On Wed, Mar 15, 2023, Li,Rongqing wrote: > > Rather than have the guest rely on host KVM behavior clearing PV_UNHALT > > when HLT is passed through), would it make sense to add something like > > KVM_HINTS_HLT_PASSTHROUGH to more explicitly tell the guest that HLT isn't > > intercepted? > > KVM_HINTS_HLT_PASSTHROUGH is more obvious, but it need both kvm and guest support Yeah, that's the downside. But modifying KVM and/or the userspace VMM shouldn't be difficult, i.e the only meaningful cost is the rollout of a new kernel/VMM. On the other hand, establishing the heuristic that !PV_UNHALT == HLT_PASSTHROUGH could have to subtle issues in the future. It safe-ish in the context of this patch as userspace is unlikely to set KVM_HINTS_REALTIME, hide PV_UNHALT, and _not_ passthrough HLT. But without the REALTIME side of things, !PV_UNHALT == HLT_PASSTHROUGH is much less likely to hold true.
