Re: [Qemu-devel] [0.14?][PATCH 3/4] ioapic: Prepare for base address relocation

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2011-02-03 18:54, Blue Swirl wrote:
> On Thu, Feb 3, 2011 at 5:43 PM, Jan Kiszka <jan.kiszka@siemens.com> wrote:
>> On 2011-02-03 18:36, Blue Swirl wrote:
>>> On Thu, Feb 3, 2011 at 5:18 PM, Jan Kiszka <jan.kiszka@siemens.com> wrote:
>>>> On 2011-02-03 18:03, Blue Swirl wrote:
>>>>> On Thu, Feb 3, 2011 at 2:55 PM, Jan Kiszka <jan.kiszka@siemens.com> wrote:
>>>>>> The registers of real IOAPICs can be relocated during runtime (via
>>>>>> chipset registers). We don't support this yet, but qemu-kvm carries the
>>>>>> current base address in its version 2 vmstate.
>>>>>>
>>>>>> To align both implementations for migratability, add the proper
>>>>>> infrastructure to accept initial as well as updated base addresses and
>>>>>> include the current address in the vmstate. This is done in a way that
>>>>>> will also allow multiple IOAPICs in the future.
>>>>>
>>>>> Nack, the addresses should be device properties.
>>>>
>>>> Hmm.... we could make default_base_address a property. Will change that.
>>>> But current_base_address is just the same as apicbase and can't be a
>>>> property.
>>>
>>> Oh, right. What will current_base_address used for? Why can't board
>>> just unmap IOAPIC from current address and remap it at the new
>>> address? Then the device would not need to know its base address.
>>
>> The board could do this. The question is where we put this service, in
>> the context if the IOAPIC as ioapic_set_base_address (compare to
>> cpu_set_apic_base - which is buggy as it lacks sysbus_mmio_map) or into
>> each and every board code. In the latter case, the boards would also be
>> responsible for saving/restoring the address.
> 
> How is the device relocated? Where are the chipset registers you mention?

Intel's PIIX chipsets contain a register called APICBASE (but it means
the IOAPIC), and that defines the location. The analogy in the APIC
world is the MSR_IA32_APICBASE which we maintain via the APIC state.

Jan

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