Messages in this thread | | | Date | Wed, 27 Apr 2022 12:14:00 -0300 | From | Jason Gunthorpe <> | Subject | Re: [PATCH v6 15/21] KVM: s390: pci: add routines to start/stop interpretive execution |
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On Tue, Apr 26, 2022 at 04:08:36PM -0400, Matthew Rosato wrote:
> +int kvm_s390_pci_register_kvm(struct zpci_dev *zdev, struct kvm *kvm) > +{ > + if (!zdev) > + return 0; > + > + /* > + * Register device with this KVM (or remove the KVM association if 0). > + * If interpetation facilities are available, enable them and let > + * userspace indicate whether or not they will be used (specify SHM bit > + * to disable). > + */ > + if (kvm) > + return register_kvm(zdev, kvm); > + else > + return unregister_kvm(zdev); > +} > +EXPORT_SYMBOL_GPL(kvm_s390_pci_register_kvm);
I think it is cleaner to expose both the register/unregister APIs and not multiplex them like this
> +void kvm_s390_pci_clear_list(struct kvm *kvm) > +{ > + struct kvm_zdev *tmp, *kzdev; > + LIST_HEAD(remove); > + > + spin_lock(&kvm->arch.kzdev_list_lock); > + list_for_each_entry_safe(kzdev, tmp, &kvm->arch.kzdev_list, entry) > + list_move_tail(&kzdev->entry, &remove); > + spin_unlock(&kvm->arch.kzdev_list_lock); > + > + list_for_each_entry_safe(kzdev, tmp, &remove, entry) > + unregister_kvm(kzdev->zdev);
Hum, I wonder if this is a mistake in kvm:
static void kvm_destroy_vm(struct kvm *kvm) { [..] kvm_arch_destroy_vm(kvm); kvm_destroy_devices(kvm);
kvm_destroy_devices() triggers the VFIO notifier with NULL. Indeed for correctness I would expect the VFIO users to have been notified to release the kvm before the kvm object becomes partially destroyed?
Maybe you should investigate re-ordering this at the KVM side and just WARN_ON(!list_empty) in the arch code?
(vfio has this odd usage model where it should use the kvm pointer without taking a ref on it so long as the unregister hasn't been called)
If you keep it like this then the locking in register/unregister looks not broad enough and has to cover the zdev->kzdev also.
Overall I think it is OK designed like this, aside from the ugly symbol_get in vfio which I hope you can resolve.
Jason
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