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

Paolo Bonzini
2014-09-21T12:39:01Z

Il 19/09/2014 22:46, Andy Lutomirski ha scritto:
>> >
>> > However, it sounds to me that at least for KVM, it is very easy just to emulate the RDRAND instruction. The hypervisor would report to the guest that RDRAND is supported in CPUID and the emulate the instruction when guest executes it. KVM already traps guest #UD (which would occur if RDRAND executed while it is not supported) - so this scheme wouldn’t introduce additional overhead over RDMSR.
> Because then guest user code will think that rdrand is there and will
> try to use it, resulting in abysmal performance.

KVM could expose a CPUID leaf that says "RDRAND is not there, but if you
execute it the hypervisor will try to do something slow but sane".

Paolo
_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org