On Wed, Sep 16, 2015 at 04:33:11PM -0700, Andy Lutomirski wrote: > Setting CONFIG_PARAVIRT=y has an unintended side effect: it silently > turns all rdmsr and wrmsr operations into the safe variants without > any checks that the operations actually succeed. > > This is IMO awful: it papers over bugs. In particular, KVM gueests > might be unwittingly depending on this behavior because > CONFIG_KVM_GUEST currently depends on CONFIG_PARAVIRT. I'm not > aware of any such problems, but applying this series would be a good > way to shake them out. > > Fix it so that the MSR operations work the same on CONFIG_PARAVIRT=n > and CONFIG_PARAVIRT=y as long as Xen isn't being used. The Xen > maintainers are welcome to make a similar change on top of this. > > Since there's plenty of time before the next merge window, I think > we should apply and fix anything that breaks. > > Doing this is probably a prerequisite to sanely decoupling > CONFIG_KVM_GUEST and CONFIG_PARAVIRT, which would probably make > Arjan and the rest of the Clear Containers people happy :) So I actually like this, although by Ingo's argument, its a tad risky. But the far greater problem I have with the whole virt thing is that you cannot use rdmsr_safe() to probe if an MSR exists at all because, as you told me, these virt thingies return 0 for all 'unknown' MSRs instead of faulting. -- 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
