Re: IA32_FEATURE_CONTROL MSR in nested virt

[Gleb Natapov <gleb@redhat.com>]

On Wed, Jul 03, 2013 at 04:24:33PM +0800, Arthur Chunqi Li wrote:
> 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.
> 
NOVA cannot write to it and expect anything but #GP since BIOSes usually
lock the MSR. So I agree with Paolo about returning 5 on read and #GP on
write. Later we can implement locking functionality and make BIOS
enable/disable nested vmx.

> 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.
> 
> Thanks,
> Arthur
> 
> --
> Arthur Chunqi Li
> Department of Computer Science
> School of EECS
> Peking University
> Beijing, China

--
			Gleb.