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

[Jim Mattson]

On Wed, Jan 2, 2019 at 11:55 PM Wei Wang <wei.w.wang@xxxxxxxxx> wrote:

> Right, thanks. Probably better to change it to below:
>
> msr_info->data = 0;
> data = native_read_msr(MSR_IA32_PERF_CAPABILITIES);
> if (vcpu->kvm->arch.lbr_in_guest)
>      msr_info->data |= (data & X86_PERF_CAP_MASK_LBR_FMT);
>

This still breaks backwards compatibility. Returning 0 and raising #GP
are not the same.