Re: [PATCH] s390/vfio-ap: fix memory leak in mdev remove callback

From: Christian Borntraeger
Date: Wed May 05 2021 - 13:46:22 EST

On 05.05.21 19:28, Tony Krowiak wrote:
The mdev remove callback for the vfio_ap device driver bails out with
-EBUSY if the mdev is in use by a KVM guest. The intended purpose was
to prevent the mdev from being removed while in use; however, returning a
non-zero rc does not prevent removal. This could result in a memory leak
of the resources allocated when the mdev was created. In addition, the
KVM guest will still have access to the AP devices assigned to the mdev
even though the mdev no longer exists.

To prevent this scenario, cleanup will be done - including unplugging the
AP adapters, domains and control domains - regardless of whether the mdev
is in use by a KVM guest or not.
static int vfio_ap_mdev_create(struct mdev_device *mdev)
struct ap_matrix_mdev *matrix_mdev;
@@ -366,16 +392,9 @@ static int vfio_ap_mdev_remove(struct mdev_device *mdev)
struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);
- /*
- * If the KVM pointer is in flux or the guest is running, disallow
- * un-assignment of control domain.
- */
- if (matrix_mdev->kvm_busy || matrix_mdev->kvm) {
- mutex_unlock(&matrix_dev->lock);
- return -EBUSY;
- }
+ WARN(vfio_ap_mdev_has_crycb(matrix_mdev),
+ "Removing mdev leaves KVM guest without any crypto devices");
+ vfio_ap_mdev_clear_apcb(matrix_mdev);

Triggering a kernel warning due to an administrative task is not good.
Can't you simply clear the crycb? Maybe do a printk, but not a WARN.