Messages in this thread | | | Subject | Re: [PATCH v6 14/21] s390: vfio-ap: implement mediated device open callback | From | Halil Pasic <> | Date | Fri, 13 Jul 2018 12:48:49 +0200 |
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On 07/12/2018 06:03 PM, Tony Krowiak wrote: >>> +static int vfio_ap_mdev_open(struct mdev_device *mdev) >>> +{ >>> + struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev); >>> + struct ap_matrix_dev *matrix_dev = >>> + to_ap_matrix_dev(mdev_parent_dev(mdev)); >>> + unsigned long events; >>> + int ret; >>> + >>> + if (!try_module_get(THIS_MODULE)) >>> + return -ENODEV; >>> + >>> + ret = vfio_ap_verify_queues_reserved(matrix_dev, matrix_mdev->name, >>> + &matrix_mdev->matrix); >>> + if (ret) >>> + goto out_err; >>> + >>> + matrix_mdev->group_notifier.notifier_call = vfio_ap_mdev_group_notifier; >>> + events = VFIO_GROUP_NOTIFY_SET_KVM; >>> + >>> + ret = vfio_register_notifier(mdev_dev(mdev), VFIO_GROUP_NOTIFY, >>> + &events, &matrix_mdev->group_notifier); >>> + if (ret) >>> + goto out_err; >>> + >>> + ret = kvm_ap_validate_crypto_setup(matrix_mdev->kvm); >> >> At this point you assume that your vfio_ap_mdev_group_notifier callback >> was called with VFIO_GROUP_NOTIFY_SET_KVM and that you do have >> matrix_mdev->kvm set up properly. >> >> Based on how callbacks usually work this seems rather strange. It's >> probably cleaner to set up he cyrcb (including all the validation >> that needs to be done immediately before) in the callback >> (vfio_ap_mdev_group_notifier). >> >> If that is not viable I think we need a comment here explaining why is this >> OK (at least). > > This was originally in the callback and moved out, to the best of my recollection, > because the validation at that time was done on the CRYCB and if that validation > failed, there was no way to notify the client (QEMU) that configuration of the > guest's CRYCB failed from the notification callback. This works - at least as far > as I can tell from testing - because the registration of the notifier invokes the > notification callback if KVM has already been set and that appears to be the case. > You are correct, however; we probably shouldn't bank on that given that > I don't think we can guarantee that to be the case 100% of the time. Consequently, > I will move this back into the notification callback and since consistency checking > is now being done on the mdev devices instead of the CRYCB, we don't need KVM at open > time.
Sounds good to me. Making the open fail was not a good way to communicate this error condition to userspace anyway.
Regards, Halil
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