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 15:35:48 -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.

Right.

> 
> Does reverting commit a4d0b2fdbcf7 ("KVM: VMX: Use VMX feature flag to
> query BIOS enabling") resolve the issue?
> 

Will try.

> 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.
> 

It's unmodified net-next as of commit: 3b3e808cd883 ("Merge tag
'mac80211-next-for-net-next-2020-02-24' of
git://git.kernel.org/pub/scm/linux/kernel/git/jberg/mac80211-next")

Config is based off the fedora 30 config with make olddefconfig. I
attached a copy.

I've been staring at it too, and it doesn't make sense.

Could it be some sort of timing thing where we check for bios disabling
kvm before that init thing runs? but then.. X86_MSR_FEAT_CTL should not
be set... Very weird.

Thanks,
Jake

View attachment "broken-net-next-config-kvm-panic.config" of type "text/plain" (217618 bytes)