Messages in this thread Patch in this message |  | | From | Laurent Dufour <> | Subject | [PATCH v2 08/20] mm: Protect SPF handler against anon_vma changes | Date | Fri, 18 Aug 2017 00:05:07 +0200 |
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The speculative page fault handler must be protected against anon_vma changes. This is because page_add_new_anon_rmap() is called during the speculative path.
In addition, don't try speculative page fault if the VMA don't have an anon_vma structure allocated because its allocation should be protected by the mmap_sem.
In __vma_adjust() when importer->anon_vma is set, there is no need to protect against speculative page faults since speculative page fault is aborted if the vma->anon_vma is not set.
When calling page_add_new_anon_rmap() vma->anon_vma is necessarily valid since we checked for it when locking the pte and the anon_vma is removed once the pte is unlocked. So even if the speculative page fault handler is running concurrently with do_unmap(), as the pte is locked in unmap_region() - through unmap_vmas() - and the anon_vma unlinked later, because we check for the vma sequence counter which is updated in unmap_page_range() before locking the pte, and then in free_pgtables() so when locking the pte the change will be detected.
Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com> --- mm/memory.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/mm/memory.c b/mm/memory.c index da3bd07bb052..68e4fdcce692 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -615,7 +615,9 @@ void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *vma, * Hide vma from rmap and truncate_pagecache before freeing * pgtables */ + write_seqcount_begin(&vma->vm_sequence); unlink_anon_vmas(vma); + write_seqcount_end(&vma->vm_sequence); unlink_file_vma(vma); if (is_vm_hugetlb_page(vma)) { @@ -629,7 +631,9 @@ void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *vma, && !is_vm_hugetlb_page(next)) { vma = next; next = vma->vm_next; + write_seqcount_begin(&vma->vm_sequence); unlink_anon_vmas(vma); + write_seqcount_end(&vma->vm_sequence); unlink_file_vma(vma); } free_pgd_range(tlb, addr, vma->vm_end, -- 2.7.4
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