[PATCH v16 00/14] s390/vfio-ap: dynamic configuration support

Tony Krowiak
2021-05-10T16:44:39Z

Note: Patch 1, "s390/vfio-ap: fix memory leak in mdev remove callback"
does not belong to this series. It is currently being reviewed
and is included here because it will be a pre-req for this series
when it is accepted and merged.

The current design for AP pass-through does not support making dynamic
changes to the AP matrix of a running guest resulting in a few
deficiencies this patch series is intended to mitigate:

1. Adapters, domains and control domains can not be added to or removed
from a running guest. In order to modify a guest's AP configuration,
the guest must be terminated; only then can AP resources be assigned
to or unassigned from the guest's matrix mdev. The new AP
configuration becomes available to the guest when it is subsequently
restarted.

2. The AP bus's /sys/bus/ap/apmask and /sys/bus/ap/aqmask interfaces can
be modified by a root user without any restrictions. A change to
either mask can result in AP queue devices being unbound from the
vfio_ap device driver and bound to a zcrypt device driver even if a
guest is using the queues, thus giving the host access to the guest's
private crypto data and vice versa.

3. The APQNs derived from the Cartesian product of the APIDs of the
adapters and APQIs of the domains assigned to a matrix mdev must
reference an AP queue device bound to the vfio_ap device driver. The
AP architecture allows assignment of AP resources that are not
available to the system, so this artificial restriction is not
compliant with the architecture.

4. The AP configuration profile can be dynamically changed for the linux
host after a KVM guest is started. For example, a new domain can be
dynamically added to the configuration profile via the SE or an HMC
connected to a DPM enabled lpar. Likewise, AP adapters can be
dynamically configured (online state) and deconfigured (standby state)
using the SE, an SCLP command or an HMC connected to a DPM enabled
lpar. This can result in inadvertent sharing of AP queues between the
guest and host.

5. A root user can manually unbind an AP queue device representing a
queue in use by a KVM guest via the vfio_ap device driver's sysfs
unbind attribute. In this case, the guest will be using a queue that
is not bound to the driver which violates the device model.

This patch series introduces the following changes to the current design
to alleviate the shortcomings described above as well as to implement
more of the AP architecture:

1. A root user will be prevented from making edits to the AP bus's
/sys/bus/ap/apmask or /sys/bus/ap/aqmask if the change would transfer
ownership of an APQN from the vfio_ap device driver to a zcrypt driver
while the APQN is assigned to a matrix mdev.

2. Allow a root user to hot plug/unplug AP adapters, domains and control
domains for a KVM guest using the matrix mdev via its sysfs
assign/unassign attributes.

4. Allow assignment of an AP adapter or domain to a matrix mdev even if
it results in assignment of an APQN that does not reference an AP
queue device bound to the vfio_ap device driver, as long as the APQN
is not reserved for use by the default zcrypt drivers (also known as
over-provisioning of AP resources). Allowing over-provisioning of AP
resources better models the architecture which does not preclude
assigning AP resources that are not yet available in the system. Such
APQNs, however, will not be assigned to the guest using the matrix
mdev; only APQNs referencing AP queue devices bound to the vfio_ap
device driver will actually get assigned to the guest.

5. Handle dynamic changes to the AP device model.

1. Rationale for changes to AP bus's apmask/aqmask interfaces:
----------------------------------------------------------
Due to the extremely sensitive nature of cryptographic data, it is
imperative that great care be taken to ensure that such data is secured.
Allowing a root user, either inadvertently or maliciously, to configure
these masks such that a queue is shared between the host and a guest is
not only avoidable, it is advisable. It was suggested that this scenario
is better handled in user space with management software, but that does
not preclude a malicious administrator from using the sysfs interfaces
to gain access to a guest's crypto data. It was also suggested that this
scenario could be avoided by taking access to the adapter away from the
guest and zeroing out the queues prior to the vfio_ap driver releasing the
device; however, stealing an adapter in use from a guest as a by-product
of an operation is bad and will likely cause problems for the guest
unnecessarily. It was decided that the most effective solution with the
least number of negative side effects is to prevent the situation at the
source.

2. Rationale for hot plug/unplug using matrix mdev sysfs interfaces:
----------------------------------------------------------------
Allowing a user to hot plug/unplug AP resources using the matrix mdev
sysfs interfaces circumvents the need to terminate the guest in order to
modify its AP configuration. Allowing dynamic configuration makes
reconfiguring a guest's AP matrix much less disruptive.

3. Rationale for allowing over-provisioning of AP resources:
-----------------------------------------------------------
Allowing assignment of AP resources to a matrix mdev and ultimately to a
guest better models the AP architecture. The architecture does not
preclude assignment of unavailable AP resources. If a queue subsequently
becomes available while a guest using the matrix mdev to which its APQN
is assigned, the guest will be given access to it. If an APQN
is dynamically unassigned from the underlying host system, it will
automatically become unavailable to the guest.

