From: Halil Pasic <pasic@linux.ibm.com>
To: Matthew Rosato <mjrosato@linux.ibm.com>
Cc: Tony Krowiak <akrowiak@linux.ibm.com>,
linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org, freude@linux.ibm.com,
borntraeger@de.ibm.com, cohuck@redhat.com,
alex.williamson@redhat.com, kwankhede@nvidia.com,
fiuczy@linux.ibm.com, frankja@linux.ibm.com, david@redhat.com,
hca@linux.ibm.com, gor@linux.ibm.com
Subject: Re: [PATCH v13 11/15] s390/vfio-ap: implement in-use callback for vfio_ap driver
Date: Tue, 12 Jan 2021 17:49:35 +0100 [thread overview]
Message-ID: <20210112174935.41cbda87.pasic@linux.ibm.com> (raw)
In-Reply-To: <d717a554-6d0c-6075-38fd-e725b9622437@linux.ibm.com>
On Tue, 12 Jan 2021 09:14:07 -0500
Matthew Rosato <mjrosato@linux.ibm.com> wrote:
> On 1/11/21 8:20 PM, Halil Pasic wrote:
> > On Tue, 22 Dec 2020 20:16:02 -0500
> > Tony Krowiak <akrowiak@linux.ibm.com> wrote:
> >
> >> Let's implement the callback to indicate when an APQN
> >> is in use by the vfio_ap device driver. The callback is
> >> invoked whenever a change to the apmask or aqmask would
> >> result in one or more queue devices being removed from the driver. The
> >> vfio_ap device driver will indicate a resource is in use
> >> if the APQN of any of the queue devices to be removed are assigned to
> >> any of the matrix mdevs under the driver's control.
> >>
> >> There is potential for a deadlock condition between the matrix_dev->lock
> >> used to lock the matrix device during assignment of adapters and domains
> >> and the ap_perms_mutex locked by the AP bus when changes are made to the
> >> sysfs apmask/aqmask attributes.
> >>
> >> Consider following scenario (courtesy of Halil Pasic):
> >> 1) apmask_store() takes ap_perms_mutex
> >> 2) assign_adapter_store() takes matrix_dev->lock
> >> 3) apmask_store() calls vfio_ap_mdev_resource_in_use() which tries
> >> to take matrix_dev->lock
> >> 4) assign_adapter_store() calls ap_apqn_in_matrix_owned_by_def_drv
> >> which tries to take ap_perms_mutex
> >>
> >> BANG!
> >>
> >> To resolve this issue, instead of using the mutex_lock(&matrix_dev->lock)
> >> function to lock the matrix device during assignment of an adapter or
> >> domain to a matrix_mdev as well as during the in_use callback, the
> >> mutex_trylock(&matrix_dev->lock) function will be used. If the lock is not
> >> obtained, then the assignment and in_use functions will terminate with
> >> -EBUSY.
> >>
> >> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> >> ---
> >> drivers/s390/crypto/vfio_ap_drv.c | 1 +
> >> drivers/s390/crypto/vfio_ap_ops.c | 21 ++++++++++++++++++---
> >> drivers/s390/crypto/vfio_ap_private.h | 2 ++
> >> 3 files changed, 21 insertions(+), 3 deletions(-)
> >>
> > [..]
> >> }
> >> +
> >> +int vfio_ap_mdev_resource_in_use(unsigned long *apm, unsigned long *aqm)
> >> +{
> >> + int ret;
> >> +
> >> + if (!mutex_trylock(&matrix_dev->lock))
> >> + return -EBUSY;
> >> + ret = vfio_ap_mdev_verify_no_sharing(NULL, apm, aqm);
> >
> > If we detect that resources are in use, then we spit warnings to the
> > message log, right?
> >
> > @Matt: Is your userspace tooling going to guarantee that this will never
> > happen?
>
> Yes, but only when using the tooling to modify apmask/aqmask. You would
> still be able to create such a scenario by bypassing the tooling and
> invoking the sysfs interfaces directly.
>
>
Since, I suppose, the tooling is going to catch this anyway, and produce
much better feedback to the user, I believe we should be fine degrading
the severity to info or debug.
I would prefer not producing a warning here, because I believe it is
likely to do more harm, than good (by implying a kernel problem, as I
don't think based on the message one will think that it is an userspace
problem). But if everybody else agrees, that we want a warning here, then
I can live with that as well.
