Re: [PATCH] vhost-user: add support for VHOST_USER_SET_STATUS

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, May 14, 2020 at 04:12:32PM +0200, Maxime Coquelin wrote:
> 
> 
> 
> On 5/14/20 12:44 PM, Michael S. Tsirkin wrote:
> > On Thu, May 14, 2020 at 09:33:32AM +0200, Maxime Coquelin wrote:
> >> It is usefull for the Vhost-user backend to know
> >> about about the Virtio device status updates,
> >> especially when the driver sets the DRIVER_OK bit.
> >>
> >> With that information, no more need to do hazardous
> >> assumptions on when the driver is done with the
> >> device configuration.
> >>
> >> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> >> ---
> >>
> >> This patch applies on top of Cindy's "vDPA support in qemu"
> >> series, which introduces the .vhost_set_state vhost-backend
> >> ops.
> >>
> >>  docs/interop/vhost-user.rst | 12 ++++++++++++
> >>  hw/net/vhost_net.c          | 10 +++++-----
> >>  hw/virtio/vhost-user.c      | 35 +++++++++++++++++++++++++++++++++++
> >>  3 files changed, 52 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
> >> index 3b1b6602c7..f108de7458 100644
> >> --- a/docs/interop/vhost-user.rst
> >> +++ b/docs/interop/vhost-user.rst
> >> @@ -815,6 +815,7 @@ Protocol features
> >>    #define VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD       12
> >>    #define VHOST_USER_PROTOCOL_F_RESET_DEVICE         13
> >>    #define VHOST_USER_PROTOCOL_F_INBAND_NOTIFICATIONS 14
> >> +  #define VHOST_USER_PROTOCOL_F_STATUS               15
> >>  
> >>  Master message types
> >>  --------------------
> >> @@ -1263,6 +1264,17 @@ Master message types
> >>  
> >>    The state.num field is currently reserved and must be set to 0.
> >>  
> >> +``VHOST_USER_SET_STATUS``
> >> +  :id: 36
> >> +  :equivalent ioctl: VHOST_VDPA_SET_STATUS
> >> +  :slave payload: N/A
> >> +  :master payload: ``u64``
> >> +
> >> +  When the ``VHOST_USER_PROTOCOL_F_STATUS`` protocol feature has been
> >> +  successfully negotiated, this message is submitted by the master to
> >> +  notify the backend with updated device status as defined in the Virtio
> >> +  specification.
> >> +
> >>  Slave message types
> >>  -------------------
> >>  
> >> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> >> index 463e333531..37f3156dbc 100644
> >> --- a/hw/net/vhost_net.c
> >> +++ b/hw/net/vhost_net.c
> >> @@ -517,10 +517,10 @@ int vhost_set_state(NetClientState *nc, int state)
> >>  {
> >>      struct vhost_net *net = get_vhost_net(nc);
> >>      struct vhost_dev *hdev = &net->dev;
> >> -    if (nc->info->type == NET_CLIENT_DRIVER_VHOST_VDPA) {
> >> -        if (hdev->vhost_ops->vhost_set_state) {
> >> -                return hdev->vhost_ops->vhost_set_state(hdev, state);
> >> -             }
> >> -        }
> >> +
> >> +    if (hdev->vhost_ops->vhost_set_state) {
> >> +        return hdev->vhost_ops->vhost_set_state(hdev, state);
> >> +    }
> >> +
> >>      return 0;
> >>  }
> >> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> >> index ec21e8fbe8..b7e52d97fc 100644
> >> --- a/hw/virtio/vhost-user.c
> >> +++ b/hw/virtio/vhost-user.c
> >> @@ -59,6 +59,7 @@ enum VhostUserProtocolFeature {
> >>      VHOST_USER_PROTOCOL_F_HOST_NOTIFIER = 11,
> >>      VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD = 12,
> >>      VHOST_USER_PROTOCOL_F_RESET_DEVICE = 13,
> >> +    VHOST_USER_PROTOCOL_F_STATUS = 15,
> >>      VHOST_USER_PROTOCOL_F_MAX
> >>  };
> >>  
> >> @@ -100,6 +101,7 @@ typedef enum VhostUserRequest {
> >>      VHOST_USER_SET_INFLIGHT_FD = 32,
> >>      VHOST_USER_GPU_SET_SOCKET = 33,
> >>      VHOST_USER_RESET_DEVICE = 34,
> >> +    VHOST_USER_SET_STATUS = 36,
> >>      VHOST_USER_MAX
> >>  } VhostUserRequest;
> >>  
> >> @@ -1886,6 +1888,38 @@ static int vhost_user_set_inflight_fd(struct vhost_dev *dev,
> >>      return 0;
> >>  }
> >>  
> >> +static int vhost_user_set_state(struct vhost_dev *dev, int state)
> >> +{
> >> +    bool reply_supported = virtio_has_feature(dev->protocol_features,
> >> +                                              VHOST_USER_PROTOCOL_F_REPLY_ACK);
> >> +
> >> +    VhostUserMsg msg = {
> >> +        .hdr.request = VHOST_USER_SET_STATUS,
> >> +        .hdr.flags = VHOST_USER_VERSION,
> >> +        .hdr.size = sizeof(msg.payload.u64),
> >> +        .payload.u64 = (uint64_t)state,
> >> +    };
> >> +
> >> +    if (!virtio_has_feature(dev->protocol_features,
> >> +                VHOST_USER_PROTOCOL_F_STATUS)) {
> >> +        return -1;
> >> +    }
> >> +
> >> +    if (reply_supported) {
> >> +        msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK;
> >> +    }
> >> +
> >> +    if (vhost_user_write(dev, &msg, NULL, 0) < 0) {
> >> +        return -1;
> >> +    }
> >> +
> >> +    if (reply_supported) {
> >> +        return process_message_reply(dev, &msg);
> >> +    }
> > 
> > So since we are doing this anyway, let's give backend the opportunity
> > to validate features and fail FEATURES_OK?
> 
> Just to be sure I understand, the feature negotiation happens,
> then when the backend receives FEATURES_OK, it uses the REPLY_ACK
> protocol feature to NACK?

