Re: [PATCH RESEND 2/2] xen: Allow EXPERT mode to be selected from the menuconfig directly

[Julien Grall <julien@xxxxxxx>]

Hi George,

On 11/05/2020 16:27, George Dunlap wrote:
> > On May 11, 2020, at 2:30 PM, Julien Grall <julien@xxxxxxx> wrote:
> >
> > [CAUTION - EXTERNAL EMAIL] DO NOT reply, click links, or open attachments 
> > unless you have verified the sender and know the content is safe.
> >
> > Hi Ian,
> >
> > Thank you for the clarification.
> >
> > On 07/05/2020 18:01, Ian Jackson wrote:
> > > Julien Grall writes ("Re: [PATCH RESEND 2/2] xen: Allow EXPERT mode to be selected 
> > > from the menuconfig directly"):
> > > > On 04/05/2020 13:34, Ian Jackson wrote:
> > > > > George Dunlap writes ("Re: [PATCH RESEND 2/2] xen: Allow EXPERT mode to be selected 
> > > > > from the menuconfig directly"):
> > > > > > On Apr 30, 2020, at 3:50 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
> > > > > > > Well, if I'm not mis-remembering it was on purpose to make it more
> > > > > > > difficult for people to declare themselves "experts". FAOD I'm not
> > > > > > > meaning to imply I don't see and accept the frustration aspect you
> > > > > > > mention further up. The two need to be carefully weighed against
> > > > > > > one another.
> > > > > Yes, it was on purpose.  However, I had my doubts at the time and
> > > > > I think experience has shown that this was a mistake.
> > > > >
> > > > > > I don’t think we need to make it difficult for people to declare
> > > > > > themselves experts, particularly as “all” it means at the moment is,
> > > > > > “Can build something which is not security supported”.  People who
> > > > > > are building their own hypervisors are already pretty well advanced;
> > > > > > I think we can let them shoot themselves in the foot if they want
> > > > > > to.
> > > > > Precisely.
> > > > Can I consider this as an Acked-by? :)
> > > I am happy with the principle of the change.  I haven't reviewed the
> > > details of the commit message etc.
> > > I reviewed the thread and there were two concernes raised:
> > >   * The question of principle.  I disagree with this concern
> > >     because I approve of principle of the patch.
> > >   * Some detail about the precise justificaton as written in
> > >     the commit message, regarding `clean' targets.  Apparently the
> > >     assertion may not be completely true.  I haven't seen a proposed
> > >     alternative wording.
> > I have checked the latest staging, the `clean` target doesn't trash .config 
> > anymore.
> >
> > > I don't feel I should ack a controversial patch with an unresolved
> > > wording issue.  Can you tell me what your proposed wording is ?
> > > To avoid blocking this change I would be happy to review your wording
> > > and see if it meets my reading of the stated objection.
> > Here a suggested rewording:
> >
> > "EXPERT mode is currently used to gate any options that are in technical
> > preview or not security supported At the moment, the only way to select
> > it is to use XEN_CONFIG_EXPERT=y on the make command line.
> >
> > However, if the user forget to add the option when (re)building or when using 
> > menuconfig, then .config will get rewritten. This may lead to a rather 
> > frustrating experience as it is difficult to diagnostic the
> > issue.
> >
> > A lot of the options behind EXPERT would benefit to be more accessible so user 
> > can experiment with it and voice any concern before they are fully be supported.
> >
> > So rather than making really difficult to experiment or tweak your Xen (for 
> > instance by adding a built-in command line), this option can now be selected 
> > from the menuconfig.
> >
> > This doesn't change the fact a Xen with EXPERT mode selected will not be 
> > security supported.
> > "
> How about this, clarifying that top-level .config is an option, but that it’s 
> still better to put it in menuconfig?  (Also note a number of grammar tweaks.)
>
> —
>
> EXPERT mode is currently used to gate any options that are in technical
> preview or not security supported. At the moment, this is selected by adding 
> XEN_CONFIG_EXPERT=y on the make command line, or to the (currently 
> undocumented) top-level .config file.
>
> This makes the option very unintuitive to use: If the user forgets to add the 
> option when (re)building or when using menuconfig, then xen/.config will be 
> silently rewritten, leading to behavior which is very difficult to diagnose.  
> Adding XEN_CONFIG_EXPERT=y to the top-level .config is not obvious behavior, 
> particularly as the file is undocumented.
>
> A lot of the options behind EXPERT would benefit from being more accessible so 
> users can experiment with them and voice any concerns before they are fully 
> supported.
>
> To make this option more discoverable and consistent to use, make it possible 
> to select it from the menuconfig.
>
> This doesn't change the fact a Xen with EXPERT mode selected will not be 
> security supported.
I am happy this wording.

Cheers,

--
Julien Grall