On Mon, Aug 19, 2019 at 3:11 PM Sean Christopherson <sean.j.christopherson@xxxxxxxxx> wrote: > > On Tue, Aug 20, 2019 at 12:46:49AM +0300, Nikita Leshenko wrote: > > Before this commit, userspace could disable the GUEST_ACTIVITY_HLT bit in > > VMX_MISC yet KVM would happily accept GUEST_ACTIVITY_HLT activity state in > > VMCS12. We can fix it by either failing VM entries with HLT activity state when > > it's not supported or by disallowing clearing this bit. > > > > The latter is preferable. If we go with the former, to disable > > GUEST_ACTIVITY_HLT userspace also has to make CPU_BASED_HLT_EXITING a "must be > > 1" control, otherwise KVM will be presenting a bogus model to L1. > > > > Don't fail writes that disable GUEST_ACTIVITY_HLT to maintain backwards > > compatibility. > > Paolo, do we actually need to maintain backwards compatibility in this > case? This seems like a good candidate for "fix the bug and see who yells". Google's userspace clears bit 6. Please don't fail that write!
