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

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Message-ID: <5434303a-0742-3811-fd14-6445d296c0f0@intel.com>
Date:   Tue, 25 Feb 2020 15:54:34 -0800
From:   Jacob Keller <jacob.e.keller@...el.com>
To:     Sean Christopherson <sean.j.christopherson@...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 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.