Re: [PATCH RESEND v3] vdpa: reset the backend device in the end of vhost_net_stop()

[Si-Wei Liu]

On 3/31/2022 2:25 AM, qiudayu@archeros.com wrote:
> From: Michael Qiu <qiudayu@archeros.com>
>
> Currently, when VM poweroff, it will trigger vdpa
> device(such as mlx bluefield2 VF) reset many times(with 1 datapath
> queue pair and one control queue, triggered 3 times), this
> leads to below issue:
>
> vhost VQ 2 ring restore failed: -22: Invalid argument (22)
>
> This because in vhost_net_stop(), it will stop all vhost device bind to
> this virtio device, and in vhost_dev_stop(), qemu tries to stop the device
> , then stop the queue: vhost_virtqueue_stop().
>
> In vhost_dev_stop(), it resets the device, which clear some flags
> in low level driver, and in next loop(stop other vhost backends),
> qemu try to stop the queue corresponding to the vhost backend,
>   the driver finds that the VQ is invalied, this is the root cause.
>
> To solve the issue, vdpa should set vring unready, and
> remove reset ops in device stop: vhost_dev_start(hdev, false).
>
> and implement a new function vhost_dev_reset, only reset backend
> device after all vhost(per-queue) stoped.
>
> Signed-off-by: Michael Qiu<qiudayu@archeros.com>
> Acked-by: Jason Wang <jasowang@redhat.com>
> ---
> v3 --> v2:
>      Call vhost_dev_reset() at the end of vhost_net_stop().
>
>      Since the vDPA device need re-add the status bit
>      VIRTIO_CONFIG_S_ACKNOWLEDGE and VIRTIO_CONFIG_S_DRIVER,
>      simply, add them inside vhost_vdpa_reset_device, and
>      the only way calling vhost_vdpa_reset_device is in
>      vhost_net_stop(), so it keeps the same behavior as before.
>
> v2 --> v1:
>     Implement a new function vhost_dev_reset,
>     reset the backend kernel device at last.
> ---
>   hw/net/vhost_net.c        | 24 +++++++++++++++++++++---
>   hw/virtio/vhost-vdpa.c    | 15 +++++++++------
>   hw/virtio/vhost.c         | 15 ++++++++++++++-
>   include/hw/virtio/vhost.h |  1 +
>   4 files changed, 45 insertions(+), 10 deletions(-)
>
> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> index 30379d2..422c9bf 100644
> --- a/hw/net/vhost_net.c
> +++ b/hw/net/vhost_net.c
> @@ -325,7 +325,7 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
>       int total_notifiers = data_queue_pairs * 2 + cvq;
>       VirtIONet *n = VIRTIO_NET(dev);
>       int nvhosts = data_queue_pairs + cvq;
> -    struct vhost_net *net;
> +    struct vhost_net *net = NULL;
>       int r, e, i, index_end = data_queue_pairs * 2;
>       NetClientState *peer;
>   
> @@ -391,8 +391,17 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
>   err_start:
>       while (--i >= 0) {
>           peer = qemu_get_peer(ncs , i);
> -        vhost_net_stop_one(get_vhost_net(peer), dev);
> +
> +        net = get_vhost_net(peer);
> +
> +        vhost_net_stop_one(net, dev);
>       }
> +
> +    /* We only reset backend vdpa device */
> +    if (net && net->dev.vhost_ops->backend_type == VHOST_BACKEND_TYPE_VDPA) {
I would reset the device anyway regardless the first vhost_dev. Some 
ioctl calls may have well changed device state in vhost_dev_start() that 
has no way to get back than reset.

> +        vhost_dev_reset(&net->dev);
I would move this to the end as it's more sensible to reset the device 
after guest notifier is disabled.
> +    }
> +
>       e = k->set_guest_notifiers(qbus->parent, total_notifiers, false);
>       if (e < 0) {
>           fprintf(stderr, "vhost guest notifier cleanup failed: %d\n", e);
> @@ -410,6 +419,7 @@ void vhost_net_stop(VirtIODevice *dev, NetClientState *ncs,
>       VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(vbus);
>       VirtIONet *n = VIRTIO_NET(dev);
>       NetClientState *peer;
> +    struct vhost_net *net = NULL;
>       int total_notifiers = data_queue_pairs * 2 + cvq;
>       int nvhosts = data_queue_pairs + cvq;
>       int i, r;
> @@ -420,7 +430,15 @@ void vhost_net_stop(VirtIODevice *dev, NetClientState *ncs,
>           } else {
>               peer = qemu_get_peer(ncs, n->max_queue_pairs);
>           }
> -        vhost_net_stop_one(get_vhost_net(peer), dev);
> +
> +        net = get_vhost_net(peer);
> +
> +        vhost_net_stop_one(net, dev);
> +    }
> +
> +    /* We only reset backend vdpa device */
> +    if (net && net->dev.vhost_ops->backend_type == VHOST_BACKEND_TYPE_VDPA) {
Yikes, I think it needs some code refactoring here without having to 
check VHOST_BACKEND_TYPE_VDPA explicitly. Historically the 
.vhost_reset_device() op was misnamed: it was initially meant for 
RESET_OWNER but never got used. Could you add a new .vhost_reset_owner() 
op to VhostOps (via another patch) and rename properly, e.g. from 
vhost_kernel_reset_device() to vhost_kernel_reset_owner()? For 
vhost_user_reset_device(), you can safely factor out the 
VHOST_USER_RESET_OWNER case to a new vhost_user_reset_owner() function, 
and only reset the device in vhost_user_reset_device() depending on the 
VHOST_USER_PROTOCOL_F_RESET_DEVICE protocol feature.

