On 29.03.2023 13:48, Luca Fancellu wrote: >> On 28 Mar 2023, at 11:08, Jan Beulich <[email protected]> wrote: >> On 27.03.2023 12:59, Luca Fancellu wrote: >>> @@ -838,6 +838,18 @@ Controls for how dom0 is constructed on x86 systems. >>> >>> If using this option is necessary to fix an issue, please report a bug. >>> >>> +Enables features on dom0 on Arm systems. >>> + >>> +* The `sve` integer parameter enables Arm SVE usage for Dom0 domain and >>> sets >>> + the maximum SVE vector length. >>> + Values above 0 means feature is enabled for Dom0, otherwise feature is >>> + disabled. >> >> Nit: "above" suggests negative values may also enable the feature, which >> I'm sure isn't intended. You may want to consider using negative values >> to signal "use length supported by hardware". > > This is a very good suggestion, do you think I should restrict only to one > negative value, > for example -1, instead of every negative value?
That highly depends on whether there's any foreseeable use for other negative values. I can't imagine such, so I'm inclined to say that "just negative" is all that matters. >>> + Please note that the platform can supports a lower value, if the >>> requested >> >> Maybe better "... may only support ..."? > > ok > >> >>> + value is above the supported one, the domain creation will fail and the >>> + system will stop. >> >> Such behavior may be acceptable for DomU-s which aren't essential for the >> system (i.e. possibly excluding ones in dom0less scenarios), but I don't >> think that's very nice for Dom0. I'd rather suggest falling back to no >> SVE in such an event. > > I guess that with the introduction of a negative value meaning max supported > VL, it is ok to stop the system if the user provides a custom VL value that is > not OK. I remember Julien asked to stop the creation of Dom0 in such a case on > the RFC serie. Oh, okay. I don't mean to override a maintainer's view. I don't see the connection to assigning meaning to negative values though - preventing successful (even if functionally restricted) boot is imo never a good thing, when it can easily be avoided. Jan