Change log v15-v16:
------------------
* Added patch to reset queues after an adapter or domain is unassigned in
case of re-assignment to a different mdev (see patch description for
patch 9, "s390/vfio-ap: reset queues after adapter/domain unassignment").

* Fixed circular lockdep re-introduced by hot plugging of AP resources into
a KVM guest (see changes to vfio_ap_mdev_commit_apcb() function in patch
8, "s390/vfio-ap: allow hot plug/unplug of AP resources using mdev
device").

Change log v14-v15:
------------------
* Fixed bug: Unlink mdev from all queues when the mdev is removed.

Change log v13-v14:
------------------
* Removed patch "s390/vfio-ap: clean up vfio_ap resources when KVM pointer
invalidated". The patch is not necessary because that is handled
with patch 1 of this series (currently being merged) and
commit f21916ec4826 ("s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated")

* Removed patch "s390/vfio-ap: No need to disable IRQ after queue reset",
that has already been merged with
commit 6c12a6384e0c ("s390/vfio-ap: No need to disable IRQ after queue reset").

* Initialize the vfio_ap_queue object before setting the drvdata in
the probe callback

* Change return code from mdev assignment interfaces to -EAGAIN when
mutex_trylock fails for the mdev lock.

* Restored missing hunk from v12 in the group notifier callback, but
had to restore it to the vfio_ap_mdev_set_kvm() function due to
changes made via merged commits noted above.

* Reordered patch "s390/vfio-ap: sysfs attribute to display the
guest's matrix" to follow the patches that modify the shadow
APCB.

* Remove queue from APCB before resetting it in the remove
callback.

* Split the vfio_ap_mdev_unlink_queue() function into two
functions: one to remove the link from the matrix mdev to
the queue; and, one to remove the link from the queue to the matrix
mdev.

* Removed the QCI call and the shadow_apcb memcpy from the
vfio_ap_mdev_filter_apcb() function.

* Do not clear shadow_apcb when there are not adapters or domains
assigned.

* Moved filtering code from "s390/vfio-ap: allow hot plug/unplug of
AP resources using mdev device" into its own patch.

* Squashed the two patches comprising the handling of changes to
the AP configuration into one patch.

* Added code to delay hot plug during probe until the AP bus scan
is complete if the APID of the queue is in the bitmap of adapters
currently being added to the AP configuration.

Change log v12-v13:
------------------
* Combined patches 12/13 from previous series into one patch

* Moved all changes for linking queues and mdevs into a single patch

* Re-ordered some patches to aid in review

* Using mutex_trylock() function in adapter/domain assignment functions
to avoid potential deadlock condition with in_use callback

* Using filtering function for refreshing the guest's APCB for all events
that change the APCB: assign/unassign adapters, domains, control domains;
bind/unbind of queue devices; and, changes to the host AP configuration.

Change log v11-v12:
------------------
* Moved matrix device lock to protect group notifier callback

* Split the 'No need to disable IRQ after queue reset' patch into
multiple patches for easier review (move probe/remove callback
functions and remove disable IRQ after queue reset)

* Added code to decrement reference count for KVM in group notifier
callback

* Using mutex_trylock() in functions implementing the sysfs assign_adapter
and assign_domain as well as the in_use callback to avoid deadlock
between the AP bus's ap_perms mutex and the matrix device lock used by
vfio_ap driver.

* The sysfs guest_matrix attribute of the vfio_ap mdev will now display
the shadow APCB regardless of whether a guest is using the mdev or not

* Replaced vfio_ap mdev filtering function with a function that initializes
the guest's APCB by filtering the vfio_ap mdev by APID.

* No longer using filtering function during adapter/domain assignment
to/from the vfio_ap mdev; replaced with new hot plug/unplug
adapter/domain functions.

* No longer using filtering function during bind/unbind; replaced with
hot plug/unplug queue functions.

* No longer using filtering function for bulk assignment of new adapters
and domains in on_scan_complete callback; replaced with new hot plug
functions.

Change log v10-v11:
------------------
* The matrix mdev's configuration is not filtered by APID so that if any
APQN assigned to the mdev is not bound to the vfio_ap device driver,
the adapter will not get plugged into the KVM guest on startup, or when
a new adapter is assigned to the mdev.

* Replaced patch 8 by squashing patches 8 (filtering patch) and 15 (handle
probe/remove).

* Added a patch 1 to remove disable IRQ after a reset because the reset
already disables a queue.

* Now using filtering code to update the KVM guest's matrix when
notified that AP bus scan has completed.

* Fixed issue with probe/remove not inititiated by a configuration change
occurring within a config change.

Change log v9-v10:
-----------------
* Updated the documentation in vfio-ap.rst to include information about the
AP dynamic configuration support

Change log v8-v9:
----------------
* Fixed errors flagged by the kernel test robot

* Fixed issue with guest losing queues when a new queue is probed due to
manual bind operation.

