Re: [Qemu-devel] [RFC 3/3] vhost-user: support programming VFIO group in master

[Michael S. Tsirkin]

On Mon, Jul 23, 2018 at 12:59:56PM +0800, Tiwei Bie wrote:
> Introduce a slave message to allow slave to share its
> VFIO group fd to master and do the IOMMU programming
> based on virtio device's DMA address space for this
> group in QEMU.
> 
> For the vhost backends which support vDPA, they could
> leverage this message to ask master to do the IOMMU
> programming in QEMU for the vDPA device in backend.
> 
> Signed-off-by: Tiwei Bie <address@hidden>
> ---
>  docs/interop/vhost-user.txt    | 16 ++++++++++++++
>  hw/virtio/vhost-user.c         | 40 ++++++++++++++++++++++++++++++++++
>  include/hw/virtio/vhost-user.h |  2 ++
>  3 files changed, 58 insertions(+)
> 
> diff --git a/docs/interop/vhost-user.txt b/docs/interop/vhost-user.txt
> index f59667f498..a57a8f9451 100644
> --- a/docs/interop/vhost-user.txt
> +++ b/docs/interop/vhost-user.txt
> @@ -397,6 +397,7 @@ Protocol features
>  #define VHOST_USER_PROTOCOL_F_CONFIG         9
>  #define VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD  10
>  #define VHOST_USER_PROTOCOL_F_HOST_NOTIFIER  11
> +#define VHOST_USER_PROTOCOL_F_VFIO_GROUP     12
>  
>  Master message types
>  --------------------
> @@ -815,6 +816,21 @@ Slave message types
>        This request should be sent only when 
> VHOST_USER_PROTOCOL_F_HOST_NOTIFIER
>        protocol feature has been successfully negotiated.
>  
> + * VHOST_USER_SLAVE_VFIO_GROUP_MSG
> +
> +      Id: 4
> +      Equivalent ioctl: N/A
> +      Slave payload: N/A
> +      Master payload: N/A
> +
> +      When VHOST_USER_PROTOCOL_F_VFIO_GROUP is negotiated, vhost-user slave
> +      could send this request to share its VFIO group fd via ancillary data
> +      to master. After receiving this request from slave, master will close
> +      the existing VFIO group if any and do the DMA programming based on the
> +      virtio device's DMA address space for the new group if the request is
> +      sent with a file descriptor.
> +

Should it also clear out any mappings that were set on the old fd
before closing it?

Also should we limit when can this message be received?
If not you need to re-program mappings again whenever
we get a new fd.

> +
>  VHOST_USER_PROTOCOL_F_REPLY_ACK:
>  -------------------------------
>  The original vhost-user specification only demands replies for certain
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index b041343632..db958e24c7 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -52,6 +52,7 @@ enum VhostUserProtocolFeature {
>      VHOST_USER_PROTOCOL_F_CONFIG = 9,
>      VHOST_USER_PROTOCOL_F_SLAVE_SEND_FD = 10,
>      VHOST_USER_PROTOCOL_F_HOST_NOTIFIER = 11,
> +    VHOST_USER_PROTOCOL_F_VFIO_GROUP = 12,
>      VHOST_USER_PROTOCOL_F_MAX
>  };
>  
> @@ -97,6 +98,7 @@ typedef enum VhostUserSlaveRequest {
>      VHOST_USER_SLAVE_IOTLB_MSG = 1,
>      VHOST_USER_SLAVE_CONFIG_CHANGE_MSG = 2,
>      VHOST_USER_SLAVE_VRING_HOST_NOTIFIER_MSG = 3,
> +    VHOST_USER_SLAVE_VFIO_GROUP_MSG = 4,
>      VHOST_USER_SLAVE_MAX
>  }  VhostUserSlaveRequest;
>  
> @@ -949,6 +951,41 @@ static int 
> vhost_user_slave_handle_vring_host_notifier(struct vhost_dev *dev,
>      return 0;
>  }
>  
> +static int vhost_user_slave_handle_vfio_group(struct vhost_dev *dev,
> +                                              int *fd)
> +{
> +    struct vhost_user *u = dev->opaque;
> +    VhostUserState *user = u->user;
> +    VirtIODevice *vdev = dev->vdev;
> +    int groupfd = fd[0];
> +    VFIOGroup *group;
> +
> +    if (!virtio_has_feature(dev->protocol_features,
> +                            VHOST_USER_PROTOCOL_F_VFIO_GROUP) ||
> +        vdev == NULL) {
> +        return -1;
> +    }
> +
> +    if (user->vfio_group) {
> +        vfio_put_group(user->vfio_group);
> +        user->vfio_group = NULL;
> +    }
> +
> +    group = vfio_get_group_from_fd(groupfd, vdev->dma_as, NULL);
> +    if (group == NULL) {
> +        return -1;
> +    }
> +
> +    if (group->fd != groupfd) {
> +        close(groupfd);
> +    }
> +
> +    user->vfio_group = group;
> +    fd[0] = -1;
> +
> +    return 0;
> +}
> +

What will cause propagating groups to this vfio fd?


>  static void slave_read(void *opaque)
>  {
>      struct vhost_dev *dev = opaque;
> @@ -1021,6 +1058,9 @@ static void slave_read(void *opaque)
>          ret = vhost_user_slave_handle_vring_host_notifier(dev, &payload.area,
>                                                            fd[0]);
>          break;
> +    case VHOST_USER_SLAVE_VFIO_GROUP_MSG:
> +        ret = vhost_user_slave_handle_vfio_group(dev, fd);
> +        break;
>      default:
>          error_report("Received unexpected msg type.");
>          ret = -EINVAL;
> diff --git a/include/hw/virtio/vhost-user.h b/include/hw/virtio/vhost-user.h
> index fd660393a0..9e11473274 100644
> --- a/include/hw/virtio/vhost-user.h
> +++ b/include/hw/virtio/vhost-user.h
> @@ -10,6 +10,7 @@
>  
>  #include "chardev/char-fe.h"
>  #include "hw/virtio/virtio.h"
> +#include "hw/vfio/vfio-common.h"
>  
>  typedef struct VhostUserHostNotifier {
>      MemoryRegion mr;
> @@ -20,6 +21,7 @@ typedef struct VhostUserHostNotifier {
>  typedef struct VhostUserState {
>      CharBackend *chr;
>      VhostUserHostNotifier notifier[VIRTIO_QUEUE_MAX];
> +    VFIOGroup *vfio_group;
>  } VhostUserState;
>  
>  VhostUserState *vhost_user_init(void);
> -- 
> 2.18.0