linux-kernel - Re: [PATCH v5 13/19] x86/cpufeatures: Add flag to track whether MSR IA32_FEAT

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Date:   Wed, 26 Feb 2020 13:25:37 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Jacob Keller <jacob.e.keller@...el.com>
Cc:     TonyWWang-oc@...oxin.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, bp@...en8.de, bp@...e.de,
        hpa@...or.com, jacob.jun.pan@...ux.intel.com,
        jarkko.sakkinen@...ux.intel.com, jmattson@...gle.com,
        jolsa@...hat.com, joro@...tes.org, kvm@...r.kernel.org,
        lenb@...nel.org, linux-edac@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-pm@...r.kernel.org, mark.rutland@....com, mingo@...hat.com,
        namhyung@...nel.org, pbonzini@...hat.com, peterz@...radead.org,
        rkrcmar@...hat.com, shuah@...nel.org, tglx@...utronix.de,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        x86@...nel.org
Subject: Re: [PATCH v5 13/19] x86/cpufeatures: Add flag to track whether MSR
 IA32_FEAT_CTL is configured

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.