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

[Eric Farman <farman@linux.ibm.com>]

On Fri, 2022-09-23 at 11:26 +0200, Christoph Hellwig wrote:
> From: Jason Gunthorpe <jgg@nvidia.com>
> 
> 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.
> 
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> [hch: count instances per-parent instead of per-type, use an atomic_t
>  to avoid taking mdev_list_lock in the show method]
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Kirti Wankhede <kwankhede@nvidia.com>

Reviewed-by: Eric Farman <farman@linux.ibm.com>

> ---
>  drivers/s390/cio/vfio_ccw_drv.c       |  1 -
>  drivers/s390/cio/vfio_ccw_ops.c       | 15 +--------------
>  drivers/s390/cio/vfio_ccw_private.h   |  2 --
>  drivers/s390/crypto/vfio_ap_ops.c     | 13 +------------
>  drivers/s390/crypto/vfio_ap_private.h |  2 --
>  drivers/vfio/mdev/mdev_core.c         | 22 +++++++++++++++++++---
>  drivers/vfio/mdev/mdev_sysfs.c        |  5 ++++-
>  include/linux/mdev.h                  |  3 +++
>  samples/vfio-mdev/mdpy.c              | 22 ++++------------------
>  9 files changed, 32 insertions(+), 53 deletions(-)
> 
> diff --git a/drivers/s390/cio/vfio_ccw_drv.c
> b/drivers/s390/cio/vfio_ccw_drv.c
> index e5f21c725326b..7f5402fe857a2 100644
> --- a/drivers/s390/cio/vfio_ccw_drv.c
> +++ b/drivers/s390/cio/vfio_ccw_drv.c
> @@ -141,7 +141,6 @@ 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 559ca18055928..6ae4d012d8008 100644
> --- a/drivers/s390/cio/vfio_ccw_ops.c
> +++ b/drivers/s390/cio/vfio_ccw_ops.c
> @@ -44,13 +44,6 @@ static void vfio_ccw_dma_unmap(struct vfio_device
> *vdev, u64 iova, u64 length)
>         vfio_ccw_mdev_reset(private);
>  }
>  
> -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_init_dev(struct vfio_device *vdev)
>  {
>         struct vfio_ccw_private *private =
> @@ -68,9 +61,6 @@ 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;
> -
>         ret = vfio_init_device(&private->vdev, &mdev->dev,
> &vfio_ccw_dev_ops);
>         if (ret)
>                 return ret;
> @@ -88,7 +78,6 @@ static int vfio_ccw_mdev_probe(struct mdev_device
> *mdev)
>  
>  err_put_vdev:
>         vfio_put_device(&private->vdev);
> -       atomic_inc(&private->avail);
>         return ret;
>  }
>  
> @@ -130,8 +119,6 @@ static void vfio_ccw_mdev_remove(struct
> mdev_device *mdev)
>          * cycle.
>          */
>         wait_for_completion(&private->release_comp);
> -
> -       atomic_inc(&private->avail);
>  }
>  
>  static int vfio_ccw_mdev_open_device(struct vfio_device *vdev)
> @@ -605,6 +592,7 @@ 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,
> @@ -612,5 +600,4 @@ struct mdev_driver vfio_ccw_mdev_driver = {
>         },
>         .probe = vfio_ccw_mdev_probe,
>         .remove = vfio_ccw_mdev_remove,
> -       .get_available = vfio_ccw_get_available,
>  };
> diff --git a/drivers/s390/cio/vfio_ccw_private.h
> b/drivers/s390/cio/vfio_ccw_private.h
> index 52caa721ec06c..bd5fb81456af8 100644
> --- a/drivers/s390/cio/vfio_ccw_private.h
> +++ b/drivers/s390/cio/vfio_ccw_private.h
> @@ -73,7 +73,6 @@ 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
>   * @io_region: MMIO region to input/output I/O arguments/results
>   * @io_mutex: protect against concurrent update of I/O regions
>   * @region: additional regions for other subchannel operations
> @@ -97,7 +96,6 @@ struct vfio_ccw_private {
>         struct subchannel       *sch;
>         int                     state;
>         struct completion       *completion;
> -       atomic_t                avail;
>         struct ccw_io_region    *io_region;
>         struct mutex            io_mutex;
>         struct vfio_ccw_region *region;
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c
> b/drivers/s390/crypto/vfio_ap_ops.c
> index 8606f5d75188c..2884189f38771 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -689,9 +689,6 @@ static int vfio_ap_mdev_init_dev(struct
> vfio_device *vdev)
>         struct ap_matrix_mdev *matrix_mdev =
>                 container_of(vdev, struct ap_matrix_mdev, vdev);
>  
> -       if ((atomic_dec_if_positive(&matrix_dev->available_instances)
> < 0))
> -               return -EPERM;
> -
>         matrix_mdev->mdev = to_mdev_device(vdev->dev);
>         vfio_ap_matrix_init(&matrix_dev->info, &matrix_mdev->matrix);
>         matrix_mdev->pqap_hook = handle_pqap;
> @@ -770,7 +767,6 @@ static void vfio_ap_mdev_unlink_fr_queues(struct
> ap_matrix_mdev *matrix_mdev)
>  
>  static void vfio_ap_mdev_release_dev(struct vfio_device *vdev)
>  {
> -       atomic_inc(&matrix_dev->available_instances);
>         vfio_free_device(vdev);
>  }
>  
> @@ -790,11 +786,6 @@ static void vfio_ap_mdev_remove(struct
