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Re: [Qemu-devel] [PATCH 02/17] pseries: rework XICS

From: Alexey Kardashevskiy
Subject: Re: [Qemu-devel] [PATCH 02/17] pseries: rework XICS
Date: Tue, 02 Jul 2013 12:08:39 +1000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130514 Thunderbird/17.0.6

On 07/02/2013 10:21 AM, Alexander Graf wrote:
> On 02.07.2013, at 02:06, David Gibson wrote:
>> On Thu, Jun 27, 2013 at 10:17:19PM +1000, Alexey Kardashevskiy wrote:
>>> On 06/27/2013 09:47 PM, David Gibson wrote:
>>>> On Thu, Jun 27, 2013 at 04:45:45PM +1000, Alexey Kardashevskiy wrote:
>>>>> Currently XICS interrupt controller is not a QEMU device. As we are going
>>>>> to support in-kernel emulated XICS which is a part of KVM, it make
>>>>> sense not to extend the existing XICS and have multiple KVM stub functions
>>>>> but to create yet another device and share pieces between fully emulated
>>>>> XICS and in-kernel XICS.
>>>> Hmm.  So, I think changing the xics to the qdev/qom framework is a
>>>> generally good idea.  But I'm not convinced its a good idea to have
>>>> different devices for the kernel and non-kernel xics.
>>> The idea came from Alex Graf, this is already done for openpic/openpic-kvm.
>>> The normal practice is to move ioctls to KVM to KVM code and provide empty
>>> stubs for non-KVM case. There were too many so having a separate xics-kvm
>>> is kind of help.
>>>> Won't that
>>>> prevent migrating from a system with a kernel xics to one without, or
>>>> vice versa?
>>> Mmm. Do we care much about that?...
>> Enough to avoid making it impossible by design.
> We went that route with x86 too after lots of hassle trying to shoehorn the 
> in-kernel APIC into the emulation device. It's more hassle than gain.

At the moment it can be supported at no cost so next time I'll post it with
matched vmsd.

>>> At the moment it is not supported that as VMStateDescription have different
>>> .name for xics and xics-kvm but easy to fix. And we do not pass a device to
>>> vmstate_register so that must be it.
>> Ok, if you can make the ids in the vmsd match, then that should be ok.
> I really just wouldn't bother too much about it. Sooner or later QEMU-XICS is 
> going to be a legacy and debug only option.


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