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

H. Peter Anvin
2014-09-19T21:46:40Z

On 09/19/2014 01:46 PM, Andy Lutomirski wrote:
>>
>> 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.
>

Yes, the presence of RDRAND implies a cheap and inexhaustible entropy
source.

-hpa

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