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

Gleb Natapov
2010-08-02T07:58:40Z

On Mon, Aug 02, 2010 at 08:04:20AM +0300, Avi Kivity wrote:
> On 08/01/2010 04:27 PM, Gleb Natapov wrote:
> >
> >When we are going to enable e_i_g_s by default?
>
> Optimistically, 2.6.37, so six months.
>
> >May be we have enough
> >time to fix userspace?
>
> Sure we do, but will users update?
>
> 0.12 is mature enough that some users will forget about it and not
> update it.
>
So they will not update kernel too. 0.12/2.6.32 should be mature combo.
And we can add patch to 0.12/0.13 stable to work on newer kernels. But
realistically the problem will occur only if TPR access is done from big
real mode by Windows XP running on old Intel cpus. What are the chances
that this will be a problem in practice?

> >Too ancient userspace already does not run on recent
> >kvm. Or may be we can make userspace enable e_i_g_s per guest. This way
> >userspace that knows it is OK can tell kernel so.
>
> Let's make it the other way round, enable the optimization for
> userspace that declares that it does not make use of rip during
> emulation (kvm-tpr-opt can be changed by queueing a signal and
> re-entering the guest to complete the operation).
>
> Later we can make the optimization unconditional.
>
What do you call "optimization"? e_i_g_s=1? Isn't it the same as I proposed
then?

--
Gleb.