Re: [PATCH v2 1/4] x86: provide an inverted Kconfig control for shim-exclusive mode

["Roger Pau Monné" <roger.pau@citrix.com>]

On Wed, Jan 22, 2025 at 09:43:53AM +0100, Jan Beulich wrote:
> On 21.01.2025 19:02, Roger Pau Monné wrote:
> > On Tue, Jan 21, 2025 at 11:35:42AM +0100, Jan Beulich wrote:
> >> On 21.01.2025 09:52, Roger Pau Monné wrote:
> >>> On Tue, Jan 21, 2025 at 09:13:38AM +0100, Jan Beulich wrote:
> >>>> On 21.01.2025 00:27, Stefano Stabellini wrote:
> >>>>> If I understood it right, I like Andrew's suggestion. He is suggesting
> >>>>> to do the following:
> >>>>>
> >>>>> - turning PV_SHIM_EXCLUSIVE into something that does nothing
> >>>>
> >>>> FTAOD - you mean Kconfig-wise? Andrew clearly didn't say "nothing", but
> >>>> "nothing other than making the boolean be a compile time constant".
> >>>
> >>> Won't making the boolean a compile time constant would also result in
> >>> DCO kicking in and removing a fair amount of code?  So even if you
> >>> have enabled everything in Kconfig, the resulting hypervisor would
> >>> only be suitable to be used as a shim?
> >>
> >> Of course.
> > 
> > Then what's the point of this approach?  Options will be enabled in
> > Kconfig, but the resulting hypervisor build when using allyesconfig
> > would have a lot of them short-circuited, making it even worse than
> > currently?  As options will get effectively build-time disabled due
> > to DCO while enabled in Kconfig.
> 
> Well, I have to direct this question to Andrew. It is specifically
> what I'm trying to address with UNCONSTRAINED.
> 
> > Overall I think PV_SHIM_EXCLUSIVE should be excluded from
> > allyesconfig, even with Andrew's proposed change.  Otherwise the
> > purpose of allyesconfig is defeated if enabling PV_SHIM_EXCLUSIVE
> > makes the resulting hypervisor build PV shim only.  IIRC we can
> > provide a default alllyes.config with CONFIG_PV_SHIM_EXCLUSIVE=n.
> 
> Hmm, I wasn't aware of the option of using allyes.config. That might be
> the route to go, albeit it looks like people using the allyesconfig
> target then need to remember to set KCONFIG_ALLCONFIG in the environment
> (to <empty> or 1), or to explicitly specify a file name that way. (This
> of course ought to be easy enough to arrange for in our automation.)

My knowledge of Kconfig is very limited, but isn't there a default
path for such file to be picked up by Kconfig?  I see we already have
a xen/tools/kconfig/allrandom.config, I was expecting it would be a
matter of dropping an allyes.config in that directory, but I haven't
tried.

Thanks, Roger.