On 10/26/2012 12:51 PM, Paolo Bonzini wrote:
> Il 26/10/2012 21:07, H. Peter Anvin ha scritto:
>> This is surreal. Output from /dev/hwrng turns into output for
>> /dev/random... it us guaranteed worse; period, end of story.
>
> Isn't that exactly what happens in bare-metal? hwrng -> rngd -> random.
> Instead here
> we'd have, host hwrng -> virtio-rng-pci -> guest hwrng -> guest rngd -> guest
> random.
>
> The only difference is that you paravirtualize access to the host hwrng to a)
> distribute
> entropy to multiple guests; b) support migration across hosts with different
> CPUs and
> hardware.
First, hwrng is only one of the sources used by rngd. It can also
(currently) use RDRAND or TPM; additional sources are likely to be added
in the future.
Second, the harvesting of environmental noise -- timings -- is not as
good in a VM as on plain hardware, so for the no-hwrng case it is better
for this to be done in the host than in the VM.
-hpa