Change log v7-v8:
----------------
* Now logging a message when an attempt to reserve APQNs for the zcrypt
drivers will result in taking a queue away from a KVM guest to provide
the sysadmin a way to ascertain why the sysfs operation failed.

* Created locked and unlocked versions of the ap_parse_mask_str() function.

* Now using new interface provided by an AP bus patch -
s390/ap: introduce new ap function ap_get_qdev() - to retrieve
struct ap_queue representing an AP queue device. This patch is not a
part of this series but is a prerequisite for this series.

Change log v6-v7:
----------------
* Added callbacks to AP bus:
- on_config_changed: Notifies implementing drivers that
the AP configuration has changed since last AP device scan.
- on_scan_complete: Notifies implementing drivers that the device scan
has completed.
- implemented on_config_changed and on_scan_complete callbacks for
vfio_ap device driver.
- updated vfio_ap device driver's probe and remove callbacks to handle
dynamic changes to the AP device model.
* Added code to filter APQNs when assigning AP resources to a KVM guest's
CRYCB

Change log v5-v6:
----------------
* Fixed a bug in ap_bus.c introduced with patch 2/7 of the v5
series. Harald Freudenberer pointed out that the mutex lock
for ap_perms_mutex in the apmask_store and aqmask_store functions
was not being freed.

* Removed patch 6/7 which added logging to the vfio_ap driver
to expedite acceptance of this series. The logging will be introduced
with a separate patch series to allow more time to explore options
such as DBF logging vs. tracepoints.

* Added 3 patches related to ensuring that APQNs that do not reference
AP queue devices bound to the vfio_ap device driver are not assigned
to the guest CRYCB:

Patch 4: Filter CRYCB bits for unavailable queue devices
Patch 5: sysfs attribute to display the guest CRYCB
Patch 6: update guest CRYCB in vfio_ap probe and remove callbacks

* Added a patch (Patch 9) to version the vfio_ap module.

* Reshuffled patches to allow the in_use callback implementation to
invoke the vfio_ap_mdev_verify_no_sharing() function introduced in
patch 2.

Change log v4-v5:
----------------
* Added a patch to provide kernel s390dbf debug logs for VFIO AP

Change log v3->v4:
-----------------
* Restored patches preventing root user from changing ownership of
APQNs from zcrypt drivers to the vfio_ap driver if the APQN is
assigned to an mdev.

* No longer enforcing requirement restricting guest access to
queues represented by a queue device bound to the vfio_ap
device driver.

* Removed shadow CRYCB and now directly updating the guest CRYCB
from the matrix mdev's matrix.

* Rebased the patch series on top of 'vfio: ap: AP Queue Interrupt
Control' patches.

* Disabled bind/unbind sysfs interfaces for vfio_ap driver

Change log v2->v3:
-----------------
* Allow guest access to an AP queue only if the queue is bound to
the vfio_ap device driver.

* Removed the patch to test CRYCB masks before taking the vCPUs
out of SIE. Now checking the shadow CRYCB in the vfio_ap driver.

Change log v1->v2:
-----------------
* Removed patches preventing root user from unbinding AP queues from
the vfio_ap device driver
* Introduced a shadow CRYCB in the vfio_ap driver to manage dynamic
changes to the AP guest configuration due to root user interventions
or hardware anomalies.

Tony Krowiak (14):
s390/vfio-ap: fix memory leak in mdev remove callback
s390/vfio-ap: use new AP bus interface to search for queue devices
s390/vfio-ap: move probe and remove callbacks to vfio_ap_ops.c
s390/vfio-ap: manage link between queue struct and matrix mdev
s390/vfio-ap: introduce shadow APCB
s390/vfio-ap: refresh guest's APCB by filtering APQNs assigned to mdev
s390/vfio-ap: allow assignment of unavailable AP queues to mdev device
s390/vfio-ap: allow hot plug/unplug of AP resources using mdev device
s390/vfio-ap: reset queues after adapter/domain unassignment
s390/zcrypt: driver callback to indicate resource in use
s390/vfio-ap: implement in-use callback for vfio_ap driver
s390/vfio-ap: sysfs attribute to display the guest's matrix
s390/zcrypt: notify drivers on config changed and scan complete
callbacks
s390/vfio-ap: update docs to include dynamic config support

Documentation/s390/vfio-ap.rst | 383 +++++++---
drivers/s390/crypto/ap_bus.c | 249 +++++-
drivers/s390/crypto/ap_bus.h | 16 +
drivers/s390/crypto/vfio_ap_drv.c | 46 +-
drivers/s390/crypto/vfio_ap_ops.c | 1008 ++++++++++++++++++-------
drivers/s390/crypto/vfio_ap_private.h | 28 +-
6 files changed, 1322 insertions(+), 408 deletions(-)

--
2.30.2