Re: [PATCH for 8.1 v2 5/6] vdpa: move CVQ isolation check to net_init_vhost_vdpa

[Jason Wang <jasowang@redhat.com>]

On Fri, Mar 24, 2023 at 3:54 AM Eugenio Pérez <eperezma@redhat.com> wrote:
>
> Evaluating it at start time instead of initialization time may make the
> guest capable of dynamically adding or removing migration blockers.
>
> Also, moving to initialization reduces the number of ioctls in the
> migration, reducing failure possibilities.
>
> As a drawback we need to check for CVQ isolation twice: one time with no
> MQ negotiated and another one acking it, as long as the device supports
> it.  This is because Vring ASID / group management is based on vq
> indexes, but we don't know the index of CVQ before negotiating MQ.

We need to fail if we see a device that can isolate cvq without MQ but
not with MQ.

>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
> v2: Take out the reset of the device from vhost_vdpa_cvq_is_isolated
> ---
>  net/vhost-vdpa.c | 194 ++++++++++++++++++++++++++++++++++++-----------
>  1 file changed, 151 insertions(+), 43 deletions(-)
>
> diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> index 4397c0d4b3..db2c9afcb3 100644
> --- a/net/vhost-vdpa.c
> +++ b/net/vhost-vdpa.c
> @@ -43,6 +43,13 @@ typedef struct VhostVDPAState {
>
>      /* The device always have SVQ enabled */
>      bool always_svq;
> +
> +    /* The device can isolate CVQ in its own ASID if MQ is negotiated */
> +    bool cvq_isolated_mq;
> +
> +    /* The device can isolate CVQ in its own ASID if MQ is not negotiated */
> +    bool cvq_isolated;

As stated above, if we need a device that cvq_isolated_mq^cvq_isolated
== true, we need to fail. This may reduce the complexity of the code?

