MSRs load/store

MSRs load/store

[Jiaqing Du]

Hi List,

My question is about VM-Exit & VM-Entry controls for MSRs on Intel's processors.

For VM-Exit, a VMM can specify lists of MSRs to be stored and loaded
on VM exits. But for VM-Entry, a VMM can only specify a list of MSRs
to be loaded on VM entries. Why does not the processor have the
feature that stores MSRs before loading new ones for VM entries?


Thanks,
Jiaqing

Re: MSRs load/store

[Avi Kivity]

On 12/07/2009 05:07 PM, Jiaqing Du wrote:
> Hi List,
>
> My question is about VM-Exit&  VM-Entry controls for MSRs on Intel's processors.
>
> For VM-Exit, a VMM can specify lists of MSRs to be stored and loaded
> on VM exits. But for VM-Entry, a VMM can only specify a list of MSRs
> to be loaded on VM entries. Why does not the processor have the
> feature that stores MSRs before loading new ones for VM entries?
>    

Presumably the host knows what values are in those MSRs, so it doesn't 
need to store them.

-- 
error compiling committee.c: too many arguments to function

Re: MSRs load/store

[Jiaqing Du]

Hi Avi,

I did not get your point.

But if we want to multiplex some of the MSRs across the VMM and the
guest(s), it would be handy if the hardware provides this feature:
save host's version and load guest's version. Of course, we can do
this manually. I'm just wondering why this feature is missing.


Thanks,
Jiaqing

2009/12/7 Avi Kivity <avi@redhat.com>:
> On 12/07/2009 05:07 PM, Jiaqing Du wrote:
>>
>> Hi List,
>>
>> My question is about VM-Exit&  VM-Entry controls for MSRs on Intel's
>> processors.
>>
>> For VM-Exit, a VMM can specify lists of MSRs to be stored and loaded
>> on VM exits. But for VM-Entry, a VMM can only specify a list of MSRs
>> to be loaded on VM entries. Why does not the processor have the
>> feature that stores MSRs before loading new ones for VM entries?
>>
>
> Presumably the host knows what values are in those MSRs, so it doesn't need
> to store them.
>
> --
> error compiling committee.c: too many arguments to function
>
>

Re: MSRs load/store

[Avi Kivity]

On 12/07/2009 05:32 PM, Jiaqing Du wrote:
> Hi Avi,
>
> I did not get your point.
>
> But if we want to multiplex some of the MSRs across the VMM and the
> guest(s), it would be handy if the hardware provides this feature:
> save host's version and load guest's version. Of course, we can do
> this manually. I'm just wondering why this feature is missing.
>    

Well, you'll have to ask the designers of the feature.  If it can be 
done manually, why add a feature in hardware?

-- 
error compiling committee.c: too many arguments to function