Regards,
Halil
next prev parent reply other threads:[~2021-01-12 16:50 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-23 1:15 [PATCH v13 00/15] s390/vfio-ap: dynamic configuration support Tony Krowiak
2020-12-23 1:15 ` [PATCH v13 01/15] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated Tony Krowiak
2020-12-23 1:15 ` [PATCH v13 02/15] s390/vfio-ap: No need to disable IRQ after queue reset Tony Krowiak
2021-01-11 16:32 ` Halil Pasic
2021-01-13 17:06 ` Tony Krowiak
2021-01-13 21:21 ` Halil Pasic
2021-01-14 0:46 ` Tony Krowiak
2021-01-14 3:13 ` Halil Pasic
2020-12-23 1:15 ` [PATCH v13 03/15] s390/vfio-ap: move probe and remove callbacks to vfio_ap_ops.c Tony Krowiak
2020-12-23 1:15 ` [PATCH v13 04/15] s390/vfio-ap: use new AP bus interface to search for queue devices Tony Krowiak
2020-12-23 1:15 ` [PATCH v13 05/15] s390/vfio-ap: manage link between queue struct and matrix mdev Tony Krowiak
2021-01-11 19:17 ` Halil Pasic
2021-01-13 21:41 ` Tony Krowiak
2021-01-14 2:50 ` Halil Pasic
2021-01-14 21:10 ` Tony Krowiak
2020-12-23 1:15 ` [PATCH v13 06/15] s390/vfio-ap: allow assignment of unavailable AP queues to mdev device Tony Krowiak
2021-01-11 20:40 ` Halil Pasic
2021-01-14 17:54 ` Tony Krowiak
2021-01-15 1:08 ` Halil Pasic
2021-01-15 1:44 ` Halil Pasic
2021-03-31 14:36 ` Tony Krowiak
2020-12-23 1:15 ` [PATCH v13 07/15] s390/vfio-ap: introduce shadow APCB Tony Krowiak
2021-01-11 22:50 ` Halil Pasic
2021-01-14 21:35 ` Tony Krowiak
2020-12-23 1:15 ` [PATCH v13 08/15] s390/vfio-ap: sysfs attribute to display the guest's matrix Tony Krowiak
2021-01-11 22:58 ` Halil Pasic
2021-01-28 21:29 ` Tony Krowiak
2020-12-23 1:16 ` [PATCH v13 09/15] s390/vfio-ap: allow hot plug/unplug of AP resources using mdev device Tony Krowiak
2021-01-12 1:12 ` Halil Pasic
2021-01-12 17:55 ` Halil Pasic
2021-02-01 14:41 ` Tony Krowiak
2021-02-03 23:13 ` Tony Krowiak
2021-02-04 0:21 ` Halil Pasic
2020-12-23 1:16 ` [PATCH v13 10/15] s390/zcrypt: driver callback to indicate resource in use Tony Krowiak
2021-01-12 16:50 ` Halil Pasic
2020-12-23 1:16 ` [PATCH v13 11/15] s390/vfio-ap: implement in-use callback for vfio_ap driver Tony Krowiak
2021-01-12 1:20 ` Halil Pasic
2021-01-12 14:14 ` Matthew Rosato
2021-01-12 16:49 ` Halil Pasic [this message]
2020-12-23 1:16 ` [PATCH v13 12/15] s390/zcrypt: Notify driver on config changed and scan complete callbacks Tony Krowiak
2021-01-12 16:58 ` Halil Pasic
2020-12-23 1:16 ` [PATCH v13 13/15] s390/vfio-ap: handle host AP config change notification Tony Krowiak
2021-01-12 18:39 ` Halil Pasic
2020-12-23 1:16 ` [PATCH v13 14/15] s390/vfio-ap: handle AP bus scan completed notification Tony Krowiak
2021-01-12 18:44 ` Halil Pasic
2020-12-23 1:16 ` [PATCH v13 15/15] s390/vfio-ap: update docs to include dynamic config support Tony Krowiak
2021-01-06 15:16 ` [PATCH v13 00/15] s390/vfio-ap: dynamic configuration support Tony Krowiak
2021-01-07 14:41 ` Halil Pasic
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