linux-kernel - Re: [PATCH v2 21/26] userfaultfd: wp: add the writeprotect API to userfaultfd ioctl

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Date:   Thu, 21 Feb 2019 13:28:25 -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 21/26] userfaultfd: wp: add the writeprotect API to
 userfaultfd ioctl

On Tue, Feb 12, 2019 at 10:56:27AM +0800, Peter Xu wrote:
> From: Andrea Arcangeli <aarcange@...hat.com>
> 
> v1: From: Shaohua Li <shli@...com>
> 
> v2: cleanups, remove a branch.
> 
> [peterx writes up the commit message, as below...]
> 
> This patch introduces the new uffd-wp APIs for userspace.
> 
> Firstly, we'll allow to do UFFDIO_REGISTER with write protection
> tracking using the new UFFDIO_REGISTER_MODE_WP flag.  Note that this
> flag can co-exist with the existing UFFDIO_REGISTER_MODE_MISSING, in
> which case the userspace program can not only resolve missing page
> faults, and at the same time tracking page data changes along the way.
> 
> Secondly, we introduced the new UFFDIO_WRITEPROTECT API to do page
> level write protection tracking.  Note that we will need to register
> the memory region with UFFDIO_REGISTER_MODE_WP before that.
> 
> Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>
> [peterx: remove useless block, write commit message, check against
>  VM_MAYWRITE rather than VM_WRITE when register]
> Signed-off-by: Peter Xu <peterx@...hat.com>

I am not an expert with userfaultfd code but it looks good to me so:

Also see my question down below, just a minor one.

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

> ---
>  fs/userfaultfd.c                 | 82 +++++++++++++++++++++++++-------
>  include/uapi/linux/userfaultfd.h | 11 +++++
>  2 files changed, 77 insertions(+), 16 deletions(-)
> 

[...]

> diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
> index 297cb044c03f..1b977a7a4435 100644
> --- a/include/uapi/linux/userfaultfd.h
> +++ b/include/uapi/linux/userfaultfd.h
> @@ -52,6 +52,7 @@
>  #define _UFFDIO_WAKE			(0x02)
>  #define _UFFDIO_COPY			(0x03)
>  #define _UFFDIO_ZEROPAGE		(0x04)
> +#define _UFFDIO_WRITEPROTECT		(0x06)
>  #define _UFFDIO_API			(0x3F)

What did happen to ioctl 0x05 ? :)