Re: GET_RNG_SEED hypercall ABI? (Re: [PATCH v5 0/5] random,x86,kvm: Rework arch RNG seeds and get some from kvm)

On Aug 28, 2014 7:17 AM, "Gleb Natapov" [off-list ref] wrote:

On Tue, Aug 26, 2014 at 04:58:34PM -0700, Andy Lutomirski wrote:

quoted

hpa pointed out that the ABI that I chose (an MSR from the KVM range
and a KVM cpuid bit) is unnecessarily KVM-specific.  It would be nice
to allocate an MSR that everyone involved can agree on and, rather
than relying on a cpuid bit, just have the guest probe for the MSR.

CPUID part allows feature to be disabled for machine compatibility purpose
during migration. Of course interface can explicitly state that one successful
use of the MSR does not mean that next use will not result in a #GP, but that
doesn't sound very elegant and is different from any other MSR out there.

Is there a non-cpuid interface between QEMU and KVM for this?

AFAICT, even turning off cpuid bits for things like async pf doesn't
actually disable the MSRs (which is arguably an attack surface issue).

--Andy

--
                        Gleb.