Re: [PATCH v2 01/15] vfio: Add helpers for unifying vfio_device life cycle

Eric Auger
2022-09-07T19:28:33Z

Hi Kevin,
On 9/1/22 16:37, Kevin Tian wrote:
> The idea is to let vfio core manage the vfio_device life cycle instead
> of duplicating the logic cross drivers. This is also a preparatory
> step for adding struct device into vfio_device.
>
> New pair of helpers together with a kref in vfio_device:
>
> - vfio_alloc_device()
> - vfio_put_device()
>
> Drivers can register @init/@release callbacks to manage any priviate
private
> state wrapping the vfio_device.
>
> However vfio-ccw doesn't fit this model due to a life cycle mess
> that its private structure mixes both parent and mdev info hence must
> be allocated/freed outside of the life cycle of vfio device.
>
> Per prior discussions this won't be fixed in short term by IBM folks.
>
> Instead of waiting introduce another helper vfio_init_device() so ccw
s/waiting/waiting for those modifications,
> can call it to initialize a pre-allocated vfio_device.
>
> Further implication of the ccw trick is that vfio_device cannot be
> freed uniformly in vfio core. Instead, require *EVERY* driver to
> implement @release and free vfio_device inside. Then ccw can choose
> to delay the free at its own discretion.
>
> Another trick down the road is that kvzalloc() is used to accommodate
> the need of gvt which uses vzalloc() while all others use kzalloc().
> So drivers should call a helper vfio_free_device() to free the
> vfio_device instead of assuming that kfree() or vfree() is appliable.
>
> Later once the ccw mess is fixed we can remove those tricks and
> fully handle structure alloc/free in vfio core.
>
> Existing vfio_{un}init_group_dev() will be deprecated after all
> existing usages are converted to the new model.
>
> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> Co-developed-by: Yi Liu <yi.l.liu@intel.com>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> Signed-off-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Tony Krowiak <akrowiak@linux.ibm.com>
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
> drivers/vfio/vfio_main.c | 92 ++++++++++++++++++++++++++++++++++++++++
> include/linux/vfio.h | 25 ++++++++++-
> 2 files changed, 116 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
> index 7cb56c382c97..c9d982131265 100644
> --- a/drivers/vfio/vfio_main.c
> +++ b/drivers/vfio/vfio_main.c
> @@ -496,6 +496,98 @@ void vfio_uninit_group_dev(struct vfio_device *device)
> }
> EXPORT_SYMBOL_GPL(vfio_uninit_group_dev);
>
> +/* Release helper called by vfio_put_device() */
> +void vfio_device_release(struct kref *kref)
> +{
> + struct vfio_device *device =
> + container_of(kref, struct vfio_device, kref);
> +
> + vfio_uninit_group_dev(device);
> +
> + /*
> + * kvfree() cannot be done here due to a life cycle mess in
> + * vfio-ccw. Before the ccw part is fixed all drivers are
> + * required to support @release and call vfio_free_device()
> + * from there.
> + */
> + device->ops->release(device);
> +}
> +EXPORT_SYMBOL_GPL(vfio_device_release);
> +
> +/*
> + * Alloc and initialize vfio_device so it can be registered to vfio
> + * core.
> + *
> + * Drivers should use the wrapper vfio_alloc_device() for allocation.
> + * @size is the size of the structure to be allocated, including any
> + * private data used by the driver.
> + *
> + * Driver may provide an @init callback to cover device private data.
nit: this comment may rather relate to the vfio_init_device function
> + *
> + * Use vfio_put_device() to release the structure after success return.
> + */
> +struct vfio_device *_vfio_alloc_device(size_t size, struct device *dev,
> + const struct vfio_device_ops *ops)
> +{
> + struct vfio_device *device;
> + int ret;
