Roman Kagan <rkagan@xxxxxxxxxxxxx> writes: > On Mon, Dec 10, 2018 at 06:21:56PM +0100, Vitaly Kuznetsov wrote: >> + >> +Currently, the following list of CPUID leaves are returned: >> + HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS >> + HYPERV_CPUID_INTERFACE >> + HYPERV_CPUID_VERSION >> + HYPERV_CPUID_FEATURES >> + HYPERV_CPUID_ENLIGHTMENT_INFO >> + HYPERV_CPUID_IMPLEMENT_LIMITS >> + HYPERV_CPUID_NESTED_FEATURES >> + >> +HYPERV_CPUID_NESTED_FEATURES leaf is only exposed when Enlightened VMCS was >> +enabled on the corresponding vCPU (KVM_CAP_HYPERV_ENLIGHTENED_VMCS). > > IOW the output of ioctl(KVM_GET_SUPPORTED_HV_CPUID) depends on > whether ioctl(KVM_ENABLE_CAP, KVM_CAP_HYPERV_ENLIGHTENED_VMCS) has > already been called on that vcpu? I wonder if this fits the intended > usage? I added HYPERV_CPUID_NESTED_FEATURES in the list (and made the new ioctl per-cpu and not per-vm) for consistency. *In theory* KVM_CAP_HYPERV_ENLIGHTENED_VMCS is also enabled per-vcpu so some hypothetical userspace can later check enabled eVMCS versions (which can differ across vCPUs!) with KVM_GET_SUPPORTED_HV_CPUID. We will also have direct tlb flush and other nested features there so to avoid addning new KVM_CAP_* for them we need the CPUID. Another thing I'm thinking about is something like 'hv_all' cpu flag for Qemu which would enable everything by setting guest CPUIDs to what KVM_GET_SUPPORTED_HV_CPUID returns. In that case it would also be convenient to have HYPERV_CPUID_NESTED_FEATURES properly filled (or not filled when eVMCS was not enabled). -- Vitaly
