On Thu, Aug 28, 2014 at 12:46 PM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > Il 28/08/2014 18:22, Andy Lutomirski ha scritto: >> Is there a non-cpuid interface between QEMU and KVM for this? > > No. Hmm. Then, assuming that someone manages to allocate a cross-hypervisor MSR number for this, what am I supposed to do in the KVM code? Just make it available unconditionally? I don't see why that wouldn't work reliably, but it seems like an odd design. > >> AFAICT, even turning off cpuid bits for things like async pf doesn't >> actually disable the MSRs (which is arguably an attack surface issue). > > No, it doesn't. You cannot disable instructions even if you hide CPUID > bits, so KVM just extends this to MSRs (both native and paravirtual). It > sometimes helps too, for example with a particular guest OS that does > not necessary check CPUID for bits that are always present on Apple > hardware... But I bet that no one assumes that KVM paravirt MSRs are available even if the feature bit isn't set. Also, the one and only native feature flag I tested (rdtscp) actually does work: RDTSCP seems to send #UD if QEMU is passed -cpu host,-rdtscp. --Andy -- 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
