On 12/17/18, Jiri Kosina <jikos@xxxxxxxxxx> wrote: > On Mon, 17 Dec 2018, Barry Kauler wrote: > >> With CONFIG_SCHED_SMT disabled, CONFIG_RETPOLINE is not needed. > > This is not true. Retpoline protects also against a scenario where process > A posions BTB for process B that gets scheduled afterwards on the same > core, irrespective of SMT. > >> With CONFIG_SCHED_SMT enabled, then CONFIG_RETPOLINE is required for >> security reasons. > > This is answered by the above as well. Retpoline is needed irrespective of > SMT. > >> Enabling CONFIG_SCHED_SMT speeds up some operations, enabling >> CONFIG_RETPOLINE slows it down again. > > There is no 'again', as those two things are not really dependent in any > way. > >> End result, not much speed gain, far more complicated kernel. > > And therefore this is bogus :) > Thanks for the response. So I guess it comes down to basic philosophy: "SMT is a distinct feature, separate from SMP, and I think that it is important to keep that distinction." You guys have chosen to remove that distinction, and to remove the choice for many specialised, such as embedded, situations, where they would maybe want that choice. I guess this will have to be my last post on the topic, as I can't offer any other justification for my stance, other than the above. Regards, Barry Kauler
