> On 23 May 2023, at 11:31, Jan Beulich <jbeul...@suse.com> wrote: > > On 23.05.2023 12:21, Luca Fancellu wrote: >>> On 23 May 2023, at 11:02, Jan Beulich <jbeul...@suse.com> wrote: >>> On 23.05.2023 09:43, Luca Fancellu wrote: >>>> @@ -838,6 +838,22 @@ 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, the option is applicable only to >>>> AArch64 >>>> + guests. >>> >>> Why "guests"? Does the option affect more than Dom0? >> >> I used “guests” because in my mind I was referring to all the aarch64 OS >> that can be used >> as control domain, I can change it if it sounds bad. > > If you means OSes then better also say OSes. But maybe this doesn't need > specifically expressing, by saying e.g. "..., the option is applicable > only on AArch64"? Or can a Dom0 be 32-bit on Arm64 Xen?
I think there is no limitation so Dom0 can be 32 bit or 64. Maybe I can say “... AArch64 kernel guests.”? > >>>> + A value equal to 0 disables the feature, this is the default value. >>>> + Values below 0 means the feature uses the maximum SVE vector length >>>> + supported by hardware, if SVE is supported. >>>> + Values above 0 explicitly set the maximum SVE vector length for Dom0, >>>> + allowed values are from 128 to maximum 2048, being multiple of 128. >>>> + Please note that when the user explicitly specifies the value, if >>>> that value >>>> + is above the hardware supported maximum SVE vector length, the domain >>>> + creation will fail and the system will stop, the same will occur if >>>> the >>>> + option is provided with a non zero value, but the platform doesn't >>>> support >>>> + SVE. >>> >>> Assuming this also covers the -1 case, I wonder if that isn't a little too >>> strict. "Maximum supported" imo can very well be 0. >> >> Maximum supported, when platforms uses SVE, can be at minimum 128 by arm >> specs. > > When there is SVE - sure. But when there's no SVE, 0 is kind of the implied > length. And I'd view a command line option value of -1 quite okay in that > case: They've asked for the maximum supported, so they'll get 0. No reason > to crash the system during boot. Ok I see what you mean, for example when Kconfig SVE is enabled, but the platform doesn’t have SVE feature, requesting sve=-1 will keep the value to 0, and no system will be stopped. Maybe I can say: “... the same will occur if the option is provided with a positive non zero value, but the platform doesn't support SVE." > > Jan
