Re: [Qemu-devel] Re: [PATCH 3/3] Add KVM support to QEMU

Blue Swirl
2008-10-29T19:13:37Z

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.