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

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Message-ID: <20200225232900.GO9245@linux.intel.com>
Date:   Tue, 25 Feb 2020 15:29:00 -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 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.