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

[Michael S. Tsirkin]

On Thu, May 14, 2020 at 04:39:26PM +0200, Maxime Coquelin wrote:
> 
> 
> On 5/14/20 12:51 PM, Michael S. Tsirkin wrote:
> > On Thu, May 14, 2020 at 12:14:32PM +0200, Maxime Coquelin wrote:
> >>
> >>
> >> On 5/14/20 9:53 AM, Jason Wang wrote:
> >>>
> >>> On 2020/5/14 下午3:33, 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 <address@hidden>
> >>>> ---
> >>>>
> >>>> 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);
> >>>> +    }
> >>>> +
> >>>> +    return 0;
> >>>> +}
> >>>
> >>>
> >>> Interesting, I wonder how vm stop will be handled in this case.
> >>
> >> For now, my DPDK series only use DRIVER_OK to help determine when the
> >> driver is done with the initialization. For VM stop, it still relies on
> >> GET_VRING_BASE.
> > 
> > Sounds like a good fit.
> > GET_VRING_BASE is transparent to guest, as is vmstop.
> > This is more for driver 
> > 
> > 
> >>
> >> GET_VRING_BASE arrives before DRIVER_OK bit is cleared is the tests I've
> >> done (logs from backend side):
> > 
> > 
> > One problem is with legacy guests, for these you can't rely
> > on DRIVER_OK, they often kick before that, and sometimes
> > expect buffers to be used too (e.g. for scsi).
> 
> Ok, I remember this case now.
> Any idea on how the backend would detect such legacy guests?

It's mostly safe to assume that it's only the case for pre-1.0 since 1.0
spec says you must not.  A small window after 1.0 has the bug too but I
think it's safe to just ask that these guests are fixed.


> If I'm not mistaken, we discussed the idea to poll on the kick to detect
> the rings are ready to be processed. But the problem is that Qemu writes
> a kick at eventfd creation time:
> 
> vhost_user_backend_start():
> -> vhost_dev_enable_notifiers()
>       ->virtio_bus_set_host_notifier()
>               ->event_notifier_init(, 1); //1 means active
> ->vhost_dev_start();
> 
> We could change the behavior in Qemu, but the backend won't know if
> Qemu has the fix or not, so won't know if it can rely on the kick.

eventfd counts kicks. So you can read the counter and check whether
there was another kick or not. The difficulty is around migration, we
should migrate the "ring kicked" state but we don't. We really should
just fix that, it's an old bug affecting not just vhost-user but
vhost too.


> >>
> >> VHOST_CONFIG: read message VHOST_USER_GET_VRING_BASE
> >>
> >> destroy port /tmp/vhost-user1, did: 0
> >> VHOST_CONFIG: vring base idx:0 file:41
> >> VHOST_CONFIG: read message VHOST_USER_GET_VRING_BASE
> >> VHOST_CONFIG: vring base idx:1 file:0
> >> VHOST_CONFIG: read message VHOST_USER_SET_STATUS
> >> VHOST_CONFIG: New device status(0x0000000b):
> >>    -ACKNOWLEDGE: 1
> >>    -DRIVER: 1
> >>    -FEATURES_OK: 1
> >>    -DRIVER_OK: 0
> >>    -DEVICE_NEED_RESET: 0
> >>    -FAILED: 0
> >>
> >>> In the case of vDPA kernel, we probable don't want to mirror the virtio
> >>> device status to vdpa device status directly.
> >>
> >> In vDPA DPDK, we don't mirror the Virtio device status either. It could
> >> make sense to do that, but would require some API changes.
> >>
> >>> Since qemu may stop
> >>> vhost-vdpa device through e.g resting vdpa device, but in the mean time,
> >>> guest should not detect such condition in virtio device status.
> >>
> >>
> >>
> >>> So in the new version of vDPA support, we probably need to do:
> >>>
> >>> static int vhost_vdpa_set_state(struct vhost_dev *dev, bool started)
> >>> {
> >>>     if (started) {
> >>>         uint8_t status = 0;
> >>>
> >>>         vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_DRIVER_OK);
> >>>         vhost_vdpa_call(dev, VHOST_VDPA_GET_STATUS, &status);
> >>>
> >>>         return !(status & VIRTIO_CONFIG_S_DRIVER_OK);
> >>>     } else {
> >>>         vhost_vdpa_reset_device(dev);
> >>>         vhost_vdpa_add_status(dev, VIRTIO_CONFIG_S_ACKNOWLEDGE |
> >>>                                    VIRTIO_CONFIG_S_DRIVER);
> >>>         return 0;
> >>>     }
> >>> }
> >>
> >> IIUC, you have another copy of the status register not matching 1:1 what
> >> the guest sets/sees.
> >>
> >> Is vhost_vdpa_add_status() sending VHOST_VDPA_SET_STATUS to the backend?
> >>
> >> And why reading back the status from the backend? Just to confirm the
> >> change is taken into account?
> > 
> > Making sure features have been acked makes sense IMHO.
> > 
> > 
> >>> And vhost_set_state() will be called from vhost_dev_start()/stop().
> >>>
> >>> Does this work for vhost-user as well?
> >>
> >> IIUC what you did above, I think it would work. And we won't need
> >> GET_STATUS request, but just rely on the REPLY_ACK.
> > 
> > Right. Need to document that though.
> 
> Ok, will do in v2.
> 
> Thanks,
> Maxime
> 
> > 
> >>
> >> Thanks,
> >> Maxime
> >>
> >>> Thanks
> >>>
> >>>
> >>>> +
> >>>>   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,
> >>>>   };
> >