_flush(struct vm_area_struct *vma, unsigned long address,
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pte_t *ptep)
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{
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struct mm_struct *mm = (vma)->vm_mm;
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pte_t pte;
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pte = ptep_get_and_clear(mm, address, ptep);
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if (pte_accessible(mm, pte))
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flush_tlb_page(vma, address);
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return pte;
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}
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#endif
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#ifdef CONFIG_TRANSPARENT_HUGEPAGE
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#ifndef __HAVE_ARCH_PMDP_SET_ACCESS_FLAGS
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int pmdp_set_access_flags(struct vm_area_struct *vma,
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unsigned long address, pmd_t *pmdp,
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pmd_t entry, int dirty)
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{
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int changed = !pmd_same(*pmdp, entry);
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VM_BUG_ON(address & ~HPAGE_PMD_MASK);
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if (changed) {
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set_pmd_at(vma->vm_mm, address, pmdp, entry);
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flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
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}
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return changed;
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}
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#endif
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#ifndef __HAVE_ARCH_PMDP_CLEAR_YOUNG_FLUSH
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int pmdp_clear_flush_young(struct vm_area_struct *vma,
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unsigned long address, pmd_t *pmdp)
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{
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int young;
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VM_BUG_ON(address & ~HPAGE_PMD_MASK);
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young = pmdp_test_and_clear_young(vma, address, pmdp);
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if (young)
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flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
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return young;
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}
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#endif
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#ifndef __HAVE_ARCH_PMDP_HUGE_CLEAR_FLUSH
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pmd_t pmdp_huge_clear_flush(struct vm_area_struct *vma, unsigned long address,
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pmd_t *pmdp)
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{
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pmd_t pmd;
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VM_BUG_ON(address & ~HPAGE_PMD_MASK);
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VM_BUG_ON(pmd_present(*pmdp) && !pmd_trans_huge(*pmdp) &&
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!pmd_devmap(*pmdp));
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pmd = pmdp_huge_get_and_clear(vma->vm_mm, address, pmdp);
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flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
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return pmd;
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}
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#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
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pud_t pudp_huge_clear_flush(struct vm_area_struct *vma, unsigned long address,
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pud_t *pudp)
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{
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pud_t pud;
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VM_BUG_ON(address & ~HPAGE_PUD_MASK);
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VM_BUG_ON(!pud_trans_huge(*pudp) && !pud_devmap(*pudp));
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pud = pudp_huge_get_and_clear(vma->vm_mm, address, pudp);
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flush_pud_tlb_range(vma, address, address + HPAGE_PUD_SIZE);
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return pud;
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}
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#endif
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#endif
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#ifndef __HAVE_ARCH_PGTABLE_DEPOSIT
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void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp,
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pgtable_t pgtable)
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{
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assert_spin_locked(pmd_lockptr(mm, pmdp));
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/* FIFO */
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if (!pmd_huge_pte(mm, pmdp))
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INIT_LIST_HEAD(&pgtable->lru);
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else
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list_add(&pgtable->lru, &pmd_huge_pte(mm, pmdp)->lru);
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pmd_huge_pte(mm, pmdp) = pgtable;
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}
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#endif
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#ifndef __HAVE_ARCH_PGTABLE_WITHDRAW
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/* no "address" argument so destroys page coloring of some arch */
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pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp)
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{
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pgtable_t pgtable;
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assert_spin_locked(pmd_lockptr(mm, pmdp));
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/* FIFO */
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pgtable = pmd_huge_pte(mm, pmdp);
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pmd_huge_pte(mm, pmdp) = list_first_entry_or_null(&pgtable->lru,
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struct page, lru);
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if (pmd_huge_pte(mm, pmdp))
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list_del(&pgtable->lru);
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return pgtable;
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}
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#endif
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#ifndef __HAVE_ARCH_PMDP_INVALIDATE
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pmd_t pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
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pmd_t *pmdp)
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{
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pmd_t old = pmdp_establish(vma, address, pmdp, pmd_mkinvalid(*pmdp));
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flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
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return old;
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}
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#endif
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#ifndef __HAVE_ARCH_PMDP_INVALIDATE_AD
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pmd_t pmdp_invalidate_ad(struct vm_area_struct *vma, unsigned long address,
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pmd_t *pmdp)
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{
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return pmdp_invalidate(vma, address, pmdp);
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}
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#endif
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#ifndef pmdp_collapse_flush
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pmd_t pmdp_collapse_flush(struct vm_area_struct *vma, unsigned long address,
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pmd_t *pmdp)
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{
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/*
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* pmd and hugepage pte format are same. So we could
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* use the same function.
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*/
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pmd_t pmd;
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VM_BUG_ON(address & ~HPAGE_PMD_MASK);
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VM_BUG_ON(pmd_trans_huge(*pmdp));
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pmd = pmdp_huge_get_and_clear(vma->vm_mm, address, pmdp);
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/* collapse entails shooting down ptes not pmd */
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flush_tlb_range(vma, address, address + HPAGE_PMD_SIZE);
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return pmd;
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}
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#endif
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/* arch define pte_free_defer in asm/pgalloc.h for its own implementation */
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#ifndef pte_free_defer
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static void pte_free_now(struct rcu_head *head)
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{
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struct page *page;
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page = container_of(head, struct page, rcu_head);
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pte_free(NULL /* mm not passed and not used */, (pgtable_t)page);
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}
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void pte_free_defer(struct mm_struct *mm, pgtable_t pgtable)
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{
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struct page *page;
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page = pgtable;
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call_rcu(&page->rcu_head, pte_free_now);
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}
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#endif /* pte_free_defer */
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#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
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#if defined(CONFIG_GUP_GET_PXX_LOW_HIGH) && \
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(defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RCU))
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/*
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* See the comment above ptep_get_lockless() in include/linux/pgtable.h:
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* the barriers in pmdp_get_lockless() cannot guarantee that the value in
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* pmd_high actually belongs with the value in pmd_low; but holding interrupts
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* off blocks the TLB flush between present updates, which guarantees that a
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* successful __pte_offset_map() points to a page from matched halves.
