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

[Tony Krowiak]

On 5/5/21 1:44 PM, Christian Borntraeger wrote:
> 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);
> >         mutex_lock(&matrix_dev->lock);
> > -
> > -    /*
> > -     * 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.

I'll take the warning out.

> >       vfio_ap_mdev_reset_queues(mdev);
> >       list_del(&matrix_mdev->node);
> >       kfree(matrix_mdev);