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

[Jan Kiszka]

On 2011-01-19 20:32, Blue Swirl wrote:
> On Wed, Jan 19, 2011 at 4:57 PM, Anthony Liguori
> <address@hidden> wrote:
>> On 01/19/2011 07:15 AM, Markus Armbruster wrote:
>>>
>>> So they interact with KVM (need kvm_state), and they interact with the
>>> emulated PCI bus.  Could you elaborate on the fundamental difference
>>> between the two interactions that makes you choose the (hypothetical)
>>> KVM bus over the PCI bus as device parent?
>>>
>>
>> It's almost arbitrary, but I would say it's the direction that I/Os flow.
>>
>> But if the underlying observation is that the device tree is not really a
>> tree, you're 100% correct.  This is part of why a factory interface that
>> just takes a parent bus is too simplistic.
>>
>> I think we ought to introduce a -pci-device option that is specifically for
>> creating PCI devices that doesn't require a parent bus argument but provides
>> a way to specify stable addressing (for instancing, using a linear index).
> 
> I think kvm_state should not be a property of any device or bus. It
> should be split to more logical pieces.
> 
> Some parts of it could remain in CPUState, because they are associated
> with a VCPU.
> 
> Also, for example irqfd could be considered to be similar object to
> char or block devices provided by QEMU to devices. Would it make sense
> to introduce new host types for passing parts of kvm_state to devices?
> 
> I'd also make coalesced MMIO stuff part of memory object. We are not
> passing any state references when using cpu_physical_memory_rw(), but
> that could be changed.

There are currently no VCPU-specific bits remaining in kvm_state. It may
be a good idea to introduce an arch-specific kvm_state and move related
bits over. It may also once be feasible to carve out memory management
related fields if we have proper abstractions for that, but I'm not
completely sure here.

Anyway, all these things are secondary. The primary topic here is how to
deal with kvm_state and its fields that have VM-global scope.

Jan

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