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*/
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static unsigned long pmdp_get_lockless_start(void)
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{
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unsigned long irqflags;
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local_irq_save(irqflags);
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return irqflags;
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}
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static void pmdp_get_lockless_end(unsigned long irqflags)
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{
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local_irq_restore(irqflags);
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}
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#else
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static unsigned long pmdp_get_lockless_start(void) { return 0; }
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static void pmdp_get_lockless_end(unsigned long irqflags) { }
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#endif
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pte_t *__pte_offset_map(pmd_t *pmd, unsigned long addr, pmd_t *pmdvalp)
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{
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unsigned long irqflags;
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pmd_t pmdval;
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rcu_read_lock();
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irqflags = pmdp_get_lockless_start();
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pmdval = pmdp_get_lockless(pmd);
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pmdp_get_lockless_end(irqflags);
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if (pmdvalp)
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*pmdvalp = pmdval;
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if (unlikely(pmd_none(pmdval) || is_pmd_migration_entry(pmdval)))
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goto nomap;
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if (unlikely(pmd_trans_huge(pmdval) || pmd_devmap(pmdval)))
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goto nomap;
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if (unlikely(pmd_bad(pmdval))) {
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pmd_clear_bad(pmd);
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goto nomap;
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}
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return __pte_map(&pmdval, addr);
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nomap:
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rcu_read_unlock();
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return NULL;
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}
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pte_t *pte_offset_map_nolock(struct mm_struct *mm, pmd_t *pmd,
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unsigned long addr, spinlock_t **ptlp)
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{
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pmd_t pmdval;
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pte_t *pte;
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pte = __pte_offset_map(pmd, addr, &pmdval);
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if (likely(pte))
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*ptlp = pte_lockptr(mm, &pmdval);
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return pte;
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}
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/*
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* pte_offset_map_lock(mm, pmd, addr, ptlp), and its internal implementation
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* __pte_offset_map_lock() below, is usually called with the pmd pointer for
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* addr, reached by walking down the mm's pgd, p4d, pud for addr: either while
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* holding mmap_lock or vma lock for read or for write; or in truncate or rmap
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* context, while holding file's i_mmap_lock or anon_vma lock for read (or for
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* write). In a few cases, it may be used with pmd pointing to a pmd_t already
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* copied to or constructed on the stack.
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*
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* When successful, it returns the pte pointer for addr, with its page table
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* kmapped if necessary (when CONFIG_HIGHPTE), and locked against concurrent
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* modification by software, with a pointer to that spinlock in ptlp (in some
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* configs mm->page_table_lock, in SPLIT_PTLOCK configs a spinlock in table's
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* struct page). pte_unmap_unlock(pte, ptl) to unlock and unmap afterwards.
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*
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* But it is unsuccessful, returning NULL with *ptlp unchanged, if there is no
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* page table at *pmd: if, for example, the page table has just been removed,
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* or replaced by the huge pmd of a THP. (When successful, *pmd is rechecked
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* after acquiring the ptlock, and retried internally if it changed: so that a
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* page table can be safely removed or replaced by THP while holding its lock.)
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*
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* pte_offset_map(pmd, addr), and its internal helper __pte_offset_map() above,
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* just returns the pte pointer for addr, its page table kmapped if necessary;
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* or NULL if there is no page table at *pmd. It does not attempt to lock the
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* page table, so cannot normally be used when the page table is to be updated,
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* or when entries read must be stable. But it does take rcu_read_lock(): so
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* that even when page table is racily removed, it remains a valid though empty
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* and disconnected table. Until pte_unmap(pte) unmaps and rcu_read_unlock()s
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* afterwards.
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*
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* pte_offset_map_nolock(mm, pmd, addr, ptlp), above, is like pte_offset_map();
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* but when successful, it also outputs a pointer to the spinlock in ptlp - as
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* pte_offset_map_lock() does, but in this case without locking it. This helps
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* the caller to avoid a later pte_lockptr(mm, *pmd), which might by that time
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* act on a changed *pmd: pte_offset_map_nolock() provides the correct spinlock
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* pointer for the page table that it returns. In principle, the caller should
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* recheck *pmd once the lock is taken; in practice, no callsite needs that -
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* either the mmap_lock for write, or pte_same() check on contents, is enough.
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*
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* Note that free_pgtables(), used after unmapping detached vmas, or when
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* exiting the whole mm, does not take page table lock before freeing a page
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* table, and may not use RCU at all: "outsiders" like khugepaged should avoid
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* pte_offset_map() and co once the vma is detached from mm or mm_users is zero.
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*/
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pte_t *__pte_offset_map_lock(struct mm_struct *mm, pmd_t *pmd,
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unsigned long addr, spinlock_t **ptlp)
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{
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spinlock_t *ptl;
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pmd_t pmdval;
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pte_t *pte;
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again:
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pte = __pte_offset_map(pmd, addr, &pmdval);
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if (unlikely(!pte))
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return pte;
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ptl = pte_lockptr(mm, &pmdval);
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spin_lock(ptl);
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if (likely(pmd_same(pmdval, pmdp_get_lockless(pmd)))) {
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*ptlp = ptl;
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return pte;
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}
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pte_unmap_unlock(pte, ptl);
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goto again;
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}
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