Re: [PATCH v4 05/10] KVM/x86: expose MSR_IA32_PERF_CAPABILITIES to the guest

From: Andi Kleen
Date: Mon Jan 07 2019 - 13:20:23 EST

> The issue is compatibility. Prior to your change, reading this MSR
> from a VM would raise #GP. After your change, it won't. That means
> that if you have a VM migrating between hosts with kernel versions
> before and after this change, the results will be inconsistent. In the

No it will not be. All Linux kernel uses of this MSR are guarded
by a CPUID check.