Re: [PATCH stable-4.4.y] KVM: VMX: Fix x2apic check in vmx_msr_bitmap_mode()

From: Paolo Bonzini
Date: Fri Feb 22 2019 - 04:21:04 EST

On 21/02/19 18:15, Sean Christopherson wrote:
> This bug exists only in the 4.4.y backport; upstream, 4.9.y and 4.14.y
> all had the correct code from the get-go. And there is already a KVM
> unit test that *should* hit this, albeit somewhat indirectly. I'll
> verify the tests that touch the TPR actually run with x2APIC enabled.

eventinj from kvm-unit-tests should trigger it. There are other tests
that touch the TPR, but they use cr8 so they don't show the bug.

> Assuming the KVM unit test actually works, it's not a stretch for the
> bug to esacpe, e.g. if the tests weren't run on 4.4.y at all, or were
> only run on hardware with x2APIC.

Yeah, you should be able to see this with kvm_intel.enable_apicv=0 on
newer processors. But I've never run the tests for 4.4.y.