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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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