linux-kernel - Re: [PATCH] s390/vfio-ap: Clean up vfio_ap resources when KVM pointer invalidated

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Date:   Mon, 7 Dec 2020 14:05:55 -0500
From:   Tony Krowiak <akrowiak@...ux.ibm.com>
To:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     borntraeger@...ibm.com, cohuck@...hat.com, pasic@...ux.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com, david@...hat.com
Subject: Re: [PATCH] s390/vfio-ap: Clean up vfio_ap resources when KVM pointer
 invalidated



On 12/2/20 6:41 PM, Tony Krowiak 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 stashes the pointer
> and calls the kvm_get_kvm() function to increment its reference counter.
> When the notifier is called to make notification that the KVM pointer has
> been set to NULL, the driver should clean up any resources associated with
> the KVM pointer and decrement its reference counter. The current
> implementation does not take care of this clean up.
>
> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
> ---
>   drivers/s390/crypto/vfio_ap_ops.c | 21 +++++++++++++--------
>   1 file changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index e0bde8518745..eeb9c9130756 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -1083,6 +1083,17 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb,
>   	return NOTIFY_DONE;
>   }
>   
> +static void vfio_ap_mdev_put_kvm(struct ap_matrix_mdev *matrix_mdev)
> +{
> +	if (matrix_mdev->kvm) {
> +		kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
> +		matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
> +		vfio_ap_mdev_reset_queues(matrix_mdev->mdev);

This reset probably does not belong here since there is no
reason to reset the queues in the group notifier (see below).
The reset should be done in the release callback only regardless
of whether the KVM pointer exists or not.

> +		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)
>   {
> @@ -1095,7 +1106,7 @@ static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
>   	matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier);
>   
>   	if (!data) {
> -		matrix_mdev->kvm = NULL;
> +		vfio_ap_mdev_put_kvm(matrix_mdev);
>   		return NOTIFY_OK;
>   	}
>   
> @@ -1222,13 +1233,7 @@ static void vfio_ap_mdev_release(struct mdev_device *mdev)
>   	struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
>   
>   	mutex_lock(&matrix_dev->lock);
> -	if (matrix_mdev->kvm) {
> -		kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
> -		matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
> -		vfio_ap_mdev_reset_queues(mdev);

This release should be moved outside of the block and
performed regardless of whether the KVM pointer exists or
not.

> -		kvm_put_kvm(matrix_mdev->kvm);
> -		matrix_mdev->kvm = NULL;
> -	}
> +	vfio_ap_mdev_put_kvm(matrix_mdev);
>   	mutex_unlock(&matrix_dev->lock);
>   
>   	vfio_unregister_notifier(mdev_dev(mdev), VFIO_IOMMU_NOTIFY,