On Thu, Sep 19, 2019 at 09:08:11PM +0800, Jason Wang wrote: > On 2019/9/18 下午10:32, Michael S. Tsirkin wrote: > > > > > So I have some questions: > > > > > > > > > > 1) Compared to method 2, what's the advantage of creating a new vhost > > > > > char > > > > > device? I guess it's for keep the API compatibility? > > > > One benefit is that we can avoid doing vhost ioctls on > > > > VFIO device fd. > > > Yes, but any benefit from doing this? > > It does seem a bit more modular, but it's certainly not a big deal. > > Ok, if we go this way, it could be as simple as provide some callback to > vhost, then vhost can just forward the ioctl through parent_ops. > > > > > > > > 2) For method 2, is there any easy way for user/admin to distinguish > > > > > e.g > > > > > ordinary vfio-mdev for vhost from ordinary vfio-mdev? > > > > I think device-api could be a choice. > > > Ok. > > > > > > > > > > > I saw you introduce > > > > > ops matching helper but it's not friendly to management. > > > > The ops matching helper is just to check whether a given > > > > vfio-device is based on a mdev device. > > > > > > > > > 3) A drawback of 1) and 2) is that it must follow vfio_device_ops that > > > > > assumes the parameter comes from userspace, it prevents support kernel > > > > > virtio drivers. > > > > > > > > > > 4) So comes the idea of method 3, since it register a new vhost-mdev > > > > > driver, > > > > > we can use device specific ops instead of VFIO ones, then we can have > > > > > a > > > > > common API between vDPA parent and vhost-mdev/virtio-mdev drivers. > > > > As the above draft shows, this requires introducing a new > > > > VFIO device driver. I think Alex's opinion matters here. > > Just to clarify, a new type of mdev driver but provides dummy > vfio_device_ops for VFIO to make container DMA ioctl work.
I see. Thanks! IIUC, you mean we can provide a very tiny VFIO device driver in drivers/vhost/mdev.c, e.g.: static int vfio_vhost_mdev_open(void *device_data) { if (!try_module_get(THIS_MODULE)) return -ENODEV; return 0; } static void vfio_vhost_mdev_release(void *device_data) { module_put(THIS_MODULE); } static const struct vfio_device_ops vfio_vhost_mdev_dev_ops = { .name = "vfio-vhost-mdev", .open = vfio_vhost_mdev_open, .release = vfio_vhost_mdev_release, }; static int vhost_mdev_probe(struct device *dev) { struct mdev_device *mdev = to_mdev_device(dev); ... Check the mdev device_id proposed in ... ... https://lkml.org/lkml/2019/9/12/151 ... return vfio_add_group_dev(dev, &vfio_vhost_mdev_dev_ops, mdev); } static void vhost_mdev_remove(struct device *dev) { vfio_del_group_dev(dev); } static struct mdev_driver vhost_mdev_driver = { .name = "vhost_mdev", .probe = vhost_mdev_probe, .remove = vhost_mdev_remove, }; So we can bind above mdev driver to the virtio-mdev compatible mdev devices when we want to use vhost-mdev. After binding above driver to the mdev device, we can setup IOMMU via VFIO and get VFIO device fd of this mdev device, and pass it to vhost fd (/dev/vhost-mdev) with a SET_BACKEND ioctl. Thanks, Tiwei > > Thanks > > > > > Yes, it is. > > > > > > Thanks > > > > > > _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization