On May 1, 2014 12:26 PM, <tytso@xxxxxxx> wrote: > > On Thu, May 01, 2014 at 12:02:49PM -0700, Andy Lutomirski wrote: > > > > Is RDSEED really reasonable here? Won't it slow down by several > > orders of magnitude? > > That is I think the biggest problem; RDRAND and RDSEED are fast if > they are native, but they will involve a VM exit if they need to be > emulated. So when an OS might want to use RDRAND and RDSEED might be > quite different if we know they are being emulated. > > Using the RDRAND and RDSEED "api" certainly makes sense, at least for > x86, but I suspect we might want to use a different way of signalling > that a VM guest can use RDRAND and RDSEED if they are running on a CPU > which doesn't provide that kind of access. Maybe a CPUID extended > function parameter, if one could be allocated for use by a Linux > hypervisor? > I'm still not convinced. This will affect userspace as well as the guest kernel, and I don't see why guest user code should be able to access this API. RDRAND for CPL0 only would work, but that seems odd. And I think that RDSEED emulation is asking for trouble. RDSEED is synchronous, but /dev/random is asynchronous. And making bootup wait for even a single byte from /dev/random seems bad. In any event, virtio-rng should be a better interface for this. > - Ted > -- 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
