Re: random: Providing a seed value to VM guests

["H. Peter Anvin" <hpa@zytor.com>]

On 05/01/2014 03:56 PM, Andy Lutomirski wrote:
> 
> I think we're comparing:
> 
> a) cpuid to detect rdrand *or* emulated rdrand followed by rdrand
> 
> to
> 
> b) cpuid to detect rdrand or the paravirt seed msr/cpuid call,
> followed by rdrand or the msr or cpuid read
> 
> this seems like it barely makes a difference, especially since (a)
> probably requires detecting KVM anyway.

Well, it lets one do something like:

	if (boot_cpu_has(X86_FEATURE_RDRAND) ||
            boot_cpu_has(X86_FEATURE_RDRAND_SIMULATED))
		rdrand_long(...);

We need the ifs anyway for early code; the arch_*() interfaces are only
available after alternatives run.

	-hpa