Re: Question on skip_emulated_instructions()

[Gleb Natapov <gleb@redhat.com>]

On Thu, Apr 08, 2010 at 10:17:01AM +0300, Avi Kivity wrote:
> On 04/08/2010 08:27 AM, Yoshiaki Tamura wrote:
> >
> >The requirement is that the guest must always be able to replay at
> >least the instruction which triggered the synchronization on the
> >primary.
> 
> 
> You have two choices:
> 
>  - complete execution of the instruction in both the kernel and the
> device model
> 
> This is what live migration does currently.  Any mmio and pio
> requests are completed, the last instruction is finalized, and state
> is saved.
> 
>  - complete execution of the instruction in the kernel, but queue
> execution of mmio/pio requests
> 
> This is more in line with what you describe.  vcpu state will be
> after the instruction, device model state will be before instruction
> completion, when you replay the queue, the device model state will
> be consistent with the vcpu state.
> 
For "in" or "mmio read" you can't complete instruction without doing
actual IO.

> >  From that point of view, I think I need to transfer the vcpu
> >state before the instruction.  If I post a signal and let the
> >guest or emulator proceed, I'm not sure whether the guest on the
> >secondary can be replay as expected.  Please point out if I were
> >misunderstanding.
> 
> If the responses to the mmio or pio request are exactly the same,
> then the replay will happen exactly the same.
> 
> -- 
> error compiling committee.c: too many arguments to function

--
			Gleb.