Re: [PATCH 14/15] vfio/mdev: add mdev available instance checking to the core

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On Wed, 2022-07-06 at 09:42 +0200, Christoph Hellwig wrote:
> Many of the mdev drivers use a simple counter for keeping track of
> the
> available instances. Move this code to the core code and store the
> counter
> in the mdev_parent. Implement it using correct locking, fixing mdpy.
> 
> Drivers just provide the value in the mdev_driver at registration
> time
> and the core code takes care of maintaining it and exposing the value
> in
> sysfs.

If I read this right, .get_available and .max_instances are mutually
exclusive. Which means that available_instances_show() from patch 12
would need to emit parent->available_instances if .get_available is
NULL.

Eric

> 
> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> [count instances per-parent instead of per-type]
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> ---
>  drivers/s390/cio/vfio_ccw_drv.c       |  1 -
>  drivers/s390/cio/vfio_ccw_ops.c       | 14 +-------------
>  drivers/s390/cio/vfio_ccw_private.h   |  2 --
>  drivers/s390/crypto/vfio_ap_ops.c     | 21 +++------------------
>  drivers/s390/crypto/vfio_ap_private.h |  2 --
>  drivers/vfio/mdev/mdev_core.c         | 18 +++++++++++++++---
>  include/linux/mdev.h                  |  3 +++
>  samples/vfio-mdev/mdpy.c              | 23 ++++-------------------
>  8 files changed, 26 insertions(+), 58 deletions(-)
> 
> diff --git a/drivers/s390/cio/vfio_ccw_drv.c
> b/drivers/s390/cio/vfio_ccw_drv.c
> index 750d0315f1f5b..449c76b29a3b5 100644
> --- a/drivers/s390/cio/vfio_ccw_drv.c
> +++ b/drivers/s390/cio/vfio_ccw_drv.c
> @@ -149,7 +149,6 @@ static struct vfio_ccw_private
> *vfio_ccw_alloc_private(struct subchannel *sch)
>  	INIT_LIST_HEAD(&private->crw);
>  	INIT_WORK(&private->io_work, vfio_ccw_sch_io_todo);
>  	INIT_WORK(&private->crw_work, vfio_ccw_crw_todo);
> -	atomic_set(&private->avail, 1);
>  
>  	private->cp.guest_cp = kcalloc(CCWCHAIN_LEN_MAX, sizeof(struct
> ccw1),
>  				       GFP_KERNEL);
> diff --git a/drivers/s390/cio/vfio_ccw_ops.c
> b/drivers/s390/cio/vfio_ccw_ops.c
> index 6f6a0f2695059..c05d80add7be2 100644
> --- a/drivers/s390/cio/vfio_ccw_ops.c
> +++ b/drivers/s390/cio/vfio_ccw_ops.c
> @@ -70,13 +70,6 @@ static int vfio_ccw_mdev_notifier(struct
> notifier_block *nb,
>  	return NOTIFY_DONE;
>  }
>  
> -static unsigned int vfio_ccw_get_available(struct mdev_type *mtype)
> -{
> -	struct vfio_ccw_private *private = dev_get_drvdata(mtype-
> >parent->dev);
> -
> -	return atomic_read(&private->avail);
> -}
> -
>  static int vfio_ccw_mdev_probe(struct mdev_device *mdev)
>  {
>  	struct vfio_ccw_private *private = dev_get_drvdata(mdev-
> >dev.parent);
> @@ -85,9 +78,6 @@ static int vfio_ccw_mdev_probe(struct mdev_device
> *mdev)
>  	if (private->state == VFIO_CCW_STATE_NOT_OPER)
>  		return -ENODEV;
>  
> -	if (atomic_dec_if_positive(&private->avail) < 0)
> -		return -EPERM;
> -
>  	memset(&private->vdev, 0, sizeof(private->vdev));
>  	vfio_init_group_dev(&private->vdev, &mdev->dev,
>  			    &vfio_ccw_dev_ops);
> @@ -108,7 +98,6 @@ static int vfio_ccw_mdev_probe(struct mdev_device
> *mdev)
>  
>  err_atomic:
>  	vfio_uninit_group_dev(&private->vdev);
> -	atomic_inc(&private->avail);
>  	private->mdev = NULL;
>  	private->state = VFIO_CCW_STATE_IDLE;
>  	return ret;
> @@ -135,7 +124,6 @@ static void vfio_ccw_mdev_remove(struct
> mdev_device *mdev)
>  	vfio_uninit_group_dev(&private->vdev);
>  	cp_free(&private->cp);
>  	private->mdev = NULL;
> -	atomic_inc(&private->avail);
>  }
>  
>  static int vfio_ccw_mdev_open_device(struct vfio_device *vdev)
> @@ -613,6 +601,7 @@ static const struct vfio_device_ops
> vfio_ccw_dev_ops = {
>  
