On 2019/9/20 上午10:16, Tiwei Bie wrote:
On Fri, Sep 20, 2019 at 09:30:58AM +0800, Jason Wang wrote:
On 2019/9/19 下午11:45, Tiwei Bie wrote:
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 ...
To clarify, this should be done through the id_table fields in
vhost_mdev_driver, and it should claim it supports virtio-mdev device only:
static struct mdev_class_id id_table[] = {
{ MDEV_ID_VIRTIO },
{ 0 },
};
static struct mdev_driver vhost_mdev_driver = {
...
.id_table = id_table,
}
In this way, both of virtio-mdev and vhost-mdev will try to
take this device. We may want a way to let vhost-mdev take this
device only when users explicitly ask it to do it. Or maybe we
can have a different MDEV_ID for vhost-mdev but share the device
ops with virtio-mdev.
I think it's similar to virtio-pci vs vfio-pci. User can choose to
switch the driver through bind/unbind.
return vfio_add_group_dev(dev, &vfio_vhost_mdev_dev_ops, mdev);
And in vfio_vhost_mdev_ops, all its need is to just implement vhost-net
ioctl and translate them to virtio-mdev transport (e.g device_ops I proposed
or ioctls other whatever other method) API.
I see, so my previous understanding is basically correct:
https://lkml.org/lkml/2019/9/17/332
I.e. we won't have a separate vhost fd and we will do all vhost
ioctls on the VFIO device fd backed by this new VFIO driver.
Yes.
Thanks
And it could have a dummy ops
implementation for the other device_ops.
}
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.
Then what vhost-mdev char device did is just forwarding ioctl back to this
vfio device fd which seems a overkill. It's simpler that just do ioctl on
the device ops directly.
Yes.
Thanks,
Tiwei
Thanks
Thanks,
Tiwei
Thanks
Yes, it is.
Thanks
_______________________________________________
Virtualization mailing list
Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linuxfoundation.org/mailman/listinfo/virtualization
