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

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Date:   Tue, 28 Apr 2020 11:54:35 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     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>,
        Oliver Upton <oupton@...gle.com>,
        Peter Shier <pshier@...gle.com>
Subject: Re: [PATCH 01/13] KVM: nVMX: Preserve exception priority irrespective
 of exiting behavior

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>