Re: [PATCH v20 10/20] s390/vfio-ap: prepare for dynamic update of guest's APCB on assign/unassign

["Jason J. Herne" <jjherne@linux.ibm.com>]

On 6/21/22 11:51, Tony Krowiak wrote:
> The functions backing the matrix mdev's sysfs attribute interfaces to
> assign/unassign adapters, domains and control domains must take and
> release the locks required to perform a dynamic update of a guest's APCB
> in the proper order.
> 
> The proper order for taking the locks is:
> 
> matrix_dev->guests_lock => kvm->lock => matrix_dev->mdevs_lock
> 
> The proper order for releasing the locks is:
> 
> matrix_dev->mdevs_lock => kvm->lock => matrix_dev->guests_lock
> 
> Two new macros are introduced for this purpose: One to take the locks and
> the other to release the locks. These macros will be used by the
> assignment/unassignment functions to prepare for dynamic update of
> the KVM guest's APCB.
> 
> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> ---
>   drivers/s390/crypto/vfio_ap_ops.c | 69 +++++++++++++++++++++++++------
>   1 file changed, 57 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index f31db1248740..b8f901e6b580 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -75,6 +75,51 @@ static const struct vfio_device_ops vfio_ap_matrix_dev_ops;
>   	mutex_unlock(&matrix_dev->guests_lock);	\
>   })
>   
> +/**
> + * get_update_locks_for_mdev: Acquire the locks required to dynamically update a
> + *			      KVM guest's APCB in the proper order.
> + *
> + * @matrix_mdev: a pointer to a struct ap_matrix_mdev object containing the AP
> + *		 configuration data to use to update a KVM guest's APCB.
> + *
> + * The proper locking order is:
> + * 1. matrix_dev->guests_lock: required to use the KVM pointer to update a KVM
> + *			       guest's APCB.
> + * 2. matrix_mdev->kvm->lock:  required to update a guest's APCB
> + * 3. matrix_dev->mdevs_lock:  required to access data stored in a matrix_mdev
> + *
> + * Note: If @matrix_mdev is NULL or is not attached to a KVM guest, the KVM
> + *	 lock will not be taken.
> + */
> +#define get_update_locks_for_mdev(matrix_mdev) ({	\
> +	mutex_lock(&matrix_dev->guests_lock);		\
> +	if (matrix_mdev && matrix_mdev->kvm)		\
> +		mutex_lock(&matrix_mdev->kvm->lock);	\
> +	mutex_lock(&matrix_dev->mdevs_lock);		\
> +})
> +
> +/**
> + * release_update_locks_for_mdev: Release the locks used to dynamically update a
> + *				  KVM guest's APCB in the proper order.
> + *
> + * @matrix_mdev: a pointer to a struct ap_matrix_mdev object containing the AP
> + *		 configuration data to use to update a KVM guest's APCB.
> + *
> + * The proper unlocking order is:
> + * 1. matrix_dev->mdevs_lock
> + * 2. matrix_mdev->kvm->lock
> + * 3. matrix_dev->guests_lock
> + *
> + * Note: If @matrix_mdev is NULL or is not attached to a KVM guest, the KVM
> + *	 lock will not be released.
> + */
> +#define release_update_locks_for_mdev(matrix_mdev) ({	\
> +	mutex_unlock(&matrix_dev->mdevs_lock);		\
> +	if (matrix_mdev && matrix_mdev->kvm)		\
> +		mutex_unlock(&matrix_mdev->kvm->lock);		\
> +	mutex_unlock(&matrix_dev->guests_lock);		\
> +})
> +
>   /**
>    * vfio_ap_mdev_get_queue - retrieve a queue with a specific APQN from a
>    *			    hash table of queues assigned to a matrix mdev
> @@ -830,7 +875,7 @@ static ssize_t assign_adapter_store(struct device *dev,
>   
>   	struct ap_matrix_mdev *matrix_mdev = dev_get_drvdata(dev);
>   
> -	mutex_lock(&matrix_dev->mdevs_lock);
> +	get_update_locks_for_mdev(matrix_mdev);
>   
>   	/* If the KVM guest is running, disallow assignment of adapter */
>   	if (matrix_mdev->kvm) {
> @@ -862,7 +907,7 @@ static ssize_t assign_adapter_store(struct device *dev,
