On Wed, Jan 04, 2023, Borislav Petkov wrote: > On Wed, Jan 04, 2023 at 09:02:04PM +0000, Sean Christopherson wrote: > > And there's a non-zero chance we'd end up with a kernel param to allow booting > > unknown CPUs, e.g. for people doing weird things with VMs or running old, esoteric > > hardware. At that point we'd end up with a more complex implementation than > > processing dependencies on synthetic flags, especially if there's ever a more > > legitimate need to process such dependencies. > > I'm sorry but I'm still unclear on what actual use care are we even fixing here? There's no fix. What I was trying to say is that modifying the kernel to refuse to boot on unknown CPUs is opening a can of worms for very little benefit. > If it is about people who'd like to tinker with old hw or doing weird VM things, > they can just as well adjust their kernel .configs and rebuild. > > Peeking around your patchset, if all this is about dropping the > X86_FEATURE_MSR_IA32_FEAT_CTL check and checking only X86_FEATURE_VMX and in > order to do that, you want to cover those obscure cases where > init_ia32_feat_ctl() won't get run, then sure, I guess - changes look simple > enough. :) Yes, this is purely to drop the explicit X86_FEATURE_MSR_IA32_FEAT_CTL checks. Alternatively, we could just drop the checks without processing the dependency, i.e. take the stance that running KVM with a funky .config is a user error, but that feels unnecessarily hostile since it's quite easy to play nice. Or I guess do nothing and carry the explicit checks.