>  struct mdev_driver vfio_ccw_mdev_driver = {
>  	.device_api = VFIO_DEVICE_API_CCW_STRING,
> +	.max_instances = 1,
>  	.driver = {
>  		.name = "vfio_ccw_mdev",
>  		.owner = THIS_MODULE,
> @@ -620,7 +609,6 @@ struct mdev_driver vfio_ccw_mdev_driver = {
>  	},
>  	.probe = vfio_ccw_mdev_probe,
>  	.remove = vfio_ccw_mdev_remove,
> -	.get_available = vfio_ccw_get_available,
>  };
>  
>  int vfio_ccw_mdev_reg(struct subchannel *sch)
> diff --git a/drivers/s390/cio/vfio_ccw_private.h
> b/drivers/s390/cio/vfio_ccw_private.h
> index b7163bac8cc75..9be5baed0cb7f 100644
> --- a/drivers/s390/cio/vfio_ccw_private.h
> +++ b/drivers/s390/cio/vfio_ccw_private.h
> @@ -72,7 +72,6 @@ struct vfio_ccw_crw {
>   * @sch: pointer to the subchannel
>   * @state: internal state of the device
>   * @completion: synchronization helper of the I/O completion
> - * @avail: available for creating a mediated device
>   * @mdev: pointer to the mediated device
>   * @nb: notifier for vfio events
>   * @io_region: MMIO region to input/output I/O arguments/results
> @@ -96,7 +95,6 @@ struct vfio_ccw_private {
>  	struct subchannel	*sch;
>  	int			state;
>  	struct completion	*completion;
> -	atomic_t		avail;
>  	struct mdev_device	*mdev;
>  	struct notifier_block	nb;
>  	struct ccw_io_region	*io_region;
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c
> b/drivers/s390/crypto/vfio_ap_ops.c
> index edeec11c56560..69ed88fdaf383 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -461,14 +461,9 @@ static int vfio_ap_mdev_probe(struct mdev_device
> *mdev)
>  	struct ap_matrix_mdev *matrix_mdev;
>  	int ret;
>  
> -	if ((atomic_dec_if_positive(&matrix_dev->available_instances) <
> 0))
> -		return -EPERM;
> -
>  	matrix_mdev = kzalloc(sizeof(*matrix_mdev), GFP_KERNEL);
> -	if (!matrix_mdev) {
> -		ret = -ENOMEM;
> -		goto err_dec_available;
> -	}
> +	if (!matrix_mdev)
> +		return -ENOMEM;
>  	vfio_init_group_dev(&matrix_mdev->vdev, &mdev->dev,
>  			    &vfio_ap_matrix_dev_ops);
>  
> @@ -491,8 +486,6 @@ static int vfio_ap_mdev_probe(struct mdev_device
> *mdev)
>  	mutex_unlock(&matrix_dev->lock);
>  	vfio_uninit_group_dev(&matrix_mdev->vdev);
>  	kfree(matrix_mdev);
> -err_dec_available:
> -	atomic_inc(&matrix_dev->available_instances);
>  	return ret;
>  }
>  
> @@ -508,12 +501,6 @@ static void vfio_ap_mdev_remove(struct
> mdev_device *mdev)
>  	mutex_unlock(&matrix_dev->lock);
>  	vfio_uninit_group_dev(&matrix_mdev->vdev);
>  	kfree(matrix_mdev);
> -	atomic_inc(&matrix_dev->available_instances);
> -}
> -
> -static unsigned int vfio_ap_mdev_get_available(struct mdev_type
> *mtype)
> -{
> -	return atomic_read(&matrix_dev->available_instances);
>  }
>  
>  struct vfio_ap_queue_reserved {
> @@ -1427,6 +1414,7 @@ static const struct vfio_device_ops
> vfio_ap_matrix_dev_ops = {
>  
>  static struct mdev_driver vfio_ap_matrix_driver = {
>  	.device_api = VFIO_DEVICE_API_AP_STRING,
> +	.max_instances = MAX_ZDEV_ENTRIES_EXT,
>  	.driver = {
>  		.name = "vfio_ap_mdev",
>  		.owner = THIS_MODULE,
> @@ -1435,15 +1423,12 @@ static struct mdev_driver
> vfio_ap_matrix_driver = {
>  	},
>  	.probe = vfio_ap_mdev_probe,
>  	.remove = vfio_ap_mdev_remove,
> -	.get_available = vfio_ap_mdev_get_available,
>  };
>  
>  int vfio_ap_mdev_register(void)
>  {
>  	int ret;
>  
> -	atomic_set(&matrix_dev->available_instances,
> MAX_ZDEV_ENTRIES_EXT);
> -
>  	ret = mdev_register_driver(&vfio_ap_matrix_driver);
>  	if (ret)
>  		return ret;
> diff --git a/drivers/s390/crypto/vfio_ap_private.h
> b/drivers/s390/crypto/vfio_ap_private.h
> index 5dc5050d03791..b808b343b771f 100644
> --- a/drivers/s390/crypto/vfio_ap_private.h
> +++ b/drivers/s390/crypto/vfio_ap_private.h
> @@ -28,7 +28,6 @@
>   * struct ap_matrix_dev - Contains the data for the matrix device.
