linux-kernel - Re: [PATCH 01/13] KVM: nVMX: Preserve exception priority irrespective of exiting behavior

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Date:   Tue, 28 Apr 2020 13:07:15 -0700
From:   Oliver Upton <oupton@...gle.com>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Shier <pshier@...gle.com>
Subject: Re: [PATCH 01/13] KVM: nVMX: Preserve exception priority irrespective
 of exiting behavior

On Tue, Apr 28, 2020 at 11:54 AM Jim Mattson <jmattson@...gle.com> wrote:
>
> On Wed, Apr 22, 2020 at 7:26 PM Sean Christopherson
> <sean.j.christopherson@...el.com> wrote:
> >
> > Short circuit vmx_check_nested_events() if an exception is pending and
> > needs to be injected into L2, priority between coincident events is not
> > dependent on exiting behavior.  This fixes a bug where a single-step #DB
> > that is not intercepted by L1 is incorrectly dropped due to servicing a
> > VMX Preemption Timer VM-Exit.
> >
> > Injected exceptions also need to be blocked if nested VM-Enter is
> > pending or an exception was already injected, otherwise injecting the
> > exception could overwrite an existing event injection from L1.
> > Technically, this scenario should be impossible, i.e. KVM shouldn't
> > inject its own exception during nested VM-Enter.  This will be addressed
> > in a future patch.
> >
> > Note, event priority between SMI, NMI and INTR is incorrect for L2, e.g.
> > SMI should take priority over VM-Exit on NMI/INTR, and NMI that is
> > injected into L2 should take priority over VM-Exit INTR.  This will also
> > be addressed in a future patch.
> >
> > Fixes: b6b8a1451fc4 ("KVM: nVMX: Rework interception of IRQs and NMIs")
> > Reported-by: Jim Mattson <jmattson@...gle.com>
> > Cc: Oliver Upton <oupton@...gle.com>
> > Cc: Peter Shier <pshier@...gle.com>
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Reviewed-by: Jim Mattson <jmattson@...gle.com>
Reviewed-by: Oliver Upton <oupton@...gle.com>