Re: [PATCH v2 15/26] userfaultfd: wp: drop _PAGE_UFFD_WP properly when fork

Mike Rapoport
2019-02-25T18:20:09Z

On Tue, Feb 12, 2019 at 10:56:21AM +0800, Peter Xu wrote:
> UFFD_EVENT_FORK support for uffd-wp should be already there, except
> that we should clean the uffd-wp bit if uffd fork event is not
> enabled. Detect that to avoid _PAGE_UFFD_WP being set even if the VMA
> is not being tracked by VM_UFFD_WP. Do this for both small PTEs and
> huge PMDs.
>
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>

> ---
> mm/huge_memory.c | 8 ++++++++
> mm/memory.c | 8 ++++++++
> 2 files changed, 16 insertions(+)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 817335b443c2..fb2234cb595a 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -938,6 +938,14 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
> ret = -EAGAIN;
> pmd = *src_pmd;
>
> + /*
> + * Make sure the _PAGE_UFFD_WP bit is cleared if the new VMA
> + * does not have the VM_UFFD_WP, which means that the uffd
> + * fork event is not enabled.
> + */
> + if (!(vma->vm_flags & VM_UFFD_WP))
> + pmd = pmd_clear_uffd_wp(pmd);
> +
> #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> if (unlikely(is_swap_pmd(pmd))) {
> swp_entry_t entry = pmd_to_swp_entry(pmd);
> diff --git a/mm/memory.c b/mm/memory.c
> index b5d67bafae35..c2035539e9fd 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -788,6 +788,14 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
> pte = pte_mkclean(pte);
> pte = pte_mkold(pte);
>
> + /*
> + * Make sure the _PAGE_UFFD_WP bit is cleared if the new VMA
> + * does not have the VM_UFFD_WP, which means that the uffd
> + * fork event is not enabled.
> + */
> + if (!(vm_flags & VM_UFFD_WP))
> + pte = pte_clear_uffd_wp(pte);
> +
> page = vm_normal_page(vma, addr, pte);
> if (page) {
> get_page(page);
> --
> 2.17.1
>

--
Sincerely yours,
Mike.