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Re: [Qemu-devel] [PATCH 2/2] Route IOAPIC interrupts via ISA bus

From: Gleb Natapov
Subject: Re: [Qemu-devel] [PATCH 2/2] Route IOAPIC interrupts via ISA bus
Date: Thu, 27 Aug 2009 11:24:37 +0300

On Thu, Aug 27, 2009 at 09:18:32AM +0100, Jamie Lokier wrote:
> Gleb Natapov wrote:
> > On Thu, Aug 27, 2009 at 09:40:06AM +0200, Gerd Hoffmann wrote:
> > >            Or does it mean we must emulate a more recent chipset?
> > > 
> > That too will work.
> Note that if you change the chipset, it'll break some existing Windows VMs.
I don't think it worth changing chipset just to solve irq routing
problem. And PIIX4 is the same as PIIX3 in regards to pci irq routing. 

> I had this problem when porting a Windows Server 2003 VM from Virtual
> PC to QEMU: Virtual PC emulates a PIIX4, while QEMU provides a PIIX3
> (even though there's a PIIX4 in the source code, it's not used for PC
> emulation).  The ported image would not boot because of the change of
> chipset, until I patched the registry to accomodate the change.
> It will be the same the other way: When some Windows VMs see a change
> from PIIX3 to a later chipset, they will not boot.
> Some Windows VMs don't care as much.  XP seems to be more like Linux,
> in that it adapts to different devices at boot time.
> -- Jamie
> > 
> > --
> >                     Gleb.
> > 
> > 


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