Re: [PATCH v5 13/19] x86/cpufeatures: Add flag to track whether MSR IA32_FEAT_CTL is configured

Jacob Keller
2020-02-27T18:09:57Z

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