Thanks

> +
>      bool started;
>  } VhostVDPAState;
>
> @@ -361,15 +368,8 @@ static NetClientInfo net_vhost_vdpa_info = {
>          .check_peer_type = vhost_vdpa_check_peer_type,
>  };
>
> -/**
> - * Get vring virtqueue group
> - *
> - * @device_fd  vdpa device fd
> - * @vq_index   Virtqueue index
> - *
> - * Return -errno in case of error, or vq group if success.
> - */
> -static int64_t vhost_vdpa_get_vring_group(int device_fd, unsigned vq_index)
> +static int64_t vhost_vdpa_get_vring_group(int device_fd, unsigned vq_index,
> +                                          Error **errp)
>  {
>      struct vhost_vring_state state = {
>          .index = vq_index,
> @@ -378,8 +378,7 @@ static int64_t vhost_vdpa_get_vring_group(int device_fd, unsigned vq_index)
>
>      if (unlikely(r < 0)) {
>          r = -errno;
> -        error_report("Cannot get VQ %u group: %s", vq_index,
> -                     g_strerror(errno));
> +        error_setg_errno(errp, errno, "Cannot get VQ %u group", vq_index);
>          return r;
>      }
>
> @@ -479,9 +478,9 @@ static int vhost_vdpa_net_cvq_start(NetClientState *nc)
>  {
>      VhostVDPAState *s, *s0;
>      struct vhost_vdpa *v;
> -    uint64_t backend_features;
>      int64_t cvq_group;
> -    int cvq_index, r;
> +    int r;
> +    Error *err = NULL;
>
>      assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_VDPA);
>
> @@ -501,42 +500,29 @@ static int vhost_vdpa_net_cvq_start(NetClientState *nc)
>      /*
>       * If we early return in these cases SVQ will not be enabled. The migration
>       * will be blocked as long as vhost-vdpa backends will not offer _F_LOG.
> -     *
> -     * Calling VHOST_GET_BACKEND_FEATURES as they are not available in v->dev
> -     * yet.
>       */
> -    r = ioctl(v->device_fd, VHOST_GET_BACKEND_FEATURES, &backend_features);
> -    if (unlikely(r < 0)) {
> -        error_report("Cannot get vdpa backend_features: %s(%d)",
> -            g_strerror(errno), errno);
> -        return -1;
> -    }
> -    if (!(backend_features & BIT_ULL(VHOST_BACKEND_F_IOTLB_ASID)) ||
> -        !vhost_vdpa_net_valid_svq_features(v->dev->features, NULL)) {
> +    if (!vhost_vdpa_net_valid_svq_features(v->dev->features, NULL)) {
>          return 0;
>      }
>
> -    /*
> -     * Check if all the virtqueues of the virtio device are in a different vq
> -     * than the last vq. VQ group of last group passed in cvq_group.
> -     */
> -    cvq_index = v->dev->vq_index_end - 1;
> -    cvq_group = vhost_vdpa_get_vring_group(v->device_fd, cvq_index);
> -    if (unlikely(cvq_group < 0)) {
> -        return cvq_group;
> -    }
> -    for (int i = 0; i < cvq_index; ++i) {
> -        int64_t group = vhost_vdpa_get_vring_group(v->device_fd, i);
> -
> -        if (unlikely(group < 0)) {
> -            return group;
> +    if (v->dev->features & BIT_ULL(VIRTIO_NET_F_MQ)) {
> +        if (!s->cvq_isolated_mq) {
> +            return 0;
>          }
> -
> -        if (group == cvq_group) {
> +    } else {
> +        if (!s->cvq_isolated) {
>              return 0;
>          }
>      }
>
> +    cvq_group = vhost_vdpa_get_vring_group(v->device_fd,
> +                                           v->dev->vq_index_end - 1,
> +                                           &err);
> +    if (unlikely(cvq_group < 0)) {
> +        error_report_err(err);
> +        return cvq_group;
> +    }
> +
>      r = vhost_vdpa_set_address_space_id(v, cvq_group, VHOST_VDPA_NET_CVQ_ASID);
>      if (unlikely(r < 0)) {
>          return r;
> @@ -798,6 +784,116 @@ static const VhostShadowVirtqueueOps vhost_vdpa_net_svq_ops = {
>      .avail_handler = vhost_vdpa_net_handle_ctrl_avail,
>  };
>
> +/**
> + * Probe the device to check control virtqueue is isolated.
> + *
> + * @device_fd vhost-vdpa file descriptor
> + * @features features to negotiate
> + * @cvq_index Control vq index
> + *
> + * Returns -1 in case of error, 0 if false and 1 if true
> + */
> +static int vhost_vdpa_cvq_is_isolated(int device_fd, uint64_t features,
> +                                      unsigned cvq_index, Error **errp)
> +{
> +    int64_t cvq_group;
> +    int r;
> +
> +    r = vhost_vdpa_set_dev_features_fd(device_fd, features);
> +    if (unlikely(r < 0)) {
> +        error_setg_errno(errp, -r, "Cannot set device features");
> +        return r;
> +    }
> +
> +    cvq_group = vhost_vdpa_get_vring_group(device_fd, cvq_index, errp);
> +    if (unlikely(cvq_group < 0)) {
> +        return cvq_group;
> +    }
> +
> +    for (int i = 0; i < cvq_index; ++i) {
> +        int64_t group = vhost_vdpa_get_vring_group(device_fd, i, errp);
> +
> +        if (unlikely(group < 0)) {
> +            return group;
> +        }
> +
> +        if (group == (int64_t)cvq_group) {
> +            return 0;
> +        }
> +    }
> +
> +    return 1;
> +}
> +
> +/**
> + * Probe if CVQ is isolated when the device is MQ and when it is not MQ
> + *
> + * @device_fd         The vdpa device fd
