Re: [Qemu-devel] [PATCH] i386/kvm: expose HV_CPUID_ENLIGHTMENT_INFO.EAX and HV_CPUID_NESTED_FEATURES.EAX as feature words

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Eduardo Habkost <ehabkost@redhat.com> writes:

>>            [...] Some time ago when merging direct mode stimers for KVM
>> Paolo suggested we stop adding capabilities to KVM for each individulat
>> feature and replace them with something like KVM_GET_SUPPORTED_HV_CPUID
>> ioctl returning all Hyper-V related feature words. When this is done we
>> can reconsider how Qemu discoveres Hyper-V related KVM features and as
>> part of this work we can take a closer look at feature words and
>> feat_names.
>
> Why a separate ioctl instead of extending GET_SUPPORTED_CPUID?

Unfortunatelly both KVM and Hyper-V use feature leaves 0x40000000,
0x40000001 (so it's up to the userspace - qemu in our case - what to
expose to the guest) and GET_SUPPORTED_CPUID already returns KVM's. Not
sure this can be changed (to e.g. returning these leaves twice with
different flags) without breaking userspace. New ioctl is safer.

-- 
Vitaly