linux-kernel - Re: [PATCH v5 00/25] userfaultfd: write protection support

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Message-ID: <20200218161113.GA1408806@xz-x1>
Date:   Tue, 18 Feb 2020 11:11:13 -0500
From:   Peter Xu <peterx@...hat.com>
To:     Bobby Powers <bobbypowers@...il.com>
Cc:     linux-mm@...ck.org,
        Kernel development list <linux-kernel@...r.kernel.org>,
        David Hildenbrand <david@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Maya Gokhale <gokhale2@...l.gov>,
        Jerome Glisse <jglisse@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Martin Cracauer <cracauer@...s.org>,
        Denis Plotnikov <dplotnikov@...tuozzo.com>,
        Shaohua Li <shli@...com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Marty McFadden <mcfadden8@...l.gov>,
        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 v5 00/25] userfaultfd: write protection support

On Mon, Feb 17, 2020 at 07:59:12PM -0800, Bobby Powers wrote:
> On Wed, Jun 19, 2019 at 7:20 PM Peter Xu <peterx@...hat.com> wrote:
> > This series implements initial write protection support for
> > userfaultfd.  Currently both shmem and hugetlbfs are not supported
> > yet, but only anonymous memory.  This is the 4nd version of it.
> >
> > The latest code can also be found at:
> >
> >   https://github.com/xzpeter/linux/tree/uffd-wp-merged
> 
> Hi Peter - I ported the branch you had above on top of v5.4.20 (what I
> happened to be running locally), and fixed one issue that was causing
> crashes for me:
> https://github.com/bpowers/linux/commit/61086b5a0fa4aeb494e86d999926551a4323b84f

Hi, Bobby,

Thanks for playing with the branch!

Yes, this should be needed if you have 7d0325749a6c ("userfaultfd:
untag user pointers", 2019-09-25) in your base branch where the
address is replaced by its pointer.

> I wrote a small test program here:
> https://github.com/plasma-umass/Mesh/blob/master/src/test/userfaultfd-kernel-copy.cc

Just FYI that there's some other tests/libraries over there [1,2].
Also the series has the uffd selftest for write-protection as well.

> and write protection support for userfaultfd (with eventual shmem
> support) would be _hugely_ helpful for a userspace memory allocator
> I'm working on.  Is there anything I can do to help get this
> considered for mainline?  We have some time before the 5.7 merge
> window opens up.  Tested-by: Bobby Powers <bobbypowers@...il.com>

Thanks for the tag!  Yes it would be great if we can continue to work
on those, but for now let's see whether we can move on what we have
first (it's already two series without much certainty on whether it
could get merged soon).  Considering that we've got quite a few pings
again for either the mm retry series and the write-protect work, I'll
rebase the two series, test & post soon this week.  I'll keep you in
the loop.

Thanks,

[1] https://github.com/LLNL/umap
[2] https://github.com/xzpeter/clibs/blob/master/gpl/userspace/uffd-test/uffd-test.c

-- 
Peter Xu