On Tue, 2011-01-18 at 16:54 +0100, Jan Kiszka wrote: > On 2011-01-18 16:48, Anthony Liguori wrote: > > On 01/18/2011 09:43 AM, Jan Kiszka wrote: > >> On 2011-01-18 16:04, Anthony Liguori wrote: > >> > >>> On 01/18/2011 08:28 AM, Jan Kiszka wrote: > >>> > >>>> On 2011-01-12 11:31, Jan Kiszka wrote: > >>>> > >>>> > >>>>> Am 12.01.2011 11:22, Avi Kivity wrote: > >>>>> > >>>>> > >>>>>> On 01/11/2011 03:54 PM, Anthony Liguori wrote: > >>>>>> > >>>>>> > >>>>>>> Right, we should introduce a KVMBus that KVM devices are created on. > >>>>>>> The devices can get at KVMState through the BusState. > >>>>>>> > >>>>>>> > >>>>>> There is no kvm bus in a PC (I looked). We're bending the device model > >>>>>> here because a device is implemented in the kernel and not in > >>>>>> userspace. An implementation detail is magnified beyond all proportions. > >>>>>> > >>>>>> An ioapic that is implemented by kvm lives in exactly the same place > >>>>>> that the qemu ioapic lives in. An assigned pci device lives on the PCI > >>>>>> bus, not a KVMBus. If we need a pointer to KVMState, then we must find > >>>>>> it elsewhere, not through creating imaginary buses that don't exist. > >>>>>> > >>>>>> > >>>>>> > >>>>> Exactly. > >>>>> > >>>>> So we can either "infect" the whole device tree with kvm (or maybe a > >>>>> more generic accelerator structure that also deals with Xen) or we need > >>>>> to pull the reference inside the device's init function from some global > >>>>> service (kvm_get_state). > >>>>> > >>>>> > >>>> Note that this topic is still waiting for good suggestions, specifically > >>>> from those who believe in kvm_state references :). This is not only > >>>> blocking kvmstate merge but will affect KVM irqchips as well. > >>>> > >>>> It boils down to how we reasonably pass a kvm_state reference from > >>>> machine init code to a sysbus device. I'm probably biased, but I don't > >>>> see any way that does not work against the idea of confining access to > >>>> kvm_state or breaks device instantiation from the command line or a > >>>> config file. > >>>> > >>>> > >>> A KVM device should sit on a KVM specific bus that hangs off of sysbus. > >>> It can get to kvm_state through that bus. > >>> > >>> That bus doesn't get instantiated through qdev so requiring a pointer > >>> argument should not be an issue. > >>> > >>> > >> This design is in conflict with the requirement to attach KVM-assisted > >> devices also to their home bus, e.g. an assigned PCI device to the PCI > >> bus. We don't support multi-homed qdev devices. > >> > > > > With vfio, would an assigned PCI device even need kvm_state? > > IIUC: Yes, for establishing the irqfd link. We abstract this through the msi/msix layer though, so the vfio driver doesn't directly know anything about kvm_state. Alex -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
