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

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Date:   Wed, 5 May 2021 15:00:38 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>
Cc:     Tony Krowiak <akrowiak@...ux.ibm.com>, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, cohuck@...hat.com,
        pasic@...ux.vnet.ibm.com, jjherne@...ux.ibm.com,
        alex.williamson@...hat.com, kwankhede@...dia.com,
        stable@...r.kernel.org, Tony Krowiak <akrowiak@...y.rr.com>
Subject: Re: [PATCH] s390/vfio-ap: fix memory leak in mdev remove callback

On Wed, May 05, 2021 at 07:44:55PM +0200, 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.

+1

Jason