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Date: Wed, 29 Oct 2008 21:13:37 +0200
From: "Blue Swirl" <blauwirbel@gmail.com>
Subject: Re: [Qemu-devel] Re: [PATCH 3/3] Add KVM support to QEMU
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To: qemu-devel@nongnu.org
Cc: Glauber Costa <glommer@gmail.com>, Glauber Costa <glommer@redhat.com>, hollis@alumni.cmu.edu, Gerd Hoffmann <kraxel@redhat.com>, kvm-devel <kvm@vger.kernel.org>

On 10/29/08, Avi Kivity <avi@redhat.com> wrote:
> Hollis Blanchard wrote:
>
> > On Tue, Oct 28, 2008 at 6:36 PM, Anthony Liguori <anthony@codemonkey.ws>
> wrote:
> >
> >
> > > Something I was thinking about this morning, and I think the first place
> > > where we'll definitely need a hook, is how to deal with
> > > kvm_load_registers().  I think there's overlap between KVM and the IO
> thread
> > > here.
> > >
> > > There are two reasons (I can think of) that most of the device model
> code
> > > can't run in conjunction with TCG.  The first is that TCG may modify
> > > CPUState in a non-atomic way.  The device model may need to access
> CPUState
> > > although there are very few places that it does.
> > >
> > >
> >
> > Out of curiosity, where are those places?
> >
> >
>
>  local apic -- needs to access interrupt disable flag
>  acpi sleep -- halts the current processor, so tied to cpustate

It should be possible to avoid these, just use a qemu_irq for per-CPU
interrupt lines and halt signals.

>  vmport -- bad ABI requires access to registers

Ugly. Maybe there could be two parts, one in pc.c which registers the
ioport and checks EAX/ECX, maybe using a CPU specific helper, and
second part, generic port in vmport.c, which does not know about CPU
state. I don't know if this would solve the original atomicity
problem, though.