> +
> + if (WARN_ON(size < sizeof(struct vfio_device)))
> + return ERR_PTR(-EINVAL);
> +
> + device = kvzalloc(size, GFP_KERNEL);
> + if (!device)
> + return ERR_PTR(-ENOMEM);
> +
> + ret = vfio_init_device(device, dev, ops);
> + if (ret)
> + goto out_free;
> + return device;
> +
> +out_free:
> + kvfree(device);
> + return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL_GPL(_vfio_alloc_device);
> +
> +/*
> + * Initialize a vfio_device so it can be registered to vfio core.
> + *
> + * Only vfio-ccw driver should call this interface.
> + */
> +int vfio_init_device(struct vfio_device *device, struct device *dev,
> + const struct vfio_device_ops *ops)
> +{
> + int ret;
> +
> + vfio_init_group_dev(device, dev, ops);
> +
> + if (ops->init) {
> + ret = ops->init(device);
> + if (ret)
> + goto out_uninit;
> + }
> +
> + kref_init(&device->kref);
> + return 0;
> +
> +out_uninit:
> + vfio_uninit_group_dev(device);
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(vfio_init_device);
> +
> +/*
> + * The helper called by driver @release callback to free the device
> + * structure. Drivers which don't have private data to clean can
> + * simply use this helper as its @release.
> + */
> +void vfio_free_device(struct vfio_device *device)
> +{
> + kvfree(device);
> +}
> +EXPORT_SYMBOL_GPL(vfio_free_device);
> +
> static struct vfio_group *vfio_noiommu_group_alloc(struct device *dev,
> enum vfio_group_type type)
> {
> diff --git a/include/linux/vfio.h b/include/linux/vfio.h
> index e05ddc6fe6a5..e1e9e8352903 100644
> --- a/include/linux/vfio.h
> +++ b/include/linux/vfio.h
> @@ -45,7 +45,8 @@ struct vfio_device {
> struct kvm *kvm;
>
> /* Members below here are private, not for driver use */
> - refcount_t refcount;
> + struct kref kref; /* object life cycle */
> + refcount_t refcount; /* user count on registered device*/
> unsigned int open_count;
> struct completion comp;
> struct list_head group_next;
> @@ -55,6 +56,8 @@ struct vfio_device {
> /**
> * struct vfio_device_ops - VFIO bus driver device callbacks
> *
> + * @init: initialize private fields in device structure
> + * @release: Reclaim private fields in device structure
> * @open_device: Called when the first file descriptor is opened for this device
> * @close_device: Opposite of open_device
> * @read: Perform read(2) on device file descriptor
> @@ -72,6 +75,8 @@ struct vfio_device {
> */
> struct vfio_device_ops {
> char *name;
> + int (*init)(struct vfio_device *vdev);
> + void (*release)(struct vfio_device *vdev);
> int (*open_device)(struct vfio_device *vdev);
> void (*close_device)(struct vfio_device *vdev);
> ssize_t (*read)(struct vfio_device *vdev, char __user *buf,
> @@ -137,6 +142,24 @@ static inline int vfio_check_feature(u32 flags, size_t argsz, u32 supported_ops,
> return 1;
> }
>
> +struct vfio_device *_vfio_alloc_device(size_t size, struct device *dev,
> + const struct vfio_device_ops *ops);
> +#define vfio_alloc_device(dev_struct, member, dev, ops) \
> + container_of(_vfio_alloc_device(sizeof(struct dev_struct) + \
> + BUILD_BUG_ON_ZERO(offsetof( \
> + struct dev_struct, member)), \
> + dev, ops), \
> + struct dev_struct, member)
> +
> +int vfio_init_device(struct vfio_device *device, struct device *dev,
> + const struct vfio_device_ops *ops);
> +void vfio_free_device(struct vfio_device *device);
> +void vfio_device_release(struct kref *kref);
> +static inline void vfio_put_device(struct vfio_device *device)
> +{
> + kref_put(&device->kref, vfio_device_release);
> +}
> +
> void vfio_init_group_dev(struct vfio_device *device, struct device *dev,
> const struct vfio_device_ops *ops);
> void vfio_uninit_group_dev(struct vfio_device *device);
Besides

Reviewed-by: Eric Auger <eric.auger@redhat.com>

Eric