Re: [PATCH v2 0/3] Remove tmem

From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Tim Deegan <tim@xen.org>, Jan Beulich <JBeulich@suse.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	Ian Jackson <ian.jackson@citrix.com>
Subject: Re: [PATCH v2 0/3] Remove tmem
Date: Wed, 2 Jan 2019 12:27:13 -0500	[thread overview]
Message-ID: <20190102172713.GA23427@char.us.oracle.com> (raw)
In-Reply-To: <7c1a8584-9b32-86b9-9154-932089d807cb@citrix.com>

On Mon, Dec 31, 2018 at 12:43:39PM +0000, Andrew Cooper wrote:
> On 03/12/2018 09:56, Jan Beulich wrote:
> >>>> On 30.11.18 at 19:01, <wei.liu2@citrix.com> wrote:
> >> On Fri, Nov 30, 2018 at 05:09:42PM +0000, Ian Jackson wrote:
> >>> Wei Liu writes ("[PATCH v2 0/3] Remove tmem"):
> >>>> It is agreed that tmem can be removed from xen.git. See the thread starting 
> >>                                                                               
> >>     
> >>>> from <D5E866B2-96F4-4E89-941E-73F578DF2F17@citrix.com>.
> >>> Those are notes from some phone call amongst industry stakeholders.
> >>> None of the messages have a Subject line mentioning tmem.  There is no
> >>> explanation of the basis for the decision; just a confirmation from
> >>> the current maintainers that they will ack the removal.
> >>>
> >>> I think this is not really an appropriate way to carry on!  What if
> >>> there is someone else who wants to step up to maintain this ?  What
> >>> about user communication ?  Going straight from `Supported' to
> >>> `Deleted' seems rather vigorous.
> >> Step up to maintain> I would rather say step up to develop.
> >>
> >> The status in MAINTAINERS is wrong. According to SUPPORT.md, it is only
> >> experimental. Our definition of "experimental" is:
> >>
> >>    Functional completeness: No
> >>    Functional stability: Here be dragons
> >>    Interface stability: Not stable
> >>    Security supported: No
> > Exactly. Plus my proposal to remove it was posted to xen-devel
> > on Aug 30th. I don't think removal of an experimental feature
> > requires posting to xen-announce. Ian - please reconsider your
> > nack.
> 
> I concur with Wei and Jan.  TMEM has been off by default due to being
> declared "full of security holes - don't use" since XSA-15.  That was in
> 2012, and TMEM hasn't made its way back into security support in that time.
> 
> In addition, it was never fixed to work with Migration v2.  The save
> side doesn't query any TMEM state, and convert-legacy-stream raises TODO
> on encountering legacy TMEM data.
> 
> I don't know about other distributions, but it has been compiled out of
> XenServer for all versions which have Kconfig.
> 
> tl;dr It doesn't work, and at this point, it looks very unlikely to
> change.  There is a non-zero cost for retaining obsolete functionality,
> and the hypervisor maintainers want it gone in 4.12, which we think is
> entirely reasonable given the circumstances.

I agree on all counts. Can we please remove it?
> 
> ~Andrew

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