On 22/01/20 17:29, Vitaly Kuznetsov wrote: > Yes, in case we're back to the idea to filter things out in QEMU we can > do this. What I don't like is that every other userspace which decides > to enable eVMCS will have to perform the exact same surgery as in case > it sets allow_unsupported_controls=0 it'll have to know (hardcode) the > filtering (or KVM_SET_MSRS will fail) and in case it opts for > allow_unsupported_controls=1 Windows guests just won't boot without the > filtering. > > It seems to be 1:1, eVMCSv1 requires the filter. Yes, that's the point. It *is* a hack in KVM, but it is generally preferrable to have an easier API for userspace, if there's only one way to do it. Though we could be a bit more "surgical" and only remove SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES---thus minimizing the impact on non-eVMCS guests. Vitaly, can you prepare a v2 that does that and adds a huge "hack alert" comment that explains the discussion? Paolo