> mdev_device *mdev)
>         vfio_put_device(&matrix_mdev->vdev);
>  }
>  
> -static unsigned int vfio_ap_mdev_get_available(struct mdev_type
> *mtype)
> -{
> -       return atomic_read(&matrix_dev->available_instances);
> -}
> -
>  #define MDEV_SHARING_ERR "Userspace may not re-assign queue
> %02lx.%04lx " \
>                          "already assigned to %s"
>  
> @@ -1772,6 +1763,7 @@ 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,
> @@ -1780,15 +1772,12 @@ 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 441dc8dda380b..2eddd5f34ed34 100644
> --- a/drivers/s390/crypto/vfio_ap_private.h
> +++ b/drivers/s390/crypto/vfio_ap_private.h
> @@ -29,7 +29,6 @@
>   * 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
>   * @mdevs_lock: mutex for locking the AP matrix device. This lock
> will be
> @@ -46,7 +45,6 @@
>   */
>  struct ap_matrix_dev {
>         struct device device;
> -       atomic_t available_instances;
>         struct ap_config_info info;
>         struct list_head mdev_list;
>         struct mutex mdevs_lock; /* serializes access to each
> ap_matrix_mdev */
> diff --git a/drivers/vfio/mdev/mdev_core.c
> b/drivers/vfio/mdev/mdev_core.c
> index 93f8caf2e5f77..58f91b3bd670c 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;
> +       atomic_set(&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)
> +               atomic_inc(&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 +148,18 @@ int mdev_device_create(struct mdev_type *type,
> const guid_t *uuid)
>                 }
>         }
>  
> +       if (!drv->get_available) {
> +               /*
> +                * Note: that non-atomic read and dec is fine here
> because
> +                * all modifications are under mdev_list_lock.
> +                */
> +               if (!atomic_read(&parent->available_instances)) {
> +                       mutex_unlock(&mdev_list_lock);
> +                       return -EUSERS;
> +               }
> +               atomic_dec(&parent->available_instances);
> +       }
> +
>         mdev = kzalloc(sizeof(*mdev), GFP_KERNEL);
>         if (!mdev) {
>                 mutex_unlock(&mdev_list_lock);
> diff --git a/drivers/vfio/mdev/mdev_sysfs.c
> b/drivers/vfio/mdev/mdev_sysfs.c
> index 658b3bf5ed0bf..abe3359dd477f 100644
> --- a/drivers/vfio/mdev/mdev_sysfs.c
> +++ b/drivers/vfio/mdev/mdev_sysfs.c
> @@ -108,7 +108,10 @@ static ssize_t available_instances_show(struct
> mdev_type *mtype,
>  {
>         struct mdev_driver *drv = mtype->parent->mdev_driver;
>  
> -       return sysfs_emit(buf, "%u\n", drv->get_available(mtype));
> +       if (drv->get_available)
> +               return sysfs_emit(buf, "%u\n", drv-
> >get_available(mtype));
> +       return sysfs_emit(buf, "%u\n",
> +                         atomic_read(&mtype->parent-
> >available_instances));
>  }
>  static MDEV_TYPE_ATTR_RO(available_instances);
>  
> diff --git a/include/linux/mdev.h b/include/linux/mdev.h
> index 33674cb5ed5d4..139d05b26f820 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;
> +       atomic_t 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 a7cf59246ddd0..946e8cfde6fdd 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 */
> @@ -235,9 +229,6 @@ static int mdpy_init_dev(struct vfio_device
> *vdev)
>         u32 fbsize;
>         int ret = -ENOMEM;
>  
> -       if (mdpy_count >= max_devices)
> -               return ret;
> -
>         mdev_state->vconfig = kzalloc(MDPY_CONFIG_SPACE_SIZE,
> GFP_KERNEL);
>         if (!mdev_state->vconfig)
>                 return ret;
> @@ -257,8 +248,6 @@ static int mdpy_init_dev(struct vfio_device
> *vdev)
>  
>         dev_info(vdev->dev, "%s: %s (%dx%d)\n", __func__, type-
> >type.pretty_name,
>                  type->width, type->height);
> -
> -       mdpy_count++;
>         return 0;
>  
>  out_vconfig:
> @@ -292,7 +281,6 @@ static void mdpy_release_dev(struct vfio_device
> *vdev)
>         struct mdev_state *mdev_state =
>                 container_of(vdev, struct mdev_state, vdev);
>  
> -       mdpy_count--;
>         vfree(mdev_state->memblk);
>         kfree(mdev_state->vconfig);
>         vfio_free_device(vdev);
> @@ -669,11 +657,6 @@ 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 = {
>         .init = mdpy_init_dev,
>         .release = mdpy_release_dev,
> @@ -685,6 +668,7 @@ 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,
> @@ -693,7 +677,6 @@ static struct mdev_driver mdpy_driver = {
>         },
>         .probe = mdpy_probe,
>         .remove = mdpy_remove,
> -       .get_available = mdpy_get_available,
>         .show_description = mdpy_show_description,
>  };
>  
> @@ -770,5 +753,8 @@ 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)