Re: [Qemu-devel] [PATCH 28/35] kvm: x86: Introduce kvmclock device to save/restore its state

[Jan Kiszka]

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.

Jan

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