Re: [PATCH v2 1/7] hyperv: Detect Nested virtualization support for SVM

Vineeth Pillai
2021-04-16T16:10:41Z

> It may make sense to expand this a bit as it is probably unclear how the
> change is related to SVM.
>
> Something like:
>
> HYPERV_CPUID_NESTED_FEATURES CPUID leaf can be present on both Intel and
> AMD Hyper-V guests. Previously, the code was using
> HV_X64_ENLIGHTENED_VMCS_RECOMMENDED feature bit to determine the
> availability of nested features leaf and this complies to TLFS:
> "Recommend a nested hypervisor using the enlightened VMCS interface.
> Also indicates that additional nested enlightenments may be available
> (see leaf 0x4000000A)". Enlightened VMCS, however, is an Intel only
> feature so the detection method doesn't work for AMD. Use
> HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS.EAX CPUID information ("The
> maximum input value for hypervisor CPUID information.") instead, this
> works for both AMD and Intel.
Thanks for the input. Will update the commit message in next revision.

Thanks,
Vineeth