Re: [PATCH v13 00/15] s390/vfio-ap: dynamic configuration support

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On 12/22/20 8:15 PM, Tony Krowiak wrote:
Note: Patch 1, s390/vfio-ap: clean up vfio_ap resources when KVM
       pointer invalidated does not belong to this series. It has been
       posted as a separate patch to fix a known problem. It is included
       here because it will likely pre-req for this series.

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 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 (15):
   s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated
   s390/vfio-ap: No need to disable IRQ after queue reset
   s390/vfio-ap: move probe and remove callbacks to vfio_ap_ops.c
   s390/vfio-ap: use new AP bus interface to search for queue devices
   s390/vfio-ap: manage link between queue struct and matrix mdev
   s390/vfio-ap: allow assignment of unavailable AP queues to mdev device
   s390/vfio-ap: introduce shadow APCB
   s390/vfio-ap: sysfs attribute to display the guest's matrix
   s390/vfio-ap: allow hot plug/unplug of AP resources using mdev device
   s390/zcrypt: driver callback to indicate resource in use
   s390/vfio-ap: implement in-use callback for vfio_ap driver
   s390/zcrypt: Notify driver on config changed and scan complete
     callbacks
   s390/vfio-ap: handle host AP config change notification
   s390/vfio-ap: handle AP bus scan completed notification
   s390/vfio-ap: update docs to include dynamic config support

  Documentation/s390/vfio-ap.rst        | 383 ++++++++---
  drivers/s390/crypto/ap_bus.c          | 251 +++++++-
  drivers/s390/crypto/ap_bus.h          |  16 +
  drivers/s390/crypto/vfio_ap_drv.c     |  50 +-
  drivers/s390/crypto/vfio_ap_ops.c     | 891 +++++++++++++++++---------
  drivers/s390/crypto/vfio_ap_private.h |  29 +-
  6 files changed, 1170 insertions(+), 450 deletions(-)





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