On Tue, Jan 28, 2025, Manali Shukla wrote: > + if (kvm_cpu_has(X86_FEATURE_IDLE_HLT))
Well, shoot. I gave you bad input, and we're stuck. this_cpu_has() isn't correct, because the part of my previous feedback about needing to check *KVM* support was 100% correct. But kvm_cpu_has() isn't right either, because that checks what KVM supports exposing to the guest, not what KVM itself supports/uses. E.g. even if we add full nested support, the test would fail if nested=0 due to KVM not "supporting" Idle HLT despite using it under the hood. The lack of a way for KVM to communicate support to the user has come up in the past, e.g. in discussion around /proc/cpuinfo. Sadly, AFAIK there are no (good) ideas on what that should look like. For now, I'll just skip this patch, even though doing so makes me quite sad.
