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

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Date:   Tue, 25 Feb 2020 16:42:58 -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 Tue, Feb 25, 2020 at 03:54:34PM -0800, Jacob Keller wrote:
> On 2/25/2020 3:29 PM, Sean Christopherson wrote:
> > On Tue, Feb 25, 2020 at 02:52:32PM -0800, Jacob Keller wrote:
> >> On 2/25/2020 2:12 PM, Sean Christopherson wrote:
> >>> On Tue, Feb 25, 2020 at 01:49:13PM -0800, Jacob Keller wrote:
> >>>> Hi Sean,
> >>>>
> >>>> I suspect something is wrong and the features are enabled even though
> >>>> the BIOS has it disabled, leading to later failure because of this.
> >>>
> >>> Hrm.  On the failing kernel, what are the values of MSR 0x3a for all CPUs,
> >>> i.e. what's the output of 'sudo rdmsr -a 0x3a'?
> >>>
> >>
> >> On the old (fedora 30) kernel, every cpu reports as '1'.
> >>
> >> I can't easily test the failing kernel because it crashes during boot.
> > 
> > No need, your BIOS is likely locking the MSR, I doubt the value is any
> > different when running the new kernel.
> > 
> > Does reverting commit a4d0b2fdbcf7 ("KVM: VMX: Use VMX feature flag to
> > query BIOS enabling") resolve the issue?
> > 
> > Is the failing kernel an (umodified) upstream kernel?  A stable kernel?
> > Or something else?  Assuming it's an unmodified upstream kernel, can you
> > send your .config?  I've tried all the obvious Kconfig combinations but
> > haven't been able to reproduce the problem.  Staring at the code hasn't
> > yielded any revelations either.
> > 
> 
> I reverted the suggested commit and added some prints:
> 
> [   26.056398] X86_FEATURE_MSR_IA32_FEAT_CTL is enabled
> [   26.062426] X86_FEATURE_VMX is enabled
> [   26.066923] kvm: disabled by bios
> 
> So the old code flow is finding KVM to be disabled, but both features
> are set...
> 
> The code that sets this is run first:
> 
> > Feb 25 15:46:05 jbrandeb-saw1 kernel: x86/cpu: FEAT_CTL_LOCKED is set
> > Feb 25 15:46:05 jbrandeb-saw1 kernel: x86/cpu: FEAT_CTL_VMX_ENABLED_INSIDE_SMX is unset
> > Feb 25 15:46:05 jbrandeb-saw1 kernel: x86/cpu: FEAT_CTL_VMX_ENABLED_OUTSIDE_SMX is unset
> > Feb 25 15:46:05 jbrandeb-saw1 kernel: x86/cpu: MSR locked by bios
> > Feb 25 15:46:05 jbrandeb-saw1 kernel: x86/cpu: VMX (outside TXT) disabled by BIOS
> > Feb 25 15:46:05 jbrandeb-saw1 kernel: x86/cpu: disabling X86_FEATURE_VMX
> 
> But somehow... it is still set later...
> 
> So there's something weird going on. Maybe "boot_cpu_has" in the
> vmx_disabled_by_bios is wrong? Hmm.

Hmm, perhaps a bug somewhere else is overwriting the cpufeatures bit for
X86_FEATURE_VMX.  Let me see if I can reproduce from net-next.