linux-kernel - Re: [PATCH v2 15/26] userfaultfd: wp: drop _PAGE_UFFD

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Message-Id: <20190225181947.GG24917@rapoport-lnx>
Date:   Mon, 25 Feb 2019 20:19:49 +0200
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        David Hildenbrand <david@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Maya Gokhale <gokhale2@...l.gov>,
        Jerome Glisse <jglisse@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Martin Cracauer <cracauer@...s.org>, Shaohua Li <shli@...com>,
        Marty McFadden <mcfadden8@...l.gov>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Denis Plotnikov <dplotnikov@...tuozzo.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>
Subject: Re: [PATCH v2 15/26] userfaultfd: wp: drop _PAGE_UFFD_WP properly
 when fork

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@...hat.com>

Reviewed-by: Mike Rapoport <rppt@...ux.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.