Re: [PATCH v10 4/6] x86/split_lock: Enumerate split lock detection if the IA32_CORE_CAPABILITIES MSR is not supported

[Peter Zijlstra]

On Thu, Nov 21, 2019 at 06:13:18PM -0800, Andy Lutomirski wrote:

> You seem to be assuming that certain model CPUs have this feature even
> if not enumerated. You need to make sure you donât try to use it in a
> VM without the hypervisor giving you an indication that itâs available
> and permitted. My suggestion is to disable model-based enumeration if
> HYPERVISOR is set.  You should also consider probing the MSR to double
> check even if you donât think you have a hypervisor.

Yep, in patch 6 this results in an unconditinoal WRMSR, which, when ran
under a HV, will explode most mighty.

He doesn't double check, doesn't use wrmsrl_safe()...