On Tue, Jan 21, 2025 at 09:13:38AM +0100, Jan Beulich wrote: > On 21.01.2025 00:27, Stefano Stabellini wrote: > > On Mon, 20 Jan 2025, Jan Beulich wrote: > >> On 18.01.2025 00:41, Andrew Cooper wrote: > >>> On 17/01/2025 10:43 pm, Stefano Stabellini wrote: > >>>> On Fri, 17 Jan 2025, Jan Beulich wrote: > >>>>> On 17.01.2025 13:24, Alejandro Vallejo wrote: > >>>>>> On Fri Jan 17, 2025 at 10:31 AM GMT, Roger Pau Monné wrote: > >>>>>>> On Thu, Jan 16, 2025 at 04:31:46PM -0800, Stefano Stabellini wrote: > >>>>>>>> On Wed, 1 Mar 2023, Jan Beulich wrote: > >>>>>>>>> While we want certain things turned off in shim-exclusive mode, > >>>>>>>>> doing > >>>>>>>>> so via "depends on !PV_SHIM_EXCLUSIVE" badly affects allyesconfig: > >>>>>>>>> Since > >>>>>>>>> that will turn on PV_SHIM_EXCLUSIVE, other options will be turned > >>>>>>>>> off as > >>>>>>>>> a result. Yet allyesconfig wants to enable as much of the > >>>>>>>>> functionality > >>>>>>>>> as possible. > >>>>>>>>> > >>>>>>>>> Retain PV_SHIM_EXCLUSIVE as a prompt-less option such that first of > >>>>>>>>> all > >>>>>>>>> C code using it can remain as is. This isn't just for less code > >>>>>>>>> churn, > >>>>>>>>> but also because I think that symbol is more logical to use in many > >>>>>>>>> (all?) places. > >>>>>>>>> > >>>>>>>>> Requested-by: Andrew Cooper <andrew.coop...@citrix.com> > >>>>>>>>> Signed-off-by: Jan Beulich <jbeul...@suse.com> > >>>>>>>>> > >>>>>>>>> --- > >>>>>>>>> The new Kconfig control's name is up for improvement suggestions, > >>>>>>>>> but I > >>>>>>>>> think it's already better than the originally thought of > >>>>>>>>> FULL_HYPERVISOR. > >>>>>>>> I think the approach in general is OK, maybe we can improve the > >>>>>>>> naming > >>>>>>>> further. What about one of the following? > >>>>>>>> > >>>>>>>> NO_PV_SHIM_EXCLUSIVE > >>>>>>>> PV_SHIM_NOT_EXCLUSIVE > >>>>>>> IMO negated options are confusing, and if possible I think we should > >>>>>>> avoid using them unless strictly necessary. > >>>>>> The problem is that the option is negative in nature. It's asking for > >>>>>> hypervisor without _something_. I do agree with Stefano that shim > >>>>>> would be > >>>>>> better in the name. Otherwise readers are forced to play divination > >>>>>> tricks. > >>>>>> > >>>>>> How about something like: > >>>>>> > >>>>>> SHIMLESS_HYPERVISOR > >>>>>> > >>>>>> That's arguably not negated, preserves "shim" in the name and has the > >>>>>> correct > >>>>>> polarity for allyesconfig to yield the right thing. > >>>>> Except that a hypervisor with this option enabled isn't shim-less, but > >>>>> permits > >>>>> working in shim as well as in non-shim mode. > >>>> First, let's recognize that we have two opposing requirements. One > >>>> requirement is to make it as easy as possible to configure for the user. > >>>> Ideally without using negative CONFIG options, such as > >>>> NO_PV_SHIM_EXCLUSIVE. From the user point of view, honestly, > >>>> PV_SHIM_EXCLUSIVE is a pretty good name. Better than all of the others, > >>>> I think. > >>>> > >>>> On the other hand, we have the requirement that we don't want > >>>> allyesconfig to end up disabling a bunch of CONFIG options. Now this > >>>> requirement can be satisfied easily by adding something like > >>>> NO_PV_SHIM_EXCLUSIVE. However, it would go somewhat against the previous > >>>> requirement. > >>>> > >>>> So we need a compromise, something that doesn't end up disabling other > >>>> CONFIG options, to make allyesconfig happy, but also not too confusing > >>>> for the user (which is a matter of personal opinion). > >>>> > >>>> In short, expect that people will have different opinions on this and > >>>> will find different compromises better or worse. For one, I prefer to > >>>> compromise on "no negative CONFIG options" and use > >>>> PV_SHIM_NOT_EXCLUSIVE. Because it serves the allyesconfig goal, and > >>>> while it is not as clear as PV_SHIM_EXCLUSIVE, is still better than a > >>>> completely generic FULL_HYPERVISOR option, which means nothing to me. > >>>> > >>>> I cannot see a way to have a good and clear non-negated CONFIG option, > >>>> and also satisfy the allyesconfig requirement. So I prefer to compromise > >>>> on the "non-negated" part. > >>> > >>> Debating the naming is missing the point. > >>> > >>> > >>> The problem here is the wish to have PV_SHIM_EXCLUSIVE behave in a way > >>> that Kconfig is not capable of expressing. Specifically, what is broken > >>> is having "lower level" options inhibit unrelated "higher level" options > >>> when the graph gets rescanned[1]. That's why we're in the laughable > >>> position of `make allyesconfig` turning off CONFIG_HVM. > >>> > >>> Jan, you want "echo PV_SHIM_EXCLUSIVE=y >> .config && make" to mean > >>> "reset me back to a PV Shim". > >> > >> Isn't this an independent goal? Or is this a statement on what you see > >> my change (kind of) doing, indicating you consider this wrong? > > > > The way I understood it, it is the latter > > > > > >>> Kconfig spells this "make $foo_defconfig" for an appropriately given foo. > >>> > >>> > >>> There should be: > >>> > >>> 1) an option called PV_SHIM_EXCLUSIVE which does *nothing* other than > >>> making the boolean be a compile time constant. > >> > >> I fear it remains unclear to me what exactly you mean here. It feels like > >> you may be suggesting that all other uses of PV_SHIM_EXCLUSIVE should be > >> dropped, without replacement. That seems wrong to me, though. In > >> particular I'm of the opinion that besides using "make pvshim_defconfig" > >> people ought to also have the option to properly configure a shim build > >> from scratch (or from any random .config they hold in hands), requiring > >> respective "depends on" and/or "select" / "imply" to be in place. > > > > That should be done with "make pvshim_defconfig" > > Why? Specifically, why should people use only one entirely nailed down > configuration for a shim. Like a "normal" hypervisor, there are aspects > which very well can be left to the person doing the configuration.
But nothing prevents a user from starting from a shim defconfig, and then tweaking it as desired: $ make pvshim_defconfig $ make menuconfig Or there's something I'm missing here? > >> Or else they may end up with a lot of dead code. (Just consider e.g. > >> HVM=n: We also don't permit HVM-only stuff to be enabled in that case, > >> as any of that would again be dead code then.) > > > > It will always be possible to come up with poor configurations. I do not > > believe it is necessarily our responsibility to go out of our way to > > prevent them. > > Well - if so, why would we do this in some cases but not in others? > You may recall that I'm a proponent of consistency and predictability. > > >>> 2) a pvshim_defconfig target which expresses what a pvshim ought to look > >>> like. > >> > >> We have this file already. I consider it debatable though whether this file > >> should really force PV_SHIM_EXCLUSIVE=y. People may read "pvshim" in the > >> name as either "works just as shim" or "can also work as shim". > > > > 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? Thanks, Roger.