>   				   matrix_mdev->matrix.aqm, matrix_mdev);
>   	ret = count;
>   done:
> -	mutex_unlock(&matrix_dev->mdevs_lock);
> +	release_update_locks_for_mdev(matrix_mdev);
>   
>   	return ret;
>   }
> @@ -905,7 +950,7 @@ static ssize_t unassign_adapter_store(struct device *dev,
>   	unsigned long apid;
>   	struct ap_matrix_mdev *matrix_mdev = dev_get_drvdata(dev);
>   
> -	mutex_lock(&matrix_dev->mdevs_lock);
> +	get_update_locks_for_mdev(matrix_mdev);
>   
>   	/* If the KVM guest is running, disallow unassignment of adapter */
>   	if (matrix_mdev->kvm) {
> @@ -930,7 +975,7 @@ static ssize_t unassign_adapter_store(struct device *dev,
>   
>   	ret = count;
>   done:
> -	mutex_unlock(&matrix_dev->mdevs_lock);
> +	release_update_locks_for_mdev(matrix_mdev);
>   	return ret;
>   }
>   static DEVICE_ATTR_WO(unassign_adapter);
> @@ -985,7 +1030,7 @@ static ssize_t assign_domain_store(struct device *dev,
>   	struct ap_matrix_mdev *matrix_mdev = dev_get_drvdata(dev);
>   	unsigned long max_apqi = matrix_mdev->matrix.aqm_max;
>   
> -	mutex_lock(&matrix_dev->mdevs_lock);
> +	get_update_locks_for_mdev(matrix_mdev);
>   
>   	/* If the KVM guest is running, disallow assignment of domain */
>   	if (matrix_mdev->kvm) {
> @@ -1016,7 +1061,7 @@ static ssize_t assign_domain_store(struct device *dev,
>   				   matrix_mdev);
>   	ret = count;
>   done:
> -	mutex_unlock(&matrix_dev->mdevs_lock);
> +	release_update_locks_for_mdev(matrix_mdev);
>   
>   	return ret;
>   }
> @@ -1059,7 +1104,7 @@ static ssize_t unassign_domain_store(struct device *dev,
>   	unsigned long apqi;
>   	struct ap_matrix_mdev *matrix_mdev = dev_get_drvdata(dev);
>   
> -	mutex_lock(&matrix_dev->mdevs_lock);
> +	get_update_locks_for_mdev(matrix_mdev);
>   
>   	/* If the KVM guest is running, disallow unassignment of domain */
>   	if (matrix_mdev->kvm) {
> @@ -1085,7 +1130,7 @@ static ssize_t unassign_domain_store(struct device *dev,
>   	ret = count;
>   
>   done:
> -	mutex_unlock(&matrix_dev->mdevs_lock);
> +	release_update_locks_for_mdev(matrix_mdev);
>   	return ret;
>   }
>   static DEVICE_ATTR_WO(unassign_domain);
> @@ -1112,7 +1157,7 @@ static ssize_t assign_control_domain_store(struct device *dev,
>   	unsigned long id;
>   	struct ap_matrix_mdev *matrix_mdev = dev_get_drvdata(dev);
>   
> -	mutex_lock(&matrix_dev->mdevs_lock);
> +	get_update_locks_for_mdev(matrix_mdev);
>   
>   	/* If the KVM guest is running, disallow assignment of control domain */
>   	if (matrix_mdev->kvm) {
> @@ -1138,7 +1183,7 @@ static ssize_t assign_control_domain_store(struct device *dev,
>   	vfio_ap_mdev_filter_cdoms(matrix_mdev);
>   	ret = count;
>   done:
> -	mutex_unlock(&matrix_dev->mdevs_lock);
> +	release_update_locks_for_mdev(matrix_mdev);
>   	return ret;
>   }
>   static DEVICE_ATTR_WO(assign_control_domain);
> @@ -1166,7 +1211,7 @@ static ssize_t unassign_control_domain_store(struct device *dev,
>   	struct ap_matrix_mdev *matrix_mdev = dev_get_drvdata(dev);
>   	unsigned long max_domid =  matrix_mdev->matrix.adm_max;
>   
> -	mutex_lock(&matrix_dev->mdevs_lock);
> +	get_update_locks_for_mdev(matrix_mdev);
>   
>   	/* If a KVM guest is running, disallow unassignment of control domain */
>   	if (matrix_mdev->kvm) {
> @@ -1189,7 +1234,7 @@ static ssize_t unassign_control_domain_store(struct device *dev,
>   
>   	ret = count;
>   done:
> -	mutex_unlock(&matrix_dev->mdevs_lock);
> +	release_update_locks_for_mdev(matrix_mdev);
>   	return ret;
>   }
>   static DEVICE_ATTR_WO(unassign_control_domain);

Reviewed-by: Jason J. Herne <jjherne@linux.ibm.com>

-- 
-- Jason J. Herne (jjherne@linux.ibm.com)