On Tue, Sep 13, 2016 at 11:13 PM, Kyle Huey <me@xxxxxxxxxxxx> wrote: > On Mon, Sep 12, 2016 at 9:56 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: >> You should explicitly check that, if the >> feature is set under Xen PV, then the MSR actually works as >> advertised. This may require talking to the Xen folks to make sure >> you're testing the right configuration. > > This is interesting. When running under Xen PV the kernel is allowed > to read the real value of MSR_PLATFORM_INFO and see that CPUID > faulting is supported. But as you suggested, writing to > MSR_MISC_FEATURES_ENABLES doesn't actually enable CPUID faulting, at > least not in any way that works. > > It's not obvious to me how to test this, because when this feature > works, CPUID only faults in userspace, not in the kernel. Is there > existing code somewhere that runs tests like this in userspace? > Andrew, Boris: should we expect Xen PV to do anything sensible when we write to MSR_PLATFORM_INFO to turn on CPUID faulting? Should the Xen PV rdmsr hooks or perhaps the hypervisor mask out the feature if it isn't going to be supported? --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
