linux-kernel - Re: [PATCH 2/2] userfaultfd.2: Update on write-protection support

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Message-ID: <22004457-a6a8-1e9e-4220-ae15339ec94b@gmail.com>
Date:   Fri, 3 Jun 2022 19:12:53 +0200
From:   Alejandro Colomar <alx.manpages@...il.com>
To:     Peter Xu <peterx@...hat.com>, linux-kernel@...r.kernel.org,
        linux-man@...r.kernel.org, linux-mm@...ck.org
Cc:     Axel Rasmussen <axelrasmussen@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/2] userfaultfd.2: Update on write-protection support

Hi Peter,

On 5/31/22 03:11, Peter Xu wrote:
> The shmem/hugetlbfs memory types are supported for write-protection
> messages very lately.  Update the man page to reflect that.
> 
> Signed-off-by: Peter Xu <peterx@...hat.com>

Please see some source formatting comments below.

Cheers,

Alex

> ---
>   man2/userfaultfd.2 | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
> index 0928a76d2..99aae8b50 100644
> --- a/man2/userfaultfd.2
> +++ b/man2/userfaultfd.2
> @@ -273,13 +273,17 @@ Since Linux 4.11,
>   userfaultfd can be also used with hugetlbfs and shared memory mappings.
>   .\"
>   .SS Userfaultfd write-protect mode (since 5.7)
> -Since Linux 5.7, userfaultfd supports write-protect mode.
> +Since Linux 5.7, userfaultfd supports write-protect mode for anonymous memory.
>   The user needs to first check availability of this feature using
>   .B UFFDIO_API
>   ioctl against the feature bit
>   .B UFFD_FEATURE_PAGEFAULT_FLAG_WP
>   before using this feature.
>   .PP
> +Since Linux 5.19, the write-protection mode was also supported on shmem and hugetlbfs
> +memory types. It can be detected with the feature bit

See man-pages(7):

[
    Use semantic newlines
        In the source of a manual page, new sentences  should  be
        started  on new lines, and long sentences should be split
        into lines at clause breaks (commas, semicolons,  colons,
        and  so on).  This convention, sometimes known as "seman‐
        tic newlines", makes it  easier  to  see  the  effect  of
        patches,  which  often operate at the level of individual
        sentences or sentence clauses.
]

> +.BR UFFD_FEATURE_WP_HUGETLBFS_SHMEM .
> +.PP
>   To register with userfaultfd write-protect mode, the user needs to initiate the
>   .B UFFDIO_REGISTER
>   ioctl with mode
> @@ -330,8 +334,6 @@ ioctl, whose
>   should have the flag
>   .B UFFDIO_WRITEPROTECT_MODE_WP
>   cleared upon the faulted page or range.
> -.PP
> -Write-protect mode supports only private anonymous memory.
>   .SS Reading from the userfaultfd structure
>   Each
>   .BR read (2)

-- 
Alejandro Colomar
<http://www.alejandro-colomar.es/>

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