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    SubjectRe: [PATCH v12 12/31] mm: protect SPF handler against anon_vma changes
    On Tue, Apr 16, 2019 at 03:45:03PM +0200, Laurent Dufour wrote:
    > 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.ibm.com>

    Reviewed-by: Jérôme Glisse <jglisse@redhat.com>

    > ---
    > mm/memory.c | 4 ++++
    > 1 file changed, 4 insertions(+)
    >
    > diff --git a/mm/memory.c b/mm/memory.c
    > index 423fa8ea0569..2cf7b6185daa 100644
    > --- a/mm/memory.c
    > +++ b/mm/memory.c
    > @@ -377,7 +377,9 @@ void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *vma,
    > * Hide vma from rmap and truncate_pagecache before freeing
    > * pgtables
    > */
    > + vm_write_begin(vma);
    > unlink_anon_vmas(vma);
    > + vm_write_end(vma);
    > unlink_file_vma(vma);
    >
    > if (is_vm_hugetlb_page(vma)) {
    > @@ -391,7 +393,9 @@ void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *vma,
    > && !is_vm_hugetlb_page(next)) {
    > vma = next;
    > next = vma->vm_next;
    > + vm_write_begin(vma);
    > unlink_anon_vmas(vma);
    > + vm_write_end(vma);
    > unlink_file_vma(vma);
    > }
    > free_pgd_range(tlb, addr, vma->vm_end,
    > --
    > 2.21.0
    >

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