Re: [RFC PATCH 00/16] x86/split_lock: Enable #AC exception for split locked accesses

[Fenghua Yu]

On Thu, Jun 21, 2018 at 03:18:19PM -0700, Dave Hansen wrote:
> On 06/21/2018 03:08 PM, Peter Zijlstra wrote:
> > On Thu, Jun 21, 2018 at 03:00:03PM -0700, Fenghua Yu wrote:
> >> The control knob for kernel is to choose re-executing the faulting
> >> instruction (default) or kernel panic. Kernel panic may be useful in hard
> >> real time which has less tolerant to bad performance.
> > The kernel should never trigger this, ever. Any #AC is a plain bug and
> > should be fixed. So unconditional WARN+disable is suffient.
> 
> It sounds like we need to start with that functionality and then if
> Fenghua wants to do more, we have add-on patches that can be evaluated
> by themselves.

For split lock in kernel, by default, I just do warning, disable feature
in #AC handler, continue to execute the faulting instruction, and re-enable
#AC for split lock after a delay. This is the default behavior in the
current patches.

By "WAR+disable", you mean I just do this default behavior and remove the
control knob?

Thanks.

-Fenghua