>   *
>   * @device:	generic device structure associated with the AP matrix
> device
> - * @available_instances: number of mediated matrix devices that can
> be created
>   * @info:	the struct containing the output from the PQAP(QCI)
> instruction
>   * @mdev_list:	the list of mediated matrix devices created
>   * @lock:	mutex for locking the AP matrix device. This lock will
> be
> @@ -40,7 +39,6 @@
>   */
>  struct ap_matrix_dev {
>  	struct device device;
> -	atomic_t available_instances;
>  	struct ap_config_info info;
>  	struct list_head mdev_list;
>  	struct mutex lock;
> diff --git a/drivers/vfio/mdev/mdev_core.c
> b/drivers/vfio/mdev/mdev_core.c
> index 93f8caf2e5f77..9bc897235c492 100644
> --- a/drivers/vfio/mdev/mdev_core.c
> +++ b/drivers/vfio/mdev/mdev_core.c
> @@ -70,6 +70,7 @@ int mdev_register_parent(struct mdev_parent
> *parent, struct device *dev,
>  	parent->mdev_driver = mdev_driver;
>  	parent->types = types;
>  	parent->nr_types = nr_types;
> +	parent->available_instances = mdev_driver->max_instances;
>  
>  	if (!mdev_bus_compat_class) {
>  		mdev_bus_compat_class =
> class_compat_register("mdev_bus");
> @@ -115,14 +116,17 @@ EXPORT_SYMBOL(mdev_unregister_parent);
>  static void mdev_device_release(struct device *dev)
>  {
>  	struct mdev_device *mdev = to_mdev_device(dev);
> -
> -	/* Pairs with the get in mdev_device_create() */
> -	kobject_put(&mdev->type->kobj);
> +	struct mdev_parent *parent = mdev->type->parent;
>  
>  	mutex_lock(&mdev_list_lock);
>  	list_del(&mdev->next);
> +	if (!parent->mdev_driver->get_available)
> +		parent->available_instances++;
>  	mutex_unlock(&mdev_list_lock);
>  
> +	/* Pairs with the get in mdev_device_create() */
> +	kobject_put(&mdev->type->kobj);
> +
>  	dev_dbg(&mdev->dev, "MDEV: destroying\n");
>  	kfree(mdev);
>  }
> @@ -144,6 +148,14 @@ int mdev_device_create(struct mdev_type *type,
> const guid_t *uuid)
>  		}
>  	}
>  
> +	if (!drv->get_available) {
> +		if (!parent->available_instances) {
> +			mutex_unlock(&mdev_list_lock);
> +			return -EUSERS;
> +		}
> +		parent->available_instances--;
> +	}
> +
>  	mdev = kzalloc(sizeof(*mdev), GFP_KERNEL);
>  	if (!mdev) {
>  		mutex_unlock(&mdev_list_lock);
> diff --git a/include/linux/mdev.h b/include/linux/mdev.h
> index dc38ad2b07883..641ed18a61247 100644
> --- a/include/linux/mdev.h
> +++ b/include/linux/mdev.h
> @@ -45,6 +45,7 @@ struct mdev_parent {
>  	struct rw_semaphore unreg_sem;
>  	struct mdev_type **types;
>  	unsigned int nr_types;
> +	unsigned int available_instances;
>  };
>  
>  static inline struct mdev_device *to_mdev_device(struct device *dev)
> @@ -55,6 +56,7 @@ static inline struct mdev_device
> *to_mdev_device(struct device *dev)
>  /**
>   * struct mdev_driver - Mediated device driver
>   * @device_api: string to return for the device_api sysfs
> + * @max_instances: maximum number of instances supported (optional)
>   * @probe: called when new device created
>   * @remove: called when device removed
>   * @get_available: Return the max number of instances that can be
> created
