Re: [PATCH 05/31] vhost: Add Shadow VirtQueue kick forwarding capabilities

[Jason Wang <jasowang@redhat.com>]

在 2022/1/22 上午4:27, Eugenio Pérez 写道:
> At this mode no buffer forwarding will be performed in SVQ mode: Qemu
> will just forward the guest's kicks to the device.
>
> Also, host notifiers must be disabled at SVQ start, and they will not
> start if SVQ has been enabled when the device is stopped. This will be
> addressed in next patches.


We need to disable host_notifier_mr as well, otherwise guest may touch 
the hardware doorbell directly without going through eventfd.


>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>   hw/virtio/vhost-shadow-virtqueue.h |  2 ++
>   hw/virtio/vhost-shadow-virtqueue.c | 27 ++++++++++++++++++++++++++-
>   2 files changed, 28 insertions(+), 1 deletion(-)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.h b/hw/virtio/vhost-shadow-virtqueue.h
> index a56ecfc09d..4c583a9171 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.h
> +++ b/hw/virtio/vhost-shadow-virtqueue.h
> @@ -19,6 +19,8 @@ void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd);
>   const EventNotifier *vhost_svq_get_dev_kick_notifier(
>                                                 const VhostShadowVirtqueue *svq);
>   
> +void vhost_svq_stop(VhostShadowVirtqueue *svq);
> +
>   VhostShadowVirtqueue *vhost_svq_new(void);
>   
>   void vhost_svq_free(VhostShadowVirtqueue *vq);
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
> index 21534bc94d..8991f0b3c3 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -42,11 +42,26 @@ const EventNotifier *vhost_svq_get_dev_kick_notifier(
>       return &svq->hdev_kick;
>   }
>   
> +/* Forward guest notifications */
> +static void vhost_handle_guest_kick(EventNotifier *n)
> +{
> +    VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue,
> +                                             svq_kick);
> +
> +    if (unlikely(!event_notifier_test_and_clear(n))) {
> +        return;
> +    }
> +
> +    event_notifier_set(&svq->hdev_kick);
> +}
> +
>   /**
>    * Set a new file descriptor for the guest to kick SVQ and notify for avail
>    *
>    * @svq          The svq
> - * @svq_kick_fd  The new svq kick fd
> + * @svq_kick_fd  The svq kick fd
> + *
> + * Note that SVQ will never close the old file descriptor.
>    */
>   void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd)
>   {
> @@ -65,12 +80,22 @@ void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd)
>        * need to explicitely check for them.
>        */
>       event_notifier_init_fd(&svq->svq_kick, svq_kick_fd);
> +    event_notifier_set_handler(&svq->svq_kick, vhost_handle_guest_kick);
>   
>       if (!check_old || event_notifier_test_and_clear(&tmp)) {
>           event_notifier_set(&svq->hdev_kick);
>       }
>   }
>   
> +/**
> + * Stop shadow virtqueue operation.
> + * @svq Shadow Virtqueue
> + */
> +void vhost_svq_stop(VhostShadowVirtqueue *svq)
> +{
> +    event_notifier_set_handler(&svq->svq_kick, NULL);
> +}


This function is not used in the patch.

Thanks


> +
>   /**
>    * Creates vhost shadow virtqueue, and instruct vhost device to use the shadow
>    * methods and file descriptors.

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