Messages in this thread | | | Subject | Re: [PATCH v17 00/15] s390/vfio-ap: dynamic configuration support | From | Tony Krowiak <> | Date | Mon, 15 Nov 2021 10:45:43 -0500 |
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PING!
On 10/21/21 11:23 AM, Tony Krowiak wrote: > 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 v16-v17: > ------------------ > * Introduced a new patch (patch 1) to remove the setting of the pqap hook > in the group notifier callback. It is now set when the vfio_ap device > driver is loaded. > > * Patch 6: > - Split the filtering of the APQNs and the control domains into > two functions and consolidated the vfio_ap_mdev_refresh_apcb and > vfio_ap_mdev_filter_apcb into one function named > vfio_ap_mdev_filter_matrix because the matrix is actually what is > being filtered. > > - Removed ACK by Halil Pasic because of changes above; needs re-review. > > * Introduced a new patch (patch 8) to keep track of active guests. > > * Patch 9 (patch 8 in v16): > - Refactored locking to ensure KVM lock is taken before > matrix_dev->lock when hot plugging adapters, domains and > control domains. > > - Removed ACK by Halil because of changes above; needs re-review. > > * Patch 14 (patch 13 in v16): > - This patch has been redesigned to ensure proper locking order (i.e., > taking kvm->lock before matrix_dev->lock). > > - Removed Halil's Removed-by because of changes above; needs re-review. > > Tony Krowiak (15): > s390/vfio-ap: Set pqap hook when vfio_ap module is loaded > 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: keep track of active guests > s390/vfio-ap: allow hot plug/unplug of AP resources using mdev device > s390/vfio-ap: reset queues after adapter/domain unassignment > s390/ap: 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/ap: notify drivers on config changed and scan complete callbacks > s390/vfio-ap: update docs to include dynamic config support > > Documentation/s390/vfio-ap.rst | 492 ++++++--- > arch/s390/include/asm/kvm_host.h | 10 +- > arch/s390/kvm/kvm-s390.c | 1 - > arch/s390/kvm/priv.c | 45 +- > drivers/s390/crypto/ap_bus.c | 241 ++++- > drivers/s390/crypto/ap_bus.h | 16 + > drivers/s390/crypto/vfio_ap_drv.c | 52 +- > drivers/s390/crypto/vfio_ap_ops.c | 1379 ++++++++++++++++++------- > drivers/s390/crypto/vfio_ap_private.h | 66 +- > 9 files changed, 1714 insertions(+), 588 deletions(-) >
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