> @@ -63,6 +65,7 @@ static inline struct mdev_device
> *to_mdev_device(struct device *dev)
>   **/
>  struct mdev_driver {
>  	const char *device_api;
> +	unsigned int max_instances;
>  	int (*probe)(struct mdev_device *dev);
>  	void (*remove)(struct mdev_device *dev);
>  	unsigned int (*get_available)(struct mdev_type *mtype);
> diff --git a/samples/vfio-mdev/mdpy.c b/samples/vfio-mdev/mdpy.c
> index 250b7ea2df2e4..7f7ac5491407e 100644
> --- a/samples/vfio-mdev/mdpy.c
> +++ b/samples/vfio-mdev/mdpy.c
> @@ -42,11 +42,6 @@
>  
>  MODULE_LICENSE("GPL v2");
>  
> -static int max_devices = 4;
> -module_param_named(count, max_devices, int, 0444);
> -MODULE_PARM_DESC(count, "number of " MDPY_NAME " devices");
> -
> -
>  #define MDPY_TYPE_1 "vga"
>  #define MDPY_TYPE_2 "xga"
>  #define MDPY_TYPE_3 "hd"
> @@ -93,7 +88,6 @@ static struct class	*mdpy_class;
>  static struct cdev	mdpy_cdev;
>  static struct device	mdpy_dev;
>  static struct mdev_parent mdpy_parent;
> -static u32		mdpy_count;
>  static const struct vfio_device_ops mdpy_dev_ops;
>  
>  /* State of each mdev device */
> @@ -234,9 +228,6 @@ static int mdpy_probe(struct mdev_device *mdev)
>  	u32 fbsize;
>  	int ret;
>  
> -	if (mdpy_count >= max_devices)
> -		return -ENOMEM;
> -
>  	mdev_state = kzalloc(sizeof(struct mdev_state), GFP_KERNEL);
>  	if (mdev_state == NULL)
>  		return -ENOMEM;
> @@ -265,8 +256,6 @@ static int mdpy_probe(struct mdev_device *mdev)
>  	mdpy_create_config_space(mdev_state);
>  	mdpy_reset(mdev_state);
>  
> -	mdpy_count++;
> -
>  	ret = vfio_register_emulated_iommu_dev(&mdev_state->vdev);
>  	if (ret)
>  		goto err_mem;
> @@ -293,8 +282,6 @@ static void mdpy_remove(struct mdev_device *mdev)
>  	kfree(mdev_state->vconfig);
>  	vfio_uninit_group_dev(&mdev_state->vdev);
>  	kfree(mdev_state);
> -
> -	mdpy_count--;
>  }
>  
>  static ssize_t mdpy_read(struct vfio_device *vdev, char __user *buf,
> @@ -658,11 +645,6 @@ static ssize_t mdpy_show_description(struct
> mdev_type *mtype, char *buf)
>  		       type->width, type->height);
>  }
>  
> -static unsigned int mdpy_get_available(struct mdev_type *mtype)
> -{
> -	return max_devices - mdpy_count;
> -}
> -
>  static const struct vfio_device_ops mdpy_dev_ops = {
>  	.read = mdpy_read,
>  	.write = mdpy_write,
> @@ -672,6 +654,7 @@ static const struct vfio_device_ops mdpy_dev_ops
> = {
>  
>  static struct mdev_driver mdpy_driver = {
>  	.device_api = VFIO_DEVICE_API_PCI_STRING,
> +	.max_instances = 4,
>  	.driver = {
>  		.name = "mdpy",
>  		.owner = THIS_MODULE,
> @@ -680,7 +663,6 @@ static struct mdev_driver mdpy_driver = {
>  	},
>  	.probe = mdpy_probe,
>  	.remove	= mdpy_remove,
> -	.get_available = mdpy_get_available,
>  	.show_description = mdpy_show_description,
>  };
>  
> @@ -757,5 +739,8 @@ static void __exit mdpy_dev_exit(void)
>  	mdpy_class = NULL;
>  }
>  
> +module_param_named(count, mdpy_driver.max_instances, int, 0444);
> +MODULE_PARM_DESC(count, "number of " MDPY_NAME " devices");
> +
>  module_init(mdpy_dev_init)
>  module_exit(mdpy_dev_exit)




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