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SubjectRe: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by kernel parameter

* Peter Zijlstra <peterz@infradead.org> wrote:

> On Thu, Nov 21, 2019 at 07:04:44AM +0100, Ingo Molnar wrote:
> > * Fenghua Yu <fenghua.yu@intel.com> wrote:
>
> > > + split_lock_detect
> > > + [X86] Enable split lock detection
> > > + This is a real time or debugging feature. When enabled
> > > + (and if hardware support is present), atomic
> > > + instructions that access data across cache line
> > > + boundaries will result in an alignment check exception.
> > > + When triggered in applications the kernel will send
> > > + SIGBUS. The kernel will panic for a split lock in
> > > + OS code.
> >
> > It would be really nice to be able to enable/disable this runtime as
> > well, has this been raised before, and what was the conclusion?
>
> It has, previous versions had that. Somehow a lot of things went missing
> and we're back to a broken neutered useless mess.
>
> The problem appears to be that due to hardware design the feature cannot
> be virtualized, and instead of then disabling it when a VM runs/exists
> they just threw in the towel and went back to useless mode.. :-(
>
> This feature MUST be default enabled, otherwise everything will
> be/remain broken and we'll end up in the situation where you can't use
> it even if you wanted to.

Agreed.

> And I can't be arsed to look it up, but we've been making this very
> same argument since very early (possible the very first) version.

Yeah, I now have a distinct deja vu...

Thanks,

Ingo

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