Re: [PATCH v3 2/2] KVM: X86: Introduce KVM_HC_PAGE_ENC_STATUS hypercall

[Paolo Bonzini]

On 04/05/21 01:22, Steve Rutherford wrote:
> As far as I know, because of MSR filtering, the only "code" that needs
> to be in KVM for MSR handling is a #define reserving the PV feature
> number and a #define for the MSR number.
>
> Arguably, you don't even need to add the new PV bits to the supported
> cpuid, since MSR filtering is really what determines if kernel support
> is present.

Not only I don't need to do that, I must not. :)

> > At this point I very much prefer the latter, which is basically Ashish's
> > earlier patch.
>
> The minor distinction would be that if you expose the cpuid bit to the
> guest you plan on intercepting the MSR with filters, and would not
> need any handler code in the kernel.

Yep, and it's not a minor distinction after all (especially from the PoV 
of the guy who actually ends up maintaining the code, i.e. me), so 
that's what I'm going for.

Paolo