[Qemu-devel] Re: [questions] savevm|loadvm

[Avi Kivity]

On 04/01/2010 10:35 PM, Wenhao Xu wrote:
> Does current qemu-kvm (qemu v0.12.3) use the irqchip, pit of KVM? I
> cannot find any KVM_CREATE_IRQCHIP and KVM_CREATE_PIT in the qemu
> code.
>
>    

Are you looking at qemu or qemu-kvm?

> Concerning the interface between qemu and kvm, I have the following confusion:
> 1. How irqchip and pit of KVM collaborating with the irq and pit
> emulation of QEMU? As far as I see, qemu-kvm still uses qemu's irq and
> pit emulation, doesn't it?
>    

No, they're completely separate.

> 2. For return from KVM to QEMU, I cannot get the meaning of two exit reasons:
>     case KVM_EXIT_EXCEPTION:
>         What exception will cause KVM exit?
>    

I think that's obsolete.

>     default:
>              dprintf("kvm_arch_handle_exit\n");
>              ret = kvm_arch_handle_exit(env, run);
>         What exit reasons are default?
>
> 3. How could DMA interrupt the cpu when it finishes and the qemu-kvm
> is still running in kvm now?
>    

Usually the device that does the dma will raise an interrupt, which qemu 
is waiting for.

> I am still working in the patch, but these confusions really prevent
> me moving forward. Thanks first for you guys giving me more hints.
>
>
> The following is the code so far I write:
> The main idea is synchronizing the CPU state and enter into the
> emulator mode when switching from kvm to emulator. I only do the
> switch when the exit reason is KVM_EXIT_IRQ_WINDOW_OPEN.
>    

That doesn't happen with qemu-kvm.

> However, I got the following errors:
> Whenever switch from kvm to qemu, the interrupt request in qemu will
> cause qemu enter into smm mode which is definitely a bug.
>    

Definitely shouldn't happen.

--
Do not meddle in the internals of kernels, for they are subtle and quick to 
panic.