On Thu, Sep 3, 2020 at 9:43 AM Dario Faggioli <[email protected]> wrote: > > On Thu, 2020-09-03 at 00:34 -0400, Joel Fernandes wrote: > > On Wed, Sep 2, 2020 at 12:57 PM Dario Faggioli <[email protected]> > > wrote: > > > 2) protection of the kernel from the other thread running in > > > userspace > > > may be achieved in different ways. This is one, sure. ASI will > > > probably > > > be another. Hence if/when we'll have both, this and ASI, it would > > > be > > > cool to be able to configure the system in such a way that there is > > > only one active, to avoid paying the price of both! :-) > > > > Actually, no. Part of ASI will involve exactly what this patch does - > > IPI-pausing siblings but ASI does so when they have no choice but to > > switch away from the "limited kernel" mapping, into the full host > > kernel mapping. I am not sure if they have yet implemented that part > > but they do talk of it in [1] and in their pretty LPC slides. It is > > just that ASI tries to avoid that scenario of kicking all siblings > > out > > of guest mode. So, maybe this patch can be a stepping stone to ASI. > > > Ah, sure! I mean, it of course depends on how things get mixed > together, which we still don't know. :-) > > I know that ASI wants to do this very same thing some times. I just > wanted to say that we need/want only one mechanism for doing that, in > place at any given time. > > If that mechanism will be this one, and ASI then uses it (e.g., in a > scenario where for whatever reason one wants ASI with the kicking but > not Core Scheduling), then great, I agree, and everything does makes > sense.
Agreed, with some minor modifications, it should be possible. > > Why do you feel that ASI on its own offers some magical protection > > that eliminates the need for this patch? > > > I don't. I was just trying to think of different use cases, how they > mix and match, etc. But as you're suggesting (and as Thomas has shown > very clearly in another reply to this email), the thing that makes the > most sense is to have one mechanism for the kicking, used by anyone > that needs it. :-) Makes sense. Thanks, - Joel
