Xin and I were discussing the dependencies we have going here. For arch reasons, CET supervisor shadow stack was waiting for FRED support. And for KVM development process reasons KVM FRED support is waiting for KVM CET support. It’s almost a circle. It looks like Chao has re-arranged the patches such that the space saving optimization could be dropped. It would just look like switching to the pretty trivial patches 1-3 I guess. However, he didn’t actually advocate for that to happen. But the subtext seems to be that it should be considered? I think there aren't concerns with the bones of the optimization in the later patches. It’s just polishing that is needed. But some of the polishing needed (i.e. the long debated naming of for the guest category of features) is downstream of the growing complexity of the FPU, which we were planning to accept. So maybe it’s turning out more costly than we expected? In any case, at this point I think we need to either double down on polishing this thing up (by pausing other work) and have a clear “please do this with these patches" request, or declare failure and argue for the smaller version. I guess I still lean towards keeping the optimization. But I do think it's worth considering at this point. Rick
