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

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Message-ID: <38e05b7a-aea2-1da1-56b5-1505615c55fb@intel.com>
Date:   Thu, 27 Feb 2020 10:09:51 -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 2/26/2020 6:12 PM, Sean Christopherson wrote:
> On Tue, Feb 25, 2020 at 01:49:13PM -0800, Jacob Keller wrote:
> 
> One other thing that's been bothering me; you mention in a later email that
> this bug resulting in a crash during boot.  The low timestamps also suggest
> the system is fairly early in its bringup.
> 
> But KVM only does VMXON when it actually creates a VM[*].  During boot I
> would expect the bug to result in KVM being incorrectly loaded/enabled, but
> that alone wouldn't trigger a crash.

It crashes during hardware enable, specifically in the kvm_cpu_vmxon
during the hardware_enable() function.

It doesn't crash until near the end of bootup, and it didn't crash when
I kept the system in single-user boot mode.

> 
> I assume/hope your system is automatically running some form of virt
> process at boot?  Not that there's anything wrong with that, it's just
> suprising and I want to make sure there's not something really funky going
> on.
> 

The system has libvirtd enabled. My guess is that libvirtd starts up and
enables hardware. I don't see any actual virtual machines enabled, but I
think you're right that this is why it crashes.

Thanks,
Jake