With this change, vhost_reset_device will be effectively a no-op on 
vhost_kernel (NULL) and vhost_user (only applicable to vhost-user-scsi 
backend which supports VHOST_USER_PROTOCOL_F_RESET_DEVICE).
> +        vhost_dev_reset(&net->dev);
I would move this to the end as it's more sensible to reset the device 
after guest notifier is disabled.

>       }
>   
>       r = k->set_guest_notifiers(qbus->parent, total_notifiers, false);
> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> index c5ed7a3..3ef0199 100644
> --- a/hw/virtio/vhost-vdpa.c
> +++ b/hw/virtio/vhost-vdpa.c
> @@ -708,6 +708,11 @@ static int vhost_vdpa_reset_device(struct vhost_dev *dev)
>   
>       ret = vhost_vdpa_call(dev, VHOST_VDPA_SET_STATUS, &status);
>       trace_vhost_vdpa_reset_device(dev, status);
> +
> +    /* Add back this status, so that the device could work next time*/
> +    vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE |
> +                               VIRTIO_CONFIG_S_DRIVER);
> +
Hmmm, this might not be the ideal place, but I'm fine to leave it as-is. 
It would need some more future work in code refactoring for e.g. live 
migration and error recovery.

Thanks,
-Siwei

>       return ret;
>   }
>   
> @@ -719,14 +724,14 @@ static int vhost_vdpa_get_vq_index(struct vhost_dev *dev, int idx)
>       return idx;
>   }
>   
> -static int vhost_vdpa_set_vring_ready(struct vhost_dev *dev)
> +static int vhost_vdpa_set_vring_ready(struct vhost_dev *dev, unsigned int 
> ready)
>   {
>       int i;
>       trace_vhost_vdpa_set_vring_ready(dev);
>       for (i = 0; i < dev->nvqs; ++i) {
>           struct vhost_vring_state state = {
>               .index = dev->vq_index + i,
> -            .num = 1,
> +            .num = ready,
>           };
>           vhost_vdpa_call(dev, VHOST_VDPA_SET_VRING_ENABLE, &state);
>       }
> @@ -1088,8 +1093,9 @@ static int vhost_vdpa_dev_start(struct vhost_dev *dev, 
> bool started)
>           if (unlikely(!ok)) {
>               return -1;
>           }
> -        vhost_vdpa_set_vring_ready(dev);
> +        vhost_vdpa_set_vring_ready(dev, 1);
>       } else {
> +        vhost_vdpa_set_vring_ready(dev, 0);
>           ok = vhost_vdpa_svqs_stop(dev);
>           if (unlikely(!ok)) {
>               return -1;
> @@ -1105,9 +1111,6 @@ static int vhost_vdpa_dev_start(struct vhost_dev *dev, 
> bool 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;
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index b643f42..7e0cdb6 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -1820,7 +1820,6 @@ fail_features:
>   void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev)
>   {
>       int i;
> -
>       /* should only be called after backend is connected */
>       assert(hdev->vhost_ops);
>   
> @@ -1854,3 +1853,17 @@ int vhost_net_set_backend(struct vhost_dev *hdev,
>   
>       return -ENOSYS;
>   }
> +
> +int vhost_dev_reset(struct vhost_dev *hdev)
> +{
> +    int ret = 0;
> +
> +    /* should only be called after backend is connected */
> +    assert(hdev->vhost_ops);
> +
> +    if (hdev->vhost_ops->vhost_reset_device) {
> +        ret = hdev->vhost_ops->vhost_reset_device(hdev);
> +    }
> +
> +    return ret;
> +}
> diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
> index 58a73e7..b8b7c20 100644
> --- a/include/hw/virtio/vhost.h
> +++ b/include/hw/virtio/vhost.h
> @@ -114,6 +114,7 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
>   void vhost_dev_cleanup(struct vhost_dev *hdev);
>   int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev);
>   void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev);
> +int vhost_dev_reset(struct vhost_dev *hdev);
>   int vhost_dev_enable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev);
>   void vhost_dev_disable_notifiers(struct vhost_dev *hdev, VirtIODevice *vdev);
>