Re: [RFD] x86/split_lock: Request to Intel

Thomas Gleixner
2019-10-18T09:02:58Z

On Fri, 18 Oct 2019, Xiaoyao Li wrote:
> On 10/17/2019 8:29 PM, Thomas Gleixner wrote:
> > The more I look at this trainwreck, the less interested I am in merging any
> > of this at all.
> >
> > The fact that it took Intel more than a year to figure out that the MSR is
> > per core and not per thread is yet another proof that this industry just
> > works by pure chance.
> >
>
> Whether it's per-core or per-thread doesn't affect much how we implement for
> host/native.

How useful.

> And also, no matter it's per-core or per-thread, we always can do something in
> VIRT.

It matters a lot. If it would be per thread then we would not have this
discussion at all.

> Maybe what matters is below.
>
> > Seriously, this makes only sense when it's by default enabled and not
> > rendered useless by VIRT. Otherwise we never get any reports and none of
> > the issues are going to be fixed.
> >
>
> For VIRT, it doesn't want old guest to be killed due to #AC. But for native,
> it doesn't want VIRT to disable the #AC detection
>
> I think it's just about the default behavior that whether to disable the
> host's #AC detection or kill the guest (SIGBUS or something else) once there
> is an split-lock #AC in guest.
>
> So we can provide CONFIG option to set the default behavior and module
> parameter to let KVM set/change the default behavior.

Care to read through the whole discussion and figure out WHY it's not that
simple?

Thanks,

tglx