Re: How to get a few MSR values from userspace?

[Razvan Cojocaru <rzvncj@gmail.com>]

>> I need access to some MSR values that are not currently being saved in
>> struct hvm_hw_cpu. Among them are MSR_IA32_MC0_CTL, MSR_IA32_MISC_ENABLE
>> and MSR_IA32_ENERGY_PERF_BIAS.
>
> I can't see why, and this is quite likely related to the reason for
> them not being accessible in the first place.

Because they offer heuristic information about the type of OS running in 
the domU domain, and there are classes of applications interested in that.

> Not to me, no. These records are use for save/restore/migrate,
> and so far there hasn't been a need to include here the MSRs you
> mention.

Interesting. I've assumed that those would be saved (and perhaps ignored 
on restore if they became irrelevant) in a migration scenario.

> For MSR_IA32_MC0_CTL, why not? These should be fine for
> anything that is architectural to x86.
>
> The other two MSRs are Intel specific iirc, and hence wouldn't
> be validly dealt with in vendor independent code.

I agree, however, as I've said before, _some_ applications _are_ 
interested in vendor-specific information for heuristic purposes.

Whether this would make a interesting patch for Xen or not, I would 
appreciate any advice on how best to implement said functionality (if 
only for MSR_IA32_MC0_CTL).

Thanks,
Razvan Cojocaru