Re: [PATCH v2 04/13] vdpa: move vhost reset after get vring base

[Jason Wang <jasowang@redhat.com>]

在 2023/2/8 17:42, Eugenio Pérez 写道:
> The function vhost.c:vhost_dev_stop calls vhost operation
> vhost_dev_start(false). In the case of vdpa it totally reset and wipes
> the device, making the fetching of the vring base (virtqueue state) totally
> useless.
>
> The kernel backend does not use vhost_dev_start vhost op callback, but
> vhost-user do. A patch to make vhost_user_dev_start more similar to vdpa
> is desirable, but it can be added on top.
>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>   include/hw/virtio/vhost-backend.h |  4 ++++
>   hw/virtio/vhost-vdpa.c            | 22 ++++++++++++++++------
>   hw/virtio/vhost.c                 |  3 +++
>   3 files changed, 23 insertions(+), 6 deletions(-)
>
> diff --git a/include/hw/virtio/vhost-backend.h b/include/hw/virtio/vhost-backend.h
> index c5ab49051e..ec3fbae58d 100644
> --- a/include/hw/virtio/vhost-backend.h
> +++ b/include/hw/virtio/vhost-backend.h
> @@ -130,6 +130,9 @@ typedef bool (*vhost_force_iommu_op)(struct vhost_dev *dev);
>   
>   typedef int (*vhost_set_config_call_op)(struct vhost_dev *dev,
>                                          int fd);
> +
> +typedef void (*vhost_reset_status_op)(struct vhost_dev *dev);
> +
>   typedef struct VhostOps {
>       VhostBackendType backend_type;
>       vhost_backend_init vhost_backend_init;
> @@ -177,6 +180,7 @@ typedef struct VhostOps {
>       vhost_get_device_id_op vhost_get_device_id;
>       vhost_force_iommu_op vhost_force_iommu;
>       vhost_set_config_call_op vhost_set_config_call;
> +    vhost_reset_status_op vhost_reset_status;
>   } VhostOps;
>   
>   int vhost_backend_update_device_iotlb(struct vhost_dev *dev,
> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> index cbbe92ffe8..26e38a6aab 100644
> --- a/hw/virtio/vhost-vdpa.c
> +++ b/hw/virtio/vhost-vdpa.c
> @@ -1152,14 +1152,23 @@ static int vhost_vdpa_dev_start(struct vhost_dev *dev, bool started)
>       if (started) {
>           memory_listener_register(&v->listener, &address_space_memory);
>           return vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
> -    } else {
> -        vhost_vdpa_reset_device(dev);
> -        vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE |
> -                                   VIRTIO_CONFIG_S_DRIVER);
> -        memory_listener_unregister(&v->listener);
> +    }
>   
> -        return 0;
> +    return 0;
> +}
> +
> +static void vhost_vdpa_reset_status(struct vhost_dev *dev)
> +{
> +    struct vhost_vdpa *v = dev->opaque;
> +
> +    if (dev->vq_index + dev->nvqs != dev->vq_index_end) {
> +        return;
>       }
> +
> +    vhost_vdpa_reset_device(dev);
> +    vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE |
> +                                VIRTIO_CONFIG_S_DRIVER);
> +    memory_listener_unregister(&v->listener);
>   }
>   
>   static int vhost_vdpa_set_log_base(struct vhost_dev *dev, uint64_t base,
> @@ -1346,4 +1355,5 @@ const VhostOps vdpa_ops = {
>           .vhost_vq_get_addr = vhost_vdpa_vq_get_addr,
>           .vhost_force_iommu = vhost_vdpa_force_iommu,
>           .vhost_set_config_call = vhost_vdpa_set_config_call,
> +        .vhost_reset_status = vhost_vdpa_reset_status,
>   };
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index eb8c4c378c..a266396576 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -2049,6 +2049,9 @@ void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev, bool vrings)
>                                hdev->vqs + i,
>                                hdev->vq_index + i);
>       }
> +    if (hdev->vhost_ops->vhost_reset_status) {
> +        hdev->vhost_ops->vhost_reset_status(hdev);
> +    }


This looks racy, if we don't suspend/reset the device, device can move 
last_avail_idx even after get_vring_base()?

Instead of doing things like this, should we fallback to 
virtio_queue_restore_last_avail_idx() in this case?

Thanks


>   
>       if (vhost_dev_has_iommu(hdev)) {
>           if (hdev->vhost_ops->vhost_set_iotlb_callback) {