Date:   Wed, 5 Jan 2022 14:36:23 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To:     David Hildenbrand <david@redhat.com>
Cc:     Juergen Gross <jgross@suse.com>, Christoph Hellwig <hch@lst.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>,
        Seth Jennings <sjenning@redhat.com>,
        Dan Streetman <ddstreet@ieee.org>,
        Vitaly Wool <vitaly.wool@konsulko.com>,
        Matthew Wilcox <willy@infradead.org>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: remove Xen tmem leftovers
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On Wed, Jan 05, 2022 at 09:46:05AM +0100, David Hildenbrand wrote:
> On 05.01.22 07:08, Juergen Gross wrote:
> > On 04.01.22 15:31, David Hildenbrand wrote:
> >> On 24.12.21 07:22, Christoph Hellwig wrote:
> >>> Hi all,
> >>>
> >>> since the remove of the Xen tmem driver in 2019, the cleancache hooks are
> >>> entirely unused, as are large parts of frontswap.  This series against
> >>> linux-next (with the folio changes included) removes cleancaches, and cuts
> >>> down frontswap to the bits actually used by zswap.
> >>>
> >>
> >> Just out of curiosity, why was tmem removed from Linux (or even Xen?).
> >> Do you have any information?
> > 
> > tmem never made it past the "experimental" state in the Xen hypervisor.
> > Its implementation had some significant security flaws, there was no
> > maintainer left, and nobody stepped up to address those issues.
> > 
> > As a result tmem was removed from Xen.
> 
> Interesting, thanks for sharing. I know tmem mostly from the papers and
> thought it was an interesting approach in general. There was even papers
> about a virtio implementation, however, actual code never appeared in
> the wild :)

There is a repo of it .. I can find it if you are interested - but as
Juergen mentioned - I didn't have enough steam to finish up the security
rework so code removed.