Messages in this thread | | | From | Andrew Cooper <> | Subject | Re: [PATCH 0/3] xen: remove some checks for always present Xen features | Date | Thu, 22 Apr 2021 16:51:27 +0100 |
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On 22/04/2021 16:42, Jan Beulich wrote: > On 22.04.2021 17:28, Juergen Gross wrote: >> On 22.04.21 17:23, Jan Beulich wrote: >>> On 22.04.2021 17:17, Juergen Gross wrote: >>>> On 22.04.21 17:16, Jan Beulich wrote: >>>>> On 22.04.2021 17:10, Juergen Gross wrote: >>>>>> Some features of Xen can be assumed to be always present, so add a >>>>>> central check to verify this being true and remove the other checks. >>>>>> >>>>>> Juergen Gross (3): >>>>>> xen: check required Xen features >>>>>> xen: assume XENFEAT_mmu_pt_update_preserve_ad being set for pv guests >>>>>> xen: assume XENFEAT_gnttab_map_avail_bits being set for pv guests >>>>> I wonder whether it's a good idea to infer feature presence from >>>>> version numbers. If (at some point in the past) you had inferred >>>>> gnttab v2 being available by version, this would have been broken >>>>> by its availability becoming controllable by a command line option >>>>> in Xen. >>>> I'm testing the feature to be really present when booting and issue a >>>> message if it is not there. >>> And how does this help if the feature really isn't there yet other code >>> assumes it is? >> Did you look at the features I'm testing? > I did, yes. > >> Those are really just low >> level additions I can't imagine will ever be removed again. > I don't expect them to be removed. But I don't think the people having > contributed gnttab v2 expected any such for it, either.
The trainwreck around gnttab v2 is a mistake I hope we're never going to make again. I don't think it's a useful argument here.
The logic is fine. It's checking for the actual features in the ABI upon which Linux depends.
Sure - someone could modify Xen to take the feature out, but they'd get a red wall in CI as they break every Linux kernel released in the past decade.
~Andrew
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