Re: [PATCH] KVM: X86: Expose KVM_HINTS_REALTIME in KVM_GET_SUPPORTED_CPUID

[Jim Mattson]

On Fri, Oct 23, 2020 at 2:07 AM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
> On 22/10/20 19:13, Jim Mattson wrote:
> > We don't actually use KVM_GET_SUPPORTED_CPUID at all today. If it's
> > commonly being misinterpreted as you say, perhaps we should add a
> > KVM_GET_TRUE_SUPPORTED_CPUID ioctl. Or, perhaps we can just fix this
> > in the documentation?
>
> Yes, I think we should fix the documentation and document the best
> practices around MSRs and CPUID bits.  Mostly documenting what QEMU
> does, perhaps without all the quirks it has to support old kernels that
> messed things up even more.
>
> Paolo

I'd really like to be able to call an ioctl that will help me
determine whether the host can support the guest CPUID information
that I already have (e.g. on the target of a live migration). At first
glance, KVM_GET_SUPPORTED_CPUID appeared to be that ioctl. Sadly, it
appears that no such ioctl exists.