Re: [PATCH v5 2/5] KVM: x86: Add IBPB support

[Jim Mattson]

On Wed, Jan 31, 2018 at 11:37 AM, KarimAllah Ahmed <karahmed@xxxxxxxxx> wrote:

> +       nested_vmx_disable_intercept_for_msr(msr_bitmap_l1, msr_bitmap_l0,
> +                                            MSR_IA32_PRED_CMD,
> +                                            MSR_TYPE_W);
> +

I still think this should be predicated on L1 having
guest_cpuid_has(vcpu, X86_FEATURE_IBPB) or guest_cpuid_has(vcpu,
X86_FEATURE_SPEC_CTRL), because of the potential impact to the
hypertwin. If L0 denies the feature to L1 by clearing those CPUID
bits, L1 shouldn't be able to bypass that restriction by launching L2.