Re: [PATCH v10 04/16] s390/zcrypt: driver callback to indicate resource in use

[Tony Krowiak]

On 9/17/20 8:14 AM, Cornelia Huck wrote:
> On Tue, 15 Sep 2020 15:32:35 -0400
> Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
>
> > On 9/14/20 11:29 AM, Cornelia Huck wrote:
> > > On Fri, 21 Aug 2020 15:56:04 -0400
> > > Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
> > >   
> > > > Introduces a new driver callback to prevent a root user from unbinding
> > > > an AP queue from its device driver if the queue is in use. The intent of
> > > > this callback is to provide a driver with the means to prevent a root user
> > > > from inadvertently taking a queue away from a matrix mdev and giving it to
> > > > the host while it is assigned to the matrix mdev. The callback will
> > > > be invoked whenever a change to the AP bus's sysfs apmask or aqmask
> > > > attributes would result in one or more AP queues being removed from its
> > > > driver. If the callback responds in the affirmative for any driver
> > > > queried, the change to the apmask or aqmask will be rejected with a device
> > > > in use error.
> > > >
> > > > For this patch, only non-default drivers will be queried. Currently,
> > > > there is only one non-default driver, the vfio_ap device driver. The
> > > > vfio_ap device driver facilitates pass-through of an AP queue to a
> > > > guest. The idea here is that a guest may be administered by a different
> > > > sysadmin than the host and we don't want AP resources to unexpectedly
> > > > disappear from a guest's AP configuration (i.e., adapters, domains and
> > > > control domains assigned to the matrix mdev). This will enforce the proper
> > > > procedure for removing AP resources intended for guest usage which is to
> > > > first unassign them from the matrix mdev, then unbind them from the
> > > > vfio_ap device driver.
> > > >
> > > > Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
> > > > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > > This looks a bit odd...
> > I've removed all of those. These kernel test robot errors were flagged
> > in the last series. The review comments from the robot suggested
> > the reported-by, but I assume that was for patches intended to
> > fix those errors, so I am removing these as per Christian's comments.
> Yes, I think the Reported-by: mostly makes sense if you include a patch
> to fix something on top.
>
> > >   
> > > > ---
> > > >    drivers/s390/crypto/ap_bus.c | 148 ++++++++++++++++++++++++++++++++---
> > > >    drivers/s390/crypto/ap_bus.h |   4 +
> > > >    2 files changed, 142 insertions(+), 10 deletions(-)
> > > >   
> > > (...)
> > >   
> > > > @@ -1107,12 +1118,70 @@ static ssize_t apmask_show(struct bus_type *bus, char *buf)
> > > >    	return rc;
> > > >    }
> > > >    
> > > > +static int __verify_card_reservations(struct device_driver *drv, void *data)
> > > > +{
> > > > +	int rc = 0;
> > > > +	struct ap_driver *ap_drv = to_ap_drv(drv);
> > > > +	unsigned long *newapm = (unsigned long *)data;
> > > > +
> > > > +	/*
> > > > +	 * No need to verify whether the driver is using the queues if it is the
> > > > +	 * default driver.
> > > > +	 */
> > > > +	if (ap_drv->flags & AP_DRIVER_FLAG_DEFAULT)
> > > > +		return 0;
> > > > +
> > > > +	/* The non-default driver's module must be loaded */
> > > > +	if (!try_module_get(drv->owner))
> > > > +		return 0;
> > > > +
> > > > +	if (ap_drv->in_use)
> > > > +		if (ap_drv->in_use(newapm, ap_perms.aqm))
> > > > +			rc = -EADDRINUSE;
> > > ISTR that Christian suggested -EBUSY in a past revision of this series?
> > > I think that would be more appropriate.
> > I went back and looked and sure enough, he did recommend that.
> > You have a great memory! I didn't respond to that comment, so I
> > must have missed it at the time.
> >
> > I personally prefer EADDRINUSE because I think it is more indicative
> > of the reason an AP resource can not be assigned back to the host
> > drivers is because it is in use by a guest or, at the very least, reserved
> > for use by a guest (i.e., assigned to an mdev). To say it is busy implies
> > that the device is busy performing encryption services which may or
> > may not be true at a given moment. Even if so, that is not the reason
> > for refusing to allow reassignment of the device.
> I have a different understanding of these error codes: EADDRINUSE is
> something used in the networking context when an actual address is
> already used elsewhere. EBUSY is more of a generic error that indicates
> that a certain resource is not free to perform the requested operation;
> it does not necessarily mean that the resource is currently actively
> doing something. Kind of when you get EBUSY when trying to eject
> something another program holds a reference on: that other program
> might not actually be doing anything, but it potentially could.

I'll go ahead and change it to -EBUSY.

>