linux-kernel - Re: [PATCH stable-4.4.y] KVM: VMX: Fix x2apic check in vmx_msr_bitmap

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Date:   Fri, 22 Feb 2019 10:20:55 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Joerg Roedel <jroedel@...e.de>, Joerg Roedel <joro@...tes.org>,
        stable@...r.kernel.org,
        Ben Hutchings <ben.hutchings@...ethink.co.uk>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Jim Mattson <jmattson@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH stable-4.4.y] KVM: VMX: Fix x2apic check in
 vmx_msr_bitmap_mode()

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.

Paolo