linux-kernel - Re: [PATCH v2 1/1] userfaultfd/sysctl: add vm.unprivileged

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Message-ID: <a5aa7dfd-b4a9-0ab2-9392-d7889897382f@huawei.com>
Date:   Thu, 28 May 2020 16:50:49 +0800
From:   Xiaoming Ni <nixiaoming@...wei.com>
To:     Peter Xu <peterx@...hat.com>
CC:     <aarcange@...hat.com>, <akpm@...ux-foundation.org>,
        <cracauer@...s.org>, <dplotnikov@...tuozzo.com>,
        <gokhale2@...l.gov>, <hannes@...xchg.org>, <hughd@...gle.com>,
        <jglisse@...hat.com>, <kirill@...temov.name>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <maxime.coquelin@...hat.com>, <mcfadden8@...l.gov>,
        <mcgrof@...nel.org>, <mgorman@...e.de>, <mike.kravetz@...cle.com>,
        <pbonzini@...hat.com>, <rppt@...ux.vnet.ibm.com>,
        <xemul@...tuozzo.com>, <keescook@...omium.org>
Subject: Re: [PATCH v2 1/1] userfaultfd/sysctl: add
 vm.unprivileged_userfaultfd

On 2020/5/27 22:21, Peter Xu wrote:
> On Wed, May 27, 2020 at 02:54:13PM +0800, Xiaoming Ni wrote:
>>
>> On Tue, Mar 19, 2019 at 11:07:22AM +0800, Peter Xu wrote:
>>> Add a global sysctl knob "vm.unprivileged_userfaultfd" to control
>>> whether userfaultfd is allowed by unprivileged users.  When this is
>>> set to zero, only privileged users (root user, or users with the
>>> CAP_SYS_PTRACE capability) will be able to use the userfaultfd
>>> syscalls.
>>
>> Hello
> 
> Hi, Xiaoming,
> 
>> I am a bit confused about this patch, can you help to answer it.
>>
>> Why the sysctl interface of fs/userfaultfd.c belongs to vm_table instead of
>> fs_table ?
>>
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=cefdca0a86be517bc390fc4541e3674b8e7803b0
> 
> Because I think it makes more sense to put the new key into where it suites
> better, irrelevant to which directory the variable is declared.  To me,
> unprivileged_userfaultfd is definitely more suitable for vm rather than fs,
> because userfaultfd is really about memory management rather than file system.
> 
> Thanks,
> 

Thank you for your answer
Since userfaultfd and vm are more closely related, will there be 
consideration to move fs/userfaultfd.c to the mm directory in the future?

Thanks
Xiaoming Ni