Re: [PATCH v3 13/21] KVM:VMX: Emulate reads and writes to CET MSRs

[Yang, Weijiang]

On 5/23/2023 4:21 PM, Binbin Wu wrote:
> On 5/11/2023 12:08 PM, Yang Weijiang wrote:
> > Add support for emulating read and write accesses to CET MSRs.
> > CET MSRs are universally "special" as they are either context switched
> > via dedicated VMCS fields or via XSAVES, i.e. no additional in-memory
> > tracking is needed, but emulated reads/writes are more expensive.
[...]
> > +
> > +    if (!guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) &&
> > +        !guest_cpuid_has(vcpu, X86_FEATURE_IBT))
> > +        return false;
> > +
> > +    if (msr->index == MSR_IA32_PL3_SSP &&
> > +        !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
> > +        return false;
> It may be better to merge the two if statements into one to avoid 
> calling guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) twice.
Yeah, it sounds good to me, thanks!

> e.g,
>
>     if (!guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) &&
>         (!guest_cpuid_has(vcpu, X86_FEATURE_IBT) || msr->index == 
> MSR_IA32_PL3_SSP))
>         return false;
>
>
> > +
> > +    return true;
> > +}
> > +EXPORT_SYMBOL_GPL(kvm_cet_is_msr_accessible);
> > +
> >   EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_entry);
> >   EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit);
> >   EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_fast_mmio);
> ...