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

[Jan Beulich <jbeulich@xxxxxxxx>]

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.)

Jan