Re: IA32_FEATURE_CONTROL MSR in nested virt

[Bandan Das <bsd@redhat.com>]

Gleb Natapov <gleb@redhat.com> writes:

> 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.

I vaguely recalled Nadav had posted a patch related to this MSR a
while back and found this :

http://permalink.gmane.org/gmane.comp.emulators.kvm.devel/88478

Shouldn't this work ?

>> 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.
> --
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