Re: [kvmarm] [RFC PATCH 0/3] KVM: ARM: Get rid of hardcoded VGIC addresses

[Avi Kivity <avi@redhat.com>]

On 10/18/2012 03:49 PM, Alexander Graf wrote:
> 
> On 18.10.2012, at 15:48, Christoffer Dall wrote:
> 
>> On Wed, Oct 17, 2012 at 7:58 PM, Benjamin Herrenschmidt
>> <benh@kernel.crashing.org> wrote:
>>> On Thu, 2012-10-18 at 09:10 +1100, Paul Mackerras wrote:
>>>> 
>>>> With the XICS, there are two types of irqchip: a source controller and
>>>> a presentation controller.  There is one presentation controller per
>>>> vcpu and typically one source controller per PCI host bridge (a source
>>>> controller can manage multiple sources).  The "buid" above is
>>>> basically an identifier for a source controller.
>>>> 
>>>> So with the above, it would be quite easy to add new types and
>>>> arguments for them.
>>> 
>>> The only possible issue is that afiak, the ioctl number depends on the
>>> structure size, no ? If it does, then we should add some padding to the
>>> union to leave room for new types.
>>> 
>> It sounds overall ok to me, however, Peter Maydell pointed out that
>> QEMU is architected in such a way that creating the IRQ chip happens
>> before QEMU knows how the chip fits with the model it is emulating and
>> therefore lacks bits of information that we require for initializing
>> the irq chip.
>> 
>> Specifically on ARM the information needed is the base address of a
>> hardware peripheral, which is virtualization aware, and is mapped
>> directly into the guest's physical address space.
>> 
>> One could argue that's not a concern for designing a good kernel api,
>> but on the other hand, qemu is already quite a large system on its
>> own, and we have to be practical.
>> 
>> Another alternative is to just let qemu init the device, later give
>> the base address and check before each execution of the vcpu whether
>> the base address has been set and simply return an error if not. This
>> latter approach just seems horrible and unintuitive to me.
>> 
>> Thoughts?
> 
> Wasn't there some "sane" field in the vcpu structs that you can hijack to make sure you only ever VCPU_RUN when the VM is complete?

vcpu->requests is checked on each entry.


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