Or ack but clear FEATURES_OK in the response.

> 
> In DPDK backend, we already check the feature set by SET_FEATURES are
> supported by the backend.

But that assumes all possible combinations of features in the bitmap
always work. That might not be the case.

> If it is not the case, either the master did
> set NEED_REPLY flag and error would be reported to the master, or the
> NEED_REPLY flag isn't set in the message and the backend disconnects.
> 
> Looking at Qemu side, it does not seem to set the NEED_REPLY flag on
> SET_FEATURES, so basically the backend close the sockets if it happened.

That is not the best ay to handle that imho.

> 
> I wonder whether it would be better for Qemu to set the NEED_REPLY flag
> on SET_FEATURES, so that when the backend is running and VHOST_F_LOG_ALL
> feature bit is set, we are the sure the master starts the live-migration
> only once the SET_FEATURES is fully handled on backend side.
> 
> What do you think?

features are set before backend is started so there's nothing to
migrate really.

> 
> >> +
> >> +    return 0;
> >> +}
> >> +
> >>  bool vhost_user_init(VhostUserState *user, CharBackend *chr, Error **errp)
> >>  {
> >>      if (user->chr) {
> >> @@ -1947,4 +1981,5 @@ const VhostOps user_ops = {
> >>          .vhost_backend_mem_section_filter = vhost_user_mem_section_filter,
> >>          .vhost_get_inflight_fd = vhost_user_get_inflight_fd,
> >>          .vhost_set_inflight_fd = vhost_user_set_inflight_fd,
> >> +        .vhost_set_state = vhost_user_set_state,
> >>  };
> >> -- 
> >> 2.25.4
> >