Re: [PATCH 1/2] KVM: x86 emulator: don't update vcpu state if instruction is restarted.

Gleb Natapov
2010-08-01T12:23:20Z

On Sun, Aug 01, 2010 at 03:17:10PM +0300, Avi Kivity wrote:
> On 08/01/2010 01:53 PM, Gleb Natapov wrote:
> >
> >>That requires everyone to update, or suffer major breakage.
> >>
> >They will suffer major breakage when they update to a kvm that calls to
> >kvm-tpr-opt.c from emulator anyway.
>
> Why?
>
Because tpr code will be called with wrong rip. Emulator always updated rip at the end
of an instruction emulation in writeback stage.

> >>>IIRC it was always this way in emulator. I'd rather fix userspace than
> >>>break emulator.
> >>It wasn't a problem because the emulator wasn't (and still isn't)
> >>used for this. But it has the potential to break badly once we make
> >>emulate_invalid_guest_state=1 the default.
> >>
> >So what can we do about it?
> >
>
> Keep the existing behaviour.
>
Existing behaviour will cause breakage.

--
Gleb.