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Re: [Xen-devel] How to get a few MSR values from userspace?



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

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