From: Matthew Rosato <mjrosato@linux.ibm.com>
To: Halil Pasic <pasic@linux.ibm.com>, Tony Krowiak <akrowiak@linux.ibm.com>
Cc: 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 09:14:07 -0500 [thread overview]
Message-ID: <d717a554-6d0c-6075-38fd-e725b9622437@linux.ibm.com> (raw)
In-Reply-To: <20210112022012.4bad464f.pasic@linux.ibm.com>
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.
next prev parent reply other threads:[~2021-01-12 14:15 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 [this message]
2021-01-12 16:49 ` Halil Pasic
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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