Re: [PATCH v5 13/19] x86/cpufeatures: Add flag to track whether MSR IA32_FEAT_CTL is configured

Sean Christopherson
2020-02-26T21:25:40Z

On Wed, Feb 26, 2020 at 01:03:01PM -0800, Jacob Keller wrote:
> On 2/26/2020 12:57 PM, Sean Christopherson wrote:
> > Bummer. Using clear_cpu_cap() instead of setup_clear_cpu_cap() was me
> > being fancy and trying to allow KVM to identify the case where VMX is
> > available and configured on some CPUs but not all. I'll work on a fix.
> >
> Hmm. Right. For that to work, you'd need to make this disabling happen
> significantly later, and/or fix setup_pku to somehow honor this properly.

Arguably, setup_pku() should be a little less heavy handed in updating
cpufeatures for X86_FEATURE_OSPKE, but init_ia32_feat_ctl() should also be
more robust.

I've reproduced the bug, should have a fix ready by EOD.

> But it looks like rdmsr is global and not tied to a given CPU anyways?

For better or worse, the MSR is thread scoped.