linux-kernel - Re: [PATCH v2 10/26] userfaultfd: wp: add UFFDIO_COPY_MODE

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Message-ID: <20190221172919.GJ2813@redhat.com>
Date:   Thu, 21 Feb 2019 12:29:19 -0500
From:   Jerome Glisse <jglisse@...hat.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>,
        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 10/26] userfaultfd: wp: add UFFDIO_COPY_MODE_WP

On Tue, Feb 12, 2019 at 10:56:16AM +0800, Peter Xu wrote:
> From: Andrea Arcangeli <aarcange@...hat.com>
> 
> This allows UFFDIO_COPY to map pages wrprotected.
> 
> Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>
> Signed-off-by: Peter Xu <peterx@...hat.com>

Minor nitpick down below, but in any case:

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

> ---
>  fs/userfaultfd.c                 |  5 +++--
>  include/linux/userfaultfd_k.h    |  2 +-
>  include/uapi/linux/userfaultfd.h | 11 +++++-----
>  mm/userfaultfd.c                 | 36 ++++++++++++++++++++++----------
>  4 files changed, 35 insertions(+), 19 deletions(-)
> 

[...]

> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> index d59b5a73dfb3..73a208c5c1e7 100644
> --- a/mm/userfaultfd.c
> +++ b/mm/userfaultfd.c
> @@ -25,7 +25,8 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
>  			    struct vm_area_struct *dst_vma,
>  			    unsigned long dst_addr,
>  			    unsigned long src_addr,
> -			    struct page **pagep)
> +			    struct page **pagep,
> +			    bool wp_copy)
>  {
>  	struct mem_cgroup *memcg;
>  	pte_t _dst_pte, *dst_pte;
> @@ -71,9 +72,9 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
>  	if (mem_cgroup_try_charge(page, dst_mm, GFP_KERNEL, &memcg, false))
>  		goto out_release;
>  
> -	_dst_pte = mk_pte(page, dst_vma->vm_page_prot);
> -	if (dst_vma->vm_flags & VM_WRITE)
> -		_dst_pte = pte_mkwrite(pte_mkdirty(_dst_pte));
> +	_dst_pte = pte_mkdirty(mk_pte(page, dst_vma->vm_page_prot));
> +	if (dst_vma->vm_flags & VM_WRITE && !wp_copy)
> +		_dst_pte = pte_mkwrite(_dst_pte);

I like parenthesis around around and :) ie:
    (dst_vma->vm_flags & VM_WRITE) && !wp_copy

I feel it is easier to read.

[...]

> @@ -416,11 +418,13 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
>  	if (!(dst_vma->vm_flags & VM_SHARED)) {
>  		if (!zeropage)
>  			err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
> -					       dst_addr, src_addr, page);
> +					       dst_addr, src_addr, page,
> +					       wp_copy);
>  		else
>  			err = mfill_zeropage_pte(dst_mm, dst_pmd,
>  						 dst_vma, dst_addr);
>  	} else {
> +		VM_WARN_ON(wp_copy); /* WP only available for anon */

Don't you want to return with error here ?

>  		if (!zeropage)
>  			err = shmem_mcopy_atomic_pte(dst_mm, dst_pmd,
>  						     dst_vma, dst_addr,

[...]