Re: [PATCH v3] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated

[Halil Pasic]

On Mon, 14 Dec 2020 11:56:17 -0500
Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:

> The vfio_ap device driver registers a group notifier with VFIO when the
> file descriptor for a VFIO mediated device for a KVM guest is opened to
> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
> event). When the KVM pointer is set, the vfio_ap driver takes the
> following actions:
> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
>    of the mediated device.
> 2. Calls the kvm_get_kvm() function to increment its reference counter.
> 3. Sets the function pointer to the function that handles interception of
>    the instruction that enables/disables interrupt processing.
> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
>    the guest.
> 
> In order to avoid memory leaks, when the notifier is called to receive
> notification that the KVM pointer has been set to NULL, the vfio_ap device
> driver should reverse the actions taken when the KVM pointer was set.
> 
> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
> Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
> ---
>  drivers/s390/crypto/vfio_ap_ops.c | 29 ++++++++++++++++++++---------
>  1 file changed, 20 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index e0bde8518745..cd22e85588e1 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -1037,8 +1037,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
>  {
>  	struct ap_matrix_mdev *m;
> 
> -	mutex_lock(&matrix_dev->lock);
> -
>  	list_for_each_entry(m, &matrix_dev->mdev_list, node) {
>  		if ((m != matrix_mdev) && (m->kvm == kvm)) {
>  			mutex_unlock(&matrix_dev->lock);
> @@ -1049,7 +1047,6 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
>  	matrix_mdev->kvm = kvm;
>  	kvm_get_kvm(kvm);
>  	kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
> -	mutex_unlock(&matrix_dev->lock);
> 
>  	return 0;
>  }
> @@ -1083,35 +1080,49 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb,
>  	return NOTIFY_DONE;
>  }
> 
> +static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
> +{
> +	kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
> +	matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;


This patch LGTM. The only concern I have with it is whether a
different cpu is guaranteed to observe the above assignment as
an atomic operation. I think we didn't finish this discussion
at v1, or did we?

Regards,
Halil

> +	vfio_ap_mdev_reset_queues(matrix_mdev->mdev);
> +	kvm_put_kvm(matrix_mdev->kvm);
> +	matrix_mdev->kvm = NULL;
> +}
> +
>  static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
>  				       unsigned long action, void *data)
>  {
> -	int ret;
> +	int ret, notify_rc = NOTIFY_DONE;
>  	struct ap_matrix_mdev *matrix_mdev;
> 
>  	if (action != VFIO_GROUP_NOTIFY_SET_KVM)
>  		return NOTIFY_OK;
> 
>  	matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier);
> +	mutex_lock(&matrix_dev->lock);
> 
>  	if (!data) {
> -		matrix_mdev->kvm = NULL;
> -		return NOTIFY_OK;
> +		if (matrix_mdev->kvm)
> +			vfio_ap_mdev_unset_kvm(matrix_mdev);
> +		notify_rc = NOTIFY_OK;
> +		goto notify_done;
>  	}
> 
>  	ret = vfio_ap_mdev_set_kvm(matrix_mdev, data);
>  	if (ret)
> -		return NOTIFY_DONE;
> +		goto notify_done;
> 
>  	/* If there is no CRYCB pointer, then we can't copy the masks */
>  	if (!matrix_mdev->kvm->arch.crypto.crycbd)
> -		return NOTIFY_DONE;
> +		goto notify_done;
> 
>  	kvm_arch_crypto_set_masks(matrix_mdev->kvm, matrix_mdev->matrix.apm,
>  				  matrix_mdev->matrix.aqm,
>  				  matrix_mdev->matrix.adm);
> 
> -	return NOTIFY_OK;
> +notify_done:
> +	mutex_unlock(&matrix_dev->lock);
> +	return notify_rc;
>  }
> 
>  static void vfio_ap_irq_disable_apqn(int apqn)