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Date:   Tue, 12 Mar 2019 20:43:02 +0800
From:   Peter Xu <peterx@redhat.com>
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     linux-kernel@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
        Hugh Dickins <hughd@google.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Maxime Coquelin <maxime.coquelin@redhat.com>,
        kvm@vger.kernel.org, Jerome Glisse <jglisse@redhat.com>,
        Pavel Emelyanov <xemul@virtuozzo.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Martin Cracauer <cracauer@cons.org>,
        Denis Plotnikov <dplotnikov@virtuozzo.com>, linux-mm@kvack.org,
        Marty McFadden <mcfadden8@llnl.gov>,
        Maya Gokhale <gokhale2@llnl.gov>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Kees Cook <keescook@chromium.org>,
        Mel Gorman <mgorman@suse.de>, linux-fsdevel@vger.kernel.org,
        "Dr . David Alan Gilbert" <dgilbert@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-api@vger.kernel.org
Subject: Re: [PATCH 0/3] userfaultfd: allow to forbid unprivileged users
Message-ID: <20190312124302.GA2433@xz-x1>
References: <20190311093701.15734-1-peterx@redhat.com>
 <20190312074951.i2md3npcjcceywqj@kshutemo-mobl1>
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Hi, Kirill,

On Tue, Mar 12, 2019 at 10:49:51AM +0300, Kirill A. Shutemov wrote:
> On Mon, Mar 11, 2019 at 05:36:58PM +0800, Peter Xu wrote:
> > Hi,
> > 
> > (The idea comes from Andrea, and following discussions with Mike and
> >  other people)
> > 
> > This patchset introduces a new sysctl flag to allow the admin to
> > forbid users from using userfaultfd:
> > 
> >   $ cat /proc/sys/vm/unprivileged_userfaultfd
> >   [disabled] enabled kvm
> 
> CC linux-api@
> 
> This is unusual way to return current value for sysctl. Does it work fine
> with sysctl tool?

It can work, though it displays the same as "cat":

$ sysctl vm.unprivileged_userfaultfd
vm.unprivileged_userfaultfd = disabled enabled [kvm] 

> 
> Have you considered to place the switch into /sys/kernel/mm instead?
> I doubt it's the last tunable for userfaultfd. Maybe we should have an
> directory for it under /sys/kernel/mm?

I haven't thought about sysfs, if that's preferred I can consider to
switch to that.  And yes I think creating a directory should be a good
idea.

Thanks,

-- 
Peter Xu