> + * @features          Features offered by the device.
> + * @cvq_index         The control vq index if mq is negotiated. Ignored
> + *                    otherwise.
> + * @cvq_isolated      It'll be set to true if cvq is isolated if mq is not
> + *                    negotiated.
> + * @cvq_isolated_mq   It'll be set to true if cvq is isolated if mq is
> + *                    negotiated.
> + *
> + * Returns -1 in case of failure
> + */
> +static int vhost_vdpa_probe_cvq_isolation(int device_fd, uint64_t features,
> +                                          int cvq_index, bool *cvq_isolated,
> +                                          bool *cvq_isolated_mq, Error **errp)
> +{
> +    uint64_t backend_features;
> +    int r;
> +
> +    ERRP_GUARD();
> +
> +    *cvq_isolated = false;
> +    *cvq_isolated_mq = false;
> +    r = ioctl(device_fd, VHOST_GET_BACKEND_FEATURES, &backend_features);
> +    if (unlikely(r < 0)) {
> +        error_setg_errno(errp, errno, "Cannot get vdpa backend_features");
> +        return r;
> +    }
> +
> +    if (!(backend_features & BIT_ULL(VHOST_BACKEND_F_IOTLB_ASID))) {
> +        return 0;
> +    }
> +
> +    r = vhost_vdpa_cvq_is_isolated(device_fd,
> +                                   features & ~BIT_ULL(VIRTIO_NET_F_MQ), 2,
> +                                   errp);
> +    if (unlikely(r < 0)) {
> +        if (r == -ENOTSUP) {
> +            /*
> +             * The kernel report VHOST_BACKEND_F_IOTLB_ASID if the vdpa
> +             * frontend support ASID but the parent driver does not.  The CVQ
> +             * cannot be isolated in this case.
> +             */
> +            error_free(*errp);
> +            *errp = NULL;
> +            return 0;
> +        }
> +
> +        return r;
> +    }
> +
> +    *cvq_isolated = r == 1;
> +    vhost_vdpa_reset_status_fd(device_fd);
> +    if (!(features & BIT_ULL(VIRTIO_NET_F_MQ))) {
> +        return 0;
> +    }
> +
> +    r = vhost_vdpa_cvq_is_isolated(device_fd, features, cvq_index * 2, errp);
> +    if (unlikely(r < 0)) {
> +        return r;
> +    }
> +
> +    *cvq_isolated_mq = r == 1;
> +    vhost_vdpa_reset_status_fd(device_fd);
> +    return 0;
> +}
> +
>  static NetClientState *net_vhost_vdpa_init(NetClientState *peer,
>                                         const char *device,
>                                         const char *name,
> @@ -807,16 +903,26 @@ static NetClientState *net_vhost_vdpa_init(NetClientState *peer,
>                                         bool is_datapath,
>                                         bool svq,
>                                         struct vhost_vdpa_iova_range iova_range,
> -                                       uint64_t features)
> +                                       uint64_t features,
> +                                       Error **errp)
>  {
>      NetClientState *nc = NULL;
>      VhostVDPAState *s;
>      int ret = 0;
>      assert(name);
> +    bool cvq_isolated, cvq_isolated_mq;
> +
>      if (is_datapath) {
>          nc = qemu_new_net_client(&net_vhost_vdpa_info, peer, device,
>                                   name);
>      } else {
> +        ret = vhost_vdpa_probe_cvq_isolation(vdpa_device_fd, features,
> +                                             queue_pair_index, &cvq_isolated,
> +                                             &cvq_isolated_mq, errp);
> +        if (unlikely(ret)) {
> +            return NULL;
> +        }
> +
>          nc = qemu_new_net_control_client(&net_vhost_vdpa_cvq_info, peer,
>                                           device, name);
>      }
> @@ -843,6 +949,8 @@ static NetClientState *net_vhost_vdpa_init(NetClientState *peer,
>
>          s->vhost_vdpa.shadow_vq_ops = &vhost_vdpa_net_svq_ops;
>          s->vhost_vdpa.shadow_vq_ops_opaque = s;
> +        s->cvq_isolated = cvq_isolated;
> +        s->cvq_isolated_mq = cvq_isolated_mq;
>
>          /*
>           * TODO: We cannot migrate devices with CVQ as there is no way to set
> @@ -971,7 +1079,7 @@ int net_init_vhost_vdpa(const Netdev *netdev, const char *name,
>      for (i = 0; i < queue_pairs; i++) {
>          ncs[i] = net_vhost_vdpa_init(peer, TYPE_VHOST_VDPA, name,
>                                       vdpa_device_fd, i, 2, true, opts->x_svq,
> -                                     iova_range, features);
> +                                     iova_range, features, errp);
>          if (!ncs[i])
>              goto err;
>      }
> @@ -979,7 +1087,7 @@ int net_init_vhost_vdpa(const Netdev *netdev, const char *name,
>      if (has_cvq) {
>          nc = net_vhost_vdpa_init(peer, TYPE_VHOST_VDPA, name,
>                                   vdpa_device_fd, i, 1, false,
> -                                 opts->x_svq, iova_range, features);
> +                                 opts->x_svq, iova_range, features, errp);
>          if (!nc)
>              goto err;
>      }
> --
> 2.31.1
>