RE: Standardizing an MSR or other hypercall to get an RNG seed?

KY Srinivasan
2014-09-18T16:51:21Z

> -----Original Message-----
> From: Andy Lutomirski [mailto:luto@amacapital.net]
> Sent: Thursday, September 18, 2014 8:38 AM
> To: H. Peter Anvin
> Cc: KY Srinivasan; Linux Virtualization; kvm list; Gleb Natapov; Paolo Bonzini;
> Theodore Ts'o
> Subject: Re: Standardizing an MSR or other hypercall to get an RNG seed?
>
> On Thu, Sep 18, 2014 at 7:43 AM, H. Peter Anvin <hpa@zytor.com> wrote:
> > On 09/18/2014 07:40 AM, KY Srinivasan wrote:
> >>>
> >>> The main questions are what MSR index to use and how to detect the
> >>> presence of the MSR. I've played with two approaches:
> >>>
> >>> 1. Use CPUID to detect the presence of this feature. This is very
> >>> easy for KVM to implement by using a KVM-specific CPUID feature.
> >>> The problem is that this will necessarily be KVM-specific, as the
> >>> guest must first probe for KVM and then probe for the KVM feature.
> >>> I doubt that Hyper-V, for example, wants to claim to be KVM. If we
> >>> could standardize a non- hypervisor-specific CPUID feature, then this
> problem would go away.
> >>
> >> We would prefer a CPUID feature bit to detect this feature.
> >>
> >
> > I guess if we're introducing the concept of pan-OS MSRs we could also
> > have pan-OS CPUID. The real issue is to get a single non-conflicting
> > standard.
>
> Agreed.
>
> KVM currently puts 0 in 0x40000000.EAX, meaning that a feature bit in
> Microsoft's leaf 0x40000003 would probably not work well for KVM. I don't
> expect that Microsoft wants to start claiming to be KVM for the purpose of
> using a KVM-style feature bit, so, if we went the CPUID route, we would
> probably need something new.
>
> --Andy

I am copying other Hyper-V engineers to this discussion.

Regards,

K. Y
>
> >
> > -hpa
> >
> >
>
>
>
> --
> Andy Lutomirski
> AMA Capital Management, LLC