From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [Qemu-devel] [0.14?][PATCH 3/4] ioapic: Prepare for base address relocation Date: Thu, 03 Feb 2011 20:42:14 +0100 Message-ID: <4D4B0516.7070607@siemens.com> References: <0072079efad1c31da849cff7ad2cb426aeb6c29f.1296744934.git.jan.kiszka@siemens.com> <4D4AE360.1050905@siemens.com> <4D4AE95E.4070409@siemens.com> <4D4AED6D.4010009@siemens.com> <4D4AFCA0.2080308@siemens.com> <4D4B0118.3080904@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: "qemu-devel@nongnu.org" , Anthony Liguori , Gleb Natapov , Marcelo Tosatti , Alexander Graf , "kvm@vger.kernel.org" , Avi Kivity To: Blue Swirl Return-path: Received: from goliath.siemens.de ([192.35.17.28]:33335 "EHLO goliath.siemens.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756491Ab1BCTmg (ORCPT ); Thu, 3 Feb 2011 14:42:36 -0500 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 2011-02-03 20:30, Blue Swirl wrote: > On Thu, Feb 3, 2011 at 7:25 PM, Jan Kiszka w= rote: >> On 2011-02-03 20:11, Blue Swirl wrote: >>> On Thu, Feb 3, 2011 at 7:06 PM, Jan Kiszka = wrote: >>>> On 2011-02-03 20:01, Blue Swirl wrote: >>>>> On Thu, Feb 3, 2011 at 6:01 PM, Jan Kiszka wrote: >>>>>> On 2011-02-03 18:54, Blue Swirl wrote: >>>>>>> On Thu, Feb 3, 2011 at 5:43 PM, Jan Kiszka wrote: >>>>>>>> On 2011-02-03 18:36, Blue Swirl wrote: >>>>>>>>> On Thu, Feb 3, 2011 at 5:18 PM, Jan Kiszka wrote: >>>>>>>>>> On 2011-02-03 18:03, Blue Swirl wrote: >>>>>>>>>>> On Thu, Feb 3, 2011 at 2:55 PM, Jan Kiszka wrote: >>>>>>>>>>>> The registers of real IOAPICs can be relocated during runt= ime (via >>>>>>>>>>>> chipset registers). We don't support this yet, but qemu-kv= m carries the >>>>>>>>>>>> current base address in its version 2 vmstate. >>>>>>>>>>>> >>>>>>>>>>>> To align both implementations for migratability, add the p= roper >>>>>>>>>>>> infrastructure to accept initial as well as updated base a= ddresses and >>>>>>>>>>>> include the current address in the vmstate. This is done i= n 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 ca= n'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 ne= w >>>>>>>>> address? Then the device would not need to know its base addr= ess. >>>>>>>> >>>>>>>> The board could do this. The question is where we put this ser= vice, 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 woul= d also be >>>>>>>> responsible for saving/restoring the address. >>>>>>> >>>>>>> How is the device relocated? Where are the chipset registers yo= u mention? >>>>>> >>>>>> Intel's PIIX chipsets contain a register called APICBASE (but it= means >>>>>> the IOAPIC), and that defines the location. The analogy in the A= PIC >>>>>> world is the MSR_IA32_APICBASE which we maintain via the APIC st= ate. >>>>> >>>>> In ICH10 the register is called OIC=E2=80=94Other Interrupt Contr= ol Register >>>>> and the interesting bits APIC Range Select (ASEL). >>>>> >>>>> So actually PIIX should manage IOAPIC mapping, not board level. >>>> >>>> The point is we need ioapic_set_base_address logic in multiple pla= ces >>>> (once chipsets start to implement it). Better push it to a central= place >>>> from the beginning. Also the bit keeping. There is no difference t= o >>>> apicbase. >>> >>> In that case, the function should be made inline version in ioapic.= h. >> >> That still replicates the bit keeping. >> >> I don't see the benefit of moving it over, even less when we want to >> consolidate with a vmstate layout that is already in use. >=20 > The benefit is that the device model is improved. I disagree about the benefit, but I will simply drop this patch and instead add a dummy field to a vmstate version 3 so that qemu-kvm can remove the base_address evaluation logic when updating. Jan --=20 Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux