On 06/29/2018 11:11 PM, Tony Krowiak wrote:
This patch provides documentation describing the AP architecture and design concepts behind the virtualization of AP devices. It also includes an example of how to configure AP devices for exclusive use of KVM guests. Signed-off-by: Tony Krowiak <akrow...@linux.ibm.com>
I don't like the design of external interfaces except for: * cpu model features, and * reset handling. In particular: 1) The architecture is such that authorizing access (via APM, AQM and ADM) to an AP queue that is currently not configured (e.g. the card not physically plugged, or just configured off). That seems to be a perfectly normal use case. Your assign operations however enforce that the resource is bound to your driver, and thus the existence of the resource in the host. It is clear: we need to avoid passing trough resources to guests that are not dedicated for this purpose (e.g. a queue utilized by zcrypt). But IMHO we need a different mechanism. 2) I see no benefit in deferring the exclusivity check to vfio_ap_mdev_open(). The downside is however pretty obvious: management software is notified about a 'bad configuration' only at an attempted guest start-up. And your current QEMU patches are not very helpful in conveying this piece of information. I've talked with Boris, and AFAIR he said this is not acceptable to him (@Boris can you confirm). 3) We indicate the reason for failure due to a configuration problem (exclusivity or resource allocation) via pr_err() that is via kernel messages. I don't think this is very tooling/management software friendly, and I hope we don't expect admins to work with the sysfs interface long term. I mean the effects of the admin actions are not very persistent. Thus if the interface is a painful one, we are talking about potentially frequent pain. 4) If I were to act out the role of the administrator, I would prefer to think of specifying or changing the access controls of a guest in respect to AP (that is setting the AP matrix) as a single atomic operation -- which either succeeds or fails. The operation should succeed for any valid configuration, and fail for any invalid on. The current piecemeal approach seems even less fitting if we consider changing the access controls of a running guest. AFAIK changing access controls for a running guest is possible, and I don't see a reason why should we artificially prohibit this. I think the current sysfs interface for manipulating the matrix is good for manual playing around, but I would prefer having an interface that is better suited for programs (e.g. ioctl). Regards, Halil
