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    Subject[PATCH 6.0 175/862] KVM: nVMX: Unconditionally purge queued/injected events on nested "exit"
    Date
    From: Sean Christopherson <seanjc@google.com>

    commit d953540430c5af57f5de97ea9e36253908204027 upstream.

    Drop pending exceptions and events queued for re-injection when leaving
    nested guest mode, even if the "exit" is due to VM-Fail, SMI, or forced
    by host userspace. Failure to purge events could result in an event
    belonging to L2 being injected into L1.

    This _should_ never happen for VM-Fail as all events should be blocked by
    nested_run_pending, but it's possible if KVM, not the L1 hypervisor, is
    the source of VM-Fail when running vmcs02.

    SMI is a nop (barring unknown bugs) as recognition of SMI and thus entry
    to SMM is blocked by pending exceptions and re-injected events.

    Forced exit is definitely buggy, but has likely gone unnoticed because
    userspace probably follows the forced exit with KVM_SET_VCPU_EVENTS (or
    some other ioctl() that purges the queue).

    Fixes: 4f350c6dbcb9 ("kvm: nVMX: Handle deferred early VMLAUNCH/VMRESUME failure properly")
    Cc: stable@vger.kernel.org
    Signed-off-by: Sean Christopherson <seanjc@google.com>
    Reviewed-by: Jim Mattson <jmattson@google.com>
    Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
    Link: https://lore.kernel.org/r/20220830231614.3580124-2-seanjc@google.com
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/x86/kvm/vmx/nested.c | 19 +++++++++++--------
    1 file changed, 11 insertions(+), 8 deletions(-)

    --- a/arch/x86/kvm/vmx/nested.c
    +++ b/arch/x86/kvm/vmx/nested.c
    @@ -4255,14 +4255,6 @@ static void prepare_vmcs12(struct kvm_vc
    nested_vmx_abort(vcpu,
    VMX_ABORT_SAVE_GUEST_MSR_FAIL);
    }
    -
    - /*
    - * Drop what we picked up for L2 via vmx_complete_interrupts. It is
    - * preserved above and would only end up incorrectly in L1.
    - */
    - vcpu->arch.nmi_injected = false;
    - kvm_clear_exception_queue(vcpu);
    - kvm_clear_interrupt_queue(vcpu);
    }

    /*
    @@ -4602,6 +4594,17 @@ void nested_vmx_vmexit(struct kvm_vcpu *
    WARN_ON_ONCE(nested_early_check);
    }

    + /*
    + * Drop events/exceptions that were queued for re-injection to L2
    + * (picked up via vmx_complete_interrupts()), as well as exceptions
    + * that were pending for L2. Note, this must NOT be hoisted above
    + * prepare_vmcs12(), events/exceptions queued for re-injection need to
    + * be captured in vmcs12 (see vmcs12_save_pending_event()).
    + */
    + vcpu->arch.nmi_injected = false;
    + kvm_clear_exception_queue(vcpu);
    + kvm_clear_interrupt_queue(vcpu);
    +
    vmx_switch_vmcs(vcpu, &vmx->vmcs01);

    /* Update any VMCS fields that might have changed while L2 ran */

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