linux-kernel - Re: [PATCH] vfio-mdev: support mediated device creation in kernel

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Date:   Fri, 20 Mar 2020 12:34:25 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Yonghyun Hwang <yonghyun@...gle.com>
Cc:     Kirti Wankhede <kwankhede@...dia.com>,
        Cornelia Huck <cohuck@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Havard Skinnemoen <hskinnemoen@...gle.com>,
        Moritz Fischer <mdf@...nel.org>
Subject: Re: [PATCH] vfio-mdev: support mediated device creation in kernel

On Fri, 20 Mar 2020 10:59:10 -0700
Yonghyun Hwang <yonghyun@...gle.com> wrote:

> To enable a mediated device, a device driver registers its device to VFIO
> MDev framework. Once the mediated device gets enabled, UUID gets fed onto
> the sysfs attribute, "create", to create the mediated device. This
> additional step happens after boot-up gets complete. If the driver knows
> how many mediated devices need to be created during probing time, the
> additional step becomes cumbersome. This commit implements a new function
> to allow the driver to create a mediated device in kernel.

But pre-creating mdev devices seems like a policy decision.  Why can't
userspace make such a policy decision, and do so with persistent uuids,
via something like mdevctl?  Thanks,

Alex

 
> Signed-off-by: Yonghyun Hwang <yonghyun@...gle.com>
> ---
>  drivers/vfio/mdev/mdev_core.c | 45 +++++++++++++++++++++++++++++++++++
>  include/linux/mdev.h          |  3 +++
>  2 files changed, 48 insertions(+)
> 
> diff --git a/drivers/vfio/mdev/mdev_core.c b/drivers/vfio/mdev/mdev_core.c
> index b558d4cfd082..a6d32516de42 100644
> --- a/drivers/vfio/mdev/mdev_core.c
> +++ b/drivers/vfio/mdev/mdev_core.c
> @@ -350,6 +350,51 @@ int mdev_device_create(struct kobject *kobj,
>  	return ret;
>  }
>  
> +/*
> + * mdev_create_device : Create a mdev device
> + * @dev: device structure representing parent device.
> + * @uuid: uuid char string for a mdev device.
> + * @group: index to supported type groups for a mdev device.
> + *
> + * Create a mdev device in kernel.
> + * Returns a negative value on error, otherwise 0.
> + */
> +int mdev_create_device(struct device *dev,
> +			const char *uuid, int group)
> +{
> +	struct mdev_parent *parent = NULL;
> +	struct mdev_type *type = NULL;
> +	guid_t guid;
> +	int i = 1;
> +	int ret;
> +
> +	ret = guid_parse(uuid, &guid);
> +	if (ret) {
> +		dev_err(dev, "Failed to parse UUID");
> +		return ret;
> +	}
> +
> +	parent = __find_parent_device(dev);
> +	if (!parent) {
> +		dev_err(dev, "Failed to find parent mdev device");
> +		return -ENODEV;
> +	}
> +
> +	list_for_each_entry(type, &parent->type_list, next) {
> +		if (i == group)
> +			break;
> +		i++;
> +	}
> +
> +	if (!type || i != group) {
> +		dev_err(dev, "Failed to find mdev device");
> +		return -ENODEV;
> +	}
> +
> +	return mdev_device_create(&type->kobj, parent->dev, &guid);
> +}
> +EXPORT_SYMBOL(mdev_create_device);
> +
>  int mdev_device_remove(struct device *dev)
>  {
>  	struct mdev_device *mdev, *tmp;
> diff --git a/include/linux/mdev.h b/include/linux/mdev.h
> index 0ce30ca78db0..b66f67998916 100644
> --- a/include/linux/mdev.h
> +++ b/include/linux/mdev.h
> @@ -145,4 +145,7 @@ struct device *mdev_parent_dev(struct mdev_device *mdev);
>  struct device *mdev_dev(struct mdev_device *mdev);
>  struct mdev_device *mdev_from_dev(struct device *dev);
>  
> +extern int mdev_create_device(struct device *dev,
> +			const char *uuid, int group_idx);
> +
>  #endif /* MDEV_H */