Re: IA32_FEATURE_CONTROL MSR in nested virt

[Paolo Bonzini <pbonzini@redhat.com>]

Il 03/07/2013 10:24, Arthur Chunqi Li ha scritto:
> Hi Gleb and Paolo,
> When I write test cases for nested virt and found that reading/writing
>  IA32_FEATURE_CONTROL will be simply ignored or return 0 (in
> arch/x86/kvm/vmx.c) in VM. Checking this MSR will be done by some
> hypervisors (e.g. NOVA) and may cause error then, so it is necessary
> to behave right when read/write it in VM.
> 
> Are there any difficulties to handle this MSR? I have two solutions.
> The first one is return the value of physical CPU's and always return
> true when write. This is simple but may behave as if it is a VM
> because write to it after VMXON will not return GP exception. This
> solution can solve most basic problems since this MSR is not commonly
> used. Another solution is adding a field in VCPU to handle this MSR.
> This is a complex but better method.
> 
> I think I can complete this if needed.

Would it be enough to return 5 (binary 101) on reads if nested VMX is
enabled, and #GP on writes?

Paolo