On 09/22/2014 06:31 AM, Christopher Covington wrote: > On 09/19/2014 05:46 PM, H. Peter Anvin wrote: >> 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. > > A guest kernel couldn't make it look like RDRAND is not present to guest > userspace? > It could, but how would you enumerate that? A new "RDRAND-CPL-0" CPUID bit pretty much would be required. -hpa -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
